Phase formation and the role of liquid phase in the synthesis of KBBO superconductors

Phase formation during two-stage annealing of KNO3-BamBim+nOy and KNO3-BaO2 -Bi2O3 mixtures with the compositions K : Ba : Bi = 1 : 1 : 2, 2 : 3 : 5, 1 : 2 : 3, 1 3 : 4, 2: 7 : 9, and 1 : 4 : 5. was Studied. The first stage in volves the high-temperature (700-970 degreesC) annealing under an argon atm osphere (p(o2) = 1 kPa) or under air; the second stage is an oxygen anneali ng (450 degreesC, 10(2) kpa). Perovskite-related oxides KBam(-1)Bi(m+n)O(y) or KxBamBim+nOy result from the first annealing stage under the argon or a ir atmosphere. These oxides inherit the anisotropic structure of BamBim+nOy . The preparation of the KBam-1Bim+nOy and KxBamBim+nOy phases follows an i ntercalation mechanism in the presence of a liquid phase, which is either m olten potassium oxides or its own melt depending on temperature. When melt- processed under the oxygen atmosphere, KBam-1Bim+nOy phases decompose to yi eld Bi2O3 and KnBamBim+nOy. The oxides KxBamBim+nOy and KnBamBim+nOy are sa turated with oxygen, and those of them with ml(m + n) = 0.40-0.71 express s uperconducting properties. The samples that experienced melting at the firs t stage and annealed under an oxygen atmosphere show the maximum diamagneti c response intensity in the magnetic susceptibility chi = f(T) curve.