Fluoride ion conductivity of solid solutions KxPb0.86-xSn1.14F4-x

Abstract

The electrical conductivity of solid solutions with tetragonal syngony formed in 0.86(xKF–(1–x)PbF₂)–1.14SnF₂ systems has been studied by ¹⁹F-NMR and impedance spectroscopy. It was found that the Pb₀.₈₆Sn₁.₁₄F₄ phase is characterized by better values of fluoride-ion conductivity than the β-PbSnF₄ compound. It was found that the substitution of Pb²⁺ by K⁺ up to х = 0.07 in the structure of Pb₀.₈₆Sn₁.₁₄F₄ contributes to increase in electrical conductivity by an order of magnitude relative to the original Pb₀.₈₆Sn₁.₁₄F₄. The sample of composition K₀.₀3Pb₀.₈₃Sn1.14F₃.₉₇ has the highest electrical conductivity (σ₆₀₀ = = 0.38 S cm-1, σ₃₃₀ = 0.01 S cm-1). The fluoride anions in the synthesized samples of KxPb₀.₈₆-xSn1.14F4-x solid solutions occupy three structurally nonequivalent positions. It is shown that with increasing temperature, there is a redistribution of fluorine anions between positions in the anion lattice, which results in an increase in the concentration of highly mobile fluoride ions, which determine the electrical conductivity of the samples.