Pyroelectricity, Internal Domains, and Interface Charges in Triglycine Sulfate

Abstract

Using the dynamic pyroelectric technique, the spontaneous polarization of triglycine sulfate has been determined between the Curie point and -140\ifmmode^\circ\else\textdegree\fi{}C. No evidence of any phase transitions over this temperature range was found (other than the Curie point). The polarization could still be reversed by an applied field, though slowly, at the lowest temperatures attained. In the paraelectric region above the Curie point, the pyroelectric behavior shows some deviations at low applied fields from the predictions of Devonshire's theory. The cause of these deviations is not known but they may be due to nonuniform conditions, either mechanical or electrical, in the crystal.With no field applied to the crystal, pyroelectric signals can be generated temporarily above the Curie point. These are ascribed mainly to polarizations induced by the compensation charges while they last, which accumulate around residual domains that cannot be removed by the poling field at room temperature. These residual domains have been delineated using powder pattern and etching techniques and are revealed as long thin domains, pointed at both ends and lying along the ferroelectric direction, either in the interior of the crystal or intercepting the surfaces. The causes of these persistent domains are not known.It is found that on cooling a crystal through the Curie point, there is a strong tendency for it to repolarize with the same polarity it had previously. This phenomenon is ascribed to the presence of ferroelectrically inactive surface layers giving rise to interface charges.