Measurement of the pyroelectric coefficient from poling currents in thin PLZT samples under possible injection of free charge

Poling currents were measured in 24 and 9 μm thick samples of PLZT 8/65/35 under applied fields of up to 150kV/cm, at temperatures from 23 to 170°C. Stable negative currents, flowing for hours in the direction opposite to the applied field, were observed in many samples, at room temperature as well as under heating. The revealed complex character of the currents did not allow the calculation of the pyroelectric coefficient from their instantaneous values. A method was developed to separate the pyroelectric component of the current. These components then yielded for the “biased” pyroelectric coefficient λB (measured under the applied field) values from tens to hundreds of nC/cm2K, depending on the field, temperature, and the poling history of the sample. The largest values of λB were measured close to and well above the Curie temperature (111°C) of the material. Injection of free charge is discussed as possibly responsible for the observed behavior.