Electrical conduction in lanthanum orthoborates LaBO3 with the orthorhombic aragonite-type structure (Pnam) was investigated by using conductivity measurements under 0.4 to 5kPa of PH2O and 0.01 to 100kPa of PO2 at 500 to 930C. From humidity dependence and H/D isotope effect of the conductivity, it was found that LaBO3 exhibited predominantly protonic conduction under wet conditions by substituting Sr for La. Results of conductivity measurements under various PH2O and PO2 suggested that the contribution of electron hole conduction became significant as temperature increased, PO2 increased and PH2O decreased, although protonic conduction was estimated as predominant under the conditions used. The conductivities of the 1mol%Sr-doped LaBO3 were 10−5 to 2 x 10−4S/cm under moisturized conditions at 500 to 930C. The conductivity behaviors as well as the conductivity values of the Sr-doped LaBO3 with the aragonite-type structure were quite similar to those of the acceptor-doped rare earth orthophosphates, indicating a similar proton conduction mechanism in these oxo-acid salts.

High Temperature Protonic Conduction in LaBO3 with the Aragonite-Type Structure. K.Amezawa, N.Takahashi, N.Kitamura, Y.Tomii, N.Yamamoto: Solid State Ionics, 2004, 175[1-4], 575-9