POST-GARNET HIGH-PRESSURE TRANSITION - EFFECT OF HETEROGENEOUS LASER-HEATING AND INTRODUCTION OF SOME NEW TECHNIQUES

The post-garnet high-pressure transition has been studied above 25 GPa using several high-pressure apparatus. Recovered samples were charact erized using SEM and TEM coupled with energy-dispersive electron-micro probe analysis, and powder X-ray diffraction. Combined with the result s of previous work, it became clear that, in the case of garnet, the r esulting high-pressure phases differ considerably depending on the det ails of the high-pressure experiments. The current study shows that he terogeneous heating by YAG laser in the diamond anvil cell may be resp onsible for some of the complexity of previous results. Much more unif orm heating of the sample is now possible using a resistance furnace i n a Drickamer-type apparatus or CO2-laser heating in a diamond-anvil c ell. The results of the current experiments indicate that end-member p yrope garnet transforms into a mixture of perovskite and corundum phas es in the pressure range of about 30 GPa.