Structure and oxide anion conductivity in Ln(2)(TO4)O (Ln = La, Nd; T = Ge, Si)

摘要

Oxy-silicate and oxy-germanate, Ln(2)(TO4)O (Ln = La and Nd, T = Ge and Si) compounds have been prepared. Oxy-germanates can be readily obtained as highly crystalline single phases, while, the oxy-silicates are difficult to prepare as pure phases. The crystal structure of Nd-2(SiO4)O has been studied from a joint Rietveld refinement of neutron and laboratory X-ray powder diffraction data. The electrochemical characterisation indicates that these compounds display oxide anion conductivity with p-type electronic contribution under oxidising conditions. The apparent activation energies under dry flowing nitrogen, where p-type contribution is minimised, are 0.97(1), 1.05(3) and 1.17(4)eV, for Nd-2(SiO4)O, La-2(GeO4)O and Nd-2(GeO4)O, respectively. The overall conductivities at 1173 K range from 1.2 x 10(-4) S cm(-1) for Nd-2(SiO4)O to 1.3 x 10(-6) S cm(-1) for La-2(GeO4)O. Finally, the stability of these compounds under very reducing conditions has been studied and partial degradation is reported. (C) 2008 Elsevier Inc. All rights reserved.