Abstract
YBa(Co4 − x Al x )O7 + δ (114Y) crystals have been grown in the Y-Ba-Co-O system by spontaneous crystallization from a slowly cooled nonstoichiometric melt. To change the oxygen content, the crystals were isothermally annealed in air in the range of 280–490°C. The crystals grown were characterized by scanning electron microscopy and powder X-ray diffraction. According to the data of an X-ray spectroscopic quantitative microprobe analysis, the average compositions of “as-grown” and oxygen-saturated crystals were Y1.04Ba1Co3.54Al0.50O7.8 and Y1.02Ba1Co3.55Al0.51O8.4, respectively. The refinement of the crystal structure after saturation on an automatic Bruker X8APEX diffractometer with a CCD detector (MoKα radiation, graphite monochromator, θmax = 32.54°, sp. gr. P63 mc, a = 6.2746(9), c = 10.257(3) A, V = 349.71(13) A3, Z = 2, d calcd = 5.220 g/cm3) reveals the location of Al in two independent positions of Co atoms and yields the general formula of the compound as YBaCo3.26Al0.74O7. Problems related to the difference in the compositions obtained by different methods are discussed.
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