Ionic conductivity of Mn2+ doped dense tin pyrophosphate electrolytes synthesized by a new co-precipitation method

Mn2+-doped Sn1−xMnxP2O7 (x = 0–0.2) are synthesized by a new co-precipitation method using tin(II)oxalate as tin(IV) precursor, which gives pure tin pyrophosphate at 300 °C, as all the reaction by-products are vaporizable at <150 °C. The dopant Mn2+ acts as a sintering aid and leads to dense Sn1−xMnxP2O7 samples on sintering at 1100 °C. Though conductivity of Sn1−xMnxP2O7 samples in the ambient atmosphere is 10−9–10−6 S cm−1 in 300–550 °C range, it increases significantly in humidified (water vapor pressure, pH2O = 0.12 atm) atmosphere and reaches >10−3 S cm−1 in 100–200 °C range. The maximum conductivity is shown by Sn0.88Mn0.12P2O7 with 9.79 × 10−6 S cm−1 at 550 °C in ambient air and 2.29 × 10−3 S cm−1 at 190 °C in humidified air. It is observed that the humidification of Sn1−xMnxP2O7 samples is a slow process and its rate increases at higher temperature. The stability of Sn1−xMnxP2O7 samples is analyzed.