Studies of theoretical and experimental precipitation conditions of Y +3 , Ba +2 , and Cu +2 ions in oxalate-diethylamin
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C. T. Chang Department of Chemistry, National Tsing Hua University, Hsinchu, and Institute of Atomic and Molecular Science, Academia Sinica, Taipei, P.O. Box 23-166, Taiwan, Republic of China; and Materials Research Laboratories, Industrial Technology Research Institute, Chutung, Hsinchu 31015, Taiwan, Republic of China
C. Y. Shei and W-M. Hurng Materials Research Laboratories, Industrial Technology Research Institute, Chutung, Hsinchu 31015, Taiwan, Republic of China (Received 16 September 1991; accepted 18 May 1992)
In the preparation of Y I ^ O ^ O , (Y-123) superconductor, the coprecipitation method was frequently used in various solution systems due to advantages such as good homogeneity, low reaction temperature, fine and uniform particle size, easy scale-up, and economical concerns. In this paper, a detailed study of different competitive reactions such as dissociation, precipitation, complex formation, and association involving metal ions, oxalate ion, and diethylamine species is performed. The study aids in understanding the precipitation and yields an optimal coprecipitation condition for the title system. A series of experiments are also conducted which confirm that the as-derived optimal condition may be extensively applied to other systems. I. INTRODUCTION The discovery of the La 2 - x Ba J CuO 4 superconductor has stimulated tremendous activities in the search of cuprate superconductors.1"4 One of the most plausible candidates in this search is YBa 2 Cu 3 0 y (Y-123) phase which has a superconducting transition temperature (Tc) at around 93 K.2 In the preparation of the Y-123 phase, conventional solid state reactions as well as various solution methods were reported. In general, the latter was shown to have superior advantages such as good homogeneity, low reaction temperature, fine and uniform particle size, and easy scale-up as compared to the former. In solution methods, coprecipitation was extensively used and studied for the preparation of the Y-123 phase5"16 due to economical concerns although a sol-gel method was reported to form Y-123 phase at a much lower temperature (~650 °C).17"22 Among anion precipitants, oxalate is one of the most popular in the precipitation of different cations. Although several papers have reported the preparation of YBa 2 Cu 3 0), superconductor powders through a coprecipitation of metal ions with oxalate ion, the formation behaviors of these precipitates have been dealt with only to a limited extent.7'8'12 In this paper, we report a detailed study of various systems containing metal ions, oxalate ion, and diethylamine species in aqueous solution. Different competitive reactions such as dissociation, precipitation, complex formation, and J. Mater. Res., Vol. 7, No. 9, Sep 1992
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association were considered and analyzed. Our results give understanding of the precipitation process and yield an optimal coprecipitation condition for the title system. Also, a series of experiments were conducted to confirm the as-der
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