Magnesium oxide (MgO) is an important material from a fundamental physical point of view and is widely used in the fields of catalytic, optical and electrical applications. Affecting the materials' characteristics, it is recognized that defects in MgO are important for its applications. One of the important defects in MgO is an oxygen (O) vacancy. In this study, the annealing effect of the O vacancy in MgO induced by hydrogen reduction was studied by using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS).The MgO powder (~ 50 nm) was, at first, annealed at various temperatures ranging from 373 K to 873 K for 2 hours in hydrogen atmosphere.  After the annealing, each powder was slowly cooled. Mg K-edge and O K-edge NEXAFS spectra measurements of the MgO powder were performed at the beamline BL 2A of UVSOR and at the beamline BL 12 of SAGA-LS inJapan, respectively.In the NEXAFS spectra, in addition to main peaks at around 536 eV in the O K-edge region, two peaks were also observed at the lower photon energy side of the main peaks. The two peaks were not reproduced in theoretical calculation nor observed for bulk MgO, indicating the two peaks are attributed to species on the MgO surface. On the other hand, XPS spectra showed the presence of hydroxide and carbonate on the annealed MgO powder in hydrogen atmosphere. There is a possibility that the assignment of the two peaks is Mg(OH)2 and/or, MgCO3 and/or, H2O and/or, CO2 and/or, their complex. There molecules were adsorbed on the oxygen defects. The intensities of these two peaks in the NEXAFS spectra were changed by annealing in hydrogen atmosphere. These results indicate that the oxygen vacancies were induced by hydrogen reduction and the number of vacancies was dependent on the treatment temperature.

Studies of defects in MgO by using NEXAFS and XPS

248th National Meeting (2014)

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