EPR characterization of O– and trapped electrons in 20% SrF2/SmOF

Abstract

An X-ray diffraction study of the 20% SrF₂/SmOF catalyst has revealed the presence of cubic SrF₂ and rhombohedral SmOF crystal phases. The lattice of the SrF₂ crystal phase was distorted. Cationic and anionic exchanges may have occurred to cause such deformity. When the 20% SrF₂/SmOF sample was treated in helium at 1073 K, EPR signals corresponding to O^– centres were observed. Hydrogen or ethane treatment of the sample at 973 K or above resulted in the detection of superhyperfine structures corresponding to the presence of trapped electrons. No similar EPR signals were observed on the SmOF sample. We suggest that these EPR-detectable species were located in the SrF₂ lattice and existed largely in the bulk. The trapped electrons were stable in oxygen up to 673 K while O^– centres were stable in ethane or hydrogen up to a temperature as high as 873 K. We speculate that the migration of O^– centres and trapped electrons is more arduous in fluoride than in oxide. Hence the temperature for the combination of O^– centres and trapped electrons as well as for the migration of O^– centres and trapped electrons from the bulk towards the surface is higher in the former than in the latter.