HR: 1340h
AN: MR23B-0073    [Abstracts]
TI: Structural refinement for NaMgF3 perovskite under high pressure
AU: * Liu, H
EM: hliu@hpcat.aps.anl.gov
AF: High Pressure Collaborative Access Team, Carnegie Institution of Washington, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439
AU: Chen, J
EM: jichen@notes.cc.sunysb.edu
AF: Mineral Physics Institute, Stony Brook University, Stony Brook, NY 11794
AU: Hu, J
EM: jzhu@bnl.gov
AF: High Pressure Collaborative Access Team, Carnegie Institution of Washington, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439
AU: Martin, C
EM: c.dave.martin@gmail.com
AF: Mineral Physics Institute, Stony Brook University, Stony Brook, NY 11794
AU: Weidner, D J
EM: dweidner@sunysb.edu
AF: Mineral Physics Institute, Stony Brook University, Stony Brook, NY 11794
AU: H„usermann, D
EM: dhausermann@hpcat.aps.anl.gov
AF: High Pressure Collaborative Access Team, Carnegie Institution of Washington, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439
AU: Mao, H
EM: mao@gl.ciw.edu
AF: High Pressure Collaborative Access Team, Carnegie Institution of Washington, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439
AB: A fundamental understanding of the behavior of selected representatives of the perovskite family of structures to high-pressure/high-temperature conditions is valuable for establishing possible behaviors of this family in general. We have chosen to study NaMgF3 perovskite (neighborite) as it has gained significant attention as an analogue material of MgSiO3 perovskite since O'Keeffe et al pointed out their structural similarity in 1970s. Neighborite is isoelectronic with MgSiO3, and they are isostructural, possessing the same type of distortion from the ideal cubic perovskite structure to crystallize in space group Pbnm. We used a diamond anvil cell high-pressure device and synchrotron x-ray micro-diffraction to in situ study the crystalline change of the sample under high-pressure conditions. A series of experiments were carried out using various pressure-transmitting medium, the focusing beam size and grain size of the sample at NSLS beamline X17C and the High Pressure Collaborative Access Team facility at the Advanced Photon Source, to optimize the quality of diffraction data. The structural evolution of NaMgF3 under high pressure, therefore, could be analyzed from the Rietveld refinement of the high-quality x-ray diffraction patterns. The atomic positions could be obtained under high pressure. The overall trends of the octahedral tilting angles, i.e. increasing with increasing pressure, are similar for both the macro and micro approaches. The volumetric compression was dominated by the shortening of the octahedral Mg-F bond at the beginning of compression below 6 GPa. In the 6-12 GPa pressure range, the contribution from the octahedral tilting matches that of the bond length compression. This is followed by an increasing contribution from the octahedral tilting above 12 GPa. The octahedral tilting, increasing with pressure, finally destroys the perovskite structure. An experiment was carried out using silicone oil as the pressure medium, which could generate more shear stress to accelerate the phase transition. A phase transition was observed at about 19.4 GPa, and the patterns above this pressure can no longer be indexed by the Pbnm perovskite structure. The recent progress on this quenchable high pressure new phase will be addressed in a separate paper by C. D. Martin et al.
DE: 1042 Mineral and crystal chemistry (3620)
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
DE: 4465 Phase transitions
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005