Development of New High-Tc Superconductors with Record-High Tc by Synthesis under High Oxygen Pressures

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In this study project which continued for 2 years, synthesis of new high-TィイD2cィエD2 superconductors with record-high TィイD2cィエD2 have been attempted by applying heat-treatments under very high oxygen pressures. The main apparatus introduced in this study was an electric furnace equipped with high oxygen pressure generating system. Using this apparatus, high oxygen pressure up to 50MPa was achieved. The mercury-based system was adopted as a candidate mother material for new superconducting compounds, because of its high TィイD2cィエD2. However, all the various attempts of chemical substitution for this system have been failed in terms of a new record-high TィイD2cィエD2. The obtained highest TィイD2cィエD2 was as high as 135K, which is only a tie-record. On the other hand, new material research was continued for other systems and a new iron-based superconductor was discovered. Its chemical composition was FeSrィイD22ィエD2RECuィイD22ィエD2OィイD2yィエD2 (RE : rare earth element). It was found that partial substitution of iron for copper was suppressed by annealing under moderately reducing conditions, resulting in appearance of superconductivity after annealing under high oxygen pressures, 〜40MPa Its TィイD2cィエD2 is approximately 60K at the present stage, however, further increase will be achieved by optimization of synthesis procedures and conditions. It should be noted that this new TィイD2cィエD2 material is the first compound which contains 3d transition metal other than copper as a main constituent metal element. Therefore, the present discovery is believed to give a new guiding principle for material design of new high-TィイD2cィエD2 superconductors as well as exotic magnetic compounds.