A protocol to detect the phase transition in La₂Mo₂O₉ oxide ion conductor

The fast oxide ion conductor, La₂Mo₂O₉ undergoes a structural phase transition around 580 °C from room temperature monoclinic (α) to high temperature cubic (β). The β phase is the one of interest as a fast oxide ion conductor, and thus efforts are made to stabilize it to lower temperatures. The α and β phases have very similar X-ray diffraction patterns, posing characterization problem in this quest. A new reliable protocol is proposed to clearly identify the phase in a short time. This is done without referring to peak splitting, which can be problematic with fine powders. One can use scan speed of 12 s/step in the 2θ = 14°–16.5° range to detect three peaks that vanish after phase transition to the β form. This examination is extended further to detect the cubic β phase of La₂Mo_1.0W_1.0O₉ in the same scan range.