Ionic conduction and dielectric properties of anhydrous alkali metal salt forms of α-zirconium phosphate
Abstract Electric and dielectric properties of polycrystalline samples of α-layered Zr(MPO4)2 with M = Li, Na, K, were investigated between 150 and 350°C by complex-impedance measurements, at frequencies ranging from 5 Hz to 10 MHz. With increasing ionic radius of the counter-ion conductivities increase approximately from 10-8 to 10-5 ω-1 cm-1, while activation energies decrease from 21.5 to 15.6 kcal/mol. The conductivity dependence on the relative density (ϱr) of the polycrystalline samples was also investigated. It was found that the conductivity increments are proportionately higher than the corresponding ϱr increments, indicating the presence of a prevalent grain-boundary conduction. The dielectric constant of the investigated materials was derived by inverting the impedance data. The frequency dependence of the real part of the dielectric constant shows the presence of a relaxation, whose time constant is independent of ϱr; suggestions about its physical origin are made. Finally, an electrical equivalent circuit, which is able to accurately model the impedance and dielectric-constant, was derived.