Growth and Characterization of Shape-Controlled Single Crystals by a Micro-pulling-down Method
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Growth and Characterization of Shape-Controlled Single Crystals by a Micro-pulling-down Method Yuui Yokota1, Hidehiko Tanaka1, Masato Sato1,2, Valery Chani1, Kazushige Tota2, Ko Onodera2 Takayuki Yanagida1, Akira Yoshikawa1,3 1
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Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, 2-1-1 Katahira Aoba-ku Sendai Miyagi, 980-8577, JAPAN TDK Corporation, 1-1 Okinota Kisakata Nikaho Akita, 018-0193, JAPAN New Industry Creation Hatchery Center (NICHe), Tohoku University, 6-6-10 Aoba Aramaki Aoba-ku Sendai Miyagi, 980-8579, JAPAN
ABSTRACT Shape-controlled CaF2 and sapphire crystals were grown by a micro-pulling-down (μPD) method and the crystallinities were investigated. By the μ-PD method with crucibles which have special configurations, circular tube-shaped CaF2 crystal, square tube-shaped CaF2 crystal and square tube-shaped sapphire crystal with high transparency were obtained. The grown crystals indicated a single phase of CaF2 and Al2O3 in the XRD measurements. X-ray rocking curve of square tube-shaped sapphire indicated the crystal has no mosaic structure in the crystal and it has high crystallinity comparable to crystals grown by Cz method. INTRODUCTION Various functional bulk single crystals grown by Czochralski (Cz), BridgmanStockbarger (BS) and Floating Zone (FZ) methods have been applied in a wide field of application such as optical equipments, radiation medicine, single crystal substrate and so on. Relatively large bulk crystals with several inches in diameter can be obtained by these conventional methods in several days or weeks growth period. In most industrial and research fields, functional crystals must be shaped to fit on each application and evaluation by cutting and polishing with the greatest care to prevent some damages to the crystals. Therefore the processing cost of bulk crystals strongly affects final prices of various products with single crystal. In contrast, a micro-pulling-down (μ-PD) method [1] can grow relatively small crystals with a couple of millimeters in diameter at a several times faster speed than that of Cz, BS and FZ methods. In addition, the μ-PD method can control the shape of grown crystal by a crucible with a specific configuration [2]. However, shape-controlled fluoride crystal has not been grown by the μ-PD method due to a bad wetting nature between melt of materials and crucible which is a container of materials and is made of carbon. On these backgrounds, we have developed the technique of figure control on functional fluoride single crystals grown by μ-PD method. In addition, we investigated the crystallinity of shape-controlled fluoride and oxide crystals.
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EXPERIMENT Circular tube-shaped CaF2 crystal, square tube-shaped CaF2 crystal and square tubeshaped sapphire crystal were grown by μ-PD method with carbon and molybdenum crucibles with special shapes. Schematics of the μ-PD method for oxide and fluoride crystal growth are shown in Fig.1. Starting materials, CaF2 ( > 3 N purity ) and Al2O3 ( > 4 N purity ) powders, were e
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