Design, Synthesis and Characterization of New Superconductors

Design and synthesis of new materials are a long-standing goal for chemistry, physics and material science, especially those with intriguing properties such as magnetism and superconductivity. With consideration and incorporation of the highlights in some existing design rules, we successfully designed and discovered the superconductivity in BaPt2Bi2, SrSnP and YbxPt5P. With the help of valence electron counting method, we synthesized a new intermetallic compound, BaIr2Ge2, which was then found to be non-superconducting above 1.8 K. Thus, we considered both valence electron counting and chemical pressure adjustment to reach the superconductivity of BaPt2Bi2 (Tc = 2.0 K) which crystallizes in a structure highly related to the parent compound of one of the high-temperature superconductors, BaFe2As2. According to the bonding analysis, Pt-Pt and Pt-Bi antibonding interactions are believed to be responsible to superconductivity in such system. In order to find more superconductors with Pt-Bi critical charge transfer pair, with the help from adaptive genetic algorithm, we synthesized SrPtBi2 for the first time. Theoretical calculation reveals that Pt-Bi antibonding interaction exists in SrPtBi2 but does not induce superconductivity while few Pt-Pt interaction can be found. Guided by the famous bismuthate superconductor, Ba1-xKxBiO3, we successfully observed the superconductivity in a known compound, SrSnP, at Tc = 2.3 K. The bonding analysis indicates that the Sn-P antibonding interaction and Sr-P bonding interaction are essential in releasing more electrons from Sn atom and, thus, provide more possibilities for electrons to form Cooper pair which is significant for superconductivity based on BCS theory. Due to the fact that there exist many superconducting Pt-rich materials, the ones with Pt-P charge transfer pair were also tested with the success in synthesizing APt8P2 (A = Ca and La) and YbxPt5P. APt8P2 compounds were determined to be non-superconducting above 1.8 K. The bonding analyses for them provided the evidence for structural stability. However, YbxPt5P was observed to be superconducting below Tc = 0.6 K while large heat capacity anomaly attributed to magnetism can be found below Tc which implies the possible coexistence of superconductivity and magnetism