Leeds 2Silica glass specimens were heated in water vapour and the resulting infra-red absorption at 2.7 p was measured. Betwecn 600" and 1200"C, the diffusion coefficient for entry of absorbing centres wasand for removalAt 1OOO"C the saturation concentration of absorbing centres varied as the square root of the pressure of the surrounding water vapour, suggesting that the water molecule dissociates on entry, with the production of two hydroxyl groups in the atomic network of the glass. Using a value of extinction coefficient determined for the hydroxyl group in the molecule of triphenylsilanol, the solubility under 700 mm Hg water vapour pressure, expressed as the number of hydroxyl groups per Si02 "molecule", was estimated to range from 6 x 10-3 at 600°C to 3 x 10-3 at 1200°C.
Grain size effects in polycrystalline BaTiO are reviewed in terms of the "internal stress model". By considering polarization dependent terms in the Devonshire free energy expression, the dielectric constant may be calculated for the whole ferroelectric temperature region, under various stress systems. Encouraging comparisons with measured values may be made. 3
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