Analysis of the electronic polarizabilities of ions in alkaline earth chalcogenides

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.     

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.     

Crystal radii of ions in alkaline earth chalcogenides

The crystal radii of ions in alkaline earth chalcogenides have been calculated from the effective nuclear charges of isoelectronic ions. The ionic radii thus calculated are found to follow the polarizability—radius cubed relation, according to which the ratio of the electronic polarizability of an ion to the cube of its radius in the free state is nearly equal to that in the crystalline state. The interionic separations in alkaline earth chalcogenides and also AB₂ and A₂B type crystals obtained from the ionic radii reported in the present paper agree closely with the experimental values.     

Electronic polarizabilities of ions in the chalcogenides of Zn and Cd

In the present communication we show that the energy level analysis yields consistent values of the electronic polarizabilities of individual ions in crystals of chalcogenides of Zn and Cd. It has been possible to explain the loosening of cations and the tightening of anions in the crystalline state relative to the free state.     

Correlation between electronic polarizabilities and ionic radii in alkali halides

An analysis of the electronic polarizabilities and sizes of ions in alkali halides has been carried out by considering a relationship according to which the electronic polarizability of an ion should vary as the n th power of its radius. The values of crystal radii, polarizabilities and the exponent “n”have been calculated using the free ion data reported by Pauling. The values of “n” are found to be nearly 3 in most of the crystals suggesting the validity of the polarizability radius cube relation. The polarizabilities and crystal radii calculated in the present study agree well with those estimated by earlier investigators.     

Analysis of polarizabilities of alkali halides using Narayan-Ramaseshan repulsive potential

The repulsive potential in ionic crystals recently proposed by Narayan and Ramaseshan (NR) can be expressed as the sum of the contributions from the individual ions. In the present paper we show that using this repulsive potential it is possible to divide the polarizability arising from the relative displacement of ions into its ionic constituents. NR have also derived the ionic radii in alkali halides which we have used to estimate the electronic polarizabilities of ions with the help of polarizability-radius cube relation. The electronic polarizabilities of alkali and halogen ions thus evaluated show a good agreement with those deduced from the experimental refraction data.     

Electronic polarizabilities of ions in transition metal oxides

A method for evaluating the electronic polarizabilities from ionic radii in transition metal oxides has been suggested. The ionic radii used in the present calculations are those deduced from the electron density measurements. The calculated polarizabilities agree closely with the experimental values obtained from the electronic dielectric constant.     

Electronic polarizabilities of ions in transition metal oxides

A method for evaluating the electronic polarizabilities from ionic radii in transition metal oxides has been suggested. The ionic radii used in the present calculations are those deduced from the electron density measurements. The calculated polarizabilities agree closely with the experimental values obtained from the electronic dielectric constant.     

Electronic polarizabilities and sizes of ions in AN B10−N type semiconductors

Electronic polarizabilities and sizes of ions in A^N B^10?N type semiconductors (PbS, PbSe, PbTe and SnTe) have been deduced in the present study. The free ion polarizabilities of Sn²⁺ and Pb²⁺ ions are estimated approximately following the procedure of Pauling. The effect of crystalline potential is then estimated on free cation polarizabilities. An empirical relation between ionic radii and polarizabilities has been applied to deduce the ionic sizes and anion polarizabilities. The calculated molecular electronic polarizabilities agree well with the experimental values. The variation of dielectric constant with strain has also been estimated in each crystal and the results are explained in terms of the optical anisotropy parameter.     

Electronic polarizabilities of ions in II–VI crystals

The electronic polarizabilities of O^2?, S^2?, Se^2? and Te^2? ions are reported for the first time using two models, an additive law and an interaction law. The calculations show that the additive law does not hold good for II–VI group compounds, and therefore, one has to include some sort of interaction term to calculate the polarizabilities of these ions.     

Static polarizabilities of helium and alkali atoms,and their isoelectronic ions

A rather simple method of calculation of the scalar and tensor components of static polarizability was developed for a wide range of atoms and ions. The general formulas for polarizabilities of SL terms, J levels, and F components of hyperfine structure are given. The results of calculation for ground and some excited states of He and alkali atoms (Li, Na, K, Rb, Cs) are presented. The comparison of the results with available theoretical and experimental data shows that, in most cases, the differences do not exceed 10%. The polarizabilities for the Li+, Be+, B²+, C³+, Ne⁷+, Mg+, Al²+, Si³+, Ar⁷+, Ca⁺, Sc²+, Ti³+, Sr⁺, and Ba⁺ ions are also given.     

Theoretical tensile strength of alkali and alkaline earth halides along the edge and body diagonal of the cubic cell

The Zwicky method for calculating the theoretical tensile strength of a NaCl crystal along the edge of the cubic cell is refined. The theoretical tensile strengths of alkali and alkaline earth halides are. calculated along the edge and body diagonal of the cubic cells. The Young's moduli of these crystals are calculated for these directions. It is shown that the theoretical strength depends strongly on the extension direction.Translated from. Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 7, pp. 60–64, July, 1969.     

Off-centre position of excited s2 ions in alkali halides

Abstract

Off-centre displacement of Ga⁺ and In⁺ ions in the triplet relaxed excited state, occurring in the plane perpendicular to the tetragonal Jahn-Teller distortion axis of the centre, has been found. This effect may be caused by the vibronic mixing of the one-electron triplet relaxed excited state of (ns) (np) configuration with two-electron triplet excited states of (np) (np) configuration. Some experimental manifestations of the latter states have been detected.     

Observation of negative alkali ions from alkali halides during 248-nm laser irradiation

Below laser fluences where a plasma is formed (the so-called plasma or plume formation threshold) a number of fundamental phenomena can occur where particles such as atomic and molecular ions, atoms and molecular neutrals, and electrons can be emitted. An understanding of such processes is necessary to develop predictive models for material removal from laser irradiated surfaces—at the foundation of laser etching, machining, and pulsed laser deposition. We have reported on a number of the mechanisms for such emission processes. Here, due to space limitations, we present a summary of our studies on the formation of negative alkali ions from single crystal KCl during exposure to pulsed 248-nm radiation at fluences well below the threshold for plasma formation. Despite the high electron affinities of the corresponding halogen atoms, negative halogen ions were not detected. Significantly, the positive and negative alkali ion distributions overlap strongly in time and space, consistent with K formation by the sequential attachment of two electrons to K⁺. Negative alkali ions are also observed under comparable conditions from LiF, NaCl, and KBr. In each material, the strong overlap between the positive and negative alkali ion distributions, and the lack of detected negative halogen ions, suggest that negative ion formation involves a similar mechanism.     

Dielectric properties of alkali halide and alkaline earth oxide crystals

The deviations of ionic charge and compressibility from their nominal values in alkali halides and alkaline earth oxide crystals have been discussed and explained in terms of a theory based on shell model and exchange charge interactions originally developed by Dick and Overhauser. The exchange charge polarization parameters have been evaluated in the present study using the appropriate values of overlap integrals. It has been concluded that the second neighbour short range forces have significnant magnitudes in alkaline earth oxides.