Thermal and mechanical properties of BaWO4 crystal

A large single crystal of barium tungstate $\left({\mathrm{BaWO}}_4\right)$ with dimensions of $22\text{-}\mathrm{mm}\text{diameter}\times 80\text{-}\mathrm{mm}$ length was grown by the Czochralski method using an iridium crucible. The melting point, molar enthalpy of fusion, and molar entropy of fusion of the crystal were determined to be 1775.10 K, $96913.80\mathrm{J}{\mathrm{mol}}^{-1}$ , and $54.60\mathrm{J}{\mathrm{K}}^{-1}{\mathrm{mol}}^{-1}$ , respectively. The average linear thermal-expansion coefficients are ${\alpha }_a=10.9526\times {10}^{-6}∕\mathrm{K}$ , ${\alpha }_b=10.8069\times {10}^{-6}∕\mathrm{K}$ , and ${\alpha }_c=35.1063\times {10}^{-6}∕\mathrm{K}$ in the temperature range from 303.15 to 1423.15 K along the three respective crystallographic axes. The density of the crystal follows an almost linear decrease from $6.393\times {10}^3$ to $6.000\times {10}^3\mathrm{kg}{\mathrm{m}}^{-3}$ when the temperature is increased from 303.15 to 1423.15 K. The measured specific heat are $115.56\text{–}130.96\mathrm{J}{\mathrm{K}}^{-1}{\mathrm{mol}}^{-1}$ in the temperature range of 323.15–1173.15 K. The thermal diffusion coefficient of the crystal was measured in the temperature range of 297.15–563.15 K. The calculated thermal conductivity is $2.256\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ along the [001] direction and $2.324\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ along the [100] direction at 323.15 K. The microhardness of the ${\mathrm{BaWO}}_4$ single crystal in the (001) and (100) planes is 1393 and 1814 MPa under a load of 0.050 kg.