S.C. Goyal

Elastic properties of alkaline earth oxides under high pressure

In this article, we have investigated the high-pressure structural phase transition of alkaline earth oxides using the three-body potential (TBP) model. Phase transition pressures are associated with elastic constants. An effective inter-ionic interaction potential (TBP) with long-range Coulomb interactions and the Hafemeister–Flygare type short-range overlap repulsion and the vdWl interaction is developed. The present calculations have revealed reasonably good agreement with the available experimental data on structural transition (B1–B2 structure). The phase transition pressures Pt of MgO, CaO, SrO, and BaO occur at 220, 45, 40, and 100 GPa, respectively. 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 rocksalt (B1)-type crystal structure. It is found that TBP promises that we would be able to predict phase transition pressure and elastic constants for other chalcogenides as well. The results may be useful for geophysical study.

Bulk modulus of semiconductors and its pressure derivatives

Expressions for the bulk modulus and its first and second pressure derivatives for group I–VII, II–VI, III–V and IV–IV semiconductor binary compounds are derived using an ab initio pseudopotential approach to the total crystal energy within the framework of local density functional formalism. The computed results are very close to the available experimental data.

Pressure derivatives of isothermal bulk modulus of rare gas solids

In the present study we have derived the expression for the bulk modulus using the Hildebrand approximation and the lattice potential energy for rare gas solids (RGS). The derived relation is further used to derive the expression for first and second order pressure derivatives of the bulk modulus for RGS. The derived relations are also used to compute the values of these constants in the case of Ne, Ar, Kr and Xe which are compared with the available values.

Temperature Dependence of Elastic Constants of Alkaline Earth Oxides

The elastic properties of alkaline earth oxides (AEOs) under high temperature are discussed within the framework of many body Lundqvist potential incorporating the contribution of thermal phonon pressure. The short-range repulsive interaction is taken up to the second nearest neighbors. The derived expressions are used to compute the values of second-order elastic constants (SOECs) and bulk modulus of alkaline earth oxides at different temperatures (300K°–2000K°). The results are found to be satisfactory and are in agreement with available experimental and the theoretical results.

Equation of State for Mg2SiO4 (α‐forsterite, β‐wadsleyite and γ‐ringwoodite): ab‐Initio

The compression of Mg2SiO4, (α‐forsterite, β‐wadsleyite and γ‐ringwoodite) up to 24 GPa pressure is analysed with the help of two equation of state :first Birch‐Murnaghan and second based on ab‐initio pseudopotential approach. It is concluded that the EOS based on ab‐initio pseudopotential approach show the systematic compression with increase of pressure in all three phases of Mg2SiO4 as compared to widely used Birch–Murnaghan EOS. The second EOS also yields the value of end point as 1.6 which is in good agreement with the Fermi gas analysis.

Lattice energy and phase transition of alkaline earth chalcogenide

In this study, we have investigated the high-pressure structural phase transition of alkaline earths chalcogenides within the framework of three-body potentials. We are considering short-range repulsive interactions up to the second nearest neighbors. The structural phase transition from the low-pressure NaCl (B1) to the high-pressure CsCl (B2) structure is estimated by Gibbs free energy calculations. The results are satisfactory and in agreement with the available experimental and other theoretical results.

Isobaric Study of the Elastic Properties for Alkaline Earth Oxides under High Temperature

A simple and straightforward theoretical model is developed to investigate the elastic properties of alkaline earth oxides under the effect of temperature as well as pressure. The calculation is performed with the help of high pressure-high temperature equation of state based on thermodynamic analysis. The anharmonic term arising due to thermal expansion has been taken into account in the expansion of logarithmic series of the thermodynamic data. The results obtained for alkaline earth oxides are discussed and compared with experimental data under the combined effect of high temperature and high pressure. The results are found to be in good agreement with available experimental results.

Effect of temperature on elastic properties of alkaline earth oxides (AEO)

A simple and straightforward theoretical model is developed to investigate the elastic properties of alkaline earth oxides under the effect of temperature as well as pressure. The calculation are performed with the help of high pressure-high temperature equation of state (EOS) based on thermodynamic analysis. The anharmonic term arising due to thermal expansion, has been taken into account in the expansion of logarithmic series of the thermodynamic data. The results obtained for alkaline earth oxides are discussed and compared with experimental data under the effect of high temperature at zero pressure. The results are found to be in good agreement with available experimental results and thus may be helpful in analyzing the others experimental results.