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We report the formation, structures, temperature- dependent phase transitions, and high-temperature reactivity o f the potential proton and oxide ion conductors BaCe1-xMxO3 (M3+ = In3+, La3+). The present in situ diffraction studies show oxidative platinum uptake at temperatures as low as 950 °C into BaCeO3, forming the cubic Ba2CePtO6 double perovskite. The transient B-site double perovskite expels platinum at around 1200-1250 °C. Platinum oxidation via BaCeO3 is investigated by in situ powder X-ray and neutron diffraction experiments in various atmospheres. Doped BaCe1-xMxO3 phases show the formation o f Ba2CePtO6 without incorporating the M3+ dopant Oxidative platinum uptake is also observed during the synthesis o f BaCeO3 on platinum metal. We report the reaction pathway for the low-temperature oxidative formation o f Ba2CePtO6 and the subsequent liberation o f platinum for the barium cerate system. The findings are supported by ambient-temperature X-ray diffraction, in situ powder X-ray, and powder neutron diffraction as well as XPS. [ABSTRACT FROM AUTHOR]

We report the first in-situ powder X-ray diffraction (PXRD) study of the BaCO3-CeO2-In2O3 and CeO2-ln2O3 systems in air over a wide range of temperature between 25 and 1200 °C. Herein, we are investigating the formation pathway and chemical stability of perovskite-type BaCe1-xlnxO3-δ, (x= 0.1, 02, and 0.3) and corresponding fluorite-type Ce1-xInxO2-δ phases. The potential direct solid state reaction between CeO2 and ln2O3 for the formation of indium-doped fluorite-type phase is not observed even up to 1200 °C in air. The formation of the BaCe1-xInxO3-δ perovskite structures was investigated and rationalized using in-situ PXRD. Furthermore the decomposition of the indium-doped perovskites in CO2 is followed using high temperature diffraction and provides insights into the reaction pathway as well as the thermal stability of the Ce1-xlnxO3-δ system. In CO2 flow, BaCe1-xlnxO3-δ, decomposes above T= 600 °C into BaCO3 and Ce1-xlnxO2-δ. Furthermore, for the first time, the in-situ PXRD confirmed that Ce1-xInxO2-δ decomposes above 800°C and supported the previously claimed metastability. The maximum In-doping level for CeO2 has been determined using PXRD. The lattice constant of the fluotite-type structure Ce1-xInxO2-δ follows the Shannon ionic radii trend, and crystalline domain sizes were found to be dependent on indium concentration. [ABSTRACT FROM AUTHOR]