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.

Scanning Quantum Cryogenic Atom Microscope

“…The superior low-temperature and high-frequency imaging abilities of these scanning SQUIDs is complemented by the higher DC sensitivity and high-temperature compatibility of the SQCRAMscope. Specifically, these highresolution SQUIDs lose sensitivity above sample temperatures of ∼20 K due to weak thermal links to the sample, bringing the SQUID close to its superconducting critical temperature [24]. (High-T c SQUIDs provide less sensitivity.)…”