Electron spin resonance of chromia-yttria solid solutions

Electron spin resonance spectra of chromia-yttria solid solutions have been studied at room temperature for Cr concentrations between 0.20 and 2.00 mol%. Isolated Cr3+ ions in sites with two different symmetries were observed, as well as well as Cr3+ ions coupled by the exchange interaction. The relative concentration of isolated to coupled Cr3+ ions decreases with increasing chromium concentration. The results are consistent with the assumption that the chromium ions occupy preferentially the C2 symmetry sites. A theoretical calculation based on this model yields an effective range of the exchange interaction between Cr3+ ions of 0.64 nm, of the same order as that of Cr3+ ions in MgO.