SINGLE-CRYSTALS OF ND1-XCU3-YGAYO7-DELTA, AND THEIR CHARACTERIZATION(XBA2)

Large Nd1+xBa2-xCu3-yGayO7-delta single crystals measuring up to 22 x 15 x3 mm have been obtained from an oxide flux which was stepwise cool ed from 1030 to 960 degrees C in air, In the crystals the upper solubi lity 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 mol ten solution. X-ray single crystal diffraction studies show that the t etragonal symmetry occurs in three states, i.e., (1) x greater than or equal to 0.18, y = 0; (2) x = 0, y > 0.10 and (3) x + y greater than or equal to 0.16. Optical polarizing microscopy reveals the twin domai n structure existing in pure Nd1+xBa2-xCu3O7-delta crystals with x = 0 .15. Transmission electron microscopy studies provide the evidence of the tweed tetragonal phase in the highly Ga-doped compound. The resist ivity measurements reveal superconductivity of all samples with y less than or equal to 0.08, metallicity with y = 0.09-0.10, and semiconduc tion with y greater than or equal to 0.15.