Protonic conduction in perovskite-type oxide ceramics based on LnScO3 (Ln = La, Nd, Sm or Gd) at high temperature

Ionic transport propel ties of perovskite-type oxides based on LnScO(3), Ln(1-x)Ca(x)ScO(3-alpha) (Ln = La, Nd, Sm and Gd) and LaSc1-xMgxO3-alpha 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-xCaxScO3-alpha and LaSc1-xMgxO3-alpha. Gd0.9Ca0.1ScO3-alpha showed lower conductivity than Ln(1-x)Ca(x)ScO(3-alpha) (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 LnSc(1-x)Mg(x)O(3-alpha) 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 cat-tiers under such conditions were holes.