Values Of Phase Transition Pressure Research Articles

Theoretical Investigation of Pressure Dependent Structural and Elastic Properties of MnSi Compound

MnSi is a metallic compound that exhibits a structural phase transition as a function of pressure. At ambient conditions, MnSi has a cubic structure such as NaCl type crystal structure. However, at high pressures, it undergoes a structural phase transition to a CsCl type crystal structure. The pressure-dependent structural phase transition in MnSi has been studied using various experimental and theoretical techniques. In the present work, we have used an efficient inter-ionic potential approach to predict pressure dependent structural phase change and associated volume collapse in MnSi. Therein, the potential includes the long-range Coulomb, van der Waals (vdW) interaction, and the short-range repulsive interaction up to second neighbour ions. It has been demonstrated that the Hafemeister and Flygare approach successfully evaluates the equation of state for change in volume with respect to applied pressure. We have identified a structural phase transition from B1(NaCl) type structure to B2 (CsCl) type structure in this compound. The estimated value of phase transition pressure (Pt) is 42 GPa, which is consistent with the available reported data. The identified first order phase transformation showed a volume collapse of about 10% in the vicinity of transition. In addition, we have also investigated second order of elastic constants for MnSi compound.

Theoretical studies of pressure induced structural phase transformation and elastic properties in nickel silicide

In this study, we have explored pressure dependent structural phase transformation and related volume collapse in the vicinity of transition in Nickel Silicide (NiSi) with the help of an effective inter-ionic potential approach. It was observed that by employing an effective interionic interaction approach, which is basically based on phenomenological models of lattice dynamics, includes the long-range Coulomb, van der Waals (vdW) interaction, and the short-range repulsive interaction in the framework of the Hafemeister and Flygare approach. Our results indicate that the material parameters evaluated by such an approach provide a successful evaluation of the equation of state for change in volume with respect to the applied pressure. The estimated value of phase transition pressure (Pt) is 25 GPa for NiSi, which is in line with the information that we have in the literature. This transition corresponds to the transformation of a B1 (NaCl) type structure to a B2 (CsCl) type structure and is a first-order phase transition. This first order phase transformation showed a volume collapse of about 11.44% at 25 GPa for NiSi. Later on, the relationship between pressure and the variation of second-order elastic constants is examined in greater detail.

Study of structural phase transition and elastic properties of ZnTe semiconducting compound under high pressure

The high-pressure structural phase transition and pressure induced elastic properties of cubic zinc-blende phase (B3) to rock-salt phase (B1) structure of Zinc Telluride (ZnTe) semiconducting compound were studied by using the effective inter-ionic potential method, which contains the long-range Coulomb and van der Waals (vdW) interactions and the short-range repulsive interaction of up to second-neighbor ions within the Hafemeister and Flygare approach. The structural phase transition from B3 to B1 structure is reflected using estimated values of phase transition pressure and volumetric abrupt changes in the pressure–volume phase diagram. The calculated results first predict the phase transformation of ZnTe from B3 to B1, which occurs at 19GPa and is consistent with the reported data. Later on, using the effective inter-ionic potential technique, we were able to predict the second order elastic characteristics of the ZnTe system.

Study of Structural, Elastic Properties and their Pressure Dependence in IrN Compound

A theoretical study of the elastic behavior in IrN compound using effective interionic interaction potential is carried out. The estimated values of phase transition pressure and the vast volume discontinuity in pressure-volume (PV) phase diagram indicate the structural phase transition from zinc blende (B3) to CsCl structure (B2). C11, C12 and C44 increase nearly linearly with pressure. At phase transition pressure IrN has shown a discontinuity in second order elastic constants, which is in accordance with the first-order character of the phase transition.

Pressure Induced Properties of U<sub>X</sub>La<sub>1-X</sub>S Compound

The crystal structural, mechanical and thermal properties of UXLa1-XS compound with different concentrations (x= 0.00, 0.08 and 0.40) are investigated using modified inter-ionic potential theory (MIPT), which parametrically includes the effect of coulomb screening by the delocalized f-electrons. Our calculated values of phase transition pressure, bulk modulus and volume change are agree well with the theoretical and experimental data. We have also calculated the second order elastic constants and Debye temperature of these three concentrations.

First-principles investigations on structural, electronic and elastic properties of BeSe under high pressure

The structural, electronic and elastic properties of BeSe in both B3 and B8 structures have been studied by first-principles calculations within the generalized gradient approximation (GGA). The calculated lattice parameters and bulk modulus of BeSe are in reasonable agreement with previous results. The predicted value of phase transition pressure from B3 to B8 is 50.24 GPa, which is well in line with the experimental data (56 ± 5 GPa). The calculation of the electronic band structure shows that the energy gap is indirect for B3 and B8 phases. Especially, the elastic constants of B8 BeSe under high pressure were studied for the first time. The bulk modulus, shear modulus, compressional and shear wave velocities of B8 BeSe evaluated from elastic constants as a function of pressure were investigated. In addition, Poisson's radio, elastic anisotropy and Debye temperature were analyzed successfully.

High Pressure Phase Transition Phenomena in CeS and LaS

In present study we have investigated the high pressure phase transition pressures, volume collapses, elastic and thermo-physical properties of cerium and lanthanum sulphides using the three body interaction potential (TBIP) approach. The CeS and LaS belong to the wide class of binary rare-earth monochalcogenides which crystallize in NaCl-type structure and undergo a transformation into CsCl-type structure under pressure. The values of phase transition pressure and associated volume collapse estimated by us are found to be well suited with experimental values.

Study of semiconducting nanomaterials under pressure

The pressure induced structural and mechanical properties of nanocrystalline ZnO, ZnS, ZnSe, GaN, CoO, CdSe, CeO(2), SnO(2), SiC, c-BC(2)N, and β-Ga(2)O(3) with different grain sizes have been analyzed under high pressures. The molecular dynamics simulation model has been used to compute isothermal equation of state, volume collapse and bulk modulus of these materials in nano and bulk phases at ambient and high pressures and compared with the experimental data. It is evident from these calculations that the change in particle size affects directly the phase transition pressure and bulk modulus. The values of phase transition pressure and bulk modulus increase with decrease in grain size of the material. The equilibrium cell volume and volume collapse in parent phase is directly proportional to the grain size of the materials. Present results are in good agreement with experimental data. The model is able to explain these thermodynamic properties at varying temperatures and pressures successfully.

Pressure dependent mechanical and thermodynamical properties of Hg0.91Mn0.09Te semiconductor

The mechanical, thermodynamical and elastic properties of Hg0.91Mn0.09Te compound are calculated by formulating an effective interionic interaction potential. This potential consists of the long-range Coulomb, three body force parameter, the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbor ions and the van der Waals (vdW) interaction. The estimated values of phase transition pressure have revealed reasonably good agreement with the available experimental data on the phase transition pressure Pt = 11.5 GPa and the vast volume discontinuity in pressure-volume (PV) phase diagram indicate the structural phase transition from zincblende (B3) to rock salt (B1) structure. Later on, the Poisson’s ratio ν, the ratio RS/B of S (Voigt averaged shear modulus) over B (bulk modulus), elastic anisotropy parameter, elastic wave velocity, average wave velocity and Debye temperature as functions of pressure is calculated. From Poisson’s ratio and the ratio RS/B it is inferred that Hg0.91Mn0.09Te is brittle in nature in both B3 phase and B1 phase. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of ductile (brittle) nature of Hg0.91Mn0.09Te compounds and still awaits experimental confirmations.

STRUCTURAL PHASE TRANSITION IN BORON COMPOUNDS AT HIGH PRESSURE

The high-pressure induced structural phase transitions and pressure induced elastic and anharmonic behavior of boron compounds viz. BN, BP, and BAs have been investigated using an inter-ionic potential approach based on charge transfer effect. These compounds go to NaCl phase (B1) under pressure from zinc blende phase (B3). The variations of second-order elastic constants and their combinations follow a systematic trend with pressure, identical to that observed in other compounds of zinc blende structure family. Shear stiffness constants decrease with increasing pressure up to phase transition pressure. The bulk moduli of these compounds are in reasonably good agreement with other theoretical and experimental data. The values of phase transition pressure of these compounds obtained by using the present approach are also in good agreement with those predicted by using the pseudo potential approach. The present approach has also succeeded in predicting the Born and relative stability criterion for stable zinc blende phase of these compounds. We also present a set of third-order elastic constants and pressure derivatives of second-order elastic constants for boron compounds.

Pressure dependent elastic and structural ( B3– B1) properties of Ga based monopnictides

By formulating an effective interionic interaction potential that incorporates the long-range Coulomb, the covalency effects, the charge transfer caused by the deformation of the electron shells of the overlapping ions, the Hafemeister and Flygare type short-range overlap repulsion extended up to the second neighbour ions and the van der Waals (vdW) interaction, the pressure dependent elastic and thermodynamical properties of the III–V semiconductors as Ga Y ( Y = N, P, As) are studied. The estimated values of phase transition pressure of Ga Y ( Y = N, P, As) are in reasonably good agreement with the available data on the phase transition pressures ( P t = 41, 22, 17 GPa). The vast volume discontinuity in pressure–volume phase diagram identifies a structural phase transition from zinc-blende ( B3) to rock salt ( B1) structure. Later on, the Poisson's ratio ν, the ratio R S/ B of S (Voigt averaged shear modulus) over B (bulk modulus), elastic anisotropy parameter, elastic wave velocity, average wave velocity and Debye temperature as functions of pressure is calculated. From Poisson's ratio and the ratio R S/ B it is inferred that Ga Y ( Y = N, P, As) is brittle [ductile] in zinc-blende ( B3) [Sodium Chloride ( B1)] phase. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of ductile (brittle) nature of Ga Y compounds and still awaits experimental confirmations.

Pressure induced structural phase transition and elastic properties in BSb, AlSb, GaSb and InSb compounds

By formulating an effective interionic interaction potential that incorporates the long-range Coulomb, the covalency effects, the charge transfer caused by the deformation of the electron shells of the overlapping ions, the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbour ions and the van der Waals (vdW) interaction, the pressure dependent elastic and thermodynamical properties of the III–V antimonide semiconductors as YSb (Y=B, Al, Ga, and In) are investigated. Estimated values of phase transition pressure of YSb antimonides are consistent with the available data on the phase transition pressures. The ratio R S / B of S (Voigt averaged shear modulus) over B (bulk modulus), elastic wave velocity, average wave velocity and Debye temperature as functions of pressure is calculated. From the ratio R S / B it is inferred that YSb (Y=Al, Ga, and In) are ductile and BSb is brittle in zinc blende (B3) phase. To our knowledge this is the first quantitative theoretical prediction of the ductile (brittle) nature of YSb antimonides and still awaits experimental confirmations.

High pressure structural phase transition and elastic properties of Ga1-xInxAs semiconducting compounds

The present paper addresses the high-pressure phase transformation and mechanical properties of Ga1-xInxAs (x = 0.25, 0.5 and 0.75) by formulating an effective interionic interaction potential. This potential consists of the long-range Coulomb and charge transfer caused by the deformation of the electron shells of the overlapping ions and the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbor ions and the van der Waals (vdW) interaction. The estimated values of phase transition pressure and the vast volume discontinuity in pressure-volume (PV) phase diagram indicate the structural phase transition from zinc blende (B3) to rock salt (B1). The equation of state curves plotted between V (P)/ V (0) and pressure are for both the zincblende (B3) and rocksalt (B1) structures. Further, the variations of the second and third order elastic constants with pressure have followed a systematic trend, which are almost identical to those exhibited by the observed data measured for other compounds of this family.

Structural phase transition and elastic properties of thorium pnictides at high pressure

In the present paper we have pointed out the weaknesses of the approach by Aynyas et al [1] to study the structural phase transition and elastic properties of thorium pnictides. The calculated values of phase transition pressure and other elastic properties using the realistic and actual approach are also given and compared with the experimental and previous theoretical work.

Dielectric—metal structural phase transition in alkali halide crystals under conditions of extremely high pressures

The dielectric—metal structural phase transition in alkali halide metals under conditions of extremely high pressures is studied using the method of electron density functional (MDF). The values of metallization pressure are calculated for both infinite crystals and nano-size samples. The dimensional dependence of metallization pressure is revealed, namely, the dependence of the value of phase transition pressure on the initial size of crystal.

Study of Elastic Properties and Their Pressure Dependence of Semi Magnetic Semiconductors

A theoretical study of the elastic behavior in diluted magnetic semiconductors Zn 1- x Mn x Se ( x =0.016, 0.026 and 0.053) using a three-body interaction (TBI) caused by the electron-shell deformation of the overlapping ions is carried out. The estimated values of phase transition pressure and the vast volume discontinuity in pressure–volume (PV) phase diagram indicate the structural phase transition from zinc blende ( B 3) to rock salt ( B 1). The variation of second-order elastic constants with pressure resembles that observed in other compounds of zinc blende structure family. However, the inconsistency in the value of pressure derivative of theoretical and the experimental value of bulk modulus is attributed to the fact that we have derived our expressions neglecting thermal effects and assuming the overlap repulsion significant only up to nearest neighbors. The present approach has also succeeded in predicting the Born and relative stability criteria. It is revealed that interionic potential approac...

High pressure phase transition and variation of elastic constants of diluted magnetic semiconductors

AbstractA theoretical study of the high‐pressure phase transition and elastic behavior in diluted magnetic semiconductors Zn0.83Mn0.17Se, using a three‐body interaction (TBI) potential caused by the electron‐shell deformation of the overlapping ions is carried out. The estimated values of phase transition pressure and the vast volume discontinuity in pressure‐volume (PV) phase diagram indicate the structural phase transition from zincblende (B3) to rock salt (B1). The variation of second‐order elastic constants with pressure resembles that observed in some binary semiconductors. The inconsistency in the deduced value of pressure derivative of second order elastic constant with the available data is attributed to the fact that we derive expressions neglecting thermal effects and assuming the overlap repulsion significant only up to nearest neighbors. The vdW interaction is effective in obtaining the thermodynamical parameters such as Debye temperature, Gruneisen parameter, thermal expansion coefficient, compressibility as well phase stability in diluted magnetic semiconductors. It is revealed that TBI model has a promise to predict the phase transition pressure and the pressure variation of elastic constants of other semiconductors as well. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural Properties of KBr: Elastic Behaviour and Pressure Effects

We have studied the pressure induced B1-B2 transition and the elastic behaviour of KBr using three-body potential model. It is found that the inclusion of the three-body forces in the potential model yields more reasonable values of phase transition pressure, second-order elastic constants and bulk modulus than those obtained by others (wherever available). Results of high-pressure experiments carried out on KBr for volume transitions are also reported in this paper in order to verify theoretical studies.