Structural Energy Differences in Al3Ti: The Role of Tetragonal Distortion in APB and Twin Energies

1988 ◽  
Vol 133 ◽  
Author(s):  
O. M. Nicholson ◽  
G. M. Stocks ◽  
W. M. Temmerman ◽  
P. Sterne ◽  
D. G. Pettifor
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
Ground State ◽  
Critical Role ◽  
Tetragonal Distortion ◽  
Standard Approach ◽  
Fcc Lattice ◽  
Major Impediment ◽  
The Ideal

ABSTRACTAt stoichiometry, DO22 is the observed ground state of Al2Ti and has a C/A ratio of 2.23, but as a function of both concentration and temperature other ordered arrangements of APB's are observed. These phase transitions have sparked many studies in which the energy has been treated as that of chemical rearrangement on an fcc lattice. We have found that at the ideal C/A ratio, the Ll2 structure is lower in energy, but as the tetragonal distortion increases the DO22 energy drops below that of Ll2. The critical role played by the tetragonal distortion in the balance between Ll2 and DO22 energies precludes the use of any model based on the undistorted lattice.The major impediment to the development of Al3Ti as a high-temperature material is its lack of ductility. The standard approach is to make alloy additions which transform the structure to Ll2. An alternate approach is to work toward the enhancement of ductility in the DO22 phase. As a first step we have calculated the twinning energy in Al3Ti.

scholarly journals Molecular-scale investigation of the oxidation behavior of chromia-forming alloys in high-temperature CO2

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Richard P. Oleksak ◽  
Rafik Addou ◽  
Bharat Gwalani ◽  
John P. Baltrus ◽  
Tao Liu ◽  
...  
Keyword(s):  
High Temperature ◽  
Power Systems ◽  
High Purity ◽  
Photoelectron Spectroscopy ◽  
Ambient Pressure ◽  
Critical Role ◽  
Atomic Scale ◽  
Atomic Diffusion ◽  
Carbon Transport

AbstractCurrent and future power systems require chromia-forming alloys compatible with high-temperature CO2. Important questions concerning the mechanisms of oxidation and carburization remain unanswered. Herein we shed light onto these processes by studying the very initial stages of oxidation of Fe22Cr and Fe22Ni22Cr model alloys. Ambient-pressure X-ray photoelectron spectroscopy enabled in situ analysis of the oxidizing surface under 1 mbar of flowing CO2 at temperatures up to 530 °C, while postexposure analyses revealed the structure and composition of the oxidized surface at the near-atomic scale. We found that gas purity played a critical role in the kinetics of the reaction, where high purity CO2 promoted the deposition of carbon and the selective oxidation of Cr. In contrast, no carbon deposition occurred in low purity CO2 and Fe oxidation ensued, thus highlighting the critical role of impurities in defining the early oxidation pathway of the alloy. The Cr-rich oxide formed on Fe22Cr in high purity CO2 was both thicker and more permeable to carbon compared to that formed on Fe22Ni22Cr, where carbon transport appeared to occur by atomic diffusion through the oxide. Alternatively, the Fe-rich oxide formed in low purity CO2 suggested carbon transport by molecular CO2.

scholarly journals Unconventional phase transitions in strongly anisotropic 2D (pseudo)spin systems

2018 ◽  
Vol 185 ◽  
pp. 08006
Author(s):  
Vitaly Konev ◽  
Evgeny Vasinovich ◽  
Vasily Ulitko ◽  
Yury Panov ◽  
Alexander Moskvin
Keyword(s):  
Magnetic Field ◽  
Monte Carlo ◽  
Phase Transitions ◽  
Ground State ◽  
Quantum Monte Carlo ◽  
Mean Field ◽  
Spin Systems ◽  
Field Approach ◽  
Generalized Mean

We have applied a generalized mean-field approach and quantum Monte-Carlo technique for the model 2D S = 1 (pseudo)spin system to find the ground state phase with its evolution under application of the (pseudo)magnetic field. The comparison of the two methods allows us to clearly demonstrate the role of quantum effects. Special attention is given to the role played by an effective single-ion anisotropy ("on-site correlation").

scholarly journals The Critical Role of Stereochemically Active Lone Pair in Introducing High Temperature Ferroelectricity

2021 ◽  
Author(s):  
Rafikul Ali Saha ◽  
Anita Halder ◽  
Desheng Fu ◽  
Mitsuru Itoh ◽  
Tanusri Saha-Dasgupta ◽  
...  
Keyword(s):  
High Temperature ◽  
Critical Role ◽  
Lone Pair

scholarly journals Revealing the critical role of radical-involved pathways in high temperature cyclopentanone pyrolysis

2020 ◽  
Vol 216 ◽  
pp. 280-292 ◽  
Author(s):  
Xiaorui Dong ◽  
Erik Ninnemann ◽  
Duminda S. Ranasinghe ◽  
Andrew Laich ◽  
Robert Greene ◽  
...  
Keyword(s):  
High Temperature ◽  
Critical Role

scholarly journals Mechanics of Ultra-Strength Materials

MRS Bulletin ◽  
2009 ◽  
Vol 34 (3) ◽  
pp. 167-172 ◽  
Author(s):  
Ting Zhu ◽  
Ju Li ◽  
Shigenobu Ogata ◽  
Sidney Yip
Keyword(s):  
Strain Rate ◽  
Activation Volume ◽  
Critical Role ◽  
Rate Dependence ◽  
Significant Fraction ◽  
Deformation Mechanisms ◽  
Nanoscale Materials ◽  
Ideal Strength ◽  
The Ideal

AbstractRecent experiments on nanoscale materials, including nanowires, nanopillars, nanoparticles, nanolayers, and nanocrystals, have revealed a host of “ultra-strength” phenomena, defined by stresses in the material generally rising up to a significant fraction of the ideal strength—the highest achievable strength of a defect-free crystal. This article presents an overview of the strength-controlling deformation mechanisms and related mechanics models in ultra-strength nanoscale materials. The critical role of the activation volume is highlighted in understanding the deformation mechanisms, as well as the size, temperature, and strain rate dependence of ultra strength.

scholarly journals The critical role of hot carrier cooling in optically excited structural transitions

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Wen-Hao Liu ◽  
Jun-Wei Luo ◽  
Shu-Shen Li ◽  
Lin-Wang Wang
Keyword(s):  
Phase Transitions ◽  
Density Functional ◽  
Driving Forces ◽  
Energy Levels ◽  
Critical Role ◽  
Structural Phase ◽  
Nonradiative Recombination ◽  
Hot Carrier ◽  
Spatially Extended

AbstractThe hot carrier cooling occurs in most photoexcitation-induced phase transitions (PIPTs), but its role has often been neglected in many theoretical simulations as well as in proposed mechanisms. Here, by including the previously ignored hot carrier cooling in real-time time-dependent density functional theory (rt-TDDFT) simulations, we investigated the role of hot carrier cooling in PIPTs. Taking IrTe2 as an example, we reveal that the cooling of hot electrons from the higher energy levels of spatially extended states to the lower energy levels of the localized Ir–Ir dimer antibonding states strengthens remarkably the atomic driving forces and enhances atomic kinetic energy. These two factors combine to dissolute the Ir–Ir dimers on a timescale near the limit of atomic motions, thus initiating a deterministic kinetic phase transition. We further demonstrate that the subsequent cooling induces nonradiative recombination of photoexcited electrons and holes, leading to the ultrafast recovery of the Ir–Ir dimers observed experimentally. These findings provide a complete picture of the atomic dynamics in optically excited structural phase transitions.

Do Alkanethiols Adsorb onto the Surfaces of Tl−Ba−Ca−Cu−O-Based High-Temperature Superconductors? The Critical Role of H2O Content on the Adsorption Process

Langmuir ◽  
1996 ◽  
Vol 12 (11) ◽  
pp. 2622-2624 ◽  
Author(s):  
Kaimin Chen ◽  
Feng Xu ◽  
Chad A. Mirkin ◽  
Rung-Kuang Lo ◽  
K. S. Nanjundaswamy ◽  
...  
Keyword(s):  
High Temperature ◽  
Adsorption Process ◽  
High Temperature Superconductors ◽  
Critical Role

scholarly journals Probing the role of thermal vibrational disorder in the SPT of VO$$_2$$ by Raman spectroscopy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Aminat Oyiza Suleiman ◽  
Sabeur Mansouri ◽  
Nicolas Émond ◽  
Boris Le Drogoff ◽  
Théophile Bégin ◽  
...  
Keyword(s):  
Thin Films ◽  
Phase Transitions ◽  
Transition Metal Oxides ◽  
Critical Role ◽  
Structural Phase ◽  
Electrical Measurements ◽  
Concurrent Study ◽  
The Mean ◽  
Microstructural Effect

AbstractPhase competition in transition metal oxides has attracted remarkable interest for fundamental aspects and technological applications. Here, we report a concurrent study of the phase transitions in undoped and Cr-doped VO$$_2$$ 2 thin films. The structural, morphological and electrical properties of our films are examined and the microstructural effect on the metal–insulator transition (MIT) are highlighted. We further present a distinctive approach for analyzing the Raman data of undoped and Cr-doped VO$$_2$$ 2 thin films as a function of temperature, which are quantitatively correlated to the electrical measurements of VO$$_2$$ 2 films to give an insight into the coupling between the structural phase transition (SPT) and the MIT. These data are also combined with reported EXAFS measurements and a connection between the Raman intensities and the mean Debye–Waller factors $$\sigma ^2$$ σ 2 is established. We found that the temperature dependence of the $$\sigma _{R}^{2}(V-V)$$ σ R 2 ( V - V ) as calculated from the Raman intensity retraces the temperature profile of the $$\sigma _{EXAFS}^{2}(V-V)$$ σ EXAFS 2 ( V - V ) as obtained from the EXAFS data analysis. Our findings provide an evidence on the critical role of the thermal vibrational disorder in the VO$$_2$$ 2 phase transitions. Our study demonstrates that correlating Raman data with EXAFS analysis, the lattice and electronic structural dynamics can be probed.

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