COMPOSITION AND STRUCTURE REFINEMENT OF SUPERCONDUCTING CRYSTALS Y<sub>1-<i>x</i></sub>Tb<sub><i>x</i></sub>Ba<sub>2</sub>Cu<sub>3</sub>O<sub>6+δ</sub> (<i>х</i> = 0.10; δ = 0.75)
Crystals of Y0.90Tb0.10Ba2Cu3O6.75 have been prepared by spontaneous crystallization from slowly cooled non-stoichiometric melt of the system Y-Tb-Ba-Cu-O. Average size of platelet crystals having mirror surface is 2×2, the largest - 8×9 mm with thickness 0.1-0.2 mm. The crystals have been characterized by powder X-ray diffraction and electron microprobe analysis. Tetragonal symmetry of the crystals has been determined by X-ray diffraction. Magnetic susceptibility measurements have revealed that the crystals manifest transition to superconducting state without additional annealing (Тс = 60 K). Structures and compositions - Y/Tb ratio (σ = 0.01) and oxygen content (σ = 0.04) - have been refined for two single crystals. Possibility of rhombic distortion of the tetragonal symmetry is discussed.