セルフフラックス法によるBi_2SrTa_2O_9単結晶の育成

概要

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The optimum heat-treatment process to grow single crystals of Bi_2SrTa_2O_9(BiSTa), which have been attracting much attention as a material for capacitors of ferroelectric nonvolatile memories, was determined using a Bi_2O_3-excess self-flux method. The starting mixture(Bi_2O_3:SrCO_3:Ta_2O_5=79:10.5:10.5)was inserted into a double crucible made of platinum and alumina. Single crystals were grown at 1345℃ and 1400℃ in a vertical furnace. With a short hold time, the main product was α-Bi_2O_3 and with an excessively long hold time, SrTa_4O_<11> and Sr_2Ta_2O_7 were also synthesized. For the purpose of successfully obtaining BiSTa crystals in a single-phase state, complete vaporization of the excess Bi_2O_3 flux in the double crucible was essential under an appropriate heat-treatment condition, such as a hold time of 2h at 1400℃ and a cooling rate of 2℃/h to 1150℃. The obtained crystals were transparent and rectangular thin plate, with the long side of 300μm-1mm. The compositional ratio of the crystal was 1.91±0.05:1.27±0.05:2.00 for Bi:Sr:Ta, suggesting that not only is the crystal Bi poorer but Sr richer, compared to the stoichiometric ratio.
社団法人日本セラミックス協会の論文
1998-05-01