Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) have been used to characterize the local structure and electronic properties of Tl2Ba2Ca2Cu3O10 single crystals prepared from 4:1:3:6 and 4:1:3:10 stoichiometry melts. Magnetic-susceptibility, resistivity, x-ray-fluorescence, and x-ray-diffraction measurements indicate that samples prepared from the 4:1:3:6 melts (type 1) have a chemical inhomogeneity, while crystals obtained from the 4:1:3:10 melts (type 2) are high quality. STM studies of the type-1 crystals demonstrate that the inhomogeneities can be associated with distortions in the TlO layer atomic structure. STS measurements on the distorted TlO layer of the type-1 samples have shown that this layer is also metallic. STM and STS investigations of the type-2 samples have shown, however, that the TlO layer in these crystals is tetragonal and semiconducting. In addition, a superstructure that is localized over small regions of the TlO surface has been characterized in the type-1 crystals. These results demonstrate that single crystals of the same average structure and composition can exhibit substantial differences in the local-structure electronic states and superconducting properties.
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