Abstract
The influence of isovalent substitutions of Pb2+ by Cd2+ and heterovalent substitutions of Pb2+ by Sc3+ on a superionic Faraday transition in Pb1 – xCdxF2 (x = 0.33) and Pb1 – x ScxF2+x (x = 0.1) solid solutions based on the fluorite-type modification β-PbF2 with sp. gr. Fm¯3m has been studied. The Faraday phase transition can be characterized by the temperature Tλ corresponding to maximum on the heat capacity curve and temperature Tα corresponding to the beginning of the structural disorder anion sublattice. Both of these temperatures are found on the temperature conductivity dependence σdc(T ) of β-PbF2, Pb0.67Cd0.33F2 and Pb0.9Sc0.1F2.1 crystals. The values of Tλ and Tα in solid solutions compared with β-PbF2 matrix (Tλ = 715 ± 10K, Tα = 597 ± 12 K) decrease by 100–110 and 30–45 K for Pb0.67Cd0.33F2 and Pb0.9Sc0.1F2.1, respectively. Decreasing of temperature Tλ leads to an increase in temperature interval of existence of the superionic state. For T > Tλ the anionic conductivity of fluorite-type Pb0.67Cd0.33F2, Pb0.9Sc0.1F2.1, and β-PbF2 crystals reaches anomalously high values of σdc = 1–2 S/cm (873 K) at an ion transfer activation enthalpy equals to Hσ = 0.3 eV.
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