Correlation between the thermal diffusivity and the velocity of ultrasound in YVO

Four single crystals of YVO4 were examined to determine their thermal and elastic properties. The thermal diffusivity was investigated by photothermal method using the mirage effect. The velocity of ultrasound in crystals was measured using the pulse echo method. Two of investigated samples were doped with neodymium (1 at.% and 2 at.% of Nd), one with calcium and thulium (0.4 at.% of Ca and 5 at.% of Tm), and one was pure crystal. Experimental results showed anisotropy of the thermal diffusivity and the velocity of ultrasound. The thermal diffusivity as well as the sound velocity is lower in (001) crystallographic plane than in [001] direction (c-axis). Both quantities decrease with growing concentration of dopants for all crystallographic direction, but the influence of dopants is more distinct in the case of the thermal diffusivity. This fact allows to draw the conclusion that impurity atoms create scattering centres in crystal structure which result in shortening of phonon mean free paths and lowering of the thermal conductivity