Reducibility of La2Mo2O9 based ceramics versus porosity

Different batches of La2Mo2−xWxO9 (x = 0; x = 0.5; x = 1) ceramics with increasing relative densities (expected values of 70%, 85%, 95% of theoretical density dth) were prepared by solid state reaction, mechanical milling and appropriate thermal treatments. The electrical and mechanical properties during and after partial chemical reduction in 10 vol. % Ar–H2 mixture at 650 °C were investigated as a function of composition and microstructure. In particular, the effects of tungsten composition and porosity on the appearance of cracks and subsequent mechanical damages with the oxygen release were examined.The reduced samples show an increase of the electrical conductivity at high temperature which is dependent on both porosity and tungsten content. The conductivity becomes mainly of electronic nature. The increase of the electrical conductivity when porosity increases is attributed to the highest ceramic/gas contact interface yielding faster reduction of Mo6+. Mechanical degradations decrease when the porosity fraction increases. On the contrary, dense samples present strong damages except for La2Mo1.5W0.5O9. The appearance of cracks seems to be a non-linear phenomenon in the La2Mo2−xWxO9 solid solution domain.

► Tungsten doped La2Mo2O9 ceramics were prepared with different relative densities. The relative density and the chemical composition were found to have significant effects on the reducibility of the ceramics and in particular on the formation of macroscopic cracks.