Pressure dependence of the interfacial polarization and negative activation volume for dielectric relaxation in heterogeneous systems

Negative activation volumes for dielectric relaxation are rarely reported in solid state physics and are limited to atomic scale processes. Broadband Dielectric Spectroscopy on heterogeneous systems, such as polycrystalline calcite and magnesite, hosting water in their porous space, detected intense dielectric relaxation mechanisms related to interfacial polarization. The characteristic relaxation frequency increased upon hydrostatic compression, indicating that the activation volumes for relaxation are negative. However, a theoretical interpretation for the negative sign of the activation volume is lacking up to date. Within the frame of effective medium approximation for mesoscopic heterogeneous two phase solid – fluid systems, we investigate how the synergy of the pressure dependencies of polarization and electric charge transport, respectively, dictate the pressure dependence of interfacial relaxation, predicting the value of the effective activation volume. Our theoretical approach succeeds in predicting the negative sign and magnitudes of the activation volume in water saturated polycrystalline materials.