Upper‐Phase Stability Limit of Bi‐2212

Abstract

The upper stability line for Bi2Sr2CaCu2O8+α (Bi‐2212) was determined over the temperature range 540°–800°C and the oxygen partial pressure range 1.5 ×101‐7.4× 10‐3 atm using coulometric titration and high oxygen pressure annealing. The decomposition products resulting from Bi‐2212 oxidation are CuO, two alkaline‐earth bismuthates, and the Raveau phase, Bi11Sr9Cu5Oy. The main alkaline‐earth bismuthate is a known phase of cation composition Bi:Sr:Ca = 2.00:2.48:1.19 (Bi:Sr:Ca 9:11:5). The other alkaline‐earth bismuthate is a minor phase of cation composition Bi:Sr:Ca = 2.00:0.53:0.39. The kinetics for Bi‐2212 decomposition are very slow; e.g., at 700°C in air, the reaction is incomplete after 7 days.

Fabrication of Ag/Bi2Sr2Ca1Cu2O8±x superconducting tapes by the oxidation and postoxidation (partial melt) annealing of malleable, metal-bearing precursors

“…However, the distinct peaks observed in Fig. [34][35][36][37][38][39] Diffraction peaks for CuO were also observed, along with a weak peak that was consistent with the strongest reflection for Sr 14 Cu 24 O 41 . 3(b).…”

“…5(b). [34][35][36][37][38][39]41 Image analyses indicated that the (Sr x Ca 1−x )CuO 2 particles comprised 9 vol% of the specimen of Fig. 5(a), dark and bright particles were observed to be dispersed in a gray matrix.…”

“…The absence of distinct reflections for an oxidized calcium-bearing phase [e.g., CaO, CaCO 3 , Ca(OH) 2 , etc.] [36][37][38][39]59,60 In the latter case (e.g., after heat treatment for 5 h at 800°C and at an oxygen fugacity of 0.85 MPa), the 2212 compound has been found to decompose to form a mixture of 2201, 91150, and CuO, as indicated by the following net reaction: 36 In order to allow for enhanced 2212 grain alignment and, hence, higher critical current densities, the oxidized, 2212-bearing tapes were exposed to the heat treatment shown in Fig. 48 Bismuth (or Bi 2 O 3 ) was not detected within the silver sheath or on the outside silver surface after the 350°C/12 h heat treatment, which indicated that the oxidation of strontium and calcium at 350°C occurred predominantly by direct reaction with gaseous oxygen and not via displacement reactions (1a) and (1b).…”