Influence of excess platinum and yttrium containing additives on the microstructural and phase formation kinetics in the YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} system
- Alfred Univ., NY (United States)
Results are presented concerning the influence of excess yttrium additions, i.e., Y{sub 2}O{sub 3} (200), Y{sub 2}Cu{sub 2}O{sub 5} (202), Y{sub 2}BaCuO{sub 5} (211), and Pt on the microstructural development in the YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (123) system. Both the single 123 phase precursor and melt powder melt quench (MPMG) precursor containing a phase mixture of BaCuO{sub 2} + BaCu{sub 2}O{sub 2} + 200 were studied. Quantitative determinations are presented concerning the activation energies for 211 formation upon peritectic 123 decomposition subsequent 123 solidification during melt processing. The activation energy for 211 formation (E{sub a-211}) in MPMG precursor system had a value in comparison to single phase 123 as determined by real time dynamic XRD analysis. The E{sub a-211} formation energies were {approximately}160kJ/mol in the MPMG precursor system while {approximately}870kJ/mol for the 123 phase precursor system. The 123 phase solidification temperature upon cooling (E{sub a-123}) determined by DTA was seen to: (1) increase with Pt addition up to 1.0 mol % addition, (2) decrease with excess yttrium addition to 123, (3) decrease with addition of both Pt and 211, and (4) result in the lowest E{sub a-123} for 200 addition. Quantitative XRD analysis for 211 phase content on melt processed samples revealed an increased final 211 content in linear manner with amount addition with yttrium containing additives. The addition of Pt was seen to increase 123 solidification temperature while decreasing 211 content up to 0.1 mol % above which the 211 fraction constant. Additions of 211 + Pt showed an increased 211 content with the addition, but at significantly lower levels versus 211 alone. At 1,100 C the 211 content was {approximately}30 wgt % vs {approximately}10 wgt % for 123 phase precursors as compare to NWMG precursors.
- OSTI ID:
- 187918
- Report Number(s):
- CONF-950729--
- Country of Publication:
- United States
- Language:
- English
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