N. Kaurav

B1–B2 structural phase transition and elastic properties of UX (X = S, Se, and Te) compounds at high pressure

Pressure induced structural phase transformation and mechanical properties of NaCl-type (B1) to CsCl-type (B2) structure in uranium monochalcogenides (UX; X = S, Se, and Te) are presented. An effective interionic interaction potential is constructed, consisting of the long-range Coulomb and the Hafemeister and Flygare type short-range overlap repulsion extended up to the second-neighbour ions and the van der Waals (vdW) interaction. Particular attention is devoted to evaluate the vdW coefficients following the Slater–Kirkwood variational method, as both the ions are polarizable. Our calculated results have revealed reasonably good agreement with the available experimental data on the phase transition pressures (Pt = 81, 21, 13 GPa) and the elastic properties of UX (X = S, Se, and Te). The equation of state curves (plotted between V (P)/V (0) and pressure) for both the NaCl-type (B1) and CsCl-type (B2) structures obtained by us are in fairly good agreement with the experimental results. The calculated values of the volume collapses (ΔV (P)/V (0)) are also closer to their observed data. The variations of the second- and third-order elastic constants with pressure have followed systematic trends, which are almost identical to those exhibited by the measured and observed data in other compounds of the NaCl-type structure family.

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...

Study of elastic properties and their pressure dependence of lanthanum monochalcogenides

An effective interionic interaction potential (EIOP) approach is employed for the description of phase transitions and equations of state of lanthanum monochalcogenides LaX {X=S, Se, Te} compound semiconductors. The long-range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction up to second neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in an EIOP. We have obtained a reasonably good agreement between the present theoretical and available experimental values on the phase transition pressures (P t=25.5, 12.4 and 16.8 GPa) and elastic properties in all materials under consideration. The associated volume collapses at the phase transitions have been found to be 8.1%, 10.4% and 7.2% for lanthanum monochalcogenides. The vast volume discontinuity in pressure volume phase diagram identifies the structural phase transition from NaCl type (B1) to CsCl type (B2) structure. The variations of elastic constants and their combinations with pressure follow a systematic trend identical to that observed in other compounds of NaCl type structure family. The present approach has also succeeded in predicting the Born and relative stability criteria.

Structural phase transition and elastic properties of ZnSe at high pressure

We have evolved an effective interionic interaction potential to investigate the pressure-induced phase transitions from zinc blende (B3) to rock salt (B1) structure in II-VI [ZnSe] semiconductors. The elastic constants, including 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, are deduced. Keeping in mind that both of the ions are polarisable, we employed the Slater-Kirkwood variational method to estimate the vdW coefficients. The estimated value of the phase transition pressure (P t ) is higher than in the reported data, and the magnitude of the discontinuity in volume at the transition pressure is consistent with that data. The major volume discontinuity in the pressure-volume phase diagram identifies the structural phase transition from zinc blende to rock salt structure. The variation of second-order elastic constants with pressure resembles that observed in some binary semiconductors. It is inferred that the vdW interaction is effective in obtaining the thermodynamic parameters such as the Debye temperature, the Gruneisen parameter, the thermal expansion coefficient and the compressibility. However, the inconsistency between the thermodynamic parameters as obtained from present model calculations and their experimental values is attributed to the fact that we have derived our expressions by assuming the overlap repulsion to be significant only up to the nearest second-neighbor ions, as well as neglecting thermal effects. It is thus argued that full analysis of the many physical interactions that are essential to binary semiconductors will lead to a consistent explanation of the structural and elastic properties of II–VI semiconductors.

Dielectric, magnetic, and thermodynamic properties of Y1−xSrxMnO3 (x = 0.1 and 0.2)

We report the effect of strontium (Sr) doping on dielectric, magnetization, and thermodynamic properties of polycrystalline Y1−xSrxMnO3 (x = 0.1, 0.2) samples prepared by conventional solid-state reaction method. The temperature dependent dielectric permittivity and specific heat curves noticeably show the anomalies near its magnetic transition point, i.e., Neel temperature (TN), which are probably generated by the frustrated Mn3+ spins (S = 2) on a triangular Mn lattice showing the magneto-electric coupling between the electric and magnetic orders. However, the magnetic transition is not clearly evident in the magnetic susceptibility due to the frustration on the Mn triangular lattice and the dominating paramagnetic susceptibility of the Y3+ spins. The electronic transport mechanism in these materials was analyzed within the framework of conventional Arrhenius Law, i.e., ρ(T) = C exp(Ea/kBT) applied to low frequency ac resistivity data, and through the peak method employed to the permittivity and loss ta...

Naturally self-assembled nickel nanolattice

This is the first report on the critical nature of nanolattice formability of different particle sizes (∼4–10 nm) of monodispersed nickel nanoparticles. They exhibit strikingly hexagonal close-packed (hcp) nanolattices without extra forces whenever trioctylphosphine (TOP) is one of the surfactant(s). This clearly establishes the unique role of nanolattice formability of TOP. The c/a ratios are interestingly identical to those of atomic lattices. An attempt has also been made to explain them based on the balanced attractive and repulsive forces of the surfactant-generated cation–anion pairs on the surface of the nanoparticles. The present findings therefore will provide a far-reaching vista for the fabrication of varieties of natural nanolattices and their understanding on applications in a new paradigm.

Pressure dependence of elastic properties of ZnX (X = Se,S and Te): Role of charge transfer

An effective interaction potential (EIOP) is developed to invoke the pressure induced phase transition from zinc blende (B3) to rocksalt (B1) structure and anharmonic properties in ZnX (X = Se, S, Te) semiconductors. The effective interaction potential incorporates the long range Coulomb interaction, van der Waals interaction and short-range repulsive interaction up to second neighbour ions within the Hafemeister and Flygare approach as well as the charge transfer effects caused by the electron-shell deformation of the overlapping ions. The van der Waals coefficients are computed by the Slater Kirkwood variation method as a first step. Later on, we evaluate volume collapse, second order and third order elastic constants with pressure pointing to the systematic trends in all compounds of zinc blende structure and their thermal properties such as force constant, Gruneisen parameter, compressibility, Debye temperature etc. The vast volume discontinuity in pressure-volume (PV) phase diagram identifies the structural phase transition from zinc blende (B3) to rock salt (B1) structure and is consistent with those revealed from earlier reports.

Pressure induced phase transition (B1–B2) and elastic properties in alkaline earth BaX (X = S, Se and Te) chalcogenides

Pressure induced structural aspects of NaCl-type (B1) to CsCl-type (B2) structure in alkaline-earth-chalcogenides (BaX; X = S, Se and Te) are presented. An effective interionic interaction potential (EIoIP) with long-range Coulomb and three-body interactions and the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbour ions and the van der Waals (vdW) interaction is developed. Emphasis has been given to evaluate the vdW coefficients following the Slater-Kirkwood variational method, as both the ions are polarizable. The lattice model calculations have revealed reasonably good agreement with the available experimental data on the phase-transition pressures (P t = 7.0, 7.0, 6.0 GPa) and the elastic properties of BaX (X = S, Se and Te). The equation of state curves (plotted between V (P)/V(0) and pressure) for both the B1and B2 structures obtained by us are in fairly good agreement with the experimental results. The calculated values of the volume collapses [ΔV(P)/V(0)] are also closer to their observed data. Further, the variations of the second order elastic constants with pressure have followed a systematic trend, which are almost identical to those exhibited by the observed data measured for other semiconducting compounds with B1 → B2 structural phase transitions.

Pressure induced B3-B1 structural phase transition and elastic properties of monopnictides InX (X = N, P, As)

An effective interionic interaction potential is developed to discuss the pressure induced structural phase transformation and mechanical properties of InX (X = N, P, As) semiconducting compounds. The effective interionic potential consists of the long-range Coulomb and three-body interactions and the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbour ions and the van der Waals interaction. The present calculations have revealed reasonably good agreement with the available experimental data on the phase transition pressures (Pt = 11.5, 10, 7.5 GPa) and the elastic properties of InX (X = N, P, As). The equation of state curves (plotted between V (P)/V(0) and pressure) for both the structures zincblende (B3) and rocksalt (B1) structures obtained by us are in fairly good agreement with the experimental results. The calculated values of the volume collapses [ΔV(P)/V(0)] are also closer to their observed data.

HIGH-PRESSURE INDUCED STRUCTURAL PHASE TRANSITION AND ELASTIC PROPERTIES OF DILUTED MAGNETIC SEMICONDUCTORS Zn1-xMnxSe

An effective interionic interaction potential is developed to study the pressure-induced phase transitions from zinc blende (B3) to rock salt (B1) structure in diluted magnetic semiconductors Zn1-xMnxSe (x=0.08 and 0.15). As a first step, the elastic constants, including the long-range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction up to second-neighbor ions within the Hafemeister and Flygare approach, are derived. Assuming that both the ions are polarizable, the Slater–Kirkwood variational method is employed to estimate the vdW coefficients. The estimated values of the phase transition pressure (Pt) increase with Mn concentration. The vast volume discontinuity in the pressure volume phase diagram identifies the structural phase transition from zinc blende to rock salt structure. The variation of second-order elastic constants with pressure resembles that observed in some binary semiconductors. It is noticed that the vdW interaction is effective in obtaining the thermodynamical parameters such as Debye temperature, Gruneisen parameter, and thermal expansion coefficient. However, the inconsistency in the value of pressure derivative of the theoretical and experimental value of C44 is attributed to the fact that we have derived the expressions by assuming that the overlap repulsion is significant only up to nearest neighbors, as well as neglecting thermal effects.