Structural and conductivity studies of Y10-xLaxW2O21

The aim of this work was to determine structural parameters of the Y10-xLaxW2O21 (x=0-10) solid solution series and investigate their electric properties. Crystallographic data shows a gradual increase in symmetry with increasing La content, as the structure evolves from orthorhombic, Y10W2O21, towards the pseudo-cubic structure of Y5La5W2O21. The solubility limit of La2O3 was found to be 50% (x=5). Above this level two phases were observed, La6W2O15 and (La,Y)(10+x)W2-xO21-delta. The conductivity of Y rich samples was very low, with sigma of the order 2 x 10(-5)-5 x 10(-5)S cm(-1) at 1000 degrees C, whilst ionic conductivity was observed for most La rich doped samples. The highest conductivity was observed for La10W2O21 and its doped analogues, at 1 x 10(-3)-5 x 10(-3)S cm(-1) at 1000 degrees C. Unit cell parameters were determined as a function of temperature from 0 to 1000 degrees C, and thermal expansion of these materials was determined from temperature studies carried out at the Australian Synchrotron facility in Melbourne, Victoria, Australia. (C) 2010 Elsevier Inc. All rights reserved.