Abstract
A novel in situ cell was developed for simultaneous X-ray absorption fine structure and X-ray diffraction (XAFS/XRD) measurements at high temperatures up to 1773 K in a gas atmosphere such as air containing reactive oxygen, in which typical heat-resistant or environmental-barrier materials are used. This new cell can provide multimodal information by combining the following complementary information: (a) chemical states of a specific element and the short-range order (SRO) structure around the atoms, via XAFS measurements, and (b) the long-range order (LRO) crystal structure, via XRD. In situ observation of XAFS/XRD is essential to characterize materials under severe conditions, because reactions sometimes accompany metastable states, and quenching high-temperature states down to room temperature is quite difficult.The performance of the new cell was checked by in situ XAFS/XRD observation of the phase transition of TiO2 from anatase to rutile. Then, the developed technique was applied to a new type of environmental-barrier coating material, Yb2Si2O7, which was exposed to heat cycles up to 1773 K in air. The bulk structure maintained the chemical state of Yb3+ and the crystal structure of Yb2Si2O7, and no reaction phase was observed. The developed technique could provide fundamental information to understand the behaviors of materials used at high temperatures.
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