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GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L04304, doi:10.1029/2004GL022068, 2005

Octahedral tilting evolution and phase transition in orthorhombic NaMgF₃ perovskite under pressure

H.-Z. Liu

High Pressure Collaborative Access Team, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, USA

J. Chen

Mineral Physics Institute, State University of New York at Stony Brook, Stony Brook, New York, USA

J. Hu

Geophysical Laboratory, Carnegie Institution of Washington, Washington, D. C., USA

C. D. Martin

Mineral Physics Institute, State University of New York at Stony Brook, Stony Brook, New York, USA

D. J. Weidner

Mineral Physics Institute, State University of New York at Stony Brook, Stony Brook, New York, USA

D. Häusermann

High Pressure Collaborative Access Team, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, USA

H.-K. Mao

High Pressure Collaborative Access Team, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, USA

Abstract

Rietveld refinement of monochromatic synchrotron x-ray powder diffraction data was used to study the evolution of octahedral tilting in the orthorhombic NaMgF₃ perovskite under pressure. Hydrostatic pressure conditions were ensured up to 16 GPa using helium as a pressure medium. The tilting angles of MgF₆ octahedral framework were observed to increase with increasing pressure. The compression mechanism was observed to be dominated by the shortening of the octahedral Mg-F bond below 6 GPa, and then controlled by the increase of the octahedral tilting above 12 GPa. The bulk modulus of NaMgF₃ was estimated as 76.0 ± 1.1 GPa. A phase transition was observed at about 19.4 GPa in a separate run when silicone oil was used as pressure medium, and this high-pressure phase could be rationalized in term of a post-perovskite structural model.

Received 23 November 2004; accepted 21 January 2005; published 17 February 2005.

Index Terms: 1042 Geochemistry: Mineral and crystal chemistry (3620); 3924 Mineral Physics: High-pressure behavior; 3954 Mineral Physics: X-ray, neutron, and electron spectroscopy and diffraction; 3919 Mineral Physics: Equations of state.

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Citation: Liu, H.-Z., J. Chen, J. Hu, C. D. Martin, D. J. Weidner, D. Häusermann, and H.-K. Mao (2005), Octahedral tilting evolution and phase transition in orthorhombic NaMgF₃ perovskite under pressure, Geophys. Res. Lett., 32, L04304, doi:10.1029/2004GL022068.

Copyright 2005 by the American Geophysical Union.