The morphology, periodical modulation structure and effects of heat treatment on the superconductivity of (Tl, Pb)(Sr, Ba)-1223 single crystals

Surface morphologies and microstructures of (Tl, Pb)(Sr, Ba)-1223 single crystals were investigated by using a scanning electronic microscope (SEM) and an atomic force microscope (AFM). The SEM images showed that a Tl-1223 single crystal grown by self-flux obeys a layer-by-layer growth mechanism. Periodic modulation structures 200 nm in width and about 0.7-0.8 nm in height were observed using an AFM. Heat treatments in different atmospheres of argon and oxygen at 500 °C were carried out with different treatment times. T c and J c have been improved through optimized heat treatment for 3 h in argon gas. Crystals were also heat treated in PbO. Results showed that the magnetic properties were significantly improved, with large increases in T c and J c , indicating that the ratio of Tl to Pb in the crystal is another important factor in addition to the oxygen content in affecting the superconducting properties. The modulation structure is probably responsible for the strong flux pinning in (Tl, Pb)(Sr, Ba)-1223 crystals and the large J c .