TeO2 (Tellurium Dioxide) crystal is colorless, uniaxial crystal grown by Czochralski method from melt on seed. It has high refractive index (2.2-2.4), birefringence and high optical activity (20-500deg./mm depending on wavelength) and depending on seed properties it can be left-rotating or right-rotating. Also TeO2 crystals are distinguished on α- and β- structures. For acousto-optical purposes α-TeO2 is used and it generally calls as Paratellurite. It has tetragonal structure with a=b≠c and α=β=γ=90̊. High piezoelectric and optical activity is conditioned by the fact that paratellurite belongs to the point group D4=422.
Complete paratellurite physical characteristics you can find in Material properties part.