Electrochemical crystal growth of superconducting cuprates and copper-less oxides

本研究旨在开发低温合成氧化物超导体单晶的新技术。本论文主要研究了用电化学方法合成超导铜酸盐和无铜氧化物。本研究包括三个部分：1.不同成分的Ba1-x&Gt；K_xBiO_3晶体的合成和输运性质的表征。超导铜酸盐单晶的合成与表征。寻找新的无铜超导氧化物。项目一：通过对成分范围较宽的晶体进行精确的电阻率和霍尔效应测量，揭示了该材料的输运性质。特别指出，输运性质与晶相的变化密切相关，并且氧的组成对超导电性也有影响。此外，Ba1-x&gt；K_xBiO_…的能带方案项目二：成功地生长了La_2CuO_4和Nd_2CuO_2-x&Gt；Ce_xCuO_4系统的晶体，表明电化学法是生长超导铜酸盐晶体的唯一方法。特别是La_2CuO_&lt；4+在高压氧中未经任何热处理的情况下表现出超导电性，这表明用电化学方法生长的晶体中含有足够的氧来显示超导性。项目二：合成了含Nb、Mo和Ru的氧化物。已经成功地生长了BaRuO_3等晶体，并对其性能进行了表征。除了这些项目外，我们还开发了新的“电解槽法”来合成氧化物晶体。该方法利用电极上产生的电动势进行晶体生长。将该方法应用于BaLt；1-x&Gt；KxBiO3晶体的合成，证实了该方法可以生长出高质量的晶体。较少

This study has been performed to develop new technique to synthesize single crystals of oxide superconductors at low temperature. The study has focused on the synthesis of superconducting cuprates and copper-less oxides by means of electrochemical method. The study consists of three projects ;1. Synthesis and characterization of transport properties of Ba_<1-x>K_xBiO_3 crystals with various compositions.2. Synthesis and characterization of single crystal of superconducting cuprates.3. Search of new copper-less superconducting oxides.The results of the projects are as follows ;Project 1 : Transport properties of the material have been revealed by means of precise resistivity and Hall-effect measurements for the crystal with wide range of composition. It is shown, in particular, that the transport property correlates strongly to the changes in the crystallographic phase and that the composition including oxygen affects to the superconductivity. In addition, band scheme of Ba_<1-x>K_xBiO_ … More 3 has been characterized directly by X-ray absorption measurement in the collaboration with Dept.of Science, Tokyo Univ..Project 2 : Crystals of the La_2CuO_<4+delta> and Nd_<2-x>Ce_xCuO_4 systems have been successfully grown, and it is shown that the electrochemical method is a unique method for the crystal growth of superconducting cuprates. In particular, La_2CuO_<4+delta> shows superconductivity in as-grown state without any heat treatment in high pressure oxygen, and it is revealed that the crystals grown by the electrochemical method contain enough oxygen to show superconductivity.Project 2 : Synthesis of oxides containing Nb, Mo, and Ru has been performed. Crystals such as BaRuO_3 have been successfully grown, and characterization of their properties is in progress.In addition to the projects, we developed new "Electrolysis-cell method" for the synthesis of oxide crystals. In this method electromotive force appeared at the elettrodes is used for the crystal growht. The method was applied to the synthesis of Ba_<1-x>K_xBiO_3 crystal, and it is confirmed that high quality crystals can be grown by the method. Less