Proton conductivity in SiO2-LaPO4 composites

Abstract SiO2-LaPO4 composite powders are prepared hydrothermally and proton conduction behaviours are investigated for high temperature electrochemical applications. The obtained powders are systematically characterized by X-ray powder diffraction, FTIR and Raman spectroscopies. Both diffractograms of SiO2-LaPO4 and LaPO4 powders are similar and corresponding to the monoclinic structure lanthanum phosphate. The Nyquist plots at various temperatures indicate the non Debye nature of the relaxation mechanism for all samples. At 600 °C temperature, the protonic DC conductivity value is found to be 1.5 × 10−6 S cm−1 for SiO2-LaPO4 composites, which is 7.5 times better than of the single phase LaPO4 (2.1 × 10−7 S cm−1). In addition, SiO2-LaPO4 composites exhibit lower activation energy (0.79 eV) over a temperature range from 480 to 600 °C, compared to the single phase LaPO4 (1.35 eV). The power law exponent, n, is found to be temperature and composition dependent, suggesting that the most probably transport pathway is a tunneling of proton through potential barriers between oxygen-oxygen ions, along sequential PO4 tetrahedral.