Crystal growth of thin-plate β-alumina by liquid transport
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Single crystals of β-alumina (Na20.11Al2O3) were grown by liquid transportat 1030–1150 °C and for durations of 4–140 h, using an Na3AlF6 solvent and α- or β-alumina as the nutrient. The maximum size of β-alumina crystal grown using a small platinum crucible was 1.1 cm in length and 0.6 mm in thickness. On the other hand, a single crystal 1.8 m long and 0.7 mm thick was grown using a large crucible. These grown single crystals were hexagonal, thin platelike, and very transparent. Screw dislocation-like patterns were observed on the surfaces of grown β-alumina single crystals; each pattern showed a right-handed rotation. Small crystals on a matrix crystal grew spirally about the c-axis and formed a new, flat surface on the matrix crystal, evidently an intrusive twin. The angle between the two inclined crystals was ∼ 2.9–2.8 °. The twin face seemed to be w(14, 14, 3). The growth rates of β-alumina single crystals treated for less than 12 h using large and small crucibles were 3.3 × 10−1 and 4.0 × 10−1 mm h−1, respectively. For treatment ranging from 12 to 40 h growth rates were 1.1 × 10−1 and 1.5 × 10−1 mm h−1 for the large and small crucible, respectively; rates for 40–100 h treatment were 0.3 × 10−1 mm h −1 for both crucibles. The grown β-alumina single crystals had fairly good crystallinity. The growth mechanism of the β-alumina single crystal can be estimated from transport through liquid film in the crucible, i.e. a creeping phenomenon.
KeywordsAl2O3 Hexagonal Crystal Growth Flat Surface Liquid Film
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