  BaTiO3 appears in cubic and hexagonal variants, both of which are
centrosymmetric. Samples of cubic BaTiO3 are known to exhibit breaking of the
centric symmetry locally and globally. It has been proposed that the local
symmetry breaking originates in polar regions, the precursors of the
ferroelectric phase. Origins of the macroscopic symmetry breaking, which are
not well understood, have been previously tentatively correlated with
inhomogeneities in the samples, such as strain gradients that may align or
redistribute objects such as charged point defects or polar regions making
material macroscopically polar. No such data are available for BaTiO3 with
hexagonal symmetry. We compare dielectric, elastic, and pyroelectric properties
of the two materials in polycrystalline form. In contrast to cubic BaTiO3,
hexagonal BaTiO3 does not exhibit macroscopic pyroelectric response at room
temperature. This is consistent with apparent absence of polar regions in the
hexagonal material and the fact that in hexagonal BaTiO3 strain rather then
polarization is the order parameter for the phase transition into
ferroelectric-ferroelastic phase. The thermally stimulated currents measured in
hexagonal and cubic BaTiO3, however, show that both materials exhibit
noncentric macroscopic symmetry. This result supports the idea that extrinsic
factors such as strain gradients, which are apparently common for both
materials, may break the macroscopic symmetry, which may then lead to alignment
and redistribution of polar regions or charged defects.
