A theoretical method based on interionic potentials is developed for evaluating the compression of alkali halide crystals corresponding to different values of pressure. The short range overlap repulsive interactions between first neighbours as well as between second neighbour ions are taken into account. The traditional Born method for determining the repulsive parameters is replaced by a more plausible method due to Decker.
The structural phase transformation of CsC1 crystals under the effect of high temperature is investigated using an interionic potential model which takes account of repulsive interactions up to second neighbours and of van der Waals (vdW) interactions between dipole-dipole and dipolequadrupole. It is found that the transition temperature a t which the CsCl crystal transforms from B, (CsCI) to B, (NaCl) structure can be predicted correctly only if larger values of vdW potentials are used in calculations. The same potential parameters are used to predict the high pressure equation of state for CsCl, CsBr, and CsI crystals. The use of overlap integrals in the Born-Mayer potential form yields good agreement between theory and experiment for the high pressure compression data.Mit einem Interionenpotentialmodell, das abstoDende Wechselwirkung bis zu zweiten Nachbarn und die Van der Waals (vdW)-Dipol-Dipol-und Dipol-Quadrupol-Wechselwirkung einschlieh, wird die strukturelle Phasentransformation von CsC1-Kristallen unter dem EinfluB hoher Temperatur untersucht. Es wird gefunden, daB die obergangstemperatur, bei der der CsC1-Kristall von der B, (CsC1)-in die B, (NaC1)-Struktur ubergeht, sich korrekt nur dann voraussagen laDt, wenn groDere Werte der vdW-Potentiale in den Berechnungen benutzt werden. Dieselben Potentialparameter werden benutzt, urn die Hochdruckzustandsgleichung fur CsC1-, CsBr-und CsJ-Kristalle vorherzusagen. Die Benutzung von Uberlappungsintegralen in dem Born-Mayer-Potentialausdruck liefert gute Ubereinstimmung zwischen Theorie und Experiment fiir die Hochdruckkompressionsdaten.
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