Free energy variation due to a space charge formation

A polycrystalline ceramic (Y₂ O₃ + 1 at.% La) has been charged under electron irradiation. The specific heat C_p of both an uncharged and of a charged sample has been measured by the microcalorimetric technique, showing that C_p decreases after charge implantation. The variation of C_p(T) as a function of the temperature of the charged sample has also been investigated. The extra contribution of the polarization introduced in C _p vanishes at about 400°C. The variation of C_p after charging and the observed dipolar relaxation in Y₂O₃ are interpreted with a simple qualitative model. It has been shown that charge trapping modifies the thermodynamic variables of insulators and therefore can be at the origin of structural modifications in a variety of materials subject to stresses such as the recrystallization of polymers or the phase transition of zirconia