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The in-situ X-ray diffraction approach is employed to explain the various reaction pathways of the Ba[CO.sub.3]-Ce[O.sub.2]-[In.sub.2][O.sub.3] and Ce[O.sub.2]-[In.sub.2][O.sub.3] systems. The formation and the properties of these structures are also analyzed.

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]

The novel oxide defect fluorite phase ScTiO3.5 is formed during the topotactic oxidation of ScTiO3 bixbyite. We report the oxidation pathway of ScTiO3 and structure evolution of ScTiO3.5, Sc4Ti3O12, and related scandium-deficient phases as well as high-temperature phase transitions between room temperature and 1300 °C using in-situ X-ray diffraction. We provide the first detailed powder neutron diffraction study for ScTiO3. ScTiO3 crystallizes in the cubic bixbyite structure in space group Ia3 (206) with a = 9.7099(4) Å. The topotactic oxidation product ScTiO3.5 crystallizes in an oxide defect fluorite structure in space group Fm3m (225) with a = 4.89199(5) Å. Thermogravimetric and differential thermal analysis experiments combined with in-situ X-ray powder diffraction studies illustrate a complex sequence of a topotactic oxidation pathway, phase segregation, and ion ordering at high temperatures. The optimized bulk synthesis for phase pure ScTiO3.5 is presented. In contrast to the vanadium-based defect fluorite phases AVO3.5+x (A = Sc, In) the novel titanium analogue ScTiO3.5 is stable over a wide temperature range. Above 950 °C ScTiO3.5 undergoes decomposition with the final products being Sc4Ti3O12 and TiO2. Simultaneous Rietveld refinements against powder X-ray and neutron diffraction data showed that Sc4Ti3O12 also exists in the defect fluorite structure in space group Fm3m (225) with a = 4.90077(4) Å. Sc4Ti3O12 undergoes partial reduction in CO/Ar atmosphere to form Sc4Ti3O11.69(2). [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]

We report the formation pathway of ScVO4 zircon from ScVO3 bixbyite with emphasis on the synthesis and stability of the novel intermediate defect zircon phase ScVO4-x (0.0< x ⩽ 0.1). The formation pathway has been investigated by means of thermogravimetric/differential thermal analysis and in situ powder X-ray diffraction. The oxidation of ScVO3 to ScVO4 involves two intermediates of composition ScVO3.5+y, (0.00 ⩽ y ⩽ 0.22) and the novel phase ScVO4-x. ScVO4-x crystallizes in the defect zircon structure in space group /41/amd (141) with a = 6.77761 (5) Å and c = 6.14045(8) Å. Oxygen defect concentrations in bulk ScVO4-x samples range from 0.0 < x ⩽ 0.1. ScVO4-x is compared with the fully oxidized zircon structure ScVO4 using powder X-ray diffraction, neutron diffraction, and bulk magnetic susceptibility data as well as 45Sc and 51V solid state NMR spectroscopy. ScVO4-x can only be obtained by oxidation of ScVO3 or ScVO3.5+y while the reduction of ScVO4 does not yield the novel defect structure. Mechanistic insights into the oxidative formation of ScVO4 via the defect structure are presented. [ABSTRACT FROM AUTHOR]

We report the formation, structures, temperature-dependent phase transitions, and high-temperature reactivity of the potential proton and oxide ion conductors BaCe(1-x)M(x)O3 (M(3+) = In(3+), La(3+)). 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 BaCe(1-x)M(x)O3 phases show the formation of Ba2CePtO6 without incorporating the M(3+) dopant. Oxidative platinum uptake is also observed during the synthesis of BaCeO3 on platinum metal. We report the reaction pathway for the low-temperature oxidative formation of Ba2CePtO6 and the subsequent liberation of 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.