Bridgman Growth and Physical Properties Anisotropy of CeF₃ Single Crystals

Bulk c-oriented CeF₃ single crystals (sp. gr. $P\overline{3}c1$) were grown successfully by the vertical Bridgman technique in a fluorinating atmosphere. A description of the crystal growth procedure and the solution of the difficulties during the growth process are presented in detail. The anisotropy of the mechanical, thermal and electrophysical properties were studied for the first time. The maximum values of the thermal conductivity coefficient (α = 2.51 ± 0.12 W·m⁻¹·K⁻¹) and the ionic conductivity (σ_dc = 2.7 × 10⁻⁶ S/cm) at room temperature are observed in the [0001] direction for the CeF₃ crystals. The Vickers (H_V) and Berkovich (H_B) microhardnesses for the $(0001)$, $(10\overline{1}0)$ and $(11\overline{2}0)$ crystallographic planes were investigated. The H_B values were higher than the H_V ones and decreased from 3.8 to 2.9 GPa with an increase in the load in the range of 0.5–0.98 N for the hardest $(0001)$ plane. The $\left\{11\overline{2}0\right\}$, $\left\{10\overline{1}0\right\}$ and $\left\{0001\right\}$ cleavage planes were observed during the indentation process of the CeF₃ crystals. The variability of Young’s, the shear modules and Poisson’s ratio were analyzed. A significant correlation between the shapes of the Vickers indentation patterns with Young’s modulus anisotropy was found. The relationship between the anisotropy of the studied properties and the features of the CeF₃ trigonal crystal structure is discussed.