Protonic Conduction in Perovskite-type Oxide Ceramics Based on LnScO 3 (Ln=La, Nd, Sm or Gd) at High Temperature

Abstract

Ionic transport properties of perovskite-type oxides based on LnScO3, Ln1- xCaxScO3-α (Ln=La, Nd, Sm and Gd) and LaSc1-xMgxO3-α were studied using an electrochemical method at elevated temperatures. Conductivity in these oxide systems increased by more than three orders of magnitude upon doping with divalent atoms such as Ca or Mg. However, when x≥0.1, conductivities are almost independent of x in La1- xCaxScO_3-α and LaSc1- xMgxO3-α. Gd0.9Ca0.1ScO3-α showed lower conductivity than Ln1-xCaxScO3-α (Ln=La, Nd and Sm). Protonic conduction in these oxides under hydrogen containing atmospheres was confirmed by emf measurements of hydrogen concentration cells and by electrochemical hydrogen pumping using these oxides as a diaphragm. In LaSc1-xMgxO3-α the transport number of protons under hydrogen containing atmosphere was unity, suggesting that electronic conduction never became dominant, even under strong reducing conditions. Under condition of high oxygen partial pressure, the transport number of ions was less than 0.1, suggesting that the majority conductive carriers under such conditions were holes.