Melting and Polymorphism at High Pressures in Some Group IV Elements and III-V Compounds with the Diamond/Zincblende Structure

Abstract

The fusion curves of several elements and III-V compounds crystallizing in the diamond/zincblende structure have been determined to 50, or sometimes 70, kbar by means of differential thermal analysis. The melting slopes are (in \ifmmode^\circ\else\textdegree\fi{}C/kbar); Si, -5.8 (lower bound); Ge, -3.8; InAs, -4.3; GaAs, -3.4; InP, -2.9; AlSb, -6.9 (provisional); GaSb, -5. Gallium antimonide has a triple point near 56.5 kbar and 385\ifmmode^\circ\else\textdegree\fi{}C; its high pressure metallic polymorph melts with an initial slope of +3.4 \ifmmode^\circ\else\textdegree\fi{}C/kbar. Progressively more negative slopes for the melting of the diamond/zincblende structures are apparently correlated with increasing atomic volume and decreasing normal melting point. Extension of these correlations suggests that diamond melts with only a slightly negative slope. The sequence of pressure-induced polymorphic transitions strikingly reflects straightforward increases in coordination.