CATION SELF-DIFFUSION IN SINGLE CRYSTAL CAO

The self-diffusion coefficient of calcium in single crystals of calcium oxide has been measured in the temperature range, 1465-1760°C, using vapordeposited thin film of radioactive Ca45O and boundary conditions for diffusion from a plane source into a semi-infinite medium. The temperature dependence of the diffusivity can be expressed as: D = (11.25 ±2.2) × 10-5 exp[-(64,300±1400)/RT]. In this temperature range, diffusion appears to be intrinsic. The activation energy of 64.3 kcal/mole is suggested to be the sum of energy of cation vacancy migration and one half the energy of cation vacancy formation by Schottky disorder. After a reanalysis of the raw data from a previous investigation [2] of cation self-diffusion in calcium oxide single crystals in the temperature range 1000-1400°C, an activation energy of 28.2 kcal/mole is obtained for cation vacancy migration. From the experimental results the energy of Schottky defect formation in calcium oxide is calculated to be 3.08 eV, a value in satisfactory agreement with the theoretical estimate of Yamashita and Kurosawa. © 1969.