Electrical conduction in Ca-doped YPO4 with the tetragonal xenotime-type structure was investigated by using conductivity and thermoelectric power measurements under 0.4 to 8kPa of p(H2O) and 0.01 to 100kPa of p(O2) at 500 to 930C. The conductivity of the 3mol%Ca-doped YPO4 was 4 x 10-6 to 2 x 10-4S/cm in moisturized conditions at 500 to 930C. From humidity dependence and H/D isotope effect of the conductivity, it was found that YPO4 exhibited protonic conduction in moisturized conditions by substituting Ca for Y. Results of conductivity and thermoelectric power measurements versus p(H2O) and p(O2) showed that protonic conduction in Ca-doped YPO4 was rather dominant, and that contribution of other ions or electronic conduction to the total conductivity was regarded as negligible. The magnitude of H/D isotope effect was from 1.3 to 1.6 and the activation energy for the D2O-treated sample was 0.03eV higher than that for the H2O-treated sample, indicating semi-classical behavior in the free proton-hopping process in the material.

High-Temperature Protonic Conduction in Ca-Doped YPO4. K.Amezawa, Y.Tomii, N.Yamamoto: Solid State Ionics, 2003, 162-163, 175-80