Stability and Conductivity of In3+-Doped SnP2O7 with Varying Phosphorous to Metal Ratios

In-doped tin pyrophosphate materials were synthesized with varying metal to phosphate ratios to assess the influence of an excess amorphous polyphosphate phase on conductivity. Total conductivity at 250 degrees C increased with phosphorus to metal (P:M) ratio, with the 2.81 P:M ratio material exhibiting maximum conductivity of 10(-2) and 10(-1) Scm(-1) in dry and humidified N-2. XRD measurements revealed no systematic change in lattice parameter with increasing P:M. These results combined with supporting spectroscopy, suggest that a grain-boundary polyphosphate phase is required to achieve high conductivity in the low-intermediate temperature range. The materials were relatively stable and provided steady conductivities at 250 degrees C. (c) 2013 The Electrochemical Society.