Abstract
Unusual structural phenomena have been observed through high temperature X-ray diffraction in fast oxide-ion conductor La 1.92Ca 0.08Mo 2O 8.96. A demixion process occurs above 640 °C, with calcium segregation leading to the formation of CaMoO 4 impurity. It recombines at higher temperature to reform the pure cubic LAMOX phase (β-type disordered form). In addition, at lower temperature, a double reversed β/α/β phase transition (where α is the monoclinic ordered form) is observed. It is due to the metastability of the β-type structure at low temperature. Depending on the thermal history, La 1.92Ca 0.08Mo 2O 8.96 can therefore be obtained in either its α or its β form at room temperature. Sample shaping as a pellet with high relative density suppresses the low temperature phase transitions and stabilizes the cubic β form.
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