STATIC P-T-V MEASUREMENTS ON MgO: COMPARISON WITH SHOCK WAVE DATA

Simultaneous P-V-T measurements of MgO have been carried out at pressures to 20 GPa and simultaneously to 680 K in a high pressure-temperature diamond-anvil cell using the x-ray diffraction technique and the radiation source at Stanford Synchrotron Research Laboratory. The sample temperature was measured with a precalibrated Pt-Pt% Rh thermocouple and the pressure was determined from an internal Au standard by using the deduced shock wave data of Jamieson et al _. [1982]. The experimental P-V isotherms are approximately parallel, indicating the invariance of KT with temperature at a constant volume, as observed in alkali metals and alkali halides. At high temperatures, however, the present isothermal data yield consistently ˜0.5% higher compression (V/VO) values as compared to the deduced shock wave data, resulting in higher pressure values (˜1 GPa) from the gold standard than from MgO. Until this discrepancy is resolved, the suitability of MgO as a pressure calibrant at high temperatures cannot be established.