Abstract
The complex dielectric constant/ac electrical conductivity was investigated as a function of the frequency and temperature in four fluorides systems, K3Fe5F15, K3Fe2Cr3F15, (NH4)2FeF6, and Pb5Cr3F19. All studied fluorides systems undergo ferroelectric (or antiferroelectric) phase transition at higher temperatures, and ferromagnetic (or antiferromagnetic) transition at low temperatures. At lower temperatures, in all studied systems, the real part of the complex ac electric conductivity was found to follow the universal dielectric response σ′ ∝ ν s , being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that, at low temperatures, this mechanism governs the charge transport in all studied fluoride systems.
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