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

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 ^/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^; its high pressure metallic polymorph melts with an initial slope of +3. 4 ^/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.