Observation of high-Tc superconductivity in inhomogeneous combinatorial ceramics.

Abstract A single-sample synthesis concept based on multi-element ceramic samples can produce a variety of local products. When applied to cuprate superconductors (SC), statistical modelling predicts the occurrence of possible compounds in a concentration range of ∼50 ppm. In samples with such low concentrations, determining which compositions are superconducting is a challenging task and requires local probes or separation techniques. Here, we report results from samples with seven components: BaO 2 , CaCO 3 , SrCO 3 , La 2 O 3 , PbCO 3 , ZrO 2 and CuO oxides and carbonates, starting from different grain sizes. The reacted ceramics show different phases, particular grain growth, as well as variations in homogeneity and superconducting properties. High-T c superconductivity up to 118 K was found. Powder x-ray diffraction (XRD) in combination with energy-dispersive spectroscopy (EDS), scanning transmission electron microscopy (STEM) can assign "Pb1223" and "(Sr,Ca,Ba) 0.7-1.0 CuO 2 " phases in inhomogeneous samples milled with 10 mm ball sizes. Rather uniform samples featuring strong grain growth were obtained with 3 mm ball sizes, resulting in T c ∼70 K superconductivity of the "La(Ba,Ca) 2 Cu 3 O x " based phase. Scanning SQUID microscopy (SSM) establishes locally formed superconducting areas at a level of a few microns in inhomogeneous superconducting particles captured by a magnetic separation technique. The present results demonstrate a new synthetic approach for attaining high-T c superconductivity in compounds without Bi, Tl, Hg, or the need for high-pressure synthesis. Graphical abstract Image 1 Highlights • Superconducting grains with T c ∼118 K in mixture of Ca, Sr, Ba, La, Zr, Pb, Cu, O. • Magnetic separation of individual grains. • Scanning SQUID microscopy. [ABSTRACT FROM AUTHOR]