Ab initio investigations of TlI-type compounds under high pressure

2004 ◽  
Vol 219 (6) ◽  
Author(s):  
Daniel Becker ◽  
Horst P. Beck
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Electron Pair ◽  
Elevated Pressure ◽  
Type Structure ◽  
Electronic Density ◽  
Structure Changes ◽  
Cscl Type ◽  
Wide Pressure Range ◽  
The Stability

AbstractIn this work, we present a theoretical study (based on DFT-calculations) in a wide pressure range of the structural and electronic properties and the stability of compounds crystallising in a TlI- or CrB-type structure. Both structure types have the characteristic structural feature of zigzag chains with unusual short homonuclear distances. The main focus of this study is to elucidate the nature of bonding within these zigzag chains at ambient and elevated pressure. For this purpose we discuss the evolution of the distances within the zigzag chains with pressure, the transition pressure of the phase transition to a CsCl-type arrangement (high-pressure phase) and compressibilities of the low- and high-pressure phases. For a better understanding of the structure and bonding, the band structures of these compounds are evaluated. The calculations are complemented by an orbital analysis using the crystal orbital Hamilton population (COHP) and an analysis of the electronic density topology with the electron localisation function (ELF). Our study indicates that there is a bonding electron pair in compounds crystallising in the CrB-type structure and that the nature of the electron pair does not change significantly at elevated pressure up to the phase transition. However, the “character” of the additional electron pair in the In-monohalides (TlI-type structure) changes with increasing pressure from nonbonding to bonding. The phase transition to a CsCl- type structure implies a fundamental change to nonbonding stereochemically inert electron pairs for all compounds.

First-Principles Investigations of Structural Stability of LuN

2013 ◽  
Vol 690-693 ◽  
pp. 559-563 ◽  
Author(s):  
Xiao Cui Yang ◽  
En Jie Zhang ◽  
Hong Yuan Ma ◽  
Jun Ping Xiao
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Structural Stability ◽  
First Principles ◽  
Phonon Dispersion ◽  
Type Structure ◽  
First Principles Calculations ◽  
Phonon Dispersion Curves ◽  
Elevated Pressures ◽  
Cscl Type

An investigation on structural stability of LuN under high pressure has been conducted using first-principles calculations. At elevated pressures LuN is predicted to undergo a phase transition from NaCl-type structure (B1) into CsCl-type structure (B2). The predicted transition pressure is 220 GPa. The phonon dispersion curves of B1 and B2 at 0 and 220 GPa are presented.

scholarly journals Persistence of the stereochemical activity of the Bi3+ lone electron pair in Bi2Ga4O9 up to 50 GPa and crystal structure of the high-pressure phase

2010 ◽  
Vol 66 (3) ◽  
pp. 323-337 ◽  
Author(s):  
Alexandra Friedrich ◽  
Erick A. Juarez-Arellano ◽  
Eiken Haussühl ◽  
Reinhard Boehler ◽  
Björn Winkler ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Pressure ◽  
Density Functional ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
High Pressure Phase ◽  
Functional Theory ◽  
Pressure Phase ◽  
Stereochemical Activity

The crystal structure of the high-pressure phase of bismuth gallium oxide, Bi2Ga4O9, was determined up to 30.5 (5) GPa from in situ single-crystal in-house and synchrotron X-ray diffraction. Structures were refined at ambient conditions and at pressures of 3.3 (2), 6.2 (3), 8.9 (1) and 14.9 (3) GPa for the low-pressure phase, and at 21.4 (5) and 30.5 (5) GPa for the high-pressure phase. The mode-Grüneisen parameters for the Raman modes of the low-pressure structure and the changes of the modes induced by the phase transition were obtained from Raman spectroscopic measurements. Complementary quantum-mechanical calculations based on density-functional theory were performed between 0 and 50 GPa. The phase transition is driven by a large spontaneous displacement of one O atom from a fully constrained position. The density-functional theory (DFT) model confirmed the persistence of the stereochemical activity of the lone electron pair up to at least 50 GPa in accordance with the crystal structure of the high-pressure phase. While the stereochemcial activity of the lone electron pair of Bi^{3+} is reduced at increasing pressure, a symmetrization of the bismuth coordination was not observed in this pressure range. This shows an unexpected stability of the localization of the lone electron pair and of its stereochemical activity at high pressure.

Phase transitions of BaCO3 at high pressures

2008 ◽  
Vol 72 (2) ◽  
pp. 659-665 ◽  
Author(s):  
S. Ono ◽  
J. P. Brodholt ◽  
G. D. Price
Keyword(s):  
Phase Transition ◽  
Experimental Study ◽  
High Pressure ◽  
Phase Transitions ◽  
Bulk Modulus ◽  
First Principles ◽  
High Pressures ◽  
Ambient Conditions ◽  
The Stability ◽  
Previous Experimental Study

AbstractFirst-principles simulations and high-pressure experiments were used to study the stability of BaCO3 carbonates at high pressures. Witherite, which is orthorhombic and isotypic with CaCO3 aragonite, is stable at ambient conditions. As pressure increases, BaCO3 transforms from witherite to an orthorhombic post-aragonite structure at 8 GPa. The calculated bulk modulus of the post-aragonite structure is 60.7 GPa, which is slightly less than that from experiments. This structure shows an axial anisotropicc ompressibility and the a axis intersects with the c axis at 70 GPa, which implies that the pressure-induced phase transition reported in previous experimental study is misidentified. Although a pyroxene-like structure is stable in Mg- and Ca-carbonates at pressures >100 GPa, our simulations showed that this structure does not appear in BaCO3.

HIGH-PRESSURE PHASE TRANSITION AND STABILITY OF CeSb, LaSb, AND LuSb WITH NaCl-TYPE STRUCTURE

2010 ◽  
Vol 24 (18) ◽  
pp. 3543-3550 ◽  
Author(s):  
SADHNA SINGH ◽  
R. K. SINGH ◽  
ATUL GOUR
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Zero Point ◽  
Relative Volume ◽  
Type Structure ◽  
Zero Point Energy ◽  
Volume Changes ◽  
Point Energy ◽  
High Pressure Phase Transition ◽  
Vdw Interaction

We have predicted the phase transition pressures and corresponding relative volume changes of CeSb , LaSb , and LuSb having NaCl -type structure under high pressure using three-body interaction potential approach (TBIPA) incorporated with short-range van der Walls (vdW) interaction and zero point energy effects. We have obtained phase transition pressures and relative volume changes which are in close agreement with measured values. Thus TBIPA with vdW interaction and zero point energy effects are found to be promising potential models for the prediction of transition pressure and stability of rare-earth compounds.

High-pressure investigations of lanthanoid oxoarsenates: I. Single crystals of scheelite-type Ln[AsO4] phases with Ln = La–Nd from monazite-type precursors

2016 ◽  
Vol 71 (5) ◽  
pp. 439-445 ◽  
Author(s):  
Sebastian J. Metzger ◽  
Florian Ledderboge ◽  
Gunter Heymann ◽  
Hubert Huppertz ◽  
Thomas Schleid
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
High Temperature ◽  
Molar Volume ◽  
Single Crystals ◽  
Coordination Number ◽  
Type Structure ◽  
Temperature Conditions ◽  
Type Phase

AbstractTransparent single crystals of the scheelite-type Ln[AsO4] phases with Ln = La–Nd are obtained by the pressure-induced monazite-to-scheelite type phase transition in a Walker-type module under high-pressure and high-temperature conditions of 11 GPa at 1100–1300 °C. Coinciding with this transition, there is an increase in density and a reduction in molar volume of about 4.5 % for the scheelite-type phases (tetragonal, I41/a) for La[AsO4] (a = 516.92(4), c = 1186.1(9) pm), Ce[AsO4] (a = 514.60(1), c = 1175.44(2) pm), Pr[AsO4] (a = 512.63(4), c = 1168.25(9) pm), and Nd[AsO4] (a = 510.46(4), c = 1160.32(11) pm) as compared to the well-known monazite-type phases (monoclinic, P21/n). Surprisingly enough, the scheelite-type oxoarsenates(V) exhibit a lower coordination number for the Ln3+ cations (CN = 8 versus CN = 8 + 1), whereas the isolated tetrahedral [AsO4]3– anions (d(As–O) = 168.9–169.3 pm for the scheelites as compared to d(As–O) = 167.1–169.9 pm for the monazites) remain almost unchanged. So the densification must occur because of the loss of two edge-connections of the involved [LnO8+1]15– polyhedra with the [AsO4]3– tetrahedra in the monazite- resulting in exclusively vertex connected [LnO8]13– and [AsO4]3– units in the scheelite-type structure.

scholarly journals Unbiased crystal structure prediction of NiSi under high pressure

2015 ◽  
Vol 48 (3) ◽  
pp. 906-908 ◽  
Author(s):  
Pavel N. Gavryushkin ◽  
Zakhar I. Popov ◽  
Konstantin D. Litasov ◽  
Alex Gavryushkin
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Structure Prediction ◽  
Type Structure ◽  
Stable Phase ◽  
Stable Form ◽  
Model Structure ◽  
Crystal Structure Prediction ◽  
Cscl Type ◽  
Pressure Phase

On the basis of an unbiased structure prediction, it is shown that the stable form of NiSi under pressures of 100 and 200 GPa is thePmmnstructure. Furthermore, a new stable phase has been discovered: the deformed tetragonal CsCl-type structure witha= 2.174 Å andc= 2.69 Å at 400 GPa. Specifically, the sequence of high-pressure phase transitions is the following: thePmmnstructure below 213 GPa, the tetragonal CsCl type in the range 213–522 GPa, and cubic CsCl higher than 522 GPa. As the CsCl-type structure is considered as the model structure of the FeSi compound at the conditions of the Earth's core, this result implies restrictions on the Fe–Ni isomorphic miscibility in FeSi.

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