Protons in Ca-doped La 2O 3, Nd 2O 3 and LaNdO 3

Abstract

Using the ac conductivity and EMF methods, the conductivity contributions from protons, native ions, and electronic defects have been measured as a function of temperature (600–1200°C) in wet oxygen/air for the hexagonal systems La 2O 3+1 mol% CaO, Nd 2O 3+1 mol% CaO, and LaNdO 3+5 mol% CaO. All exhibit significant proton conductivity as well as native-ion and electronic p-type conductivities at all temperatures. The oxides dissolve protons to compensate for the acceptor doping at the expense of native positive defects. In wet atmospheres and at reduced temperatures, protons become the dominating positive defects. In terms of concentration and conductivity, protons are relatively less important in hexagonal than in cubic rare earth sesquioxides.