Photonic Na₆Mo₁₁O₃₆ Crystals: Growth, Morphology, and Crystal Structure

Bulk Na₆Mo₁₁O₃₆ single crystals with dimensions 70*40*20 and 70*40*40 mm³ were obtained by the low-thermal gradient Czochralski technique. The uniformity of the grown boules was assessed using the following characterization techniques: X-ray diffraction (XRD) and differential scanning calorimetry. The crystal structure was thoroughly examined through single-crystal X-ray diffraction (SCXRD). Space group was determined by SCXRD as C2/c (a = 7.2229(1) Å, b = 17.8065(4) Å, c = 22.2789(5) Å, β = 90.311(1)°). Na₆Mo₁₁O₃₆ crystals exhibited a strong tendency to formation of twins up to the change of crystallization direction on 90° during the growth process, which is a unique event for Czochralski technique crystal growth. Crystal faceting was studied, and Miller indexes of developed facet families were determined by the XRD method; a reference model of the Na₆Mo₁₁O₃₆ crystal was visualized based on obtained data. Optimal growth direction for obtaining uniform bulk Na₆Mo₁₁O₃₆ crystals was determined to be [010]. Photoluminescence was registered on a 10 × 10 × 10 mm³ sample from 175 K temperature and below.