HR: 1340h
AN: MR43C-1526 [Abstracts]
TI: Structural Phase Transitions in AuIn2 at High Pressure
AU: Clark, S M
EM: smclark@lbl.gov
AF: Advanced Light Source, LBNL, 1 Cyclotron Road, Berkeley, CA 94720, United States
AU: Speziale, S
EM: Sergio Speziale
AU: Voltolini, M
EM: voltolini@berkeley.edu
AF: Earth & Planetary Science, University of California, McCone Hall, Berkeley, CA 94720,
United States
AU: * Godwal, B K
EM: godwal@berkeley.edu
AF: Earth & Planetary Science, University of California, McCone Hall, Berkeley, CA 94720,
United States
AU: Jeanloz, R
EM: Raymond Jeanloz
AB:
The intermetallic compound AuIn2 provides an analog for the high-pressure phases of SiO2, as it is initially in the
Fm3m fluorite (CaF2) structure. Synchrotron-based angular-dispersive x-ray diffraction (Advanced Light Source
beamline 12.2.2) reveals subtle anomalies in the pressure variation of normalized stress (F) versus Eulerian
strain (f) around 3 GPa, coinciding with anomalies observed in fusion, transport and optical data, and potentially
associated with the onset of an electronic phase transition. Our diamond-cell experiments (gasketted sample
with methanol-ethanol pressure medium) show continuous broadening of diffraction peaks beyond 12 GPa,
leading to amorphization near 24 GPa. On further increase of pressure, a crystalline phase appears around 28
GPa and persists upon unloading from 30 GPa to about 5 GPa, then reverting back to the original CaF2 phase.
We find the sequence of pressure-induced phase transition documented for CaF2 (fluorite structure Fm3m
PbCl2 Pnma Ni2In-type P63/mmc and a combination of PbCl2 and Ni2In) to be inadequate in fitting the
observed high-pressure diffraction patterns of AuIn2. However, the post-cotunnite structure of PbCl2, BaCl2,
BaBr2 and SnCl2 (P1121/c, Z=8) is able to account for most of the prominent peaks in our high-pressure
diffraction patterns (a=10.983, b=9.875, c=4.350, =96.6). Many oxides of geophysical interest occur in the CaF2
structure, and study of intermetallic compounds such as AuIn2 may prove useful in suggesting high-pressure
metallic phases for these oxides.
DE: 3924 High-pressure behavior
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting