Oxygen self-diffusion in undoped and doped cobaltous oxide

ii 3.

ABSTRACTS OF PAPERS TO APPEAR IN OXYGEN SELF-DIFFUSION IN UNDOPED AND DOPED COBALTOUS OXIDE W.K. Chen and R.A. Jackson (Argonne National Laboratory, Argonne, Illinois

5.

J.

PHYS. CHEM. SOLIDS

Vol. 7, No.3

HYDROXIDE AND OXIDE IMPURITIES IN CALCIUM HALOPHOSPHATES J.S. Prener, W.W. Piper, and R.M. Chrenko (General Electric Research and Developmeat Center Schenectady, New York)

60439) The diffusion coefficient of 0—18 in CoO has been measured in the temperature range from 1175 to 1560°C. Diffusion was measured in undoped CoO crystals and in crystals containing from 0.1 to 0.5 molar per cent of aluminium or lithium. The diffusion coefficient in the undoped crystals is representod by the expression, D = 50 expt—(95,000 ±5000))/RTcma/sec, at P0 = 0.21 atm. At a constant temperature and a constant oxygen partial pressure, the diffusion coefficient In doped crystals was found to increase or decrease with increasing concentration of lithium or aluminium in the oxide crystals. The results are discussed in terms of oxygen diffusion by a vacancy mechanism. (Received 7 October 1968) (Revised 12 December 1968)

4.

FLUORESCENCE OF Nd~IN LITHIUM YTTRIUM FLUORIDE A.L. Harmer, A. Linz and D.R. Gabbe (Center for Materials Science and Engineering and Department of Electrical Engineering, Massachusetts Institute of Technology)

Crystals of the scheelite structure fluoride LiYF4 have been grown doped with 0.24, 1.4, and 2.2 at. % Nd~ The polarized fluorescence and absorption, excitation spectra, lifetime decay and linewidths have been measured at 77°Kand 300°K. The optical data of LiYF4 :Nd ~ have been compared with data spectroscopic on the isomorphous oxide 3+. The features of CaWO4:Nd LIYF 4 :Nd’~are: a long lifetime of 500 ~sec which decreases rapidly with increasing Ndconcentration; a narrow linewidth of 2cm’ at 77°K;and a high absorption in the near infrared, These factors have been related to its potential as a laser material. (Received 25 November 1968)

A number of defects giving rise to specific optical absorption and fluorescence, and to the formation of color and paramagnetic centers upon X-ray irradiation, can be produced in polycrystalline Ca10 (PO4)eF2 (calcium fluorapatite). Heating in vacuum results in the formation of F ion vacancies. Heating in water vapor introduces OH ions which substitute for F ions and heating in water vapor followed by heating in vacuum results in the formation of oxide ion impurities at F ion sites and F ion vacancies which can associate. Models for several color and paramagnetic centers proposed on the basis of the results of earlier EPR studies on single crystals are supported. A new paramagnetic defect consisting of a hole trapped at an 0—OH ion pair is reported for the first time. Some ideas on the defects responsible for extrinsic u.v. absorption bands seen previously in fluorapatite axe presented. Finally, chiorapatite is shown to behave in an analogous manner. (Received 25 October 1968) (Revised 16 December 1968)

6.

ANTIPHASE BOUNDARIES IN SEMI CONDUCTING COMPOUNDS D.B. Holt (Metallurgy Department, Imperial College, London, S.W.7)

Within crystals of semiconducting compounds regions can exist between which reversals of crystallographic polarity occur. These regions are antiphase domains. Antiphase boundaries (APBs) are crystallographic defect surfaces and type 2 APBs non-stoichiometric excess atomsIncorporate of one of the constitutents of the compound. The geometry of APBs and their interactions with grain boundaries and with dislocations in semiconducting compounds with the sphalerite structure are treated and the properties of APBs are discussed. The evidence for their existence is