Single-crystal growth and properties of substituted

Abstract

Single crystals of have been grown from a BaO-CuO flux under 600 bar of at . , BeO, and MgO materials were used for crucibles, resulting in , 76, 74 and 55 K, respectively. Good quality of crystals grown in crucibles was confirmed by single-crystal x-ray diffraction, magnetic and transport measurements. Angle-resolved photoemission showed the presence of the `extended' Van Hove singularity close to along the direction. Optical conductivity, resistivity and thermopower measurements along the a, b and c directions indicate a change in the character of the transport along the c direction at . First Zn- and Ni-substituted crystals with sharp superconducting transitions at for Zn and for Ni have been grown to study the effect of magnetic and nonmagnetic impurities located in the plane. Ratios of the starting flux compositions to the compositions substituted in crystals are close to 3.5 and 1 for Zn and Ni, respectively. Optical conductivity shows that the low-energy electronic states are at the verge of localization. The irreversibility line and critical currents were studied for pure and substituted crystals showing that intrinsic flux pinning is not significantly modified by Zn substitution on the planes.