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.

Epitaxial growth and properties of YBaCuO thin films

“…In these calculations the mean one-dimensional vibration amplitude for Mg and 0 used was 0.063 A. This value was obtained from temperature dependent Debye-Waller factor measurements by X-ray diffraction [52]. The measured SPA is also in good agreement with the calculated one ( Table 1) which indicates that cleaved as well as properly polished surfaces are nearly free of defects or structural distortions.…”

Temperature factors and thermodynamic properties of crystals

“…James, 1948, page 220;Baldwin & Tompson, 1964), it is remarked that O M should always exceed 0 c by perhaps a few per cent. James, 1948, page 220;Baldwin & Tompson, 1964), it is remarked that O M should always exceed 0 c by perhaps a few per cent.…”

The X-ray debye temperatures of some II—VI compounds

“…Figure 5 shows the relation between OM and average atomic number for II-VI compounds and also for the Group IV elements for comparison. The OM's for MgO , CaS, BaTe and MgS are from Baldwin and Tompson (1964) MgS, ZnSe and CdTe seem to fall on the same sketched curve. This can be understood in terms of the atoms in these compounds being symmetrically related to Si, Ge and Sn, respectively, in the periodic table.…”

“…Thus, although there is some charge transfer between atoms, the covalent effects predominate. The x-ray Debye temperatures of some 'ionic' II-VI compounds have been measured by Baldwin and Tompson (1964). Figure 5 shows the relation between OM and average atomic number for II-VI compounds and also for the Group IV elements for comparison.…”

“…If the temperature difference is made large ( > loo"^), so that the uncertainty in 0, is -8%, then we are averaging over too large a temperature range. Baldwin and Tompson (1964) chose an 8 0 "~ temperature interval as a reasonable compromise. Using this interval for our results indicates that we could not detect a variation of less than 20% in 0, over the temperature range 9 6 "~-3 0 0 "~.…”