Title: Low-temperature aqueous solution growth of the acousto-optic TeO2 single crystals

Abstract: $\alpha$-TeO2 is widely used in acousto-optic devices due to its excellent physical properties. Conventionally, $\alpha$-TeO2 single crystals were grown using melt methods. Here, we report for the first time the growth of $\alpha$-TeO2 single crystals using the aqueous solution method below 100 {\deg}C. Solubility curve of $\alpha$-TeO2 was measured, and then single crystals with dimensions of 3.5x3.5x2.5 mm3 were successfully grown using seed crystals that were synthesized from spontaneous nucleation. The as-grown single crystals belong to the P41212 space group, evidenced by single crystal X-ray diffraction and Rietveld refinement on powder diffraction. Rocking curve measurements show that the as-grown crystals exhibit high crystallinity with a full-width at half maxima (FWHM) of 57.2''. Ultraviolet-Visible absorption spectroscopy indicates the absorption edge is 350 nm and the band gap is estimated to be 3.58 eV. The density and Vickers hardness of as-grown single crystals are measured to be 6.042 g/cm3 and 404 kg/mm2, repectively. Our findings provide an easy-to-access and energy-saving method for growing single crystals of inorganic compounds.