Abstract: High quality Cr-, Fe- and Ni- doped Al₂O₃ (A:Al₂O₃) single crystals with a diameter of 6?8 mm and a length of 60-80 mm were successfully produced by the floating zone technique. The relationship between crystal quality and growth conditions was discussed, and the optimum preparation parameter was obtained. The crystals growth direction was determined as <001> by X-ray diffraction. The X-ray rocking curve of the crystal had a FWMH of 0.089o, proving excellent quality of the crystal. The as-grown crystals were characterized by polarized optical microscope and scanning electron microscope, as well as X-ray diffraction. The observed primary crystal defects were sub-angle grain boundaries, inclusions and solute trails. The absorption spectra properties and dielectric constant measurements of A:Al₂O₃ crystals and fluorescence spectra for Cr:Al₂O₃ crystals were investigated. In view of the fact that grown A:Al₂O₃ crystals show good quality, a respectively high dielectric constant e_r (12.1-15.7), low dielectric loss tan? (0.0020?0.0002), and favorable thermal stability suggests their utilization as laser matrix, dielectric material for microelectronics and substrate material.

Key words: A:Al₂O₃, single crystal growth, floating zone technique, crystal defects