Accession Number : AD0629481

Title :   DIFFUSION OF OXYGEN IN MAGNESIUM OXIDE.

Descriptive Note : Technical rept.,

Corporate Author : CORNELL UNIV ITHACA N Y DEPT OF ENGINEERING PHYSICS

Personal Author(s) : Rovner,L. H.

Report Date : 01 MAR 1966

Pagination or Media Count : 159

Abstract : Diffusion of oxygen in magnesium oxide is measured in the temperature range 750-1150C at 1 torr oxygen pressure. The measurements utilized an oxygen-18 isotopic exchange technique to measure diffusion coefficients as small as 10 to the minus 20th power sq cm/sec. Interference from diffusion down enhanced diffusivity channels is observed. Both intrinsic and extrinsic lattice diffusion is observed. In the intrinsic region the activation energy, Q, is 82.1 plus or minus 3 kcal/mole and D varies as P(02) to the 0.22 plus or minus 0.1 power sq cm/sec. For extrinsic diffusion Q = 30. 2 plus or minus 3 kcal/mole. This same activation energy is found in a crystal doped with chromium: Q = 34.0 plus or minus 4 kcal/mole. Also, D varies as P(02) to the 0.48 plus or minus 0.05 power. These data are compatible with an interstitial oxygen mechanism for both crystals. In a lithium-doped crystal, Q = 42.6 plus or minus 4 kcal/mole and D varies as P(02) to the minus 0.7 plus or minus 0.25 power sq cm/sec. This is consistent with an oxygen vacancy mechanism. Under conditions appropriate for intrinsic diffusion, magnesium oxide is shown to be an oxygen excess structure. Charge compensation is by formation of trapped-hole defects. In lithium-doped material, trapped-electron defects are present. These defect species are important to the electrical conductivity properties of magnesium oxide. (Author)

Descriptors :   (*OXYGEN, DIFFUSION), (*DIFFUSION, CERAMIC MATERIALS), (*MAGNESIUM COMPOUNDS, OXIDES), CRYSTAL DEFECTS, TRANSPORT, PRESSURE, HEAT OF ACTIVATION

Subject Categories : Physical Chemistry
      Ceramics, Refractories and Glass
      Crystallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE