Preparation of conducting In-based copper oxide by annealing under high pressure

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By annealing InBa_2CuO_4.44 in oxygen at a pressure of 60MPa, a new conducting cuprate InBa_2CuO_4.54 with having a- and c-axis lengths of 4.190A and 8.363A was formed. Its crystal structure was refined by the X-ray Rietveld analysis method. The factors R_wp, R_e, and S were 9.11%, 9.12%, and 1.0, respectively, indicating that the refined structure is an appropriate one. There were four distinct differences between InBa_2CuO_4.44 and InBa_2CuO_4.54. The first was an increase in the oxygen occupancy in the CuO_2 plane; the oxygen occupancy in the CuO_2 plane increased from 26.5% to 27%. The second was a drastic increase in the c-axis length from 8.09A to 8.36A . The third was the inter-substitution of In and Cu. About 35% of In and Cu atoms were substituted each other in the InBa_2CuO_4.54. The fourth was a drastic decrease in the electrical resistivity; the resistivity at room temperature decreased from 28.8MΩcm to 90.3kΩcm. These differences are discussed in connection with the oxygen content in the InBa_2CuO_y.　PACS 74.72.Jt　　key words: CuO_2 layer, Cu valence, high pressure synthesis, nBa_2CuO_y, oxygen content, tetragonal phase, orthorhombic phase,
2007-02-15