We focused on Sr-substituted CePO 4 -i. e., (Ce,Sr)PO 4 -with the monazite structure and synthesized the orthophosphates hydrothermally. As for the obtained products, we investigated the particle morphologies by SEM and electrical conduction properties by conductivity measurements. In order to estimate the crystal and electronic structures, neutron and synchrotron X-ray diffraction measurements were also carried out. As a result, it was found that (Ce,Sr)PO 4 with a single phase of the monazite structure was successfully prepared by the hydrothermal method and the substitution amount of Sr was almost equal to the nominal one. It was also demonstrated that a powder morphology of the (Ce,Sr)PO 4 depended on the synthetic conditions; i.e, concentrations of cation sources and pH of aqueous solution in the hydrothermal process. The Sr-substituted sample showed much higher conductivities than the unsubstituted one, in the same way as the (Ce,Sr)PO 4 synthesized by other methods reported previously.
We focused on monazite-type Ce(P,V)O4 as a proton-electron mixed conductor, and investigated electrical conduction properties, and crystal and electronic structures by synchrotron X-rays. From conductivity measurements, it was found that the electrical conductivity increased with increasing V content. As for the specimens, we performed X-ray absorption fine structure and synchrotron X-ray diffraction measurements. The XANES spectra demonstrated that an electronic structure of Ce was varied by partially substituting V for P. The maximum entropy method using the diffraction data also indicated that an electron density between Ce and O was increased by the substitution. Such a change of the electronic structure might lead to the improvement of the electrical conduction property.
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