CRYSTAL-GROWTH OF THIN-PLATE BETA-ALUMINA BY LIQUID TRANSPORT

Single crystals of beta-alumina (Na2O.11Al(2)O(3)) were grown by liquid transport at 1030-1150 degrees C and for durations of 4-140 h, using an Na3AlF6 solvent and alpha- or beta-alumina as the nutrient. The maximum size of beta-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 beta-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 a ng le between the two inclined crystals was similar to 2.9-2.8 degrees. The twin face seemed to be w(14, 14, 3). The growth rates of beta-alumina single crystals treated for less than 12 h using large and small crucibles were 3.3 x 10(-1) and 4.0 x 10(-1) mm h(-1), respectively. For treatment ranging from 12 to 40 h growth rates were 1.1 x 10(-1) and 1.5 x 10(-1) mm h(-1) for the large and small crucible, respectively; rates for 40-100 h treatment were 0.3 x 10(-1) mm h(-1) for both crucibles. The grown beta-alumina single crystals had fairly good crystallinity. The growth mechanism of the beta-alumina single crystal can be estimated from transport through liquid film in the crucible, i.e. a creeping phenomenon.