ESR investigation of Cr3+ diffusion in MgO powders

The electron spin resonance (ESR) technique was used to investigate the diffusion of Cr3+ in magnesium oxide (MgO) powders. The ESR absorption intensity was measured for several annealing times and four different temperatures of isothermal annealing: 1223, 1273, 1323 and 1373 K. The activation temperature for diffusion, calculated from the experimental data using a theoretical model based on the Fick equation, was found to be EA=212±9 kJ mol−1. This result is about 30% smaller than similar data obtained for single-crystal MgO using the radioactive-tracer sectioning technique. The difference is attributed to a higher concentration of defects in the powder relative to single crystals.