scholarly journals PHASE TRANSITION OF PRASEODYMIUM MONO-PNICTIDES UNDER HIGH PRESSURE

2013 ◽  
Vol 22 ◽  
pp. 491-496
Author(s):  
DINESH CHANDRA GUPTA ◽  
GAJENDRA SINGH RAYPURIA
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Relative Volume ◽  
Many Body ◽  
Rare Earth Atom ◽  
Phase Transition Pressure ◽  
Volume Collapse ◽  
Cscl Type ◽  
Nearest Neighbours ◽  
Many Body Interactions

The Phase transition and elastic properties of Praseodymium-monopnictides have been investigated under pressure by means of a modified charge-transfer potential model which incorporates the Coulomb screening due to the delocalization of f-electron of rare-earth atom leading to many-body interactions, along with Coulomb interaction, covalency effect and overlap repulsion extended up to second-nearest neighbours. These compunds undergo transition from NaCl structure to high pressure body-centered tetragonal (BCT) structure (distorted CsCl-type P4/mmm). The calculated values of cohesive energy, lattice constant, phase transition pressure, relative volume collapse. Present model explains the Cauchy’s discrepancy correctly.

Structural Properties of CaS1-xSex Mixed Crystal under High Pressure

2014 ◽  
Vol 1047 ◽  
pp. 51-59
Author(s):  
Anita Singh ◽  
Ekta Sharma ◽  
Umesh Kumar Sakalle
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Structural Properties ◽  
Rock Salt ◽  
Cesium Chloride ◽  
Relative Volume ◽  
Transition Pressure ◽  
Phase Transition Pressure ◽  
Volume Collapse ◽  
Vegard’S Law

The mixed ionic crystals are formed by the mixing of pure components and are truly crystalline and their lattice constants change linearly with concentration from one pure member to another. The present work is intended to investigate structural properties of CaS1-xSexunder high pressure. The structural properties of mixed compound CaS1-xSex(0≤x≤1) under high pressures have been evaluated using three body potential model (TBPM). This interaction potential has been calculated by using three model parameters. For this mixed compound, the experimental data has been generated by the application of Vegard’s law to experimental values available for pure end-point members.The Structure of CaS and CaSe has been Rock Salt (B1) at ambient pressure and with increasing pressure Rock Salt (B1) structure undergo a transition in Cesium Chloride (B2) at 40GPa and 38 GPa respectively and CaS1-xSexunder goes Rock Salt to Cesium Chloride (B1→B2) structure. The difference in phase transition pressure in end-point members is low. In the present work we have investigated structural properties at high pressure for five different concentration x (x=0, 0.25, 0.50, 0.75, 1) for CaS1-xSex. Phase transition pressure and relative volume collapse at different phase transition pressure for different values of x has been calculated. Predicted phase transition pressure and relative volume collapse are found in good agreement with experimental and other theoretical data. Linear variation of phase transition pressure and lattice constant of different composition show that Vegard’s law is valid for this alloy. We have evaluated the phase transition pressure from graphical analysis where the Gibb’s free energy difference ΔG [G(B1)-G(B2)] have been plotted against pressure (P) for CaS1-xSexfor different concentration x. The pressure at which ΔG approaches zero corresponds to phase –transition pressure (Pt). The relative volume changes, ΔV(Pt)/V(0), associated with the above mentioned compression have also been computed and plotted against pressure to get the phase diagram for CaS1-xSexin different concentration.

Phase transition of iron doped MgO under high pressure by first-principles study

2015 ◽  
Vol 26 (02) ◽  
pp. 1550020 ◽  
Author(s):  
K. S. Yang ◽  
S. L. Li ◽  
J. Zhang ◽  
Z. Zeng ◽  
X. Y. Qin ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Density Functional ◽  
Iron Concentration ◽  
Mantle Minerals ◽  
Phase Transition Pressure ◽  
Deep Interior ◽  
Cscl Type ◽  
Iron Doped ◽  
Damped Oscillation

The ( Mg, Fe ) O solid solution is one of the major lower mantle minerals, and studying its properties and structures under high pressure is a fundamental step toward understanding Earth's deep interior. Here within the framework of density functional theory, we first discuss the relationship between the total energy and iron doped positions of ( Mg, Fe ) O , and find that the doped iron favors to be dispersive. Then the pressure-induced phase transitions of ( Mg, Fe ) O from NaCl -type (B1) to CsCl -type (B2) are probed. It is found that the phase transition pressure of ( Mg, Fe ) O decreases with damped oscillation, as the increase of iron concentration. This phenomenon is essentially determined by the iron concentration as well as iron doped positions. The electronic structures of MgO and ( Mg 0.75 Fe 0.25) O at 436 GPa are calculated, and the results show that the doped irons play a crucial role in the metallicity of ( Mg 0.75 Fe 0.25) O . Our results are in agreement with the experimental counterparts. This study would provide some useful information for understanding the behavior of pressure-induced phase transition and geoscience.

Phase transition in CeSe, EuSe and LaSe under high pressure

Open Physics ◽  
2007 ◽  
Vol 5 (4) ◽  
Author(s):  
Sadhna Singh ◽  
R. Singh ◽  
Atul Gour
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Elastic Behavior ◽  
Transition Pressure ◽  
High Pressure Phase Transition ◽  
Phase Transition Pressure ◽  
Volume Collapse ◽  
Range Overlap ◽  
Three Body ◽  
Repulsive Forces

AbstractThe high pressure phase transition and elastic behavior of rare earth monoselenides (CeSe, EuSe and LaSe) which crystallize in a NaCl-structure have been investigated using the three body interaction potential (TBIP) approach. These interactions arise due to the electronshell deformation of the overlapping ions in crystals. The TBP model consists of a long range Coulomb, three body interactions and the short range overlap repulsive forces operative up to the second neighboring ions. The authors of this paper estimated the values of the phase transition pressure and the associated volume collapse to be closer than other calculations. Thus, the TBIP approach also promises to predict the phase transition pressure and pressure variations of elastic constants of lanthanide compounds.

Phase transition and electronic properties of SbI3: First-principles calculations

2017 ◽  
Vol 31 (18) ◽  
pp. 1750200 ◽  
Author(s):  
Xiao-Xiao Sun ◽  
Cong Li ◽  
Qing-Yu Hou ◽  
Yue Zhang
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Electronic Properties ◽  
First Principles ◽  
Structural Phase ◽  
Relative Volume ◽  
First Principles Calculations ◽  
Volume Collapse ◽  
Pseudopotential Calculations ◽  
Indirect Band Gap

We have performed the first-principles pseudopotential calculations to investigate the structural phase transition and electronic properties of SbI3 considering several possible phases as a function of pressure from 0 GPa to 100 GPa. Our calculations show that this material undertakes a structural transformation from the R-3 phase to high-pressure [Formula: see text] phase at about 6.5 GPa with a relative volume collapse of 4.3%. We also have investigated the elastic properties and energy band structure of SbI3 under hydrostatic pressure. The calculation suggests that the R-3 phase is a semiconductor with an indirect band gap of about 2.16 eV at 0 Gpa. Under the influence of pressure, we have found that high-pressure [Formula: see text] phase has transformed to metal at about 55 GPa.

scholarly journals Role of temperature in the numerical analysis of CaO under high pressure

2010 ◽  
Vol 8 (1) ◽  
pp. 126-133 ◽  
Author(s):  
Purvee Bhardwaj ◽  
Sadhna Singh
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Numerical Analysis ◽  
Thermodynamic Properties ◽  
Elastic Constants ◽  
Volume Change ◽  
Thermodynamical Properties ◽  
Phase Transition Pressure ◽  
Different Temperatures

AbstractIn this paper we focus on the elastic and thermodynamic properties of the B1 phase of CaO by using the modified TBP model, including the role of temperature. We have successfully obtained the phase transition pressure and volume change at different temperatures. In addition elastic constants and bulk modulus of B1 phase of CaO at different temperatures are discussed. Our results are comparable with the previous ones at high temperatures and pressures. The thermodynamical properties of the B1 phase of CaO are also predicted.

Phase Stability and Elastic Properties of оne Dimensional Long Period Structures of Al3Ti under High Pressure

2016 ◽  
Vol 850 ◽  
pp. 354-361
Author(s):  
Ping Ying Tang ◽  
Guo Hua Huang ◽  
Qing Lian Xie ◽  
Jin Li Huang
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Elastic Properties ◽  
Phase Stability ◽  
Antiphase Boundary ◽  
First Principles Calculations ◽  
One Dimensional ◽  
Long Period ◽  
Phase Transition Pressure ◽  
Order Polynomial

Phase stability and elastic properties of seven one dimensional long period structures (1D-LPSs) of Al3Ti under high pressure have been systematically investigated by first-principles calculations. The enthalpy differences indicate that Al3Ti will undergo a phase transition from 1D-LPSs to L12 structure at high pressure. With increase of antiphase boundary period parameter M’, the enthalpy initially decreases and then increases, and the enthalpy for D023 is the smallest. Oppositely, the phase transition pressure firstly increases and then decreases, and the maximum is for D023. The elastic constants and elastic moduli B, G and E increase monotonically with increase of pressure, and the corresponding second-order polynomial fits are also obtained. Interestingly, the pressure dependence of Poisson’s ratio show similar tendency with that of B/G ratio. Both the B/G ratios and the Cauchy pressures reveal that these 1D-LPSs exhibit brittleness at high pressure.

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.

Structural Analysis of Rare Earth Compound with NaCl-Structure

2016 ◽  
Vol 28 ◽  
pp. 53-58
Author(s):  
Purvee Bhardwaj ◽  
Sadhna Singh
Keyword(s):  
Rare Earth ◽  
Structural Properties ◽  
Structural Parameters ◽  
Structural Phase ◽  
Rare Earth Compound ◽  
Phase Transition Pressure ◽  
Volume Collapse ◽  
Cscl Type ◽  
Realistic Interaction ◽  
Good Agreement

The structural properties of rare earth compound in NaCl-structure are studied in the present investigation. To study these properties of erbium telluride (ErTe), the Realistic Interaction Potential Approach (RIPA) model has been used. Present compound shows NaCl-type to CsCl-type structural phase transformation. The structural properties, including phase transition pressure and volume collapse are obtained and compared with available literature. The calculated equilibrium structural parameters are in good agreement with the available experimental and theoretical results. Further more to study the electronic properties, band structure and density of state are reported.

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