A compact furnace for in situ X-ray absorption spectroscopy: design, fabrication and study of cationic oxidation states in PrO and NiO.

A well designed compact furnace has been designed for in situ X-ray absorption spectroscopy (XAS). It enables various heat ramps from 300 K to 1473 K. The furnace consists of heaters, a quartz tube, a circulated refrigerator and a power controller. It can generate ohmic heating via an induction process with tantalum filaments. The maximum heating rate exceeds 20 K min. A quartz tube with gas feedthroughs allows the mixing of gases and adjustment of the flow rate. The use of this compact furnace allows in situ XAS investigations to be carried out in transmission or fluorescence modes under controlled temperature and atmosphere. Moreover, the furnace is compact, light and well compatible to XAS. The furnace was used to study cationic oxidation states in PrO and NiO compounds under elevated temperature and reduced atmosphere using the in situ X-ray absorption near-edge structure (XANES) technique at beamline 5.2 SUT-NANOTEC-SLRI of the Synchrotron Light Research Institute, Thailand. At room temperature, PrO contains a mixture of Pr and Pr cations, resulting in an average oxidation state of +3.67. In situ XANES spectra of Pr (L-edge) show that the oxidation state of Pr cations was totally reduced to +3.00 at 1273 K under H atmosphere. Considering NiO, Ni species were present under ambient conditions. At 573 K, the reduction process of Ni occurred. The Ni/Ni ratio increased linearly with respect to the heating temperature. Finally, the reduction process of Ni was completely finished at 770 K.