David attended the 11th Conference on Multiscale Materials Modelling (MMM11) in Prague and presented the work on segregation in compositionally complex alloy done by Dominik. The Big CMS group from Leoben was well represented in Prague with another seven colleagues!

Using a combination of synchrotron measurements, electron microscopy, DFT and FEM simulations, we identified a novel hydride phase formed in NiTi shape mamery alloy during charding with hydrogen.
This is an international collaboration of several research groups and was coordinated by Antonín Dlouhý from IPM, Brno, Czechia.

A. Weiser, J. Todt, J. Holcova, T. Zalezak, A.M. Paulik, D. Holec, M. Jary, O. Zobac, J. Mrazek, J. Frenzel, J. Keckes, A. Dlouhy: "Hydrogen penetration into the NiTi superelastic alloy investigated in-situ by synchrotron diffraction experiments". Acta Mater., 277(120217), 120217 (2024). DOI: 10.1016/j.actamat.2024.120217

What summer would it be without a traditional informal summer bbq. This year also with several formal group membes!

Ganesh performed DFT calculations revealing the impact of Si and vacancy content on the lattice parameter of TiSiN. Using them we could show that vacancies play only subordinate role for reaching the range of the measured lattice parameters, hence highlighting the primary impact of the Si content. The paper also present a comprehensive microstructural investigration of the TiSiN coatings.
This work resulted from an internal collaboration with the group of Nina Schalk and Michael Tkadletz.

N. Schalk, Y. Moritz, G. Nayak, D. Holec, C. Hugenschmidt, V. Burwitz, L. Mathes, M. Schiester, C. Saringer, C. Czettl, M. Pohler, C. Mitterer, M. Tkadletz: "Nanocomposite versus solid solution formation in the TiSiN system". Acta Mater., 275, 120063 (2024). DOI: 10.1016/j.actamat.2024.120063

Amin and David attended the International Conference of Chemists and Chemical Engineers of Bosnia and Herzegovina. Amin reported about his study of impact of tramp and trace elements on reversible temper embrittlement in steels, while David spoke about the hydrogen storage research. In addition to interesting scientific meeting, we could enjoy (again!) the local hospitality and absorb some of the vibrations of Sarajevo!

Despite the bad weather, we left the comfort of our offices, disconnected from the internet, and replaced tablets with paper and pencils. On an old remote barn with almost no cell phone reception, we engaged for a full day in scientific and organizational discussions, planning our activities for the near future. Great things are in the line, stay tuned ;-)

Have you ever wondered what happens to materials as we increase the amount of recycled material? In our latest work we have used DFT calculations to reveal the impact of the tramp elements As, Sb and Sn and their interaction with traditional alloying elements such as Ni, Cr and Mo in iron. We were able to show that As, Sb and Sn segregate more than Ni, Cr and Mo and also weaken the grain boundaries more severely. By studying co-segregation, we proposed that the ability of Mo to mitigate reversible temper embrittlement in steels is primarily due to its cohesion-enhancing effect and its ability to repel tramp elements from GBs, rather than scavenging them within the bulk as suggested by previous literature. See our paper for more details!

A. Sakic, R. Schnitzer, D. Holec: "Interplay between alloying and tramp element effects on temper embrittlement in bcc iron: DFT and thermodynamic insights". Acta Mater., 275, 120044 (2024). DOI: 10.1016/j.actamat.2024.120044

This paper, based on Ulrich's Master's thesis, presents a model for predicting the catalytic activity of different metal surfaces for methane pyrolysis. Our model uses only DFT inputs and therefore allows unbiased predictions over a large set of material systems.

U. Pototschnig, M. Matas, D. Scheiblehner, D. Neuschitzer, R. Obenaus-Emler, H. Antrekowitsch, D. Holec: "Predictive Model for Catalytic Methane Pyrolysis". J. Phys. Chem. C, 128(22), 9034–9040 (2024). DOI: 10.1021/acs.jpcc.4c01690

The 3rd Materials Science Colloquium (68. Metallkunde-Kolloquim), also known as the “Arlberg Colloquium”, took place in Lech am Arlberg, Austria, from 15 to 19 April. Great talks were mixed with some outdoor fun in surprise delivery of fresh powder and numerous discussions in the halls, lecture room, bar or sauna.
Thomas gave a well-received talk entitled “Testing the entire periodic table for adsorption properties on graphene using neural‐network‐powered molecular dynamics simulations”.

Donglan used ab intio calculation to shed light on energetics and kinetics of oxygen vacancies in Ta/HfO₂ heterostructures, and thereby proposed a physics-motivated process of conductive filament formation in the resistive random access memory devices. Interested in more details? Have a read!

D. Zhang, J. Wang, Q. Wu, Y. Du, D. Holec: "Ab initio study of oxygen vacancy filament formation at Ta/HfO₂ interface". Surfaces and Interfaces, 49, 104418 (2024). DOI: 10.1016/j.surfin.2024.104418

In mid-March, the CMS group attended the DPG Spring Meeting in Berlin. We presented our work in a total of 6 talks and had numerous interactions and discussions with colleagues from other institutions. Apart from the scientific life, we could also spare some minutes for sightseeing and exploring the variety of restaurants in a big city.

In the past month, the CMS group underwent big personal changes. Donglan Zhang (CSC scholar) and Luiz Fernando Vierra-Correa have returned to their home universities.

Maximilian Ziegler finished his MSc studies by successfully defending his MSc thesis titled “Mechanical and electronic properties of monolayer TMDCs: A DFT study“ and passed the final exams with distinction.
Congratulations and all the best for the future!

Klemens Lechner joined our group in mid-March as a Ph.D. student who will work on the development of novel high-entropy alloys of refractory metals. Welcome!

Our colleagues report on comprehensive measurements of anomalous transport behavior of 0D–2D heterostructure composed of functionalized graphene quantum dots (GQDs) on graphene. Experimental evidence points towards possible charge density waves and superconducting phase transitions. We contributed by ab initio calculations showing the charge transfer between the graphene and the functionalized GDQ.
This work results from a long-standing collaboration with Rajarshi Roy and the group of Lenka Zajíčková (Masaryk University, Brno, Czechia).

R. Roy, D. Holec, L. Michal, D. Hemzal, S. Sarkar, G. Kumar, D. Nečas, M. Dhankhar, P. Kaushik, J. Gomez, L. Zajickova: "Possible charge ordering and anomalous transport in graphene/graphene quantum dotheterostructure". J. Phys. Condens. Matter, (2024). DOI: 10.1088/1361-648X/ad31bf

Also this year we have kept the tradition of outdoor team-building/energezing going. A day out at Präbichl was great, despite the tragic snow conditions this winter.

We present a theoretical and experimental study on the stability of orthorhombic (Mo_1−xNb_x)₂BC phase. We have theoretically predicted that the orthorhombic phase is stable up to x≈0.37, at which point the elastic modulus and the shear modulus are also the highest. These findings were confirmed experimentally by investigating magnetron-sputtered thin films. Our ab initio calculations further suggest that lattice strain is responsible for enhancing mechanical properties.
This work was coordinated by Jaroslav Ženíšek (Masaryk University, Brno, Czechia).

J. Ženíšek, P. Souček, P. Ondračka, Z. Czigány, V. Buršíková, D. Holec, K. Balázsi, P. Vašina: "Effect of Nb incorporation in Mo₂BC coatings on structural and mechanical properties — Ab initio modelling and experiment". Acta Mater., 268(119741), 119741 (2024). DOI: 10.1016/j.actamat.2024.119741

After the Corona break, the CMS group, together with Max-Planck-Institut für Eisenforschung, have been able to revive the tradition of Austrian–German Workshops “Computational Materials Science on Complex Energy Landscapes.” This year’s edition took place during the week January 15–19, 2024, in a beautiful Hotel Gasteiger Jagdschlössl in Kirchdorf in Tirol. Over 50 researchers from Technische Universität Wien, ESI Leoben, Materials Center Leoben Forschung GmbH, University of Stuttgart, ICAMS, and BAM Berlin enjoyed a dense lecture program, scientific discussions as well as an informal exchange of knowledge and ideas.

This work presents beautiful microscopy work on tungsten suboxide W₁₈O₄₉ nanowhiskers. The focus was laid on the impact of irradiation on the growth and structure of the nanowhiskers. While large parts are composed of well-documented pentagonal Magnéli columns and hexagonal channels characteristic for this phase, highly crystalline and oriented domain structures of previously unreported mixed structural arrangements were also identified. Our DFT calculations of EELS spectra for different local motifs corroborated these experiments.
Vojtěch Kundrát and Reshef Tenne from the Weizmann Institute of Science, Israel initiated and coordinated this collaboration.

V. Kundrat, K. Bukvisova, L. Novak, L. Prucha, L. Houben, J. Zalesak, A. Vukusic, D. Holec, R. Tenne, J. Pinkas: "W₁₈O₄₉ Nanowhiskers Decorating SiO2 Nanofibers: Lessons from In Situ SEM/TEM Growth to Large Scale Synthesis and Fundamental Structural Understanding". Cryst. Growth Des., (2023). DOI: 10.1021/acs.cgd.3c01094

Antonion has successfully defended his MSc thesis titled “Influence of vacancies on the N K-edge ELNES response of fcc Tantalum nitrides–Ab initio study“ and passed the final exams to get the MSc degree in Materials Science.
Congratulations!

Today, Ganesh Nayak Kumar has successfully defended his PhD thesis “A Multi-method Atomistic Study of Protective Nitride Coatings: from Crystalline to Amorphous Materials“and thereby finally “legalized“ his postdoc in Aachen. The thesis was reviewed by Prof. Paul Mayrhofer (TU Wien) and Assoc. Prof. Davide Sangiovanni (Linköping University, Sweden). Davide also acted as the second examiner.

Many congratulations to Ganesh and all the best for the future!

Clement Paulson attended the Ab initio Description of Iron and Steel (ADIS2023) meeting focusing on “Digitalization and Workflows“. This workshop was organized by MPIE at the Ringberg castle. Clemeb\nt presented a posted on his work on “Physics-informed neural network for predicting Gibbs free energy“.

Last week, David gave an invited talk at the Intermetallics Conference 2023 in a beautiful monastery, Kloster Banz. The meeting brought together friends from computational and experimental fields, sharing their passion for intermetallic alloys. Apart from great talks and engaging scientific discussions, we could enjoy the excursion to Kulmbach and jogging in the nearby forests.

What a busy week!

On Tuesday, Keegan Zetterberg finished his MSc studies of Materials Science within the international study program AMASE. His thesis was titled “The effects of grain size on the elastic response of FeCrMnNiCo high entropy alloy: a molecular dynamics study“.

The end of the week was marked with the visit of Prof. Jörg Neugebauer, Director of the Max Planck Institut für Eisenforschung in Düsseldorf. Two days were filled with intense discussions, exchange of ideas, planning of future collaborations. Jörg also gave a seminar lecture on “Metastable defect phase diagrams as a road map for defect design“.

But the major reason for Jörg's visit was purely academic: he acted as a reviewer of Dominik Gehringer’s thesis “Atomistic approaches for investigating planar defects in compositionally complex alloys“ and also as his examiner. On Thursday, Dominik successfully defended his PhD thesis and passed the final exam with distinction!

Many Congratulations to both Keegan and Dominik!

Donglan Zhang, an exchange PhD student in the Computational Materials Science group at the Department of Materials Science, attended the 2023 Fall Meeting of the European Materials Research Society (E-MRS) held September 18-21 2023 at the University of Technology in Warsaw, Poland. Donglan presented a poster on “Oxygen vacancy conductive filament formation and growth in HfO₂-based RRAM”. It was a unique and interesting experience to meet with many excellent researchers, to discuss with them face-to-face Donglan’s results, to enjoy their sharing of interesting research, and to experience the culture and beauty of the cities of Warsaw and Gdańsk!

Diborides of transition metals have a hexagonal structure composed of alternating layers of boron and metal atoms. They appear in various stackings of the metal planes and, related to that, with different puckering levels of the boron planes. In this paper, we present a theoretical work on the barriers to transformations between these allotropes and put them into the perspective of chemical and electronic trends.
This work is a collaboration with Nikola Koutná and Paul H. Mayrhofer (TU Wien) and Martin Zelený and Jozef Janovec (Brno University of Technology).

T. Leiner, N. Koutná, J. Janovec, M. Zelený, P.H. Mayrhofer, D. Holec: "On energetics of allotrope transformations in transition-metal diborides via plane-by-plane shearing". Vacuum, 215, 112329 (2023). DOI: 10.1016/j.vacuum.2023.112329

Dominik has organized an internal one-day workshop on compiling codes and linking with libraries, a skill needed for every computational materials scientist.

Ever wondered how to get the best of the two worlds, quantum mechanical DFT, and molecular mechanics? Then check out the latest publication of Dominik Gehringer on implementing the QM/MM approach for phase boundary segregation in multi-phase multi-component TiAl intermetallic system!
This work is a collaboration with Liam Huber and Jörg Neugebauer from MPIE Düsseldorf.

D. Gehringer, L. Huber, J. Neugebauer, D. Holec: "Segregation to α₂/γ interfaces in TiAl alloys: A multiscale QM/MM study". Phys. Rev. Mater., 7(6), 063604 (2023). DOI: 10.1103/PhysRevMaterials.7.063604

Last week, David gave an invited talk the 7th International Workshop of Titanium Aluminides (IWTA2023) in Toulouse. It was great to spent time with my current and former colleagues from Montanunversität Leoben, to reconnect with the TiAl family, to learn from the great talks, to visit Airbus assembly lines, and to enjoy french wine and hospitality.

Diffusion governs many important processes in materials. In this publication, Ganesh Kumar Nayak used DFT to study migration barriers for vacancy-mediated diffusion of transition metal impurities in TiN, a prototype hard coating. We show that the diffusion properties are not fully (anti-)correlated with the atom size, but the impurity bonding in both the initial and transition state plays an important role.
The work is a collaboration with Martin Zelený (Brno University of Technology).

G. Nayak, D. Holec, M. Zelený: "Impact of d-states on transition metal impurity diffusion in TiN". Sci. Rep., 13(1), 8244 (2023). DOI: 10.1038/s41598-023-34768-7

Compositionally complex alloys are fascinating and challenging at the same time. Ganesh performed a series of DFT calculations to prove that sluggish diffusion is not necessary a consequence of compositional complexity (and hence of high configurational entropy), and proposed a species-resolved quantification of local distortions which seems to correlate with (species resolved activation energies).
The work is a collaboration with Andreas Kretschmer and Paul Mayrhofer (TU Wien).

G. Nayak, A. Kretschmer, P.H. Mayrhofer, D. Holec: "On correlations between local chemistry, distortions and kinetics in high entropy nitrides: An ab initio study". Acta Mater., 255, 118951 (2023). DOI: 10.1016/j.actamat.2023.118951

In our recent publication, we applied DFT calculations to analyze the thermodynamics of the decomposition of TiAl-based high entropy alloys. In agreement with the experiment, we showed that TiAlNbV+Mn is unstable as a single-phase solid solution. We predicted that also the Mo variant should decompose. Since the experiments indicate that this phase remains stable, we concluded that TiAlNbV+Mo high entropy alloy is kinetically stabilized.

L. Hatzenbichler, S. Zeisl, H. Clemens, D. Holec: "Phase stability of TiAl-based BCC high entropy alloys". Intermetallics, 158, 107893 (2023). DOI: 10.1016/j.intermet.2023.107893

To mark the definitive end of the Corona times, we have renewed the tradition of the skiing day. With almost the last chance (for snow and skiing) we enjoyed the afterwork team-building at Semmering.

Anna and Lukas have successfully defended their MSc theses and passed the final exams. Anna's thesis was titled “Ab initio discovery of novel hydride phases in NiTi shape memory alloys“, Ulrich's “Deriving a Model for Catalytic Methane Pyrolysis: A DFT Study“. They have earned an MSc degree in Materials Science.
Congratulations!

We present a Python package for the efficient generation of special quasi-random structures (SQS) for atomic-scale calculations of disordered systems. Both, a Monte-Carlo approach or a systematic enumeration of structures can be used to carry out optimizations to ensure the best optimal configuration is found for given cell size and composition. Both SQS optimizations and analysis of structures can be carried out via a command-line interface or a Python API. Additional features, such as optimization towards partial ordering or independent sublattices allow the generation of atomistic models of modern complex materials. The output data format is compatible with ase, pymatgen and pyiron packages to be easily embeddable in complex simulation workflows.
More info about the package here.

D. Gehringer, M. Friák, D. Holec: "Models of configurationally-complex alloys made simple". Comput. Phys. Commun., 286, 108664 (2023). DOI: 10.1016/j.cpc.2023.108664

Carbon dots (CDs) display photophysical features that appear similar, if not identical, despite the variety of synthesis protocols used to obtain them. Our calculations based on density functional theory helped to elucidate the structural sequence leading to the spontaneous formation of a compact network of molecular species. The thus obtained CDs are characterised for their optical fluorescence.
The work is a collaboration with the group of Prof. Lenka Zajíčková (MU/Ceitec Brno, Czech Republic).

J.I. Gómez, M. Sulleiro, N. Pizúrová, A. Bednařík, P. Lepcio, D. Holec, J. Preisler, L. Zajíčková: "Spontaneous formation of carbon dots helps to distinguish molecular fluorophores species". Appl. Surf. Sci., 610, 155536 (2023). DOI: 10.1016/j.apsusc.2022.155536

Our colleagues applied advanced diffraction techniques to entangle the impact of Zr on the γ-TiAl alloys. We supported their investigations with first-principles calculated compositionally-dependent structural parameters. Together we have constructed sections of the ternary Ti-Al-Zr phase diagram.
The work was coordinated by Michael Musi (MUL Leoben)

M. Musi, S. Kardos, L. Hatzenbichler, D. Holec, A. Stark, M. Allen, V. Güther, H. Clemens, P. Spoerk-Erdely: "The effect of zirconium on the Ti-(42-46 at.\%)Al system". Acta Mater., 241, 118414 (2022). DOI: 10.1016/j.actamat.2022.118414

Inspired by the intriguing interplay between chemical disorder and alloying, we applied ab initio methods to study the impact on bcc cubic-to-hexagonal phase transformations in TiAl+Mo alloys. We combined SQS (local relaxations) and CPA (effective long-range disorder) approaches. We can show that both chemical disorder and Mo alloying lead to a gradual charge of the phase preference from hexagonal/B19 (no Mo) to bcc/B2 (above approx. 10at. % Mo). Most of these transformations show barrier-less character, and marginal barriers emerge for scenarios when both cubic and hexagonal phases have the same energies.
The work was a collaboration with the group of Jürgen Spitaler (MCL Leoben).

N. Abdoshahi, M. Dehghani, A.V. Ruban, M. Friák, M. Šob, J. Spitaler, D. Holec: "On the energetics of the cubic-to-hexagonal transformations in TiAl+Mo alloys". Acta Mater., 240, 118268 (2022). DOI: 10.1016/j.actamat.2022.118268

Celine has successfully defended her MSc thesis titled “Development of a semi-automated molecular dynamics workflow for testing interatomic potentials against ab-initio data“. Also Lukas successfully defended his MSc thesis titled “Prediciting Phase Stability of TiAl-based High Entropy Alloys from First-Principles“. Today they both passed their final exams and thus have earned an MSc degree in Materials Science.
Congratulations!

We used ab initio calculations to study the impact of several alloying elements, including Al, Cr, Mg, Mn, and Si, on the stability of cementite. This was quantified using the change in formation energy between the alloyed cementite and the pure cementite. Additionally, we also considered multi-phase scenario and calculated partitioning partitioning energy between cementite, ferrite and austenite, in order to make statements about the effect of alloying elements on the cementite stability. Furthermore, our calculations of elastic properties of Al and Si alloyed to cementite show that both the elements increase its stability.

A. Sakic, C. Hofer, R. Schnitzer, D. Holec: "Ab initio study of alloying impact on the stability of cementite in transformation-induced plasticity-assisted advanced steels". Adv. Eng. Mater., , 2200532 (2022). DOI: 10.1002/adem.202200532

Our calculations focused on the stability of various (Mg, Al)Ca₂ Laves phases variants, C14, C15 and C36, as a function of the Al-to-Mg ratio. We could show that the energy differences between different variants are negligible for the intermediate compositions, thus suggesting extremely low stacking fault energies. In the second part, we simulated Mg/Al₈Mn₅ interface and showed, that the Al₈Mn₅ promotes segregation of Ca from the Mg matrix. Our calculations were a basis for discussing an extensive experimental study employing analytical high-resolution electron microscopy and atom probe tomography.
The work is a collaboration of several research groups and was coordinated by Jiehua Li (MUL Leoben).

J. Li, X. Zhou, A. Breen, Z. Peng, J. Su, P. Kürnsteiner, M. Correa, M. Chwałek, H. Wang, D. Holec, J. Mayer, G. Dehm: "Elucidation of formation and transformation mechanisms of Ca-rich Laves phase in Mg-Al-Ca-Mn alloys". J. Alloys Compd., 928, 167177 (2022). DOI: 10.1016/j.jallcom.2022.167177

Anna Paulik, Dominik Gehringer, Ganesh Nayak and David Holec attended 10th International conference on Materrials Structure & Mechanics of Fracture held September 11–14 2022 in Brno, Czech Republic. We all held oral presentations, enjoyed company of our colleagues from Brno and abroad, and found new friends.

Our colleagues revisited the mechanical properties of Al-rich AlCrN coating, known for its good hard but brittle mechanical response. They could show that when wurtzite-structured precipitates appear after annealing, the mechanical properties are enhanced, and the cleavage mode changes from intergranular to transgranular mode. Our DFT calculations supported this scenario by providing interface strength energies for discussing the feasibility of such a phase-transformation-induced toughening mechanism.
The work was coordinated by Michael Meindlhumer and it is a collaboration with the groups of Jozef Keckes (MUL Leoben) and Jochen Schneider (RWTH Aachen).

M. Meindlhumer, T. Ziegelwanger, J. Zalesak, M. Hans, L. Löfler, S. Spor, N. Jäger, A. Stark, H. Hruby, R. Daniel, D. Holec, J.M. Schneider, C. Mitterer, J. Keckes: "Precipitation-based grain boundary design alters Inter- to Trans-granular Fracture in AlCrN Thin Films". Acta Mater., 237, 118156 (2022). DOI: 10.1016/j.actamat.2022.118156

Dominik Gehringer, Ganesh Nayak and David Holec attended 4th International Congress of Chemists and Chemical Engineers of Bosnia and Herzegovina held June 30–July 2 2022 in Sarajevo. We all held oral presentations, found new friends and got a brief feeling of local hospitality, culture and history.

Marcus and Zsolt performed a comprehensive study of thermal stability in (V, Al)N coatings using a correlation of transmission electron microscopy and atom probe tomography data. They concluded that the spinodal decomposition is linked to the formation of Al-rich regions which are precursors for wurtzite AlN. Our DFT calculations support their appearance by pointing to a faster Al diffusion caused by 25% lower activation energy for bulk diffusion than V.
The work was coordinated by Marcus Hans and it is a collaboration with the group of Jochen Schneider (RWTH Aachen).

M. Hans, Z. Czigány, D. Neuß, J.A. Sälker, H. Rueß, J. Krause, G.K. Nayak, D. Holec, J.M. Schneider: "Probing the onset of wurtzite phase formation in (V, Al) N thin films by transmission electron microscopy and atom probe tomography". Surf. Coat. Technol., , 128235 (2022). DOI: 10.1016/j.surfcoat.2022.128235

Though it has been over a year since Lukas has started as a PostDoc in Aachen, today he finally made a big thick line behind his PhD studies! He presented his thesis titled “Defects and their influence on mechanical properties in nitrides: an atomistic study” which had been positively reviewed and passed with distinction the oral exam.
Congratulations!

Ganesh Nayak and David Holec have attended this year's ICMCTF in San Diego. It was a refreshing experience to meet our friends and collaborators again in person, enjoy their talks in the lecture halls, and afterward get engaged in live discussions. Ganesh presented a talk on diffusion in HENs and a poster on pressure impact on diffusion in TiN. At the same time, David showed results on phase transformations in TM diborides.

In this work, we contributed by showing the charge transfer between a functionalized graphene quantum dot (GQD) and a flat graphene substrate. The GQD was modelled as a graphene flake with its dangling bonds saturated with H, NH₂, and CONH₂ groups. We could show that some charge is transferred from the graphene to the QGD, thus effectively leading to p-doping of the graphene. Our colleagues used sophisticated methods, primarily atomic force microscopy, Kelvin probe force microscopy, and Raman spectroscopy, to prove this charge transfer experimentally.
The work was coordinated by Rajarshi Roy and it is a collaboration with the groups of Lenka Zajíčková (CEITEC Brno, Czech Republic) and Christian Teichert (MUL, Leoben).

R. Roy, D. Holec, M. Kratzer, P. Muenzer, P. Kaushik, L. Michal, G. Kumar, L. Zajíčková, C. Teichert: "Probing the charge transfer and electron-hole asymmetry in graphene-graphene quantum dot heterostructure". Nanotechnology, 33(32) (2022). DOI: 10.1088/1361-6528/ac6c38

Using DFT we have investigated bonding of graphene on different Si surfaces. We could reveal that while C-Si covalent bonds are formed on the (111) and (100) orientated surfaces, only van der Waals bonding state exists on the (110) orientated one. Next, the form of the substrate bonding leads to modifications of the electronic structure near the Fermi level, resulting in an unconventional doping proposed in this work.
The work is a collaboration with the groups of Colin Humphreys and David Dunstan, Queen Mary University of London, London, UK.

Y.W. Sun, D. Holec, D. Gehringer, L. Li, O. Fenwick, D.J. Dunstan, C.J. Humphreys: "Graphene on silicon: Effects of the silicon surface orientation on the work function and carrier density of graphene". Phys. Rev. B Condens. Matter, 105(16), 165416 (2022). DOI: 10.1103/PhysRevB.105.165416

The low intrinsic fracture toughness of transition metal nitride thin films critically restrains their applicability as protective coatings. We therefore investigated the Ti_1−xW_xN_y system to provide detailed theoretical and experimental insight into simultaneous hardening and toughening effects induced by heavy-element-alloying via an enhanced metallic bonding character. The combination of structural and chemical analyses, supported by density functional theory (DFT) calculations. demonstrates that the addition of W progressively increases the concentration of nitrogen vacancies in rocksalt (rs) structured Ti_1−xW_xN_y. DFT-calculated charge density maps revealed that the superior toughness-related performance of Ti_1−xW_xN_y (with respect to TiN, which showed a pronounced radial crack formation) is linked to a metallisation of the interatomic bonds, being most pronounced for balanced W and Ti contents and N vacancies.
The work is a collaboration with the group of Paul Mayrhofer (TU Wien).

J. Buchinger, N. Koutná, A. Kirnbauer, D. Holec, P.H. Mayrhofer: "Heavy-element-alloying for toughness enhancement of hard nitrides on the example Ti-W-N". Acta Mater., , 117897 (2022).

Anna Paulik has been awarded "Wissenschaftspreis für Montanistinnen 2022" in the category Junior Scientist for her scientific work on novel NiTiH phases in the framework of her MSc thesis. This prize is awarded to female researches at the Montanuniversiät Leoben also in PreaDoc (PhD) and PostDoc categories.
Congratulations!

Interfaces between components of a material govern its mechanical strength and fracture resistance. Here we combine ab initio and classical molecular dynamics simulations, nanoindentation, and transmission electron microscopy to reveal atomistic mechanisms underlying plasticity and crack growth in B1 AlN(001)/TiN(001) superlattices under loading. Our simulations demonstrate an anisotropic response to uniaxial tensile deformation in principal crystallographic directions due to different strain-activated plastic deformation mechanisms. Superlattices strained orthogonal to (001) interfaces show modest plasticity and cleave parallel to AlN/TiN layers. Contrarily, B1-to-B3 or B1-to-B4(Bk) phase transformations in AlN facilitate a remarkable toughness enhancement upon in-plane [110] and [100] tensile elongation, respectively.
The work is a collaboration with the groups of Paul Mayrhofer (TU Wien), Davide Sangiovani (Linköping University) and Zaoli Zhang (ESI-OeAW Leoben).

N. Koutná, L. Löfler, D. Holec, Z. Chen, Z. Zhang, L. Hultman, P.H. Mayrhofer, D.G. Sangiovanni: "Atomistic mechanisms underlying plasticity and crack growth in ceramics: a case study of AlN/TiN superlattices". Acta Mater., , 117809 (2022). DOI: 10.1016/j.actamat.2022.117809

In this work use ab initio calculations top show how does the vacancy concentration impact the core electron binding energies. Our predictions on the core electron energy shifts in cubic titanium oxynitride (Ti_1-δO_xN_1-x) are beautifully correlating with measured XPS spectra. This work unequivocally demonstrates that the formation and population of Ti vacancies in cubic Ti_1-δO_xN_1-x thin films can be quantified by XPS measurements from N 1s core electron binding energy shifts.
The work is a collaboration with the group of Jochen Schneider group, RWTH Aachen, Germany.

P. Ondračka, M. Hans, D.M. Holzapfel, D. Primetzhofer, D. Holec, J.M. Schneider: "Ab initio-guided X-ray photoelectron spectroscopy quantification of Ti vacancies in Ti_1-δO_xN_1-x thin films". Acta Mater., 230(117778), 117778 (2022). DOI: 10.1016/j.actamat.2022.117778

XPS spectrum of amorphous W-B-C material was previously analyzed by fitting it using three components corresponding to the relative amount of W-W, W-B, and W-C bonds. However, using ab initio calculations we could show that the amount W-W bonds substantially influences positions of the peak components. Our calculations enabled us to formulate the relationship between the W 4f electron binding energies (BE) and the local atomic environments of W atoms. Our analysis confirms the expected W 4f chemical shifts in W-B-C caused by W-B and W-C bonds and reveals that W-W bonds shift the W 4f electronic states in the same direction as W-B bonds, which has substantial implications for the correct interpretation of the measured XPS spectra.
The work is a collaboration with the group of Petr Vašina (MU Brno).

J. Ženíšek, P. Ondračka, J. Čechal, P. Souček, D. Holec, P. Vašina: "W 4f electron binding energies in amorphous W-B-C systems". Appl. Surf. Sci., 586, 152824 (2022). DOI: 10.1016/j.apsusc.2022.152824

The formation of Al₃Zr particles within dilute aluminum alloys can contribute effectively to controlling microstructure evolution and enhancing material properties. However, the possible transformation of Al₃Zr from its initial metastable crystal structure L1₂ into its stable, tetragonal structure D0₂₃ is associated with faster coherency loss and the coarsening of Al₃Zr particles. In this regard, our study aims at identifying ternary elements that can disrupt this mechanism. In parallel to experimental investigations, we conducted ab initio calculations to investigate fundamental properties of ternary AlZrX-particles (X=Er, Sc, Hf, Y, Nb, Mn, Cu, Zn and Si) such as substitution likeliness, heat of formation and transformation mechanisms. These calculations helped to elucidate the partitioning and overall effect of alloying observed in experiments.
The work is a collaboration with the group of Stefan Pogatscher (MUL).

F. Schmid, D. Gehringer, T. Kremmer, L. Cattini, P.J. Uggowitzer, D. Holec, S. Pogatscher: "Stabilization of Al₃Zr allotropes in dilute aluminum alloys via the addition of ternary elements". Materialia, 21, 101321 (2022). DOI: 10.1016/j.mtla.2022.101321

In the framework of the departmental seminar series "Materials Science Colloquium", Pavel Ondračka (Masaryk University, Brno, Czech Republic) has presented a new combined theoretical and experimental approach for quantifying point defect contents on oxides and oxynitrides from the X-ray photoelectron spectroscopy (XPS) measurements and ab initio calculations.

An in-depth study on interactions in ternary TiAl+Mo intermetallic alloy allowed us to identity the importance of multi-site as well as some unexpectedly long-range pair-interactions. Subsequently we used them in a Monte Carlo simulation to show that Mo alloying dramatically increases the order–disorder transition temperatures in bcc and hcp Al-deficient Ti_0.5Al_0.5−xMo_x alloys.
The work is a collaboration with the group of Jürgen Spitaler (MCL Leoben).

M. Dehghani, A.V. Ruban, N. Abdoshahi, D. Holec, J. Spitaler: "Stability and ordering of bcc and hcp TiAl+Mo phases: An ab initio study". Comput. Mater. Sci., 205, 111163 (2022). DOI: 10.1016/j.commatsci.2021.111163

Within this work the effect of the B content on the microstructure, phase composition and mechanical properties of CVD Ti(B,N) coatings is investigated. With increasing B content, a transition from an fcc to an hex-dominated structure via a dual-phase fcc/h-Ti(B,N) microstructure was observed, which was accompanied by a decrease in grain size from the μm to nm range. Complementary ab initio calculations predicting the phase formation helped to interpretat the experimental results. We could conclude, that both hex-TiB₂ and dual-phase fcc/hex-Ti(B,N) coatings withmaximized B content yield superior mechanical properties over TiN and consequently improved performance.
The work is a collaboration with many groups, initiated and coordinated by Michael Tkadletz (MUL).

M. Tkadletz, N. Schalk, A. Lechner, L. Hatzenbichler, D. Holec, C. Hofer, M. Deluca, B. Sartory, A. Lyapin, J. Julin, C. Czettl: "Influence of B content on microstructure, phase composition and mechanical properties of CVD Ti(B,N) coatings". Materialia, 21, 101323 (2022). DOI: 10.1016/j.mtla.2022.101323

This paper solves a longstanding debate: Raman measurements on double-walled carbon nanotubes appear to show that significantly more pressure than expected can be transmitted to the inner tube. We reinterpret those Raman spectra consistently reported in the literature, by assigning the Raman peaks to coupled vibrational modes of both walls, instead of individual contributions from the inner and outer tubes. These coupled vibrational modes are important for the correct interpretation of the Raman shift from strained layered 2D materials (we demonstrate it on bilayer graphene as an example), for researching the mechanical properties, thermal expansion, and strain engineering of two-dimensional materials.
The work is a collaboration with the groups of Colin Humphreys and David Dunstan, Queen Mary University of London, London, UK.

Y.W. Sun, D. Gehringer, D. Holec, D.G. Papageorgiou, O. Fenwick, S.M. Qureshi, C.J. Humphreys, D.J. Dunstan: "Significant interlayer coupling in bilayer graphene and double-walled carbon nanotubes: A refinement of obtaining strain in low-dimensional materials". Phys. Rev. B Condens. Matter, 105(2), 024103 (2022). DOI: 10.1103/PhysRevB.105.024103

The CMS group wishes you Merry Christmas and prosperous and healthy 2022!

High-entropy materials have drawn lots of attention in the past decade. Typically the focus is laid on the stabilization via configurational entropy. In this publication, we show that equally important is the effect of the specific volume mismatch adding a strain-energy penalty to the overall decomposition energy balance. We have used DFT calculations to predict the stability of a massive number of hexinary nitrides (one sublattice in the B1 structure fully occupied by N while the other contains five elements with equal molar fractions). The theoretical predictions were confirmed by a dedicated experiment on PVD-synthesised thin films.
The work is a collaboration with the groups of Paul Mayrhofer (TU Wien), Jochen Schneider (RWTH Aachen) and the company Oerlikon Balzers.

A. Kretschmer, D. Holec, K. Yalamanchili, H. Rudigier, M. Hans, J. Schneider, P. Mayrhofer: "Strain-stabilized Al-containing high-entropy sublattice nitrides". Acta Mater., 224, 117483 (2022). DOI: 10.1016/j.actamat.2021.117483

Maximilan has presented his BSc thesis title “Graphene“ and thereby fulfilled all requirements of the BSc study program in “Materials Science“ at Montanuniversiät Leoben. The thesis was externally co-supervised by Dr. Rajarshi Roy.
Congratulations!

Martensitic transformation between bcc and hcp phases has been reported for the model TiAl+Mo alloy. Therefore, we have employed complementary DFT methods, namely VASP-SQS and EMTO-CPA, to report structural and mechanical properties of those phases as a function of Mo content. Discrepancies between the two employed ab initio methods in the case of the βo and B19 phases are rationalized with significant local distortions which may eventually facilitate a spontaneous phase transformation.
The work is a collaboration with the groups of Svea Mayer (MUL) and Jürgen Spitaler (MCL Leoben).

N. Abdoshahi, P. Spoerk-Erdely, M. Friák, S. Mayer, M. Šob, D. Holec: "Ab initio study of chemical disorder as an effective stabilizing mechanism of bcc-based TiAl+Mo". Phys. Rev. Materials, 4(10), 103604 (2020). DOI: 10.1103/PhysRevMaterials.4.103604

Tobias has successfully defended his MSc thesis on “Assessment of Various DFT-based Methods for Predicting Temperature Dependence of Elastic Constants“ and has passed with distinction the final exam to get an MSc degree in Materials Science.
Congratulations!

A review paper showing several examples of insights which can be obtained from DFT calculations, useful for alloy development.

D. Holec, N. Abdoshahi, D. Gehringer, L. Hatzenbichler, A. Sakic, H. Clemens: "Electrons meet alloy development: a γ-TiAl-based alloys showcase". Adv. Eng. Mater., (2021). DOI: 10.1002/adem.202100977

CHARM (Czech-Austrian colloquium on first-principles modelling of advanced materials) 2021 was the first in-person meeting after the Corona had effectively killed traditional scientific interaction. The meeting was hosted by Institute of Physics of Materials, Czech Academy of Sciences in Brno, Czech Republic, and we were able to enjoy many interesting and inspiring presentations and discussions. The Leoben's CMS group was presented by 4 talks by Neda Abdoshahi and Ganesh Nayak (WG Holec) and by Alexander Reichmann and Christoph Dösinger (WG Romaner).

Two talks were delivered in the framework of the departmental seminar series "Materials Science Colloquium": in his talk titled “Chemical shift in W-B-C systems: experiments and modeling” Jaroslav Ženíšek (MU Brno, Czech Republic) reported about their modelling activities of XPS. Tomáš Záležák (IPM Brno, Czech Republic) presented an implementation of discrete dislocation dynamics simulations in a talk titled “Numerical modelling of high temperature deformation using 3D discrete dislocation dynamics”. The seminar was virtual.

Neda has made the history: she is the first PhD student to finish within the CMS group! Her thesis “Ab initio study of martensitic and ordering transformations in intermetallic TiAl-alloys” was positively reviewed. Before passing the oral exam (held in person), Neda presented her thesis on a blackboard instead of a traditional slide presentation, again making history at MUL.
Congratulations!

A primarily theory-based report aimed to answer several questions: is magnetism important for estimating the mechanical properties of CrN-based superlattices? Furthermore, can the computationally difficult paramagnetic state be simplified for modelling to a ferromagnetic state? Lastly, can the Grismditsch and Nizzoli method be used to predict mechanical properties of SL using mechanical properties of its constituents? In short, answers to all these questions are no. Magnetism has a necessary consequence for the structural properties of the superlattices, which are also mimicked in mechanical properties. Micromechanical experiments corroborate the theoretically predicted trends.
The work is a collaboration with the group of Paul Mayrhofer and Matthias Bartosik, TU Wien, Vienna, Austria.

L. Löfler, R. Hahn, P.H. Mayrhofer, M. Bartosik, D. Holec: "Mechanical properties of CrN-based superlattices: Impact of magnetism". Acta Mater., 218, 117095 (2021). DOI: 10.1016/j.actamat.2021.117095

This paper reports on enhanced thermal stability of TiAlON thin films as compared with TiAlN coatings. An extensive experiment analysis including also TEM and APT revealed differences in formation of the wurtzite AlN phase: while this happens inside the cubic grain in TiAlN, w-AlN was observed preferentially at grain boundaries in TiAlON. These differences were eventually linked to differences in diffusion processes: while the diffusion on only metal sublattice is sufficient for decomposition of TiAlN, non-metal species must also diffuse in the TiAlON case. The calculated diffusion barriers are significantly larger for the non-metal species than for the metals, hence hindering the non-metal species diffusion and eventually increasing the thermal stability of TiAlON.
The work is a collaboration with Jochen Schneider's group, RWTH Aachen, Germany.

D.M. Holzapfel, D. Music, M. Hans, S. Wolff-Goodrich, D. Holec, D. Bogdanovski, M. Arndt, A.O. Eriksson, K. Yalamanchili, D. Primetzhofer, C.H. Liebscher, J.M. Schneider: "Enhanced thermal stability of (Ti,Al)N coatings by oxygen incorporation". Acta Mater., 218, 117204 (2021). DOI: 10.1016/j.actamat.2021.117204

First principles calculations are used to calculate diffusion coefficients of Ti and V in TiN matrix. We could show that while the barriers for the interstitial diffusion are small than for a vacancy-mediated mechanism, the latter is a faster procedure leading to an overall larger diffusion coefficient. We have also considered impact of pressure on the diffusion, which was inspired by the realconditions in cutting and tooling applications. We have concluded that the pressure is much less significant than the temperature.
The work is a collaboration with Maxim Popov, MCL Leoben, Austria.

G. Nayak, M.N. Popov, D. Holec: "Pressure- and temperature-dependent diffusion from first-principles: A case study of V and Ti in a TiN matrix". Surf. Coat. Technol., 422, 127491 (2021). DOI: 10.1016/j.surfcoat.2021.127491

A second year of a small team-building activity. We started hiking from Präbichl around 7am and reached the summit shortly after 9.15am. Back in the offices around 1.30pm. More photos in 2021 photo gallery.

Jakob presented results of of his BSc thesis title “Impact of Control Parameters on Molecular Dynamics Simulations of Mechanical Tests”. The thesis contains also original results on tensile tests of TiN/AlN superlattices. The whole work was supervised by Lukas Läfler.
Congratulations on finishing the first stage of your studies and good luck with your MSc work!

Thomas has successfully defended his MSc thesis on “Impact of the stacking sequence on the stability of transition-metal diborides“ and has passed the final exam to get an MSc degree in Materials Science.
Congratulations!

Imaging and analytical modes were used to investigate intermixing of AlN and TiN layers under the indentor tip. Our experimental colleagues could prove that while the cubic lattice (although severaly deformed) is maintained near the tip, Al and Ti metals became intermixed in the form of a TiAlN solid solution. This unique observation was corroborated by a virtual experiment using molecular dynamics, which also resulted into mixing of metallic species beyond a simple deformation-induced displacement. Employing density functional theory we also showed that pressure induced changes in diffusion barriers cannot alone explain the intermixing; other effect such as reduction of interface energy by removing the interfaces and reduction of dislocation density are equally important.
The work is a collaboration with the groups of Zaoli Zhang, ESI-OeAW, Leoben, Austria, and of Paul Mayrhofer and Matthias Bartosik, TU Wien, Vienna, Austria.

Z. Chen, Y. Zheng, L. Löfler, M. Bartosik, G. Nayak, O. Renk, D. Holec, P.H. Mayrhofer, Z. Zhang: "Atomic insights on intermixing of nanoscale nitride multilayer triggered by nanoindentation". Acta Mater., 214, 117004 (2021). DOI: 10.1016/j.actamat.2021.117004

Point defects are essential building blocks for tuning material properties. In this paper, we investigated (our well known :-) TiN synthesized using different bias voltages, leading to varying content of point defects. Analytical investigations using quantitative EELS measurements and XRD revealed compositions of individual coatings. Using DFT, we calculated the dependence of various mechanical properties on the defect concentration (vacancies, interstitials, anti-sites). We were able to correlate those with the measured mechanical properties via micromechanical tests. Thereby, we validated our structural models corresponding to the measured compositions.
The work is a collaboration with the groups of Zaoli Zhang, ESI-OeAW, Leoben, Austria, and of Paul Mayrhofer and Matthias Bartosik, TU Wien, Vienna, Austria.

Z. Zhang, A. Ghasemi, N. Koutná, Z. Xu, T. Grünstäudl, K. Song, D. Holec, Y. He, P.H. Mayrhofer, M. Bartosik: "Correlating point defects with mechanical properties in nanocrystalline TiN thin films". Mater. Des., 207, 109844 (2021). DOI: 10.1016/j.matdes.2021.109844

In this paper we introduce a concept based on a combination of atomistic modelling and continuum mechanics for a core–shell system. Considering crystalline and amorphous gold nanoparticles with radii in the range of 1 nm to 12 nm, we are finally able to independently calculate the values of surface stress and surface energy, both slightly decreasing with the increasing particle radius. Surprisingly large values of surface stress are predicted for the case of amorphous nanoparticles.
The work is a collaboration with the professors Franz Dieter Fischer (Leoben, Austria) and Dieter Vollath (Germany)

D. Holec, L. Löfler, G.A. Zickler, D. Vollath, F. Fischer: "Surface stress of gold nanoparticles revisited". Int. J. Solids Struct., 224, 111044 (2021). DOI: 10.1016/j.ijsolstr.2021.111044

Ulrich has presented content of his BSc thesis. Due to the circumstances, the presentation was online, nonetheless, it was fairly well attended with around 20 listeners in the audience (including guest outside of the Uni :-).
Congratulations on finishing the first stage of your studies!

A methodological error in our original paper (Phys. Rev. B 101, 125421 (2020)) regrettably led to an overestimation of the softening in bilayer graphene as compared with graphite. Moreover, inconsistencies in the numerical integration of charge have been corrected, now showing a much more physical picture of electron squeezing through the graphene layers. The corrected results do not qualitatively change the message. In addition to self-correcting our predictions, we have gained more insight into the evaluation of stresses in low-dimensional materials.
The work is a collaboration with the groups of Colin Humphreys and David Dunstan, Queen Mary University of London, London, UK.

Y.W. Sun, D. Holec, D. Gehringer, O. Fenwick, D.J. Dunstan, C.J. Humphreys: "Erratum: Unexpected softness of bilayer graphene and softening of A-A stacked graphene layers [Phys. Rev. B 101, 125421 (2020)]". Phys. Rev. B Condens. Matter, 103(11), 119901 (2021). DOI: 10.1103/PhysRevB.103.119901

In this paper, we present a model which accounts for lattice mismatch stress relaxation during growth by a subsequent introduction of misfit dislocations at the interfaces. The driving force for this process is the minimization of the overall elastic energy. In turn, these misfit dislocations contribute towards alternating compressive/tensile stress profile which introduces an additional barrier for a crack propagation on top of the intrinsic fracture toughness. This phenomenon, termed apparent fracture toughness, enabled rationalisation of experimentally reported enhancement of fracture toughness in CrN/TiN superlattices.
The work is a collaboration with the group of Paul Mayrhofer and Matthias Bartosik, TU Wien, Vienna, Austria.

A. Wagner, D. Holec, P.H. Mayrhofer, M. Bartosik: "Enhanced fracture toughness in ceramic superlattice thin films: On the role of coherency stresses and misfit dislocations". Materials and Design, 202 (2021). DOI: 10.1016/j.matdes.2021.109517

Using in-situ atomic-resolution electron microscopy, we report twin boundary migration mechanisms in rock-salt CrN. We show that coherent TB migration is associated with a boundary structure alternating from an N-terminated to Cr-terminated, involving Cr and N atom respective motion, i.e., asynchronous CTB migration. These observations are corroborated through strain analysis and DFT simulations which reveal the dynamic and thermodynamic mechanism of such asynchronous migration.
The work is a collaboration with the group of Zaoli Zhang, ESI-OeAW, Leoben, Austria.

Z. Chen, Y. Zheng, L. Löfler, M. Bartosik, H. Sheng, C. Gammer, D. Holec, Z. Zhang: "Real-time atomic-resolution observation of coherent twin boundary migration in CrN". Acta Mater., 208, 116732 (2021). DOI: 10.1016/j.actamat.2021.116732

MoN and TaN can be stabilized in cubic structures, however, not with a stoichiometric composition. While MoN prefers N vacancies, TaN likes metallic vacancies. In this study, we probe experimentally and theoretically the interplay between amount and type of point defects and the resulting microstructure. It turns out that modifying N partial pressure during a PVD deposition can prefer either N vacancies (low N partial pressures) or metal vacancies (high N partial pressure). In the latter case, the cubic phase tends to co-exist with a hexagonal phase, which strongly impacts the overall mechanical properties.
The work is a collaboration with the group of Paul Mayrhofer, TU Wien, Vienna, Austria.

F.F. Klimashin, L. Lobmaier, N. Koutná, D. Holec, P.H. Mayrhofer: "The MoN–TaN system: Role of vacancies in phase stability and mechanical properties". Mater. Des., 202, 109568 (2021). DOI: 10.1016/j.matdes.2021.109568

In the framework of the departmental seminar series "Materials Science Colloquium", Marcus Hans (RWTH Aachen, Germany) has presented selected examples of the application of atom probe tomography to study the thermal stability of hard coatings. The selected applications included VAlN and two examples of high-entropy on metal sublattice (HEM) coatings: HEMN and HEMB₂. The virtual seminar was attended also by our guests from TU Wien and from RWTH Aachen, with over 40 participants.

First principle calculations are utilized to probe different combinations of nitrites and carbides to form superlattices. Those are characterized with respect to their chemical and mechanical stability and mechanical properties. Additionally, also impact of point defects (vacancies) is discussed. We then apply several selection criteria to propose potentially interesting material combinations with improved ductility and fracture resistance. Among the "usual suspects" such as MoN/TaN or TiN/WN we newly propose several combinations (e.g. NbC/MoN, TaX/WN or VC/HfN) which are worth testing experimentally.
The work is a collaboration with the group of Paul Mayrhofer, TU Wien, Vienna, Austria.

N. Koutná, A. Brenner, D. Holec, P.H. Mayrhofer: "High-throughput first-principles search for ceramic superlattices with improved ductility and fracture resistance". Acta Mater., 206, 116615 (2021). DOI: 10.1016/j.actamat.2020.116615

As a part of the departmental seminar series "Materials Science Colloquium", Martin has presented summary of his work from the past 5 years focusing on ab initio investigations of intriguing interplay between local chemistry, magnetism and thermodynamics of anti-phase boundaries in FeAl intermetallics. Due to the present situation, the seminar was virtual, but still with a decent attendance.

Amin has successfully defended his MSc thesis on "Ab initio calculations of alloying impact on structural properties and stability of cementite" and has passed the final exam to get an MSc degree in Materials Science.
Congratulations!

The superlattice effect on mechanical properties was investigated in this paper. Namely, what is the impact of lattice mismatch for two elastically-matched systems. It has turned out that both hardness and marginally also fracture toughness exhibit the superlattice effect, although not as strong as for lattice-matched systems with different elastic moduli.
The work is a collaboration with the group of Paul Mayrhofer and Matthias Bartosik, TU Wien, Vienna, Austria.

J. Buchinger, A. Wagner, Z. Chen, Z.L. Zhang, D. Holec, P.H. Mayrhofer, M. Bartosik: "Fracture toughness trends of modulus-matched TiN/(Cr,Al)N thin film superlattices". Acta Mater., 202, 376–386 (2021). DOI: 10.1016/j.actamat.2020.10.068

In this work we focused on bcc-fcc martensitic transformations in Ti-Al-Mo ternary system, namely on the effect of Mo alloyed in TiAl on them. We could show that a tetragonal Bain path proceeds almost without any energy barrier between the ordered structure, hence suggesting spontaneous transformation into either γ-TiAl for low Mo content or to β-TiAl for Mo content above 8 at.%. Chemical disorder introduces barrier along the tetragonal path which to the stabilisation of the bcc β phase. Lastly, a potential connection via trigonal path has been ruled out due to too high transformation barriers.
The work is a collaboration with the group of Martin Friák and Mojmír Šob, Academy of Sciences, Brno, Czech Republic.

N. Abdoshahi, P. Spoerk-Erdely, M. Friák, S. Mayer, M. Šob, D. Holec: "Ab initio study of chemical disorder as an effective stabilizing mechanism of bcc-based TiAl+Mo". Phys. Rev. Materials, 4(10), 103604 (2020). DOI: 10.1103/PhysRevMaterials.4.103604

A small replacement for team-building activities which would have normally be a part of group's retreat. Starting at 5.30am from Leoben, we reached Präbichl started hiking around 6am. Summit photo has a timestamp 8.30am. Back in the office around 12noon. More photos in 2020 photo gallery.

By investigating structural and mechanical properties of MoN-TaN superlattices with different bilayer thickness, we develop coatings with high fracture toughness and hardness, stemming from the formation of a metastable tetragonally distorted phase of TaN up to layer thicknesses of 2.5 nm. Density functional theory calculations and experimental results further reveal a metal-vacancy stabilized cubic Ta_0.75N phase with an increased Young’s modulus but significantly lower fracture toughness. The close interplay between our experimental and ab initio data demonstrates the impact of phase formation and stabilization on the mechanical properties of MoN-TaN superlattices.
The work is a collaboration with the group of Paul Mayrhofer, TU Wien, Vienna, Austria.

R. Hahn, N. Koutná, T. Wójcik, A. Davydok, S. Kolozsvári, C. Krywka, D. Holec, M. Bartosik, P.H. Mayrhofer: "Mechanistic study of superlattice-enabled high toughness and hardness in MoN/TaN coatings". Communications Materials, 1(1), 62 (2020). DOI: 10.1038/s43246-020-00064-4

The summer celebration with a group BBQ at David' garden becomes a tradition. Also this year :-)

In this work, the structural and mechanical properties of ternary Mo-Al-N alloys are investigated by combining thin film growth experiments and density functional theory (DFT) calculations. The experimental part was done by our French collaborators, groups of Gregory Abadias and Philippe Djemia.

F. Anğay, L. Löfler, F. Tetard, D. Eyidi, P. Djemia, D. Holec, G. Abadias: "Structure, stress, and mechanical properties of Mo-Al-N thin films deposited by dc reactive magnetron cosputtering: Role of point defects". J. Vac. Sci. Technol. A, 38(5), 053401 (2020). DOI: 10.1116/6.0000292

Summer holidays start off with a brand new publication. Together with colleagues from TU Wien and ESI, we show that K_IC of TiN does not change (significantly) with temperature. The experimental findings are corroborated by modelling scaling from electronic structure, over molecular dynamics up to continuum level.

J. Buchinger, L. Löfler, J. Ast, A. Wagner, Z. Chen, J. Michler, Z.L. Zhang, P.H. Mayrhofer, D. Holec, M. Bartosik: "Fracture properties of thin film TiN at elevated temperatures". Mater. Des., 194, 108885 (2020). DOI: 10.1016/j.matdes.2020.108885

The CMS group has survived the social distancing caused by the corona outbreak without any damage. Not only we all have found out that we could do almost 100% of our work from home (or any other place with internet), but the group has been quite productive: both in getting new results as well as publishing them. Check out the list of new publications in 2020!

In order to keep tradition, we also this year we went for a half-day skiing at Präbichl. And Ganesh made his first few turns!

Multi-phase ELAStic Aggregates (MELASA) is a new web-based software tool for modelling anisotropic elastic properties of lamellar composites. It implements a linear-elasticity method by Grimsditch and Nizzoli (1986), originally developed for superlattices of any symmetry. Resulting elastic properties are visualized in the form of directional dependencies of selected elastic characteristics (Young’s modulus and linear compressibility).

M. Friák, D. Lago, N. Koutná, D. Holec, T. Rebok, M. Šob: "Multi-phase ELAStic Aggregates (MELASA) software tool for modeling anisotropic elastic properties of lamellar composites". Comput. Phys. Commun., 247, 106863 (2020). DOI: 10.1016/j.cpc.2019.106863

Neda Abdoshahi with her husband Masoud Taheri have become proud parent of little Maria. We wish you three together a happy life and congratulate to you!

Using DFT calculations we showed that N alloying to the non-metal sublattice in TaC improves its ductility. The material has been subsequently synthesised using PVD and characterised using micromechanical testing showing that TaC-based materials are harder than TiN- and CrN-based systems while exhibiting similar fracture toughness.

T. Glechner, R. Hahn, T. Wojcik, D. Holec, S. Kolozsvári, H. Zaid, S. Kodambaka, P.H. Mayrhofer, H. Riedl: "Assessment of ductile character in superhard Ta-C-N thin films". Acta Mater., 179, 17–25 (2019). DOI: 10.1016/j.actamat.2019.08.015

Intermetallics 2019 conference took place in Bad Staffelstein, Germany from 30^th September till 4^thOctober 2019 in the premises of former cloister Kloster Banz. David has presented a talk on "Impact of Mo and disorder on diffusionless transformations in TiAl intermetallic alloys" and a poster "Alloying impact on phase stability in ZrAl₃". Both works attracted attention and stimulated further interaction with other colleagues.

Dominik Nöger and Sabrina Gehringer have married last weekend. We wish you all the best on your journey together!

The 1^st group retreat took place during 6^th–8^th August 2019 at Edelrautehütte. We have enjoyed stimulating "off-line" environment with gorgeous mountain sceneries for numerous and lengthy discussions, planning future projects, updating about current progress and team binding together.

MSMF-9 (Materials Structure & Micromechanics of Fracture) conference took place in Brno, Czech Republic. During this three days meeting (June 26-28, 2019), works of Lukas Löfler and Lukas Hatzenbichler on mechanical properties of superlattices were presented, together with co-authored contributions from colleagues from TU Wien and IPM Brno.

In this ab initio study we predict a remarkable sensitivity of vacancy formation energies, their volumes and changes of local magnetic moments of neighbouring Fe atoms on the chemical composition around the vacancy.

I. Miháliková, M. Friák, N. Koutná, D. Holec, M. Šob: "An Ab Initio Study of Vacancies in Disordered Magnetic Systems: A Case Study of Fe-Rich Fe-Al Phases". Materials, 12(9) (2019). DOI: 10.3390/ma12091430

Extended approach based on quasi-harmonic approximation was applied to two non-cubic phases, namely to a (slightly) tetragonal γ-TiAl and to hexagonal α₂-Ti₃Al. Here we have compared traditional QHA calculation with the cell-shape optimised only at 0 K with novel "temperature-optimised cell shape" approach in which, for example, the c/a may differ at finite temperature from that at 0 K for the same specific volume. While the two approaches yield almost identical results for the α₂-Ti₃Al phase, in the case of γ-TiAl the new approach seem to be essential in order to obtain thermal properties in agreement with experiment.

D. Holec, N. Abdoshahi, S. Mayer, H. Clemens: "Thermal Expansion and Other Thermodynamic Properties of α₂-Ti₃Al and γ-TiAl Intermetallic Phases from First Principles Methods". Materials, 12(8) (2019). DOI: 10.3390/ma12081292

Using DFT calculations, we identified TiN/WN_0.5 superlattices as a feasible system with a supposed potential for ductility clearly exceeding that of the monolithic constituents as well as many other established TMNs. These predictions were confirmed experimentally by showing peaks in hardness and toughness as functions of the superlattices bi-layer period. Finally, applying information from DFT and a continuum-mechanics model for effective elastic properties, we were able to propose a complicated distribution of vacancies near the interfaces, leading to a stabilisation of phases with excellent mechanical properties, but not existing in a bulk form.

J. Buchinger, N. Koutná, Z. Chen, Z. Zhang, P. Mayrhofer, D. Holec, M. Bartosik: "Toughness enhancement in TiN/WN superlattice thin films". Acta Mater., 172, 18–29 (2019). DOI: 10.1016/j.actamat.2019.04.028

DPG Spring Meeting 2019 took place in Regensburg (Germany) from March 31 to April 5, 2019. Our group was well represented with 5 contributed talks and additional 4 co-authored presentations. Next to the interesting scientific programme and exciting discussions and networking, Lukas, Dominik and David managed to spare some time also for the city tour.

In this paper we explore an apparent disagreement between the nominal stoichiometry and reported elemental composition of Nb₃Al. By employing standard DFT phase stability assessment combined with evolutionary algorithms we were able to show that the phase can become mechanically and vibrationally stable when considering Nb anti-sites which additionally leads to experimentally reported composition.

N. Koutná, P. Erdely, S. Zöhrer, R. Franz, Y. Du, S. Liu, P.H. Mayrhofer, D. Holec: "Experimental Chemistry and Structural Stability of AlNb₃ Enabled by Antisite Defects Formation". Materials, 12(7), 1104 (2019). DOI: 10.3390/ma12071104

A great day out! Despite the summer-like temperatures we were able to enjoy morning skiing. Fangyu made her first steps (and turns) and by the lunch time, she was able to ski a (very) blue slope down on her own, accompanied by cheering Lukas, Dominik and David.

In this paper we use ab initio calculations to study impact of crystal structure (cubic vs. hexagonal) and interface orientation (cubic (001) or (111)) on elastic properties and tensile strength of TiN/AlN superlattices. We were able to reproduce and explain experimental trends in bi-layer period dependence of Young's modulus.

N. Koutná, P. Řehák, Z. Chen, M. Bartosik, M. Fallmann, M. Černý, Z. Zhang, M. Friák, M. Šob, P.H. Mayrhofer, D. Holec: "Correlating structural and mechanical properties of AlN/TiN superlattice films". Scr. Mater., 165, 159–163 (2019). DOI: 10.1016/j.scriptamat.2019.02.021

A series of papers focusing on stability and mechanical properties of nanocomposites, strength of interfaces and grain boundaries, elasticity of grain boundaries and pressure impact on elastic anisotropy has been recently published. These are results of a long-standing collaboration between our group and the group of Dr. Friák and Prof. Šob at the Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.

I. Miháliková, M. Friák, Y. Jirásková, D. Holec, N. Koutná, M. Šob: "Impact of Nano-Scale Distribution of Atoms on Electronic and Magnetic Properties of Phases in Fe-Al Nanocomposites: An Ab Initio Study". Nanomaterials (Basel), 8(12) (2018). DOI: 10.3390/nano8121059

M. Friák, D. Holec, M. Šob: "Quantum-Mechanical Study of Nanocomposites with Low and Ultra-Low Interface Energies". Nanomaterials (Basel), 8(12) (2018). DOI: 10.3390/nano8121057

M. Friák, P. Kroupa, D. Holec, M. Šob: "An Ab Initio Study of Pressure-Induced Reversal of Elastically Stiff and Soft Directions in YN and ScN and Its Effect in Nanocomposites Containing These Nitrides". Nanomaterials (Basel), 8(12) (2018). DOI: 10.3390/nano8121049

M. Friák, M. Zelený, M. Všianská, D. Holec, M. Šob: "An Ab Initio Study of Connections between Tensorial Elastic Properties and Chemical Bonds in Σ5(210) Grain Boundaries in Ni₃Si". Materials, 11(11), 2263 (2018). DOI: 10.3390/ma11112263

P. Šesták, M. Friák, D. Holec, M. Všianská, M. Šob: "Strength and Brittleness of Interfaces in Fe-Al Superalloy Nanocomposites under Multiaxial Loading: An ab initio and Atomistic Study". Nanomaterials, 8(11) (2018). DOI: 10.3390/nano8110873

Dominik Nöger was selected among the 20 Master theses to be awarded "WKO Steiermark Forschungsstipendien 2018". The award ceremony took place in Europasaal of the WKO Steiermark in Graz on Monday December 10, 2018.
Congratulations!

Dominik has successfully defended his MSc thesis on "Interaction of the H₂ molecule with carbon nanostructures: A DFT study" and has passed the final exam to get an MSc degree in Materials Science.
Congratulations!

After about a year of promises and discussions, the very first stub of our group website comes on-line. It is by far not complete nor in a final shape, but it is alive!

A new paper on an initio molecular dynamics study of early stages of oxidation of Ti-Al-N coatings has been accepted in Applied Surface Science. We report on impact of temperature and Al content on the structure of the oxide layer and show, that the composition strongly influences whether an Al-rich or a Ti-rich layer builds near to the interface coating-oxide.

F. Guo, J. Wang, Y. Du, D. Holec, P. Ou, H. Zhou, L. Chen, Y. Kong: "Structural evolution of oxygen on the surface of TiAlN: Ab initio molecular dynamics simulations". Appl. Surf. Sci., 470, 520–525 (2019). DOI: 10.1016/j.apsusc.2018.11.158