J. Phys.: Condens. Matter 12 (2000) 9985–9992. Printed in the UK PII: S0953-8984(00)14603-X Polarization and depolarization currents resulting from the temperature or pressure induced volume changes in polarized dielectrics A N Papathanassiou University of Athens, Department of Physics, Section of Solid State Physics, Panepistimiopolis, GR 157 84 Zografos, Athens, Greece E-mail: apapathan@in.gr Received 9 June 2000, in final form 4 August 2000 Abstract. We investigate the emission of electric current from a polarized dielectric whenever the matrix dilates. The thermal volume expansivity, the isothermal bulk modulus, its temperature and pressure derivatives and the rate of temperature or pressure variation would determine the shape and the magnitude of the electric signal. We emphasize the permanent dipole polarization and the ionic (induced) polarization. Numerical estimates of the current density, which would be recorded in polarization or depolarization experiments in a model system with cubic symmetry, such as sodium chloride doped with a small amount of divalent cation impurities, are obtained. 1. Introduction Two categories of dielectric relaxation experiments are employed so as to study the dipole dynamics and space charge relaxation in insulators. In the first type of experiment, such as the impedance spectroscopy and charging or discharging techniques, the system is maintained at equilibrium during the measuring procedure (isothermal or isobaric experiments). Another category involves the polarization or depolarization of the sample by continuous variation of temperature or pressure and therefore are regarded as quasistatic techniques. The latter experimental schemes are known as the thermal stimulated polarization (TSPC) or depolarization (TSDC) current [1, 2] and the pressure stimulated polarization (PSPC) or depolarization (PSDC) current [3, 4]. In the TSDC scheme, which is the most popular dielectric relaxation technique, a dielectric is polarized at room temperature by applying an external electric field. Afterwards, the temperature is reduced drastically to liquid nitrogen temperature (LNT), whereas the polarizing electric field is switched off. The removal of the field results in the rapid annihilation of the induced (electronic and ionic) polarization; however, the permanent dipoles remain polarized, since their relaxation time at LNT is practically infinite. Afterwards, the specimen is heated at constant pressure in the absence of an external electric field. A transient depolarization current is released at the temperature range where dipoles are mobile enough to reach a random orientation state. The PSDC scheme resembles the TSDC, but pressure is the thermodynamic parameter that is modified. The polarization state becomes ‘frozen’ by subjecting the sample to high compression. In the PSDC, the dipolar depolarization signal is produced as pressure is reduced from its initial high value to the ambient pressure. In the polarization experiments (TSPC and PSPC), the current is 0953-8984/00/489985+08$30.00 © 2000 IOP Publishing Ltd 9985