Topic: Effect of pressure on selected 4d and 5d transition metal compounds: Ag₂Te and CsAuI₃

Speaker: Dr. Shibing Wang

　　　　 Stanford Institute for Materials and Energy Science,
　　　　　　 SLAC National Accelerator Laboratory, Stanford University, USA

Time: 14:00 PM, Thursday, Dec 20, 2012

Venue: Room 457, Lee Hsun Building, IMR, CAS

Abstract

As a fundamental thermodynamic parameter, pressure can dramatically alter materials’ properties and induce structural, electronic and/or magnetic transitions. In this talk, I will present our diamond anvil cell study on two transition metal compounds Ag₂Te and CsAuI₃.

Ag₂Te is a superionic compound, a material showing large linear magnetoresistance (LMR), and by recent prediction, a topological insulator. We performed in-situ synchrotron X-ray diffraction experiments in Ag₂Te up to 42.6 GPa at room temperature and four phases are identified. Combining experimental results with first-principles calculations, we solved phase II and III structures. From phase I to phase II, the Ag-Te coordination’s increase can be seen. We also studied the compression behavior of phase III. In addition, first-principles calculations present that the insulating phase I with a narrow band gap transforms firstly to the semi-metallic phase II with the perseverance of topologically non-trivial nature, then to metallic phase III where topological nature becomes unnecessary to define. Density of states calculation indicates the contrasting transport behavior for Ag_2-δTe and Ag_2+δTe for phase I and phase II.

Cs₂Au^IAu^IIII6 (CsAuI3) is a mixed valence compound at ambient condition with Au adopting Au^I and Au^III. Pressure is suggested to induce valence transition in the compound. We carried out the x-ray powder diffraction and Raman spectroscopy up to 21 GPa in a diamond anvil cell under hydrostatic conditions. We find a reversible pressure-induced tetragonal to orthorhombic structural transition at 5.5-6 GPa, and reversible amorphization at 12-14 GPa. Two alternative structures are proposed for the high-pressure orthorhombic phase, and are discussed in the context of a possible Au valence transition.

Welcome to attend