ベルリナイト結晶の水熱合成

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タイトル別名
  • Hydrothermal Synthesis of Berlinite Crystals
  • ベルリナイト ケッショウ ノ スイネツ ゴウセイ

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Single crystals of berlinite (α-AlPO4), which is suggested to be a promising material for SAW (surface acoustic wave) and other piezoelectric devices, were hydrothermally grown.<br>A 6.1M H3PO4 solution was employed as a solvent. The autoclave used was a Pt-lined Morey-type one with the inner volume of 56ml. Because of the retrograde solubility, the crystal growth was carried out by a geometry of reverse temperature gradient, in which nutrient was placed in the upper region in the autoclave (the low temperature side) and seeds were suspended in the lower region (the high temperature side). The nutrient and seeds were fed from small berlinite crystals which were synthesized by slow-heating a charge consisting of a commercial aluminum phosphate reagent and a 6.1M H3PO4 solution in the autoclave from 150°C to 220° or 260°C. The degree of fill of the autoclave was of 80%, and the open area of a baffle plate was of 30%.<br>When growth runs were carried out at a crystallization temperature of 200°C with temperature differences of 0°-30°C, no transparent crystals could be obtained and much spontaneous nucleation was generated. This is considered to be mainly due to too large temperature differences and/or to too large fluctuations in the temperature differences influenced by the temperature change in the surrounding atmosphere. When the growth runs were conducted at 250°C with temperature differences of 10°-12°C, appreciably transparent crystals were obtained at a maximum rate of 0.43mm/day along the c-axis. The improvement on the crystal quality is considered to be due to the gentle temperature gradient of the solubility curve at 250°C permitting large temperature differences, and to the use of a electric furnace of a thick heat insulation wall decreasing the influence of the surrounding temperature change.<br>Examinations of the grown crystals by optical microscope and X-ray topography revealed that the crystals contain many dislocations, twins and inclusions of various kinds, though they are appreciably transparent.

収録刊行物

  • 窯業協會誌

    窯業協會誌 89 (1032), 433-439, 1981

    公益社団法人 日本セラミックス協会

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