欠陥制御による高密度BaPb_<0.75>Bi_<0.25>O_3焼結体の作製

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The improvement of the sintering properties of a superconducting BaPb_<0.75>Bi_<0.25>O_3 ceramic by the introduction of point defects was examined. In order to introduce Ba vacancies into the structure, a mixture of BaCO_3, Pb_3O_4 and Bi_2O_3, with Ba-deficient nominal composition, was used as a starting material. The density of the specimen increased by using this nominally Ba-deficient mixture. However, it was revealed that the grain size in the sintered material was not affected by the amount of the nominal Ba deficiency and that a second phase, composed mainly of Bi and oxygen, was generated at grain boundaries. It was concluded that Ba vacancies could not be formed in BaPb_<0.75>Bi_<0.25>O_3 lattice and that the apparent high density and electrical resistivity, which was as high as 10^<-1>Ω・cm at room temperature, is attributed to the second phase formation at grain boundaries. When sintering under low oxygen partial pressure, the density of the superconducting BaPb_<0.75>Bi_<0.25>O_3 ceramic also increased. However, it was observed that the grain size of the BaPb_<0.75>Bi_<0.25>O_3 ceramic increased without the generation of a second phase at grain boundaries while sintering under reducing atmosphere. The dependence of the grain size on the oxygen partial pressure led to the suggestion that enhanced grain growth is governed by the increase of volume diffusion due to the introduction of oxygen vacancies. After annealing under oxygen to remove oxide ion vacancies, the specimen showed an electrical resistivity at room temperature as low as 10^<-3>Ω・cm and a sharp superconducting transition at 11.5 K.
社団法人日本セラミックス協会の論文
1998-08-01

欠陥制御による高密度BaPb_<0.75>Bi_<0.25>O_3焼結体の作製

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