Method for Determining the Grüneisen Parameter of Pyroelectrics

Abstract

c  , where  is the volume thermal expansion parameter, cp is the specific heat capacity, and с0 is the volumetric speed of sound. The Gruneisen parameter is an important parameter entering into the equation of state of a condensed matter; therefore, its determination, both theoretical and experimental, is of sufficient interest. As an example, we consider a method suggested in [2] where the characteristics of a stress wave arising in the sample of the examined material as a result of fast heating by a laser radiation pulse were measured. The material was transparent for radiation. The soughtafter parameter was determined from these measurements and the energy absorbed in the material. In the present work, a method for determining the Gruneisen parameter of pyroelectrics is suggested from the characteristics of the electric response of a material sample exposed to a gamma rays or neutron pulse. The problem of the response was solved in [3, 4]. Below we briefly describe some results of these works with application to the problem being solved. We consider a plane capacitor in which a polarized pyroelectric serves as a dielectric. The capacitance of the capacitor is C0, the area of its plates is S, and the distance between the plates is L. The polarization vector P is perpendicular to the plates connected through the active resistance R. The capacitor is mechanically free. We choose the coordinate system so that the х axis coincides with the direction of the polarization vector, and the origin of coordinates is placed at the capacitor center of gravity. The capacitor is irradiated by an ionizing radiation pulse whose duration tn is much smaller than the thermal time constant of the capacitor, that is, heating of the pyroelectric material is adiabatic. The temperature is uniformly distributed in the material. The electric response of the pyroelectric to uniform heating is the sum of the primary and secondary pyroelectric effects [5]. The first of them determines the polarization change provided that the shape and volume of the pyroelectric sample remain constant upon heating; the second determines the polarization change attendant to free deformation of the sample.