The low temperature thermal expansion and Gruneisen functions of tellurium

Abstract

The coefficients of thermal expansion parallel and perpendicular to the c axis ( alpha /sub /// and alpha perpendicular to ) have been measured for tellurium over the temperature range 4 to 200 K. Throughout this temperature range alpha /sub /// is confirmed as being negative and alpha perpendicular to positive. The Gruneisen functions gamma /sub /// and gamma perpendicular to have been obtained and analysed. Accurate values for these functions for temperatures less than about 30 K are presented here for the first time: gamma perpendicular to has a broad shallow maximum centred near 30 K while gamma /sub /// is negative below about 18 K and has a sharp minimum centred near 8 K. The strain dependence of the moments of the frequency distribution gamma perpendicular to (n) and gamma /sub /// (n) have been derived for -3<or=n<or=2 and the temperature dependence of gamma perpendicular to (T) and gamma /sub /// (T) analysed in terms of the strain dependence of a simplified but realistic frequency distribution G( omega ). This analysis indicates that the lowest frequency peak in G( omega ), which is presumably associated with essentially transverse acoustic modes, contains modes (j) with predominantly negative gamma jperpendicular to values, whereas acoustic modes of higher frequency have markedly positive gamma j/sub /// values.