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摘要: 本文采用超高氧压2.3 GPa合成方法，得到超导相含量大于30%的超导化合物La2CuO4+所采用的压力是目前所见报导中对La2CuO4化合物施加的最高氧压。湿化学方法测量给出过量氧含量=0.050.01，而TGA（氮气中）给出=0.143。高氧压合成产物经在空气中、不同温度下加热，然后淬火到室温，结果发现超导体在200~300 ℃的加热处理中存在着一个一级相变。经此相变后，超导体转变成反铁磁半导体。TGA及DSC证实了此相变的存在。该相变前后所联系的氧含量变化恰好为湿化学方法给出的结果，这部分与超导电性存在联系的过量氧，实际上引起了Cu2+向Cu(2+2)+的转变。该结果强有力地排除了所谓超氧化物引起超导电性的可能性。Abstract: In this paper, La2CuO4+ compound with superconducting phase content over 30%, has been obtained by using high oxygen pressure 2.3 PGa techniques, which is the highest oxygen pressure exerted so far on the La2CuO4. It is noteworthy that the excess oxygen content determined by iodimetric titration (=0.050.01) is not consistent with that determined by TGA (in N2, =0.143). The product obtained by high oxygen pressure is heated in air at different temperatures, then quenched to room temperature. The superconductor shows a first order phase transition at temperatures between 200~300 ℃, and after this transition, the sample transformed to antiferromagnetic semiconductor. TGA and DSC also confirm the presence of this transition. The variation in the oxygen content before and after the phase transition just matches the value obtained by titration. These excess oxygen, which is responsible for the superconductivity, leads to a transformation from Cu2+ to Cu(2+2)+, and this rules out the possibility that the superconductivity is caused by superoxide.
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Key words:
- high oxygen pressure synthesis /
- La2CuO4+ /
- superconductivity /
- oxygen content /
- phase transition
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