Article
Chemistry, Physical
Wenyu Huang, Liying Hou, Yang Song, Gang Chen
Summary: Our calculations suggest that assembly of dehydrogenated pyracyclene molecules can produce novel graphene allotropes with high stabilities. The allotropes exhibit different properties, including a Dirac semimetal with tunable velocities of the massless Fermion carriers and a semiconducting material with a 1.20 eV band gap and high charge carrier mobilities. These allotropes could be used in next-generation nanoelectronics and as photovoltaic materials. Additionally, stacked layers of the allotropes show potential as anodes for lithium-ion batteries.
JOURNAL OF PHYSICAL CHEMISTRY C
(2023)
Article
Chemistry, Physical
Wenyu Huang, Liying Hou, Yang Song, Gang Chen
Summary: Our first-principles calculations suggest the assembly of dehydrogenated pyracyclene molecules can form novel graphene allotropes with high stabilities. These allotropes have the potential for various applications, such as photovoltaic materials, next-generation nanoelectronics, and lithium-ion battery anodes.
JOURNAL OF PHYSICAL CHEMISTRY C
(2023)
Article
Chemistry, Physical
Philippe F. Weck, Nathan W. Moore
Summary: The equations of state for different polymorphs of Nb2O5 were investigated, and shock Hugoniot curves were predicted using ab initio molecular dynamics simulations. The simulated results were consistent with experimental measurements of phase transitions and pressure-induced amorphization.
CHEMICAL PHYSICS LETTERS
(2023)
Article
Materials Science, Multidisciplinary
Zhigang Wu, John W. Lawson
Summary: This study reports on the unresolved problems and proposed solutions when using the ab initio approach to study NiTi alloys. The results show that including the electronic free energy in the Gibbs free energy calculations significantly reduces errors in martensitic transition temperatures and resolves controversies on the ground state of NiTi. Additionally, it is discovered that the martensitic transition path in stoichiometric NiTi is directly from B2 to B19' without intermediate phases.
Review
Chemistry, Multidisciplinary
Jorge Barroso, Sudip Pan, Gabriel Merino
Summary: The author summarizes the cases of structural transformation in clusters of no more than 40 boron atoms, where one or two dopants result in a radical change in the structure. The minimum energy structure induced by doping is usually entirely different from that of the bare cluster. Despite the difficulty in predicting the structures of these systems, they often adopt familiar shapes such as umbrella-like, wheel, tubular, and cages in various cases.
CHEMICAL SOCIETY REVIEWS
(2022)
Article
Chemistry, Physical
Chi Ding, Jianan Yuan, Yu Han, Zhongwei Zhang, Qiuhan Jia, Junjie Wang, Jian Sun
Summary: Inspired by stabilized nitrogen chains by certain metal atoms, we explored the possibility of new nitrogen polymorphs stabilized by trivalent lanthanum ions and identified three novel thermodynamically stable phases. Among them, the C2/c phase with infinite helical poly-N-6 chains becomes stable at high pressure and exhibits excellent electronic and bonding properties.
JOURNAL OF CHEMICAL PHYSICS
(2023)
Article
Materials Science, Multidisciplinary
Sven P. Rudin
Summary: Ga doping stabilizes the delta phase of Pu, but the mechanism of this stabilization is still unknown. Density functional theory calculations reveal that Ga doping affects the phonon modes of Pu, with high-frequency modes becoming softer and low-frequency modes becoming stiffer. This suggests that the stabilization is not due to a thermodynamic contribution from the phonons, and the stiffened phonon modes may impede the formation of low-temperature phases.
Article
Physics, Condensed Matter
O. I. Barkalov, M. A. Kuzovnikov, I. A. Sholin, N. S. Orlov
Summary: The phase transformations of silicon clathrate Si-136 under high hydrogen pressure were studied, revealing pressure-dependent vibrational mode frequencies that agreed with ab initio calculations. At 10 GPa, Si-136 transformed into a mixture of Si-II and Si-III phases, with no observed interaction between hydrogen and silicon during compression or decompression.
SOLID STATE COMMUNICATIONS
(2021)
Article
Chemistry, Physical
Bingmei Liu, Wangping Xu, Xia Long, Juexian Cao
Summary: The phase transition mechanism of single- and bilayer MoS2 induced by lithium intercalation has been systematically studied using first principles. It is found that lithium intercalation can effectively reduce the sliding barrier of the S atom layer. The phase transition in bilayer MoS2 is induced by S atom transition one by one, and consists of the formation, diffusion, and recombination of S vacancies. The phase transition originates from interlayer lithium defects, while monolayer MoS2 cannot undergo phase transition due to the larger sliding barrier of the S atom.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2022)
Article
Materials Science, Multidisciplinary
Zhigang Wu, John W. Lawson, Othmane Benafan
Summary: Nitinol (NiTi) is a commonly used shape memory alloy. A small change in the concentration of nickel and titanium has a dramatic effect on the martensitic transition temperature (MTT), leading to complications in manufacturing and applications of NiTi-based SMAs.
Article
Chemistry, Multidisciplinary
Zhizhou Liu, Alasdair McKay, Lili Zhao, Craig M. Forsyth, Violeta Jevtovic, Milena Petkovic, Gernot Frenking, Dragoslav Vidovic
Summary: Introducing a small phosphorus-based fragment into molecules via trapping and releasing reactive phosphorus-based molecules is an important process in synthetic chemistry. This study used electron-rich hexaphenylcarbodiphosphorane to stabilize the least thermodynamically favorable isomer of HO2P and transfer it to various substrates. Additionally, several phosphorus-based compounds were isolated and characterized using this synthetic approach.
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
(2022)
Article
Materials Science, Multidisciplinary
Antoine Jay, Olivier Hardouin Duparc, Jelena Sjakste, Nathalie Vast
Summary: The Raman spectrum of boron carbide under pressure is explained by the vibrations of (B11C) icosahedra and C-B-C chains, while the behavior of a broad Raman band at low frequency is attributed to the activation of the chain bending mode in flexured chains. The 270 cm-1 ambient-P mode is proposed as a fingerprint for identifying chain defects and deviations from rhombohedral symmetry in boron carbide.
Article
Crystallography
Vladimir A. Stephanovich, Christian Rodenbuecher, Michal Pilch, Jacek Szade, Andrzej Molak, Gustav Bihlmayer, Krzysztof Szot
Summary: We study the self-polarization phenomenon in single, electroded PbTiO3 crystals, where surface layers with a modified perovskite structure near the electrodes generate a built-in electric polarization. The self-polarization effect is attributed to the occurrence of a built-in electric field resulting from the formation of Pb-O planes within the surface layer. Experimental findings are described using a combination of phenomenological and ab initio models, taking into account the actual atomic structure at the bulk ferroelectric-surface layer-electrode interface.
Article
Chemistry, Physical
T. N. Vershinina, N. S. Kirilkin, V. A. Skuratov, A. P. Surzhikov, S. A. Ghyngazov, V. A. Boltueva, J. H. O'Connell, R. A. Rymzhanov
Summary: The paper investigates the impact of swift heavy Xe ion irradiation on partially stabilized zirconia ceramics. It finds that the efficiency of high-energy ion track formation decreases with increasing fluence and fraction of the t phase. Nanoindentation and microindentation techniques are used to study the changes in hardness, modulus, and microhardness of the ceramics. The mechanisms behind ceramic layer hardening are discussed, including phase rearrangement, compressive stress accumulation, and transformation and ferroelastic hardening.
RADIATION PHYSICS AND CHEMISTRY
(2022)
Article
Physics, Multidisciplinary
Yue Chen, Zhengtao Liu, Ziyue Lin, Qiwen Jiang, Mingyang Du, Zihan Zhang, Hao Song, Hui Xie, Tian Cui, Defang Duan
Summary: Theoretical predictions and experimental synthesis have shown that H3S and LaH10 superconductors have record high superconducting transition temperatures, making hydrogen-based superconductors a hot topic in the field of solid-state physics. In this study, a new layered structure called CaH15 with high Tc of 189 K at 200 GPa is predicted using ab initio calculations. Similar layered structures were also found in SrH15, YH15, and LaH15 at high pressures, with each material exhibiting high Tc values.
FRONTIERS OF PHYSICS
(2022)
Review
Materials Science, Multidisciplinary
David Holec, Neda Abdoshahi, Dominik Gehringer, Lukas Hatzenbichler, Amin Sakic, Helmut Clemens
Summary: Density functional theory is essential in current electronic structure calculations, particularly in its applications in materials science, providing insights beyond experimental capabilities, testing hypotheses, and isolating various phenomena. By extracting alloying trends for alloy refinement and considering site preference in constructing structural models, alloying trends in structural and mechanical properties are discussed, along with microstructure features. This unified theme explores compositional trends in properties of lightweight intermetallic gamma-TiAl-based alloys.
ADVANCED ENGINEERING MATERIALS
(2022)
Article
Materials Science, Multidisciplinary
Neda Abdoshahi, Mohammad Dehghani, Andrei Ruban, Martin Friak, Mojmir Sob, Juergen Spitaler, David Holec
Summary: Diffusionless transformations allow access to metastable phases and enrich the materials design portfolio. This study comprehensively investigates the transformation energetics between ordered and disordered phases in the TiAl+Mo model alloy system. The results show that chemical disorder flattens the energy landscape but may introduce a small barrier, while ordered phases have barrier-less energetics. Additionally, it is found that Mo stabilizes the bcc phases, leading to a barrier-less transformation from hcp to bcc.
Article
Materials Science, Multidisciplinary
Amin Sakic, Christina Hofer, Ronald Schnitzer, David Holec
Summary: In this study, ab initio calculations were used to investigate the effect of alloying elements on the stability of cementite. The partitioning energy and the change in formation energy were calculated to quantify the phase (de)stabilization. Aluminum and silicon were found to enhance the elastic stability of cementite.
ADVANCED ENGINEERING MATERIALS
(2022)
Article
Materials Science, Multidisciplinary
Michael Musi, Stefan Kardos, Lukas Hatzenbichler, David Holec, Andreas Stark, Melissa Allen, Volker Guther, Helmut Clemens, Petra Spoerk-Erdely
Summary: In recent years, Zr has emerged as a promising alloying element for intermetallic gamma-TiAl based alloys to improve their mechanical properties. This study focuses on the influence of Zr on the microstructure and thermodynamic phase equilibria in the ternary Ti-(42-46)Al-(2-4)Zr (at.%) system. The results show that alloying with Zr increases the amount of the gamma phase and enhances the hardness of the material. Additionally, the high Zr alloyed materials exhibit a decrease in solidus temperature. These findings are important for understanding and optimizing the performance of gamma-TiAl based alloys.
Article
Chemistry, Physical
I. Jennifer Gomez, Manuel Vazquez Sulleiro, Nadezda Pizurova, Antonin Bednarik, Petr Lepcio, David Holec, Jan Preisler, Lenka Zajickova
Summary: Carbon dots (CDs) exhibit similar photophysical features despite different synthesis protocols. Understanding the structure is crucial for achieving desired properties. This study provides insight into the structure and formation of CDs, identifying the presence of molecular fluorophore species. Density functional theory calculations support the spontaneous formation of a compact network of molecular species. Additionally, the study comprehensively investigates the photoluminescence properties, paving the way for CD-based logic gate fluorescent sensors.
APPLIED SURFACE SCIENCE
(2023)
Article
Chemistry, Physical
Martin Friak, Martin Zeleny, Martina Mazalova, Ivana Mihalikova, Ilja Turek, Jiri Kastil, Jiri Kamarad, Martin Misek, Zdenek Arnold, Oldrich Schneeweiss, Mojmir Sob
Summary: In this study, a quantum-mechanical investigation was conducted on the thermodynamic, elastic, magnetic, and structural properties of four different ferrimagnetic states in Ni1.9375Mn1.5625Sn0.5 martensite. The results revealed that the Mn atoms in the Ni sublattice play a crucial role in determining both the thermodynamic and magnetic properties of the system. Additionally, the mechanically stable lowest-energy configuration exhibited anti-parallel local magnetic moments of the Mn atoms in relation to the total magnetic moment. The vibrational properties of individual atoms were found to be highly sensitive to chemical disorder.
Article
Chemistry, Physical
Martin Friak, Miroslav Cerny, Mojmir Sob
Summary: The study shows that antiphase boundaries (APBs) strongly influence the thermal vibrations and phonon gap width of Fe3Al. Fe3Al with APBs exhibits higher volumetric thermal expansion and lower free energy compared to defect-free Fe3Al. The presence of APBs also reduces the bulk modulus, resulting in elastic softening of Fe3Al.
Article
Chemistry, Physical
Jiehua Li, Xuyang Zhou, Andrew Breen, Zirong Peng, Jing Su, Philipp Kuernsteiner, Maria Jazmin Duarte Correa, Huiyuan Wang, David Holec, Joachim Mayer, Gerhard Dehm, Marta Lipinska Chwanek
Summary: The formation and transformation mechanisms of Ca-rich Laves phases in Mg-Al-Ca-Mn alloys were investigated, revealing the divorced eutectic reaction responsible for the formation of C36 Laves phase and Mg-rich particles, as well as the processes involved in the transformation from C36 to C15 Laves phase, such as Mg out-diffusion, Al partitioning, and changes in stacking sequences.
JOURNAL OF ALLOYS AND COMPOUNDS
(2022)
Article
Computer Science, Interdisciplinary Applications
Dominik Gehringer, Martin Friak, David Holec
Summary: We present a Python package for generating special quasi-random structures (SQS) for atomic-scale calculations of disordered systems. The package offers efficient optimization methods and analysis tools for finding optimal structures and quantifying randomness. It also provides a command-line interface and Python API for easy integration into complex simulation workflows.
COMPUTER PHYSICS COMMUNICATIONS
(2023)
Article
Materials Science, Multidisciplinary
Ganesh Kumar Nayak, Andreas Kretschmer, Paul H. Mayrhofer, David Holec
Summary: High entropy alloys (HEAs) have attracted significant attention for their unique structural stability and excellent properties. The concept of high entropy has also been applied to protective coatings. Ab initio calculations reveal the atomic-level behavior of HEAs, particularly focusing on the interplay between high entropy, sluggish diffusion, and lattice distortions in HESN ceramics. The study shows that high entropy alone does not guarantee slow diffusion, and proposes a relationship between local distortions and activation energies. These findings emphasize the need to analyze each system individually to understand the core effects of HEAs.
Article
Chemistry, Physical
J. Kastil, J. Kamarad, M. Friak, M. Misek, U. Dutta, P. Kral, O. Kaman, Z. Arnold
Summary: The Ni2.01Mn1.58Sn0.41 alloy undergoes a diffusionless structural transition and exhibits complex magnetic and electronic structures. It shows a spin-glass state below 155 K and has clusters with strong interactions. The alloy also displays anomalous Hall effect and a positive ordinary Hall coefficient. The electrical resistance shows a flat maximum at the spin-glass transition temperature. Quantum mechanical calculations reveal local chemical variations and clustering in the alloy.
Article
Physics, Applied
Martin Friak, Tran Quynh Nhu, Mojmir Meduna, Kristyna Gazdova, Jana Pavlu, Dominik Munzar, Nguyen Hoa Hong
Summary: We have conducted a combined experimental and theoretical study on the surface-related magnetic states in TiO2. The room-temperature magnetism observed in pure TiO2 thin films is found to originate from defects, particularly from the surface of thin films and oxygen vacancies mainly located at the surface. Detailed experimental investigations are demanding, hence we performed quantum-mechanical density functional theory calculations to clarify this phenomenon. Our calculations identified non-magnetic behavior in bulk anatase TiO2 and bulk-like TiO2-terminated (001) surfaces without vacancies. However, oxygen vacancies in TiO-terminated and TiO0.75-terminated (001) surfaces led to ferromagnetic and rather complex ferrimagnetic states, respectively. Spin-polarized atoms were found in the surface and sub-surface atomic planes, particularly the Ti atoms due to the d-states. The O-terminated surfaces also exhibited magnetism, but with high surface energy.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Materials Science, Multidisciplinary
Y. W. Sun, D. Holec, D. Gehringer, L. Li, O. Fenwick, D. J. Dunstan, C. J. Humphreys
Summary: Density functional theory was used to study the properties of graphene on different orientations of silicon substrates. It was found that covalent bonds can form between graphene and silicon atoms, and the different orientations of the silicon substrate have a significant effect on the electron density and work function of graphene. These findings provide valuable guidance for the growth of graphene on silicon for electronic devices.
Article
Materials Science, Multidisciplinary
Y. W. Sun, D. Gehringer, D. Holec, D. G. Papageorgiou, O. Fenwick, S. M. Qureshi, C. J. Humphreys, D. J. Dunstan
Summary: This paper reinterprets the Raman spectra of double-walled carbon nanotubes and finds that more pressure can be transmitted to the inner tube than expected. The findings are important for understanding the mechanical properties, thermal expansion, and strain engineering of two-dimensional materials, and the correct interpretation of Raman shift in strained layered 2D materials.
