Phase stability and ionic conductivity in substituted La2W2O9

Different substitutions, i.e. Sr2+, Ba2+, K+, Nb5+ and V5+, have been performed in the triclinic α-La2W2O9 structure in order to stabilise the high temperature and better ionic conductor cubic β-phase. This approach has been used to try to obtain a new series of ionic conductors with LAMOX-type structure without molybdenum and presumably better redox stability compared to β-La2Mo2O9. Nanocrystalline materials obtained by a freeze-drying precursor method at 600 °C exhibit mainly the β-La2W2O9 structure, however, the triclinic α-form is stabilised as the firing temperature increases and the crystallite size grows. Only high levels of Ba2+ and V5+ substitutions retained the cubic form at room temperature after firing above 1100 °C. However, these phases are metastable above 700 °C, exhibiting an irreversible transformation to the low temperature triclinic α-phase. The synthesis, structure, phase stability, kinetic of phase transformation and electrical conductivity of these materials have been studied in the present report.

Graphical abstractSeveral substitutions have been tested in order to investigate the stabilisation of the high temperature cubic β-La2W2O9 and to obtain new ionic conductors with LAMOX structure without molybdenum composition.Figure optionsDownload full-size imageDownload as PowerPoint slide