Bi Fe, Co Oxide Preparation, Structure And Performance

Bi-based perovskite layered oxides have numeral useful properties. Bi-based Cu oxides show characterization of high temperature superconductor. For example, Bi 2212. Fe-based oxides show multiferrotic. However, Oxides with element of cobalt show neither multiferrotic nor superconductor for its big intrinsic magnetic moment. Therefore, the researcher converts the interest to the other aspects of properties. An excited aspect of these materials is the large-thermo power, which implies their great application potential in the field of thermo-power materials. Except the normal physical properties, this paper stresses on the electrochemical properties of the polycrystalline Bi₂Ca₃Co₂O₉ with the following results.1. Polycrystalline and single crystal Bi₂Ca₃Co₂O₉ are prepared through conventional solid state reaction and flux method, respectively. XRD measurement confirms their phase-purity. The characterization for electrochemical properties shows that they can be partly insertion/extraction with Li ions. The first discharge capacity achieves 840mAh/g. From the second cycle, they display good reversibility, which demonstrates relatively stable structure. However, further research is essential to improve the capacity and reversibility for practical application.2. The physical property measurement shows that there is a transition from semi-conductor to metal at 175K. The thermo-power Seebeck value increases with temperature, leading to nearly 300μk. These results agree well with previous literatures. Based on the analysis to the measurement, thermo-motivated semiconductor mechanism is proposed. Ca, Sr, Ba substituted polycrystalline Bi₂Ca₃Co₂O₉ have been prepared with the same method as before for the purpose to analyze the possible mechanism of Co magnetism. The data shows that part of Co inside the lattice is in its low spin configuration (t_2s5_egl).3. Bi_1-xSr_xFeO₃ (x=0.2, 0.4, 0.5, 0.6, 0.8, 1.0) ceramics have been prepared with phase-purity. First time we make the full refinement for these samples with Moud programmers. The results show that all samples are cubic with Pm-3m (space group). The lattice constant values decrease with the doping proportion x.