Mineral Physics Institute
Summer Scholars Program

Woody Schneider
Brown University
Physics Major
Mentor: Baosheng Li and Wei Liu

Currently the only method of directly measuring the interior of planets is via seismic waves. These are essentially sound waves propagating through rock which, in doing so, conform to specific elastic properties of that medium; the same behavior exhibited when sound is distorted underwater.

Within the lower mantle, 2,700 km below earths surface, at ambient pressures a million times those on the surface, a perplexing seismic singularity known as the D'' anomaly is found. It exists just above the important, and still quite mysterious, core-mantle boundary. Among the minerals believed to exist here are so called Calcium and Magnesium Perovskites.

Recent discovery of a "post-perovskite" solid->solid phase change, which becomes favorable at D'' appropriate pressure and temperature offers a possible explanation for the D'' mystery. Unfortunately, extensive experimentation concerning these post-perovskite materials is difficult, since they can only exist in painstakingly created high pressure and temperature environments, and not at ambient conditions.

We plan to study the theorized existence of a lower pressure post-perovskite phase in the analogue material, Ca Stannate. Ca Stannate possesses the same crystalline structure as the perovskites found in the lower mantle, and may share their elastic properties as well.

Using high pressure (though not nearly as high as is required for Ca and Mg Perovskites) and high temperature ultrasonic interferometry, we hope to investigate the elastic properties of this analogue material and of its theorized post-perovskite phase. This will yeald new clues about the mysterious lower mantle and the forces which drive the evolution of our most singular planet.