The ionic conductivity of single crystals of tysonite-type solid solutions Lal_xBaxFa_x(O • x • 0.095) has been studied parallel and perpendicular to the crystallographic c axis in the temperature range 293-1300 K. Three regions can be discerned in the compositional dependence of the ionic conductivity: (i) the "pure" crystal, in which at room temperature no exchange occurs between different types of anion sites in the tysonite structure; (ii) an intermediate region (0 < x < 7 X 10 -2) which reveals changes in both the conductivity activation enthalpy and the magnitude of the conductivity; (iii) a concentrated solid-solution region (x > 7 X 10-2), where fluoride ions interchange easily among the different anion sublattices. Diffusion coefficients calculated from ionic conductivity results, are in good agreement with those calculated from 19F NMR measurements. Using the present data, along with 19F NMR data, dielectric relaxation data and structural considerations, mechanisms governing the ionic conductivity are proposed.
An dem einen Ende eines 60cm langen Platinrohres befindet sich Jod-8fluorid in einem Platinschiffohen X, das durch den auf eine Asbestisolierung gewickelten Heizdraht HI auf etwa 90° erwarmt wird. Die durch die Heizung ent-fluorids zeigt Fig. I. l) Vgl. z. B. RUFF u. TSCEURCH, Ber. d. Deutsch. Chem. Ges. 46 (1913), 929. Z. anorg. u. allg. Chem. Ed. 193. 12
The reaction of single crystal germanium with water vapor and hydrogen sulfide at low partial pressures in hydrogen was studied in a gas flow system in the temperature range 650~176 At linear gas velocities of 30 cm/sec or higher and water partial pressures of 26 Torr or lower, the reaction of germanium with water vapor is surface limited with an activation energy of 46 • 2 kcal/mole. Clean and structureless surfaces were produced, independent of the dislocation density in germanium, at 900~ and a water partial pressure of 26 Torr. At low partial pressures of hydrogen sulfide in hydrogen, the etching of germanium is diffusion limited at temperatures above 800~ and is surface limited at lower temperatures with an activation energy of 20 _ 1 kcal/mole. The hydrogen-hydrogen sulfide mixture is a less effective nonpreferential etchant than the hydrogen-water vapor mixture.
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