The XPS study of pyrochlore matrixes for the radioactive waste disposal

Abstract

Two pyrochlore ceramic samples were studied in this work. The X-ray diffraction and the scanning electron microscopy showed that the ceramics with the calculated composition CaThSn2O7 was formed by the dominating pyrochlore phase with the traces of thorianite and hematite, while the CaThZr2O7 ceramics - by the dominating pyrochlore phase with the minor admixtures of thorianite and perovskite. The real compositions of pyrochlore phases determined by the scaning electron microscopy are Ca0.88Th0.92Sn2O6.72 and Ca0.84Th0.80Zr2O6.44. On the basis of the X-ray photoelectron spectral parameters of the outer and core electrons in the binding energy range of 0-1250 eV it was found that tin, zirconium and thorium in pyrochlore are at least 93%-94% tetravalent. Sn-O and Zr-O interatomic distances in BO6-octahedrons in the pyrochlore were found to be 0.210 nm and 0.220 nm, respectively, and these octahedrons are possible to be tetragonaly distorted.

Keywords

• X-ray photoelectron spectroscopy
• outer and inner valence molecular orbitals
• pyrochlore
• radioactive waste disposal