Anomalous volume expansion in Hg1-xCdxTe melts: An analysis employing the inhomogeneous structure model.

Abstract

New insights into anomalous volume expansion observed earlier in liquid HgTe are made possible if we assume that the liquid consists of a mixture of two kinds of domains and that the anomalous behavior arises from a continuous transformation of one kind into the other with increasing temperature. The analysis is consistent with some of the conclusions of the inhomogeneous structure model of Cohen and Jortner and is along the line of similar analyses carried out on liquid Te, ${\mathrm{In}}_{2}$${\mathrm{Te}}_{3}$, and ${\mathrm{Ga}}_{2}$${\mathrm{Te}}_{3}$ by various workers. Following a thermodynamic approach, we have used this model to interpret the negative thermal expansion below 750 \ifmmode^\circ\else\textdegree\fi{}C, indicating that the transformation of the liquid with heating to a structure of higher coordination number is for the most part completed when the minimum volume point is reached (at \ensuremath{\sim}750 \ifmmode^\circ\else\textdegree\fi{}C), even though appreciable heterogeneity persists above 800 \ifmmode^\circ\else\textdegree\fi{}C. The expansion at higher temperatures arises from normal volume expansion of the high-temperature phase. This description of a progressive transformation of the HgTe liquid into a high-coordination-number domain which may be more metallic is consistent with the rapid increase in the magnitude of experimental thermal diffusivity values of HgTe melts reported recently, though no direct determination of the liquid structure is available at this time. The analysis has been extended to pseudobinary ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$Te melts, containing 5, 10, and 20 mol % solutions of CdTe in HgTe, respectively. For these melts, the volumes, which have been measured earlier, can be closely approximated as sums of volumes of two separate liquids---one HgTe and the other CdTe. The CdTe in the pseudobinary melt undergoes normal volume expansion consistent with the behavior reported for a pure CdTe melt by other workers.