High Pressure Interest Group Seminar Series

Title: High pressure materials synthesis  - Examples from the Group IVa elements carbon, silicon and germanium

Speaker: Bianca Haberl, Neutron Scattering Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

When: Thursday, Feb 28^th at 4:00 p.m.

Where: Bldg. 8630 Shull Wollan Center, Room A-202

Seminar Series: High Pressure Interest Group

Abstract:

The Group IVa elements carbon, silicon and germanium exhibit a very rich polymorphism that can be accessed under the extreme conditions of pressure and temperature. This rich polymorphism results in useful metastable phases that can be recovered to ambient conditions with diamond being the prime example. Other phases also exist for silicon or germanium, phases that are expected to be superior for solar power generation and other semiconductor applications. Many further phases are predicted but experimental synthesis pathways are not established yet. This is often due to large kinetic barriers toward phase transition in crystalline precursors materials, a challenge which can be overcome through amorphous and disordered precursor materials.

In this presentation here, I will give an overview over recent work on the use of such disordered precursors for high pressure materials synthesis. This work includes in situ X-ray and neutron diffraction on pure amorphous silicon and germanium which indicates the formation of functional metastable phases at the technologically relevant pressures below 10 GPa. It also gives insights into the possible polyamorphism of these elements. I will also describe high pressure synthesis of precursor materials themselves followed by subsequent characterization using neutron total scattering and inelastic neutron scattering. Moreover, I will also present findings on a particular form of disordered carbon, glassy carbon, and the high pressure synthesis of hexagonal diamond based on electron, X-ray and neutron diffraction. Finally, I will give an outlook to future directions in high pressure neutron scattering and corresponding materials studies that could be critically important for the synthesis of novel phases from the Group IVa.

Host: Bianca Haberl

Cell: 865-805-4065