Study of crystal structures and physical properties in high pressure induced phases at low temperature

本项目取得的突出成果如下：1.首次设计和制造了一种新型的高压装置。它工作在4.2K到400K的低温和高达8 GPa2的压力下。研究了高T_c氧化物超导体的电学和分段磁学性质，包括霍尔效应。许多具有尖端氧的铜氧化物的超导转变温度随压力的增加而显著升高，而对于一些没有尖端氧的氧化物，其超导转变温度几乎不依赖于压力。结果表明，尖端氧影响的电子态对HIGT超导电性起着重要作用。在有机超导体β-(BEDT-TTf)_2I_3中对超结构进行了加压X射线衍射测量，发现超结构的波矢在100K以下变短。当用足够长的时间使无公度波矢变短时，超导临界温度至少提高到7K。研究了静水压力对低维材料石墨中磁场诱导电子相变的影响。通过在类BCS的相变温度、费米能量和态密度的压力依赖关系的表达式中考虑了压力效应。用高压技术研究了3d相变和稀土金属及其化合物的磁性和电学性质。3d过渡金属和合金中反常的小体模可以用磁贡献来很好地理解，它与磁能的局域磁矩的幅度成二次依赖关系。测量了含Yb或Ce原子的重费米子化合物的电阻率。得到了它们的磁性和导电性随压力变化的基本数据。

The outstanding results obtained by this project were as follows.1. A new type of high pressure apparatus was originally designed and made. It works at low temperatures from 4.2K to 400K and at pressures as high as 8 GPa.2. Electrical and segnetic properties including Hall effect were investigated in high-Tc oxide superconductors. The superconducting transition temperature of many copper oxides having apical oxygens was found to increase strongly with pressure, whereas it hardly depends on pressure in case of some oxides without apical oxygens. It is suggested that the electronic states affected by the apical oxygen play an essential role on the hihg-Tc super-conductivity.3. X-ray dffraction measurements of the superstructure were made under pressure in the organic superconductor beta-(BEDT -TTF)_2I_3. The wave vector of the superstructure was found to become short below about 100K. The superconducting critical temperature is raised at least up to 7K when a sufficiently long time is spent to allow the incommensurate wave vector become short.4. The effect of hydrostatic pressure was studied on the magnetic-field-induced electronic phase transition in graphite which is one of typical low dimensional materials. The pressure effect is accounted for by incorporating in the BCS-like expression for the transition temperature, the pressure dependences of the Fermi energy and the density of state.5. Magnetic and electrical properties of 3d-transition and rare-earth metals and compounds were investigated by means of high pressure techniques. The anomalously small bulk modulus in 3d-transition metals and alloys can be well understood in terms of the magnetic contributions provided a quadratic dependence on the amplitude of local magnetic moments of the magnetic energy. Electrical resistivity measurements were made on the heavy fermion compounds containing Yb or Ce atoms. Some fundamental data were obtained on the pressure dependence of their magnetism and conductivity.