Dielectric relaxation properties of Pb1-xSnxF 2 solid solutions prepared by mechanochemical milling

Abstract

The mechanochemical milling technique is employed to synthesize Pb 1-xSnxF2 solid solutions (with x ≤ 0.2-0.6) at room temperature. The obtained samples with x ≤ 0.2-0.5 show x-ray powder diffraction patterns similar to the β-PbF2 cubic structure, with the crystallite size in the range 25-29 nm. The ionic conductivity of the investigated materials, determined from impedance spectroscopy measurements, shows a maximum at x ≤ 0.5, reaching a value of 2.28 × 10-3 S cm-1 at room temperature. The electrical relaxation dynamics are studied in the electric modulus formalism in the frequency range 50 Hz-1 MHz over a wide temperature range. The conductivity relaxation time, for different compositions, is thermally activated with the same activation energy of the dc conduction. Scaling of the modulus spectra at different temperatures and compositions indicates that the relaxation dynamics are independent of temperature but depend on the microscopic structure and/or the concentration of mobile charge carriers. The frequency dependence of the dissipation factor, tan δ, shows a dielectric relaxation process, most probably originating from interfacial polarization. © 2007 IOP Publishing Ltd.