Lattice strain of hexagonal BaTiO3under hydrostatic pressures

Abstract
X-ray diffraction pattern of hexagonal BaTiO3 has been examined under hydrostatic pressures with a diamond-anvil cell. The hexagonal modification is still stable under the pressure of as high as 180kbar. The volume of the unit cell decreases by about 10% at 150kbar. From the pressure-volume data, the bulk modulus B has been estimated by using the Birch relation; the B in the hexagonal BaTiO3 turns out to be 1.10 ± 0.05 Mbar, and is smaller by about 10% than that of the perovskite BaTiO3. The difference of bulk modulus between the two polymorphic forms may be explained by a difference of the stacking sequence of Ba-O layers.