Zr-doped samarium molybdates - potential mixed electron-proton conductors

Two Zr-doped samarium molybdates Sm6-x/7Zrx/7Mo1/7O12/7+x/24-delta corresponding to x = 0.6 and 1 (SZMO) have been synthesized at 1600 degrees C for 3 h using mechanically activated mixtures of starting oxides. Fluorite-like Sm0.771Zr0.086Mo0.143O1.739 (- delta) (06SZMO) and Sm0.714Zr0.143Mo0.143O1.756 (-) (delta) (10SZMO) have similar total conductivity of about 4 x 10(-4) S/cm at 800 degrees C in air. Below 600 degrees C, the total conductivity of 06SZMO in air exceeds that of 10SZMO. An increase in bulk and grain boundary conductivity of 06SZMO observed at low temperate under wet conditions suggests there may be a proton contribution to the total conductivity. Under reducing conditions (5% H-2-Ar) 06SZMO becomes essentially an electronic conductor. Its conductivity reaches 0.25 S/cm at 800 degrees C and the activation energy decreases to 0.3 eV. (C) 2014 Elsevier B.V. All rights reserved.