Experimental verification of the correlation factor for vacancy diffusion in silver chloride

ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. diEM. SOLIDS A series of vanadium dioxide single crystals containing small concentrations of different impurity ions were grown by a thermal decomposition technique. The Impurity ions were chosen to have different electronic structure from the V~ ion they replace. It was expected that these ions would produce a systematic change in the semiconductor-metallic transition exhibited by the V0 2 phase. Contrary to expectations, no correlation with the electronic configuration of the substltuent tons could be recognized. However, this study leads to three qualitative conclusions relating the effect of impurities to the transition in conductivity: (1) The transition temperature is unaffected by the conductivity, i. e., carrier concentration, of the crystal. (2) Significant changes in the transition temperature are produced only by high doping levels on the order of 1 mol %. (3) The direction of the change in transition temperature can be correlated with the relative size 44 ion. of the impurity ion compared to that of the V (Received 18 July 1968)

Vol. 6, No. 10

Results are reported for the diffusion of Ag in single crystals of AgCl between 300 and 435°C. Diffusion coefficients are measured with radioactive tracers by the sectionining method. The correlation factor 1Ag is obtained by cornparison to the ionic conductivity with the Einstein relation. An analysis of 1Ag then shows that the Interstitial silver Ion moves by a combination of two kinds of interstitialcy jumps, with an activation energy of 0. 008 eV for the coLlinear jump and 0. 13 eV for the non-collinear jump. Earlier diffusion measurements for AgBr are also reanalyzed with more recent correlation factors and mobility data to give revised activation energies of 0. 058 eV and 0.27 eV, respectively. (Received 13 June 1968)

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4.

INTERSTITIAL INCORPORATION OF DI- AND TRWALENT COBALT IN QUARTZ Gerhard Lehmann (Institut fUr physikaltsche Chernie der Universitat Mtinster, 44 Miinster, Germany)

Trivalent cobalt in synthetic quartz shows absorption bands of a distorted octahedral cornplex indicating interstitial incorporation of this ion. Upon heating the cobalt is reduced to the divalent state. The absorption spectrum is now identical to that of synthetic quartz doped with divalent cobalt. It is compatible with a tetrahedral or cubic site symmetry and has been attributed to Co24 substituting Si44 in the lattice. From kinetic considerations and the experimental Dq value as well as the similarity of the spectrum of Co24 in high alkali glasses it is concluded that the divalent cobalt occupies an interstitial position of distorted tetrahedral symmetry arising from the octahedral site by a displacement of c/6 along the c axis channels of the quartz structure.

6.

Diffusion coefficients for Ag tracers and ionic conductivity have been measured in AgC1 contaIning 100 to 250 mole ppm Cd at temperatures of 125- 225°C. Under these circumstances cation vacancies should be dominant, thereby allowing an unambiguous comparison of the measured correlation factor to the theoretical value for vacancies on a f. c. c. lattice. In practice it is found necessary to correct for a finite concentration gradient of Cd along the length of the samples and for a small contribution of residual interstitial Ag ions at the higher temperatures. The possible contribution to diffusion of Ag by cation vacancies associated with divalent Cd ions to form complexes is shown to be negligible at all temperatures because of the very small jump frequency of the Cd ion in the complex. With these corrections complete agreement is found between experimental and theoretical correlation ~factors within the experimental error of 1. 0 1. 5%, thus demonstrating the absence of any systematic error in either diffusion or conductivity measurements. -

(Received 17 June 1968) 5.

INTERSTITIALCY MOTION IN THE SILVER HALIDES Max. D. Weber and Robert J. Friauf (University of Kansas, Lawrence, Kansas, U.S.A.)

EXPERIMENTAL VERIFICATION OF THE CORRELATION VACANCY DIFFUSIONFACTOR IN SILVER FOR CHLORIDE Joseph P. Gracey and Robert J. Friauf (University of Kansas, Lawrence, Kansas, U.S.A.)

(Received 13 June 1968) 7.

COMMENTS ON DIFFUSION BY DIVALENT IONS TN ALKALI AND SILVER HALIDES Robert J. Friauf (University of Kansas, Lawrence, Kansas, U.S.A.)