X-Ray Characteristic Temperatures of Some II—VI Ionic Compounds

Abstract

The characteristic temperatures and thermal expansion coefficients of MgO, CaO, MgS, CaS, and BaTe have been measured by observing Bragg reflections as functions of temperature in the temperature range from 100° to about 1000°K. The compounds selected were those for which the simple cubic approximation should be most applicable, and interpretation of the data was based upon the Debye approximation for a solid. For at least one of these materials, evidence was found at high temperatures for a temperature dependence of ΘM nearly equal to that predicted by the explicit dependence of ΘM on volume, while at low temperatures ΘM was a much more rapid function of temperature. For MgO the absolute value of ΘM was found to agree fairly well with the published specific heat values, after correction for the difference in averaging over the vibrational spectrum, although it was found to be somewhat larger than a value obtained from earlier x-ray measurements. Expansion coefficients for MgO and CaO were in agreement with other determinations. Neither characteristic temperatures nor expansion coefficients were found in the literature for the other materials.