Single crystals of Nd_{1 + x}Ba_{2 - X}Cu_{3 - Y}Ga_yO_{7 - δ} and their characterization

Large Nd_{1 + x}Ba_{2 - x}Cu_{3 -y}Ga_yO_{7 - δ} single crystals measuring up to 22 X 15 X 3 mm have been obtained from an oxide flux which was stepwise cooled from 1030 to 960°C in air. In the crystals the upper solubility limit of Nd is found to be x = 0.35 and that of Ga as high as y = 0.58. The Ga content is linearly related with that present in the molten solution. X-ray single crystal diffraction studies show that the tetragonal symmetry occurs in three states, i.e., (1) x ≥ 0.18, y = 0; (2) x = 0, y > 0.10 and (3) x + y ≥ 0.16. Optical polarizing microscopy reveals the twin domain structure existing in pure Nd_1+xBa_{2 - x}Cu₃O_{7 - δ} crystals with x = 0.15. Transmission electron microscopy studies provide the evidence of the tweed tetragonal phase in the highly Ga-doped compound. The resistivity measurements reveal superconductivity of all samples with y ≤ 0.08, metallicity with y = 0.09-0.10, and semiconduction with y ≥ 0.15.