Effect Of Point Defects On High-Temperature Optical Properties In Transparent Polycrystalline Lanthana-Doped Yttria

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Abstract
The effect of point defects on absorption in transparent polycrystalline lanthana-doped yttria was investigated by measuring the absorption coefficient as a function of temperature and oxygen partial pressure P02 at two wavelengths (0.357 and 3.39 μm). The composition of the specimens was controlled by preannealing at 1400°C in appropriate oxygen pressures ranging from 10-16 to 10-5 atm. The technique used for determining the absorption coefficient consisted of measuring the transmittance of two samples of different thicknesses. The absorption at 0.357 μm showed a sharp increase with temperature beginning at about 1000°C. The magnitude of this increase was a function of P02. A broad minimum was found in the high-temperature absorption at 1400°C, ranging from 10-13 to 10-10 atm P02; this represents the stoichiometry range. Initial absorption measurements in the infrared (3.39 μm) indicated much less temperature dependence, with little or no absorption increase above 1000°C at 3 x 10-13 atm P02 and only a small increase at 2 x 10-3 atm P02. Also reported in this paper are other optical properties, including refractive index, temperature coefficient of refractive index, and scattering in lanthana-doped yttria.

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