72.
Many of ilmenites ABO
3 compounds bearing transition elements have semiconductive, ferroelectric and antiferromagnetic properties. The high-pressure
diffraction studies of FeTiO
3 have been conducted up to 8.2 GPa using synchrotron radiation in KEK at Tsukuba with diamond anvil cell. The compression
mechanism of FeTiO
3 ilmenite has been investigated by the structure refinements converged to the reliable factors
R = 0.05. The deformations of the FeO
6 and TiO
6 octahedra were reduced with increasing pressure. In order to elucidate the electric conductivity change with pressure, electron
density distribution of ilmenite have been executed by maximum entropy method (MEM) using single-crystal diffraction intensity
data. MEM based on
F
obs(
hkl) of FeTiO
3 clearly shows electron density in comparison with the difference Fourier synthesis based on
F
obs(
hkl) −
F
calc(
hkl). The radial distribution of the electron density indicates electron localization around the cation positions. The bonding
electron density found in bond Fe–O and Ti–O is lowered with pressure. The isotropic temperature factors
B
iso become smaller with increasing pressure. Nevertheless the thermal vibration is considerably restrained by the compression,
the electric conductivity is enhanced with pressure. Neither charge transfer nor electron hopping between Fe and Ti along
the
c axis in FeTiO
3 is plausible under high pressure. But the electric conductivity due to electron super-exchange in Fe–Fe and Ti–Ti has been
clarified by the MEM electron density distribution. The anisotropy in the electric conductivity has been clarified.
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