Observation of high-Tc superconductivity in inhomogeneous combinatorial ceramics

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 about 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: BaO2, CaCO3, SrCO3, La2O3, PbCO3, ZrO2 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-Tc 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)0.7-1.0CuO2 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 Tc =70 K superconductivity of the La(Ba,Ca)2Cu3Ox 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-Tc superconductivity in compounds without Bi, Tl, Hg, or the need for high-pressure synthesis

Ceramic combinatorial syntheses exploring the chemical diversity of metal oxides

A ceramic combinatorial method to investigate the phase space of e.g. metal oxides by a single sample is reviewed along with its application to cuprate superconductors. The main idea behind this method is to use a large number N of starting materials (micrometer size grains) to generate local reaction centers producing possible compounds at the reaction temperature. Mathematical calculations using also empirical data on the occurrence of compounds in phase systems allow to conclude that in 1 cm3 of a sample, there are enough grains to populate all local reaction centers in order to obtain in principle what the N starting materials can produce. A variety of characterization technics have been applied to such libraries to identify e.g. cuprate superconductors. Finally the success of the concept will depend on analytical tools allowing for a simultaneous analysis of the composition and physical properties. Here, we have applied for the first time scanning SQUID microscopy to reveal local superconductivity in inhomogeneous ceramic samples

Sol gel and ceramic synthesis of Sr 2 FeMo 1−x W x O 6 (0 ≤ x ≤ 1) double perovskites series

Preparation methods (ceramic and sol–gel methods) using reducing conditions were optimized for the formation of phase pure double perovskites of Sr2FeMo(1−x)WxO6 (0 ≤ x ≤ 1) showing enhanced homogeneity and cation ordering for investigating magnetic properties. X-ray diffraction (XRD) revealed a structural transition from tetragonal to monoclinic as W replaces Mo (x = 0.5–0.6). The SQUID magnetometry confirmed a ferrimagnetic ground state for Sr2FeMoO6 whereas Sr2FeWO6 shows an antiferromagnetic state. Current results demonstrate that improved preparation methods can enhance the saturation magnetization

Exploring Multi-Component Superconducting Compounds by a High-Pressure Method and Ceramic Combinatorial Chemistry

In this short review, we provide some new insights into the material synthesis and characterization of modern multi-component superconducting oxides. Two different approaches such as the high-pressure, high-temperature method and ceramic combinatorial chemistry will be reported with application to several typical examples. First, we highlight the key role of the extreme conditions in the growth of Fe-based superconductors, where a careful control of the composition-structure relation is vital for understanding the microscopic physics. The availability of high-quality LnFeAsO (Ln = lanthanide) single crystals with substitution of O by F, Sm by Th, Fe by Co, and As by P allowed us to measure intrinsic and anisotropic superconducting properties such as Hc2, Jc. Furthermore, we demonstrate that combinatorial ceramic chemistry is an efficient way to search for new superconducting compounds. A single-sample synthesis concept based on multi-element ceramic mixtures can produce a variety of local products. Such a system needs local probe analyses and separation techniques to identify compounds of interest. We present the results obtained from random mixtures of Ca, Sr, Ba, La, Zr, Pb, Tl, Y, Bi, and Cu oxides reacted at different conditions. By adding Zr but removing Tl, Y, and Bi, the bulk state superconductivity got enhanced up to about 122 K