Phase transitions, dielectric, piezoelectric and pyroelectric properties of barium titanium germanate Ba2TiGe2O8 single crystals

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Abstract
Measurement of the dielectric permittivity ε33, the pyroelectric coefficient p3 and the piezoelectric planar coupling kp and frequency constant Np in single crystal Ba2TiGe2O8 show clear evidence of a heretofore unobserved first order phase change which occurs at - 50°C on cooling and near 0°C on heating. The balance of evidence suggests that the transition is to a reorientable but irreversible ferroelectric phase, involving a tilt of the prototypic polar c axis. The inversion of the sign of the pyroelectric effect reported earlier near 135°C is confirmed and is attributed to the changing balance between primary and secondary components in the pyroelectric coefficient.