HR: 0800h
AN: MR31A-0138    [Abstracts]
TI: Crystal Chemical Basis of the Perovskite to Post-Perovskite Transition
AU: * Ross, N L
EM: nross@vt.edu
AF: Virginia Polytechnic Institute and State University, Department of Geosciences 4044 Derring Hall, Blacksburg, VA 24061, United States
AU: Angel, R J
AF: Virginia Polytechnic Institute and State University, Department of Geosciences 4044 Derring Hall, Blacksburg, VA 24061, United States
AU: Zhao, J
AF: Virginia Polytechnic Institute and State University, Department of Geosciences 4044 Derring Hall, Blacksburg, VA 24061, United States
AU: Di, W
AF: Virginia Polytechnic Institute and State University, Department of Geosciences 4044 Derring Hall, Blacksburg, VA 24061, United States
AB: The phase transition from perovskite to post-perovskite can be understood in terms of the crystal-chemical principles that govern the compression of the perovskite structure. The structural evolution of ABO₃ perovskites with increasing pressure is determined by the relative compressibility of the octahedral "B" cation site and the extra-framework "A" cation site. When the B site is softer than the A site, as it is for perovskites with cations of formal charge +3 on both sites, the structure becomes less tilted with pressure and undergoes transitions to higher symmetries [1]. The post-perovskite transition will therefore not occur in such compounds. In +2:+4 perovskites such as MgSiO₃, the structure becomes more tilted with pressure as a result of the A cation site being softer than the octahedral B site. As the tilt angles increase, the bond valence matching principle [2] that governs the structural evolution of perovskites requires an increased rate of compression of both cation polyhedra. At high compression there comes a point at which no further tilting is possible. This can be interpreted as the structural and elastic limit within the perovskite structure that drives the transition to the post-perovskite phase. The systematics of the bond valence matching principle also allow one to estimate the Clapeyron slope of the phase transition and that the coupled substitution of +3 cations (e.g. Fe + Al for Mg + Si) in MgSiO₃ perovskite will delay the post-perovskite transition to higher pressures. [1] Angel, Zhao, Ross (2005) Phys. Rev. Lett., 95, Art. No. 025503. [2] Zhao, Ross, Angel (2004) Acta Cryst., 60, 263-271.
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3621 Mantle processes (1038)
DE: 3924 High-pressure behavior
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting