High-Pressure, High-Temperature X-ray Diffraction Measurements and the Discovery of Post-Perovskite Phase Transition

Abstract

With recent developments in x-ray diffraction (XRD) measurements at synchrotron radiation facilities, we can examine stable crystal structure and phase transition in-situ at high-pressure and -temperature (\(P\)–\(T\)) conditions corresponding to the deep Earth. MgSiO3 perovskite is a principal mineral in most parts of the lower mantle, but its stability and possible phase transition in the lowermost mantle have long been unclear. Recent synchrotron XRD experiments at SPring-8 revealed the phase transition from perovskite to post-perovskite above 120 GPa and 2400 K, the conditions at a depth of 2600-km, a few hundred kilometers above the bottom of the mantle. It is now widely accepted that post-perovskite is a primary mineral in the D” layer. The layered crystal structure of post-perovskite causes unique physical properties such as enhanced electrical and thermal conductivity. More recent progress of synchrotron XRD measurements at ultrahigh \(P\)–\(T\) conditions is also briefly reviewed.