Influence of metallic and lanthanide dopants on the thermal diffusivity of lithium niobate crystals

Abstract
The influence of crystal doping on thermal diffusivity of LiNbO ₃ crystal has been studied. Thermal diffusivities of investigated samples have been measured by modified Ångström method. This method requires that phase lag of a thermal wave propagating in the sample be determined. One plane of rectangular prismatic sample is periodically heated and cooled while others remain thermally insulated. Periodical changes in the temperature of heated plane and the plane opposite to it are measured and used to determine phase lag between the two signals. The measurements have been taken for different frequencies and thermal diffusivity value has been found from frequency dependence of phase lag. Examined crystals have been grown using Czochralski's method. One of them has been pure LiNbO ₃, others have been doped with the following elements: Cu (0.05 %at.), Fe (0.1 %at.), Dy (0.1 %at., 1.0 %at., and 1.7 %at.), Er (0.1 %at.), and Er + Yb (1.0 %at. Er + 0.1 %at. Yb, 1.0 %at. Er + 0.5 %at. Yb, 1.0 %at. Er + 1.0 %at. Yb). The measurements have been carried out for crystallographic directions [100], [120] and [001]. Measured value of thermal diffusivity of pure lithium niobate is in good agreement with values reported by other researchers, values obtained for samples doped with Cu and Fe are comparable to those obtained for pure crystals. Crystals doped with rare earth elements have considerably lower thermal diffusivities.