Doubly-associated cation-vacancy centers in magnesium oxide

• Published in: The Journal of physics and chemistry of solids 1967-01, Vol.28 (8), p.1557-1563
• Main Authors: Wertz, John E., Auzins, Peteris V.
• Format: Article
• Language: English
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/0022-3697(67)90286-7

Some Cr 3+ ions in MgO are known to be associated with a vacancy in either the nnn or nn cation positions, as inferred from their well-established ESR spectra showing tetragonal ( T) and rhombic ( R) symmetry respectively. We examine here some “satellite” spectra designated as T′ and R′, which show the same angular dependence and principal g-values respectively as the T and R spectra. They thus reflect similar tetragonal or rhombic symmetries of the centers responsible. These T′ and R′ centers are the focus of interest in this paper. The zero-field splitting parameter D for the T′ center is −864.4 G, while that of the T center is −887.1 G at 295°K. The proposed model for the T′ center is: Cr +-O- ▪-O- M +, lying along 〈001〉, 〈010〉 or 〈100〉 axes. The model for the R′ center is: Cr +- ▪- M + lying along a [110] or equivalent direction. (Only deviations from normal site charge are shown.) A sample doped with aluminum gave an ESR line intensity ratio T′ T = 90 1 after heating at 400°. This behavior is interpreted as implicating Al 3+ as M + ion in this case.