Paper No. 2
Presentation Time: 9:15 AM


ZHAO, Zhao, Physics, Stanford University, 450 Serra Mall, Stanford University, Stanford, CA 94305, WANG, Shibing, Geological & Environmental Sciences, Stanford University, Stanford, CA 94305, OGANOV, Artem, Department of Geosciences, State University of New York, Stony Brook, NY 11794, LIU, Zhenxian, Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015 and MAO, Wendy, Departement of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Braun Bldg #320, MC2115, Stanford, CA 94305,

As an important silver compound in some ores from mines in Nevada, naumannite Ag2Se exhibits many intriguing properties like high temperature superionic conduction, tunable optical band gap, and novel linear magneto resista­­nce. Through room temperature synchrotron X-ray diffraction and Infrared experiments combined with evolutionary algorithm structure predictions, we identified a sharp reversible structural transition of the bulk insulating phase I to a bulk metallic orthorhombic phase II with 2.4 percent volume drop. The transition is marked by the appearance of the distinct Se(Ag1)-Ag2-Se(Ag1) triple layers stacking pattern, observed in Ag2Te. At higher pressure, a smooth reversible transition from the phase II to a completely metallic phase III is seen, where the phase III has an abnormal c axis expansion of the orthorhombic lattice under compression. Our results highlights the interesting crystographically and electronic behaviors of Ag2Se under compression.