Structure of rhombohedral ferroelectric barium titanate

Abstract

The Profile Analysis technique for neutron powder diffraction patterns has been used to show that the lowest temperature phase of barium titanate is rhombohedral R3m with cell angle α = 89.868 ± 0.004°at 77.4 K. The atomic displacements from the cubic perovskite positions are along [111], and have magnitudes of δ (Ba) = 0.001 ± 21 Å, δ(Ti) = 0.091 Å and δ(OI) = δ (OII) = δ(OIII) = -0.091 ± 14 Å. The oxygen octahedron is slightly distorted by an additional oxygen displacement of δ⊥(O) = 0.023 ± 13 Å perpendicular to this ferroelectric axis. These values yield 34 ± 7 μC. cm-1 for the spontaneous polarization in this phase, in good agreement with the measured value of 33.5 μC.cm-1.