Structural Phase Transition of Alkali Halides Using a Modified Interaction Model

Abstract

A new interionic potential model is developed by taking into account (i) the effect of three body interactions, (ii) the recent values of van der Waals (vdW) potentials estimated from KirkwoodMuller formula, (iii) the repulsive hardness parameters evaluated from the overlap integrals using the exchange charge model, and (iv) the effect of coupling between overlap repulsive and van der Waals forces in terms of the Drude oscillator model. The modified potential model is capable of predicting correctly the relative stability of two structures viz. NaCl and CsCl structures. The calculated values of transition pressure are found t o present close agreement with experimental data.Ein neues Interionenpotentialmodell wird entwickelt unter Beriicksichtigung von ( 1 ) des Einflusses von Dreikorperwechselwirkungen (2) der neueren Werte der van der W a d s (vdW)-Potentiale, die mit der Kirkwood-Muller-Formel bcrechnet wurden, (3) der repulsiven Harteparamrter aus den tfberlappungsintegralen mit Austauschladungsmodell und (4) des Einflusses der Kopplung zwischen repulsiveu Uberlappungs-und van der Waals-Kraften aus dem Drude-Oszilbtormodell. Das modifizierte Potentialmodell ermoglicht die korrekte Vorhersage der relativen Stabilitat von znei Strukturen, NaCl-und CsC1-Struktur. Die berechneten Werte des Druckubergangs zeigen enge Ubereinstimmung mit experimentellen Werten._..

Third‐Order Elastic Constants for Alkaline Earth Oxides and Fluorides

“…This, however, does not yield an adequate picture of short-range interactions for the intermehate range of interionic separations of magnitude nearly 0.3 t o 0. 4 51 by considering the composite effect of short-range repulsive and dispersion interactions as well as by including the effect of three-body interactions. The model thus developed has been found to explain the structural stability and t o predict the transition pressures for sixteen alkali halides in good agreement with experimental data [4].…”

“…4 51 by considering the composite effect of short-range repulsive and dispersion interactions as well as by including the effect of three-body interactions. The model thus developed has been found to explain the structural stability and t o predict the transition pressures for sixteen alkali halides in good agreement with experimental data [4]. The model has also been found [5] t o produce good agreement for the elastic, dielectric, and photoelastic properties of alkali halides.…”

Elastic, Dielectric, and Photoelastic Constants of Alkali Halide Crystals

“…Recently we have developed a potential model [12] by considering the composite effect of short-range repulsive and dispersion interactions as well as by including the effect of three-body interactions. The model thus developed has been found to explain the structural stability and to predict the transition pressures for sixteen alkali halides in good agreement with experimental data.…”