title: Single-crystal structure determination of (Mg,Fe)SiO3 postperovskite.
abstract: Knowledge of the structural properties of mantle phases is critical for understanding the enigmatic seismic features observed in the Earth's lower mantle down to the core-mantle boundary. However, our knowledge of lower mantle phase equilibria at high pressure (P) and temperature (T) conditions has been based on limited information provided by powder X-ray diffraction technique and theoretical calculations. Here, we report the in situ single-crystal structure determination of (Mg,Fe)SiO3 postperovskite (ppv) at high P and after temperature quenching in a diamond anvil cell. Using a newly developed multigrain single-crystal X-ray diffraction analysis technique in a diamond anvil cell, crystallographic orientations of over 100 crystallites were simultaneously determined at high P in a coarse-grained polycrystalline sample containing submicron ppv grains. Conventional single-crystal structural analysis and refinement methods were applied for a few selected ppv crystallites, which demonstrate the feasibility of the in situ study of crystal structures of submicron crystallites in a multiphase polycrystalline sample contained within a high P device. The similarity of structural models for single-crystal Fe-bearing ppv (~10 mol% Fe) and Fe-free ppv from previous theoretical calculations suggests that the Fe content in the mantle has a negligible effect on the crystal structure of the ppv phase.
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China. lzhang@ciw.edu
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Yue
authors.initials: Y
authors.lastname: Meng
authors.forename: Przemyslaw
authors.initials: P
authors.lastname: Dera
authors.forename: Wenge
authors.initials: W
authors.lastname: Yang
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Mao
authors.forename: Ho-Kwang
authors.initials: HK
authors.lastname: Mao
mesh_terms: D018360:Crystallography, X-Ray; D058085:Iron Compounds / Q000737:chemistry*; D017633:Magnesium Silicates / Q000737:chemistry*; D008958:Models, Molecular; D014961:X-Ray Diffraction
chemical_list: D058085:Iron Compounds; D017633:Magnesium Silicates; C005013:Florisil