Growth And Characterization Of A:Al₂O₃(A=Cr, Fe, Ni) Single Crystals By The Optical Floating Zone Method

Material science is one of three backbones (energy, Information, material) of modern civilization and material foundation of new society. Single crystal as one of most important functional materials, broadly used in electrical devices, semiconductor devices and solid laser device, and other optical devices, play an important role in civil and military filed. The single crystal growth belongs to material science have developed to its foreland now. What's more, the crystal growth technique has become a intercross sciences of condensed physic and chemical and optical devices. The single crystal which abroad used include laser crystals, optical crystals, nonlinear optical crystals, sapphire crystals, semiconductor crystal and nanocrystal and so on. The methods of preparation of sapphire crystals included Verneuil, flux method, Bridgman, Hydrothermal growth, Czochralski, Edge-defined Film-fed Growth (EFG) and so on. The sapphire crystals (α-Al₂O₃, referred to as corundum) doped with different ions exhibit different color, have an excellent optical, electrical and mechanical properties, its hardness only to diamond. The crystal has a high-temperature chemical stability, good thermal conductivity and so on. As a result, high-quality large-diameter sapphire crystal synthesis is an important issue.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 crystals growth direction was determined as ?001? by X-ray diffraction. The X-ray rocking curve of the crystal has a FWMH of 0.089 o, proving the excellent quality of the crystal. The as-grown crystals were characterized by polarized optical microscopy and scanning electron microscopy, as well as X-ray diffraction. The primary crystal defects observed were sub-angle grain boundaries, inclusions and solute trails. These factors that influence the growth results includes the shape and stability of the molten zone, the quality of the feed rod, the temperature distribution, growth rate, rotating rate and shape of solid-liquid interface. All of these factors have been intensively discussed, and the optimized conditions of the growth parameters have been obtained. The formation mechanisms of these defects were discussed and the relevant approaches of restraining these defects have also been presented. The investigation of the growth defects is essential to optimize the growth parameters and improve crystal quality. The absorption spectra properties and dielectric constant measurements of A:Al₂O₃ crystals and fluorescence spectra for Cr:Al₂O₃ crystals were investigated.