Perovskite, LiNbO3, Corundum, and Hexagonal Polymorphs of (In1-xMx)MO3

LiNbO3 (LN), corundum (car), and hexagonal (hex) phases of (In1-xMx)MO3 (x = 0.143; M = Fe0.5Mn0.5) were prepared. Their crystal structures were investigated with synchrotron X-ray powder diffraction, and their properties were studied by differential thermal analysis, magnetic measurements, and Mossbauer spectroscopy. The LN-phase was prepared at high pressure of 6 GPa and 1770 K; it crystallizes in space group R3c with a = 5.25054(7) angstrom, c = 13.96084(17) angstrom, and has a long-range antiferromagnetic ordering near T-N = 270 K. The car- and hex-phases were obtained at ambient pressure by heating the LN-phase in air up to 870 and 1220 K, respectively. The car-phase crystallizes in space group R-3c with a = 5.25047(10) angstrom, c = 14.0750(2) angstrom, and the hex-phase in space group P6(3)/mmc with a = 3.34340(18) angstrom, c = 11.8734(5) angstrom. T-N of the car-phase is about 200 K, and T-N of the hex-phase is about 140 K. During irreversible transformations of LN-(In1-xMx)MO3 with the (partial) cation ordering, the In3+, Mn3+, and Fe3+ cations become completely disordered in one crystallographic site of the corundum structure, and then they are (partially) ordered again in the hex-phase. LN-(In1-xMx)MO3 exhibits a reversible transformation to a perovskite GdFeO3-type structure (space group Pnma; a = 5.2946(3) angstrom, b = 7.5339(4) angstrom, c = 5.0739(2) angstrom at 10.3 GPa) at room temperature and pressure of about 5 GPa.