Single Crystal Structure Determination of Alumina to 1 Mbar

Abstract:

Aluminum oxide (Al₂O₃) is an important ceramic material and a major oxide in the earth. Additionally, alumina is a widely used pressure standard in static high-pressure experiments (Cr³⁺-bearing corundum, ruby). The changes of its crystal structure with pressure (P) and temperature (T) are important for its applications and understanding its physical properties in the deep Earth. There have been numerous reports on the high P-T polymorphs of alumina. Previous theoretical calculations and experiments suggest that the crystal structure of Al₂O₃ evolves greatly at high P-T. In this study, we used the newly developed multigrain crystallography method combined with single-crystal x-ray diffraction analysis technique for the structure determination of alumina at high P-T to provide single-crystal structure refinement for high-pressure phases of Al₂O₃. Alumina powder was mixed with ~10% Pt and Ne was used as both pressure transmitting media and thermal insulating layers during laser-heating. Coarse-grained aggregates of Al₂O₃ were synthesized in a laser-heated diamond anvil cell. The structure change of Al₂O₃ was monitored by in situ x-ray diffraction at ~1 Mbar and 2700 K. The results allow us to distinguish the structural differences between the Rh₂O₃ (II) structure (space group Pbcn) and perovskite structure (space group Pbnm) for the first high-pressure phase of Al₂O₃. More detailed results will be discussed in the later work.