Scanning SQUID Microscopy of Local Superconductivity in Inhomogeneous Combinatorial Ceramics

Although combinatorial solid-state chemistry promises to be an efficient way to search for new superconducting compounds, the problem of determining which compositions are strongly diamagnetic in a mixed-phase sample is challenging. By means of reactions in a system of randomly mixed starting components (Ca, Sr, Ba, La, Y, Pb, Bi, Tl, and Cu oxides), samples were produced that showed an onset of diamagnetic response above 115 K in bulk measurements. Imaging of this diamagnetic response in ceramic samples by scanning SQUID microscopy (SSM) revealed local superconducting areas with sizes down to as small as the spatial resolution of a few micrometers. In addition, locally formed superconducting matter was extracted from mixedphase samples by magnetic separation. The analysis of single grains (d< 80 mm) by X-ray diffraction, elemental analysis, and bulk SQUID measurements allowed Tl2Ca3Ba2Cu4O12, TlCaBaSrCu2O7-delta, BaPb0.5Bi0.25Tl0.25O3-delta, TlBa2Ca2Cu3O9, Tl2Ba2CaCu2O8, and YBa2Cu3O7 phases to be identified. SSM, in combination with other diagnostic techniques, is therefore shown to be a useful instrument to analyze inhomogeneous reaction products in the solid-state chemistry of materials showing magnetic properties.