O.P. Sharma

Analysis of crystal binding of alkali and alkaline earth chalcogenides

Abstract An analysis of the crystal binding of alkali and alkaline earth chalcogenides is presented within the framework of the Born model of cohesion. The contributions of the overlap repulsive interactions between nearest and next nearest neighbours are considered in the evaluation of the cohesive energies of oxides, sulphides, selenides and tellurides of alkali and alkaline earth metals. In addition, the contributions arising from the van der Waals dipole-dipole and dipole-quadrupole interactions are estimated following the method recently proposed by Boswarva. Calculated values of the cohesive energies in alkaline earth chalcogenides present a close agreement with experimental values. Electron affinities of chalcogenide ions estimated in the present study, following the Born-Haber thermochemical process, are in remarkably close agreement with experimental data.

A Born-model analysis of interatomic forces in alkali halides using ultrasonic data

Abstract An analysis of interatomic forces operative in the alkali halides is performed within the framework of the Born model using recent experimental data based on ultrasonic measurements. Several forms of the potential, representing the dependence of short-range repulsive energy on interionic distance, are considered. The van der Waals dipole-dipole and the dipole-quadrupole interactions are taken into account. The Born repulsive parameters are evaluated from the Hildebrand approximation using recently obtained ultrasonic data. The cohesive energies and the Anderson-Gruneisen parameters have been calculated for alkali halides having the NaCl structure and these are compared with experimental data.

Variation of electronic polarizabilities and sizes of ions in crystals under hydrostatic pressure

A model, based on the energy level analysis performed by Ruffa and empirical relation between polarizability and ionic radius, has been developed to study the variation of electronic polarizabilities and sizes of ions in crystals under hydrostatic pressure. The model has been applied to investigate the photoelastic behavior of alkali halides and MgO. The strain derivatives of electronic polarizabilities and dielectric constants thus evaluated present a good agreement with experimental data and other theoretical investigations.

Evaluation of the second order strain derivatives of the electronic dielectric constant of alkali halides

Abstract We have evaluated the second order strain derivatives of the electronic dielectric constant of alkali halides employing two different theories viz. the Clausius—Mossotti theory of polarizability and the Penn model of energy gap. The results obtained from the two theories are in fair agreement with each other. It has been emphasised that the present calculations can be used to separate the electronic and ionic contributions to the second order strain derivative of the static dielectric constant.

Theory of the photoelasticity of cuprous halides

Abstract Recently Biegelsen et al. have observed the anomalous photoelastic behaviour of CuCl, CuBr and CuI crystals. In this communication, we present a quantitative analysis of this behaviour within the framework of the Clausius—Mossotti theory of dielectric constant.

Theory of the photoelastic effect in ZnO, ZnS and CdS crystals

Abstract It has been a general opinion that the Clausius-Mossotti dielectric theory is not capable of explaining the observed photoelastic behaviour of partially ionic crystals. However in the present communication we show that by making account of the variation of polarizabilities under compressive stress within the framework of the Clausius-Mossotti theory it is possible to obtain a reasonable agreement with experimental data on the photoelastic behaviour of ZnO, ZnS and CdS crystals.

Volume dependence of the refractive indices of rutile crystal under hydrostatic pressure

Abstract The photoelastic behaviour of rutile crystal recently observed by Davis and Vedam is peculiar in the sense that for this material the extra ordinary refractive index decreases whereas the ordinary refractive index increases with pressure. An explanation of this observation has been offered on the basis of an anisotropic model for the oxygen ion polarizability.

Theory of strain derivative of electronic dielectric constant of ionic crysts

Abstract A theoretical method for evaluating the strain derivative of the electronic dielectric constant of ionic crystals has been developed. The analysis presented here is based on the shell model and takes account of the exchange charge polarizations. Values of strain derivative of the electronic constant dielectric calculated for 6 alkali halides and MgO show a remarkable agreement with experimental data on photoelastic constants.

Effect of the crystal potential on electronic polarizabilities of ions in alkaline earth chalcogenides

The electronic polarizabilities of ions in alkaline earth chalcogenides are estimated by taking account of the effect of the crystalline potential. The polarizabilities thus obtained are found to present a good agreement with experimental data. It has been shown that the polarizabilities and radii of alkaline earth and chalcogenide ions follow the polarizability-radius cube relation approximately well.

Analysis of the electronic polarizabilities of ions in alkaline earth chalcogenides

Abstract Electronic polarizabilities of ions in II–VI crystals recently derived by Jain et al. are criticised. It has been demonstrated that the polarizabilities derived by Boswarva in alkaline earth chalcogenides on the basis of the additivity rule using crystal refraction data are consistent with those derived in the present paper employing a theoretical model originally developed by Ruffa.