THERMAL-EXPANSION STUDIES OF STISHOVITE AT 10.5 GPA USING SYNCHROTRON-RADIATION

The thermal expansion of stishovite has been studied in situ under pre ssure at 10.5(8) GPa and in the temperature range from 20 degrees C to 1000 degrees C using a cubic type apparatus combined with synchrotron radiation. The linear thermal expansivities along the crystallographi c a- and c-axes at 10.5(8) GPa and 20 degrees C are alpha(a) = 0.4978( 1) x 10(-6) K-1 and alpha(c) = 3.155(2) x 10(-6) K-1, respectively. Th e volume thermal expansivity for the same pressure-temperature conditi ons is alpha(v) = 4.080(4) x 10(-6) K-1. The Anderson-Gruneisen parame ter, delta(T), at 10.5(8) GPa decreases with increasing temperature fr om 55 at 20 degrees C to 15 at 1000 degrees C, and approaches five whe n extrapolated to 1500 degrees C.