The finite-element method has been used to study the thermal stress distribution in large-sized sapphire crystals grown with the sapphire growth technique with micro-pulling and shoulder-expanding at cooled center （S...The finite-element method has been used to study the thermal stress distribution in large-sized sapphire crystals grown with the sapphire growth technique with micro-pulling and shoulder-expanding at cooled center （SAPMAC） method. A critical defect model has been established to explain the growth and propagation of cracks during the sapphire growing process. It is demonstrated that the stress field depends on the growth rate, the ambient temperature and the crystallizing direction. High stresses always exist near the growth interfaces, at the shoulder-expanding locations, the tailing locations and the sites where the diameters undergo sharp changes. The maximum stresses always occur at the interface of seeds and crystals. Cracks often form in the critical defect region and spread in the m-planes and a-planes under applied tensile stresses during crystal growth. The experimental results have verified that with the improved system of crystal growth and well-controlled techniques, the large-sized sapphire crystals of high quality can be grown due to absence of cracks.展开更多
The sapphire （Al2O3） single crystal is a kind of excellent infrared transmission window materials. A large-sized sapphire （Ф225 mm×205 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with...The sapphire （Al2O3） single crystal is a kind of excellent infrared transmission window materials. A large-sized sapphire （Ф225 mm×205 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with micro-pulling and shoulder-expanding at cooled center）. Several kinds of inclusion in the large sapphire crystal were investigated by means of an optical microscopy （OM）, scanning electron microscopy （SEM） and electron probe microanalysis （EPMA）. The experimental results show that most inclusions are consisted of solid metallic and non-metallic particles as well as gas pores caused by the impurity of alumina as the raw material, the thermal dissociation of aluminum oxide melt and the reaction of the melt to the crucible material （Mo） at high temperatures. It is also found that in different crystal regions the inclusions are of varied sizes, morphology and chemical compositions. Finally, the measures to reduce and eliminate the inclusions are proposed to improve the crystal quality.展开更多
In this paper, large-sized sapphire （Φ230×210 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with micro-pulling and shoulder-expanding at the cooled center）. Dislocation peculiarity in la...In this paper, large-sized sapphire （Φ230×210 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with micro-pulling and shoulder-expanding at the cooled center）. Dislocation peculiarity in large sapphire boule （0001） basal plane was investigated by chemical etchiing, scanning electron microscopy and X-ray topography method. The triangular dislocation etch pit measured is 7.6× 10^1-8.0×10^2 cm^2, in which relative high-density dislocations were generated at both initial and final stages of crystal growth. The analysis of single-crystal X-ray topography shows that there are no apparent sub-grain boundaries; the dislocation lines are isolated and straight. Finally, the origins of low-density dislocation in sapphire crystal are discussed by numerical analysis method.展开更多
基金National Defence Pre-research Foundation of China (41312040404)
文摘The finite-element method has been used to study the thermal stress distribution in large-sized sapphire crystals grown with the sapphire growth technique with micro-pulling and shoulder-expanding at cooled center （SAPMAC） method. A critical defect model has been established to explain the growth and propagation of cracks during the sapphire growing process. It is demonstrated that the stress field depends on the growth rate, the ambient temperature and the crystallizing direction. High stresses always exist near the growth interfaces, at the shoulder-expanding locations, the tailing locations and the sites where the diameters undergo sharp changes. The maximum stresses always occur at the interface of seeds and crystals. Cracks often form in the critical defect region and spread in the m-planes and a-planes under applied tensile stresses during crystal growth. The experimental results have verified that with the improved system of crystal growth and well-controlled techniques, the large-sized sapphire crystals of high quality can be grown due to absence of cracks.
基金National Defensive Preliminary Research Funds of China (41312040404)
文摘The sapphire （Al2O3） single crystal is a kind of excellent infrared transmission window materials. A large-sized sapphire （Ф225 mm×205 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with micro-pulling and shoulder-expanding at cooled center）. Several kinds of inclusion in the large sapphire crystal were investigated by means of an optical microscopy （OM）, scanning electron microscopy （SEM） and electron probe microanalysis （EPMA）. The experimental results show that most inclusions are consisted of solid metallic and non-metallic particles as well as gas pores caused by the impurity of alumina as the raw material, the thermal dissociation of aluminum oxide melt and the reaction of the melt to the crucible material （Mo） at high temperatures. It is also found that in different crystal regions the inclusions are of varied sizes, morphology and chemical compositions. Finally, the measures to reduce and eliminate the inclusions are proposed to improve the crystal quality.
基金the National Defensive Preliminary Research Funds of China (No. 41312040404)
文摘In this paper, large-sized sapphire （Φ230×210 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with micro-pulling and shoulder-expanding at the cooled center）. Dislocation peculiarity in large sapphire boule （0001） basal plane was investigated by chemical etchiing, scanning electron microscopy and X-ray topography method. The triangular dislocation etch pit measured is 7.6× 10^1-8.0×10^2 cm^2, in which relative high-density dislocations were generated at both initial and final stages of crystal growth. The analysis of single-crystal X-ray topography shows that there are no apparent sub-grain boundaries; the dislocation lines are isolated and straight. Finally, the origins of low-density dislocation in sapphire crystal are discussed by numerical analysis method.
