Unquenchable high-pressure perovskite polymorphs of MnSnO3 and FeTiO3

Abstract

Abstract. New high-pressure orthorhombic (GdFeOatype) perovskite polymorphs of MnSnO3 and FeTiO3 have been observed using in situ powder X-ray diffraction in a diamond-anvil cell with synchrotron radiation. The materials are produced by the compression of the lithium niobate polymorphs of MnSnO3 and FeTiO3 at room temperature. The lithium niobate to perovskite transition occurs reversibly at 7 GPa in MnSnO3, with a volume change of -1.5%, and at 16 GPa in FeTiO3, with a volume change of -2.8%. Both transitions show hysteresis at room temperature. For MnSnO3 perovskite at 7.35 (8) GPa, the orthorhombic cell parameters are a=5.301 (2) A, b=5.445 (2) ~, c=7.690 (8) A_ and V= 221.99 (15) ~ 3. Volume compression data were collected between 7 and 20 GPa, The bulk modulus calculated from the compression data is 257 (18) GPa in this pressure region. For FeTiO3 perovskite at 18.0 (5) GPa, cell parameters are a= 5.022 (6) ~, b=5.169 (5) A,, c=7.239 (9)/k and V= 187.94 (36)~3. Based on published data on the quench phases, the FeTiOa perovskite breaks down to a rocksalt § mixture of "FeO" and TiO2 at 23 GPa. This is the first experimental verification of the pressure-induced breakdown of a perovskite to simple oxides.

High pressure densification and dielectric properties of perovskite-type oxynitride SrTaO2N

“…Pressure-induced phase decomposition has been reported in many oxides with various crystal structures [25,26]. The FeTiO 3 perovskite-type oxide (as a high pressure polymorph) was also decomposed into a mixture of rock-salt type "FeO" and TiO 2 at high pressure above 67 GPa [27,28]. The high pressure-induced decomposition can be understood by the formation of a denser assemblage of the decomposed oxides that is favorable at high pressure rather than the parent ternary oxide.…”

High-pressure phases ofFeTiO3from first principles

“…1 The Fe 2+ to Fe 3+ ratio in ilmenite under pressure has been studied experimentally as an indicator of the oxidation state of the host kimberlites, which is used to determine the origin and genesis of diamond deposits. 2 In addition to ilmenite, two other polymorphs of FeTiO 3 are known, 3 namely, the lithium niobate and perovskite structures. The lithium niobate phase forms as a quench product of the perovskite phase which is stable only at pressures greater than 16 GPa.…”

“…4 Several other oxides with ABO 3 stoichiometry transform from the ilmenite structure to a perovskite structure under pressure. Examples of these are the germanates ZnGeO 3 3 and their respective polymorphs suggests that a similar phase could also exist for FeTiO 3 .…”

Ferroelectric soft mode of polarZnTiO3investigated by Raman spectroscopy at high pressure

“…The Wu-Cohen exchange-correlation functional calculations on LN-type ATiO 3 , with A = Mn, Mg, Fe, or Zn, gave lattice parameters in very good agreement (better than 0.5%) with experiments [12,[38][39][40]. The PBE-based calculations gave results which consistently showed the well-known underbinding.…”