Intermediate temperature stable proton conductors based upon SnP 2O7, including additional H3PO4

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 31 P 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 x 10(-2) S/cm at 300 degrees 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.