Stability of W-substituted La2Mo2O9 oxide ion conductors in controlled oxygen partial pressure

JESÚS EDUARDO VEGA CASTILLO; UDAY K. RAVELLA; GWENAËL CORBEL; PHILIPPE LACORRE; ALBERTO CANEIRO

Las Vegas

Conferencia; International conference on processing and manufacturing of advanced materials; 2013

Isothermal thermogravimetric and X-ray diffraction analyses in controlled PO2 atmosphere were carried out on La2Mo2O9, La2Mo1.5W0.5O9 and La2MoWO9 phases in order to determine their thermodynamic stability [1]. Contrary to what has been earlier reported in literature [2], tungsten substitution does not extend to lower PO2 value the thermodynamic stability of La2Mo2O9 either at 608°C (10-22 atm) or at 718°C (10-15 atm). At both temperatures, tungsten only slows down the kinetics of reduction. After decreasing PO2 down to 10-23 atm, a new crystalline La2Mo2O8.96?type phase, isostructural to La2Mo2O9, appears at 608°C which remains stable in a pressure range slightly widening as the W content increases. At 718°C, the stable phase below 10-15 atm is more reduced and of the La7Mo7O30?type (La2Mo2O8.57). Tungsten extends down to 10-27 atm the thermodynamic stability range of this phase whereas La7Mo7O30 reduces slowly below 10−25 atm down to an amorphous La2Mo2O7-delta phase. This latter phase was reported as a good sulfur-tolerant anode in dual-chamber SOFC device using H2 as fuel [3]. [1] J.E. Vega-Castillo, U.K. Ravella, G. Corbel, P. Lacorre, A. Caneiro, Dalton Transactions, 41 (2012) 7266-7271. J.E. Vega-Castillo, U.K. Ravella, G. Corbel, P. Lacorre, A. Caneiro, submitted. [2] D. Marrero-Lopez, J. Canales-Vazquez, J.C. Ruiz-Morales, J.T.S. Irvine, P. Nunez, Electrochimica Acta, 50 (2005) 4385-4395. [3] X.C. Lu, J.H. Zhu, J. Electrochem. Soc., 155 (2008) B1053-B1057.