Ionic conduction in undoped SnP2O7 at intermediate temperatures

Tin pyrophosphate, SnP2O7, is prepared with various initial molar ratios of phosphorus vs. metal ions, Pini/Sn, and different heat-treating temperatures from 573 to 923 K. The preparation conditions are optimized giving consideration to the influence of H3PO4 concentration, Pini/Sn molar ratio and heat-treating temperature. The ionic conduction behaviors are investigated by means of electrochemical methods including ac impedance spectroscopy, hydrogen and water vapor concentration cells, etc. in the temperature range of 323–523 K. The results indicate that the samples obtained from 85% H3PO4 and SnO2 nanopowders with Pini/Sn ≥ 2.4 are a single cubic phase, and that in wet hydrogen atmosphere, the samples are almost pure ionic conductors, the ionic conduction is contributed mainly by proton and partially by oxide ion. An ionic conductivity of 2.17 × 10− 2 S cm− 1 is achieved for the sample prepared from Pini/Sn = 2.8 under wet hydrogen atmosphere at 448 K.