Protonic conduction and defect structures in Sr-doped LaPO4 (Sr = 0 to 7mol%) were investigated by using conductivity, magic-angle spinning nuclear magnetic resonance spectroscopy and FT-Raman spectroscopy measurements. The results revealed that hydrogen phosphate groups, possibly hydrogen phosphate ions HPO42-, and pyrophosphate ions P2O74- existed in Sr-doped LaPO4 under wet and dry conditions, respectively, in addition to orthophosphate ions PO43-. Based on the results, a defect structure model was proposed for Sr-doped LaPO4. According to this model, La

substitution by Sr led to the formation of P2O74- as intrinsic positive defects and, in a wet atmosphere, protons were introduced into the phosphate to form hydrogen phosphate groups through the equilibrium between P2O74- and water vapor. The conductivity behavior of Sr-doped LaPO4 versus water vapor and O partial pressures supported this defect structure model.

Protonic Conduction and Defect Structures in Sr-Doped LaPO4. K.Amezawa, H.Maekawa, Y.Tomii, N.Yamamoto: Solid State Ionics, 2001, 145[1-4], 233-40