Abstract
Bulk c-oriented CeF3 single crystals (sp. gr. P3¯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 (σdc = 2.7 × 10−6 S/cm) at room temperature are observed in the [0001] direction for the CeF3 crystals. The Vickers (HV) and Berkovich (HB) microhardnesses for the (0001), (101¯0) and (112¯0) crystallographic planes were investigated. The HB values were higher than the HV 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 {112¯0}, {101¯0} and {0001} 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.
Highlights
Among bulk single crystals of the rare-earth trifluorides [1], cerium fluoride attracts special attention due to a wide range of promising applications
The as-grown c-oriented CeF3 crystals were colorless and transparent, and no lightscattering inclusions were observed in the bulk of the crystals (Figure 2a)
The reason for its appearance was associated with the low isomorphic capacity of the structure of these crystals in relation to the residual amount of oxygen-containing impurities, which were pushed into the melt during the growth process and accumulated in the upper parts of the boules
Summary
Among bulk single crystals of the rare-earth trifluorides [1], cerium fluoride attracts special attention due to a wide range of promising applications. The undoped and rareearth doped CeF3 single crystals (and solid solutions based on it) are a multifunctional material for various fields of science and technology These crystals can be used as optical materials in a wide (from VUV- to mid-IR) spectral range [2,3,4,5]: rare-earth (Dy3+, Er3+, Nd3+ ions, etc.)-doped laser host materials, efficiently emitting in the visible and IR ranges [6,7,8,9,10,11], and solid electrolyte basic components for fluoride ion batteries [12,13,14,15,16]. Performance improvement studies of these crystals are ongoing for high-energy physics applications [21,22]
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