Anisotropy of Polarized Polycrystalline Barium Titanate

Square bars of polycrystalline barium titanate ceramic have been prepolarized and their lowest longitudinal resonance excited piezoelectrically on remanent polarization. Bars were prepared as twins in every way, except that one twin was electroded on its ends, the other on a pair of opposite sides. The first polarization applied was that minimum (800 v/cm for 30 minutes at 27°C) which fixed any, electromechanical activity as detected by a sensitive ac bridge, and this was taken to approximate the unpolarized, isotropic state (s11=s33). Different pairs were then given different large scale polarizations (2.5, 5.0, and 10 kv/cm cooled from above the Curie point) and changes noted. All resonant frequencies rose with time, the decay constant being between 0.01 and 0.02 hr−1, and the total change being 1 to 112% for “Ceramic A” (barium titanate), and 12% for “Ceramic B” (barium calcium titanate). For both materials the isotropic compliance was definitely much closer to s33E than to s33D, and averaged closer to s11E than to s11D. The ratios s33:s11 were 0.83 and 0.87 at constant D and 1.04, and 1.05 at constant E for the two materials after 10 kv/cm. Anisotropy varied somewhat with polarizing field strength.