Photonic Na<sub>6</sub>Mo<sub>11</sub>O<sub>36</sub> Crystals: Growth, Morphology,\nand Crystal Structure

Bulk Na<sub>6</sub>Mo<sub>11</sub>O<sub>36</sub> single\ncrystals\nwith dimensions 70*40*20 and 70*40*40 mm<sup>3</sup> were obtained\nby the low-thermal gradient Czochralski technique. The uniformity\nof the grown boules was assessed using the following characterization\ntechniques: X-ray diffraction (XRD) and differential scanning calorimetry.\nThe crystal structure was thoroughly examined through single-crystal\nX-ray diffraction (SCXRD). Space group was determined by SCXRD as <i>C</i>2/<i>c</i> (<i>a</i> = 7.2229(1) Å, <i>b</i> = 17.8065(4) Å, <i>c</i> = 22.2789(5) Å,\nβ = 90.311(1)°). Na<sub>6</sub>Mo<sub>11</sub>O<sub>36</sub> crystals exhibited a strong tendency to formation of twins up to\nthe change of crystallization direction on 90° during the growth\nprocess, which is a unique event for Czochralski technique crystal\ngrowth. Crystal faceting was studied, and Miller indexes of developed\nfacet families were determined by the XRD method; a reference model\nof the Na<sub>6</sub>Mo<sub>11</sub>O<sub>36</sub> crystal was visualized\nbased on obtained data. Optimal growth direction for obtaining uniform\nbulk Na<sub>6</sub>Mo<sub>11</sub>O<sub>36</sub> crystals was determined\nto be [010]. Photoluminescence was registered on a 10 × 10 ×\n10 mm<sup>3</sup> sample from 175 K temperature and below.