SOME STUDIES OF THE DEFECT STRUCTURE OF ALKALINE EARTH OXIDESReport as inadecuate




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Abstract : A consolidated review of work performed in our laboratory on SrO and BaO is presented. Various experiments have been conducted in order to elucidate the defect structure of these alkaline earth oxides. The various experiments do not all combine neatly to yield a clean model of the defect structure. The situation for SrO is clearer than that for BaO, however. In SrO, it appears most likely that Schottky defects exist which are doubly ionized at elevated temperatures. At one atmosphere oxygen partial pressure, excess oxygen to the extent of a few tenths of a percent can be accommodated in the material. Our data are compatible with a Schottky defect formation energy of 3.7 eV. The activation energy for strontium diffusion at high temperature is 4.61 eV. In BaO, a significant concentration of excess oxygen can be incorporated in the material at a pressure of one atmosphere of oxygen. This concentration can approach one atomic per cent. The enthalpy associated with this incorporated in the following reaction. 1-2 O2g = O0 + defect is equal to - 0.4 eV. For SrO by comparison the enthalpy of the same reaction is + 1.0 eV. In BaO the volume of the unit cell increases with added oxygen. From pressure dependence studies, the defects appear to be unionized. The activation energy for barium ion diffusion at high temperature is 4.0 eV. Possible models of the defect structure are suggested.





Author: R. Swalin

Source: https://hal.archives-ouvertes.fr/



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