Phase formation during the low-temperature synthesis of KBBO superconductors in KOH melt

Phase formation in the KOH-BaO2[Ba(OH)(2)]-Bi2O3 system under an air atmosp here between 250-400 degreesC with feed ratios of K : Ba = 3.3-55 and Ba : Bi = 0.38-1.00 was studied by X-ray powder diffraction, elemental analysis (EA) and electron diffraction (ED) in a transmission electron microscope, c hemical analysis, and magnetic susceptibility measurements. The annealing p roducts are multiphase, and their constitution essentially depends on the f eedstock composition, temperature, and annealing duration. A superconductin g product has T-c less than or equal to 30 K, the composition KnBamBim+nOy with m/(m + n) = 0.40-0.67 (Group I oxides), and a pseudocubic structure (a = 4.282-4.290 Angstrom). Its maximum yield is achieved within a narrow ran ge of the feed ratios K : Ba = 3.3-5 and Ba : Bi = 0.60-0.67 at 250-300 deg reesC and annealing duration of 2-5 h. Minority phases are normal perovskit e-related, pseudocubic oxides KnBamBim+nOy with (m + n)/m = 0.80-0.95 (Grou p II oxides) and a = 4.311-4.334 A and (K + Ba)(m+n)BimOy with (m + n)/m = 1.07-1.25 (Group III oxides) and a = 4.245-4.251 Angstrom, tetragonal oxide s (K + Ba)(m+n)BimOy (Group III oxides) with m/(m + n) = 1.27-1.67 (a = 4.2 56-4.259 Angstrom, c = 21.898-21.912 Angstrom), and non-perovskite oxides K m+nBimOy with (m + n)/m = 1.15-1.78 (a Group V oxide) and KmBim+nOy with m/ (m + n) = 0.40-0.90 (a Group VI oxide).