On some features of the properties and microstructure of lithium iodate crystals

A comprehensive study of lithium iodate (α-LiIO₃) single crystals grown from mother solutions by the isothermal evaporation method has been conducted. The main focus was on the investigation of the microstructure, optical and mechanical properties, and their anisotropy. Significant microstructural heterogeneity was revealed using methods of selective chemical etching and scanning probe microscopy. It was shown that the lateral crystal growth is characterized by an anomalously high defect density (10⁵–10⁷ cm^-2) and increased surface roughness (25 nm compared to 2 nm in the central part), as well as a complex zonal and sectorial structure. Detailed measurements of Knoop and Vickers microhardness on various crystallographic planes were performed. Anisotropy of the second kind was discovered: maximum values were recorded on pyramidal faces {10Ī1} (278–283 kgf/mm²), while minimum values were found on prismatic faces {10Ī0} (221–248 kgf/mm²). No anisotropy of the first kind was observed on the Z-cut plane. It was demonstrated that microhardness decreases along the crystal height, which is associated with a gradient of microimpurity concentration, maximum at the beginning of growth (near the seed). Based on the analysis of the microstructure and sectorial structure, a mechanism of brittle crystal fracture under mechanical impact (shock) along sector boundaries is proposed, caused by heterogeneity and dislocation pile-ups. The obtained results are important for understanding the relationship between growth conditions, microstructure, and mechanical properties of LiIO₃ crystals, which expands the possibilities for their practical application in nonlinear optical devices and allows for the optimization of processing methods.

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