Formation of Cotunnite Phase in ZrO2 under Uniaxial Stress: A First Principles Study

WOS: 000288261500051Using a constant pressure ab initio technique, we study the response of ZrO2 to uniaxial stresses and find two different phase transformations; the application of uniaxial stress along the [010] and [100] directions yields a direct phase transformation from the baddeleyite structure to the P2(1)/m and Pnma structures, respectively. Conversely, we observe structural failure of ZrO2 when it is compressed along the [001] axis

Pressure-induced phase transition of SiC

The pressure-induced phase transition in silicon carbide is studied using a constant-pressure ab initio technique. The reversible transition between the zinc-blende structure and the rock-salt structure is successfully reproduced through the simulation. The transformation mechanism at the atomistic level is characterized, and it is found that the transition is based on a tetragonal and an orthorhombic intermediate state. The space groups of the intermediate states are determined as and Imm 2.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48896/2/cm4_25_002.pd

Transformation Pathways of Silica under High Pressure

Concurrent molecular dynamics simulations and ab initio calculations show that densification of silica under pressure follows a ubiquitous two-stage mechanism. First, anions form a close-packed sub-lattice, governed by the strong repulsion between them. Next, cations redistribute onto the interstices. In cristobalite silica, the first stage is manifest by the formation of a metastable phase, which was observed experimentally a decade ago, but never indexed due to ambiguous diffraction patterns. Our simulations conclusively reveal its structure and its role in the densification of silica.Comment: 14 pages, 4 figure

Vibrational properties of amorphous germanium under pressure and its thermal expansion and Gruneisen parameters

WOS: 000277763600006We study the vibrational properties of amorphous germanium at high pressures using a constant pressure ab initio technique. With the application of pressure, the low-frequency modes gradually soften with a decrease in their acoustic-like nature while the high-frequency modes shift to larger frequencies. The acoustic-like vibrations are found to have negative Gruneisen parameters whereas the optic-like ones have positive values of about +1. A negative thermal expansion is produced below 200 K. Furthermore, we find that pressure reduces the number of localized states. Accompanied by the phase transition into a metallic high-density amorphous state, the nature of the low-frequency vibrations is changed from acoustic-like to optic-like and from bond bending to bond stretching. (C) 2010 Elsevier B.V. All rights reserved.Scientific and Technical Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [BIDEB-2221]The author is grateful to Professor D.A. Drabold for providing the FIREBALL96 MD code and Professor N. Mousseau for the initial amorphous structure. The author's visit to Ahi Evran Universitesi was facilitated by the Scientific and Technical Research Council of Turkey (TUBITAK) under the BIDEB-2221 program

Pressure-induced phase transformation of BaS: An ab initio constant pressure study

WOS: 000274180500003We present an ab initio molecular dynamics study of pressure-induced structural phase transition in BaS. We successfully observe the NaCl-to-CsCl phase transformation through the simulations. We also determine the transformation mechanism of this simple phase transformation and compare it with the previously proposed mechanisms. (C) 2009 Elsevier B.V. All rights reserved.Technical Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [BIDEB-2221]The visit of the author to Ahi Evran Universitesi was facilitated by the Scientific and Technical Research Council of Turkey (TUBITAK) BIDEB-2221. The calculations were run on Sacagawea, a 128 processor Beowulf cluster, at the University of Texas at El Paso

The structural phase transition of ZnSe under hydrostatic and nonhydrostatic compressions: an ab initio molecular dynamics study

WOS: 000263889900025PubMed ID: 21817464Ab initio constant pressure molecular dynamics simulations within a generalized gradient approximation (GGA) are carried out to study the structural phase transformation of ZnSe under hydrostatic and nonhydrostatic conditions. ZnSe undergoes a first-order phase transition from the zinc-blende structure to a rocksalt structure having practically identical transformation mechanisms under hydrostatic and nonhydrostatic compressions. This phase transformation is also analyzed using the enthalpy calculations. Our transition parameters and bulk properties are comparable with experimental and theoretical data. Furthermore, the influence of pressure on the electronic structure of ZnSe is investigated. It is found that the band gap energy increases nonlinearly under both hydrostatic and nonhydrostatic conditions and the effect of stress deviations on the band gap energy is small. The computed pressure coefficients and deformation potential of the band gap are in good agreement with experiments

Pressure-induced phase transition in AIN: An ab initio molecular dynamics study

WOS: 000267798600157An ab initio constant pressure technique is applied to study the pressure-induced phase transition in AIN. A first-order phase transformation from the wurtzite structure to a rocksalt structure is observed in the constant pressure simulations. The transformation proceeds via two fivefold coordinated intermediate states within P6(3)/mmc and Cmcm symmetry. The influence of pressure on the electronic structure of AIN is also investigated. The computed pressure coefficients and deformation potential are in good agreement with the earlier first principles calculations. (C) 2009 Elsevier B.V. All rights reserved

Orthorhombic intermediate phases for the wurtzite-to-rocksalt phase transformation of CdSe: An ab initio constant pressure study

WOS: 000276819900001Pressure-induced phase transition of CdSe is studied using constant pressure ab initio molecular dynamic simulations. A phase transition from the wurtzite structure to a rocksalt structure is successfully observed through the simulations. Based on the constant pressure simulation's results, we propose a transformation mechanism having two orthorhombic intermediate phases within Cmc2(1) and Cmcm symmetries. (c) 2010 Elsevier B.V. All rights reserved.Scientific and Technical Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [BIDEB-2221]All calculations were performed during the author's visit to Ahi Evran Universitesi supported by the Scientific and Technical Research Council of Turkey (TUBITAK) BIDEB-2221. The calculations were run on Sacagawea, 128 processor Beowulf cluster, at the University of Texas at El Paso

New transformation mechanism for a zinc-blende to rocksalt phase transformation in MgS

WOS: 000271090200004PubMed ID: 21694004The stability of the zinc-blende structured MgS is studied using a constant pressure ab initio molecular dynamics technique. A phase transition into a rocksalt structure is observed through the simulation. The zinc-blende to rocksalt phase transformation proceeds via two rhombohedral intermediate phases within R3m ( No: 160) and R3m ( No: 166) symmetries and does not involve any bond breaking. This mechanism is different from the previously observed mechanism in molecular dynamics simulations

Ab initio molecular dynamics study of pressure-induced phase transformation in KCl

WOS: 000277932700031We carry out an ab initio constant pressure molecular dynamics technique to study the pressure-induced phase transition in KCl. A phase transformation from the rocksalt structure to the CsCl type structure is successfully observed through constant pressure simulation. The rocksalt-to-CsCl phase transformation of KCl is found to proceed via a rhombohedral intermediate state. This phase transition is also analyzed from the total energy calculations. Our transition parameters and bulk properties are comparable with available experimental and theoretical data. Furthermore, we study the behavior of KCl under uniaxial stress. The uniaxial stress causes first a symmetry change to a tetragonal state with space group 14/mmm and then structural failure. (C) 2010 Elsevier B.V. All rights reserved