Intermediate temperature stable proton conductors based upon SnP2O7, including additional H3PO4

Abstract

In order to examine the influence of phosphate impurities upon the conduction properties of SnP₂O₇, SnP₂O₇-H₃PO₄ composites were synthesised through different methods with varying starting P:Sn molar ratios. The composites were then carefully characterised by XRD, SEM, HRTEM, NMR, FT-IR and a.c. impedance spectroscopy to explore the phase compositions and electrical properties. It was found that cubic SnP₂O₇ is the main crystalline phase and amorphous phases were observed when starting P:Sn ratios exceeded 2 : 1. Solid State ³¹P NMR confirmed residual phosphoric acid in samples with high starting P:Sn ratios whilst impedance spectroscopy indicated these to be good proton conductors. The highest conductivity observed was 3.5 × 10⁻² S/cm at 300 °C in air for samples with high starting P:Sn ratios and calcined at higher temperatures. The conductivity stability of the composites was found to be promising, suggesting a new approach for the development of technically useful proton conductors.