Correlation between electrochemical and structural properties in NH4PO3/(NH4)2MP4O13 (M = Ti and Si) composites at intermediate temperatures

The ammonium polyphosphate composites of NH4PO3/(NH4)2MP4O13 (M = Ti and Si) were synthesized, and the correlation between electrochemical and structural properties were investigated at intermediate temperatures. In these composites, the compound of (NH4)2MP4O13 serves as a supporting matrix. Although both composites showed similar thermal behaviors in dry Ar and ambient air, electrochemical and structural properties were quite different from each other. NH4PO3/(NH4)2TiP4O13 composite exhibited the structural change of the supporting matrix into TiP2O7 regardless of atmosphere, and its conductivity was independent of the humidity. The apparent activation energy was evaluated to be ca. 0.4 eV in both atmospheres. On the other hand, in the case of NH4PO3/(NH4)2SiP4O13 composite, the supporting matrix was stable in dry Ar whereas which was changed into SiP2O7 in air. In response to this phenomenon, the conductivity improved significantly in air with lower activation energy of ca. 0.2 eV. These results indicated the existence of different proton conduction mechanism.