Processing of Bi-Sr-Ca-Cu-O glasses using platinum and alumina crucibles
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L. S. Chumbley Ames Laboratory and Iowa State University, Ames, Iowa 50011 (Received 13 February 1992; accepted 14 April 1992)
Reactions with alumina and platinum crucibles were studied during the preparation of Bi 2 Sr 2 CaiCu 2 0 > , "2212" glasses. In particular, reactions with A12O3 are of interest since alumina is a potential substrate material in applications of this superconductor. Glasses processed using alumina crucibles were completely homogeneous and free of secondary phases although the material contained 2.26 at. % Al in solution. After heat treatments, Al was found in the form of SrCaAlO^ particles located primarily along grain boundaries of the 2212 superconducting phase. Platinum contamination was minimal ( , stoichiometry were prepared by a splat-quench method using A12O3 (sample A) or Pt (sample B) crucibles. High purity powders of Bi 2 O 3 , SrCO 3 , CaCO 3 , and CuO were mixed in the appropriate ratios, calcined at 800 °C for 30 h with an intermediate and final grinding, melted at 1075 °C for 45 min, and splat-quenched on a stainless steel plate with a heavy Cu anvil. Additional details of this process can be found elsewhere.6 Overall compo2035
© 1992 Materials Research Society IP address: 128.218.248.200
T. G. Holesinger et al.: Processing of Bi-Sr-Ca-Cu-O glasses using platinum and alumina crucibles
XRD scans of samples processed with AI2O3 (sample A) or Pt (sample B) crucibles in the as-quenched and annealed state are shown in Fig. 1. Sample A was found to contain a trace of a secondary phase that may be 2201 although investigations by SEM and TEM revealed a completely homogeneous material with no second phases. The trace of 2201 detected by XRD may result from some surface crystallization, as suggested by DeGuire et al.5 ICP analysis results in Table I showed sample A to contain approximately 2.25 at. % Al. This contamination was detected in the TEM only, presumably due to the better peak-to-background ratio. SEM/EDS analysis of the glass matrix was in agreement with ICP results for the major cations when the Al content determined by ICP was taken into account. Sample B was found to contain several secondary phases in the as-quenched state, as indicated in Fig. 1. Using a processing temperature of 1075 °C, CaO was always found in samples splat-quenched with platinum crucibles regardless of the starting composition while only samples with high Ca contents (Bi2Sr2CaxCu20y; x 3= 1.5) were found to have CaO as a second phase when alumina crucibles were used.6 The other peaks detected by XRD in sample B correspond to 2201 and Sri^Ca^Q^CUi (14-24 phase).9 Of these two phases, only a few widely scattered grains of the 14-24 phase were ever observed by TEM within the glass sample while SEM revealed only the glass matrix and CaO. ICP results in Table I show that Pt contamination accounts for approximately 0.02 at. % of the sample and is not detected by EDS analysis in either the SEM or TEM. The presence of secondary phases, particularly CaO, did not affect the composition of the glass matrix to
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