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。最初设计并制造了一种新型高压装置。它可以在4.2K到400K的低温和高达8 gpa的压力下工作。研究了高温氧化物超导体的电学和磁特性，包括霍尔效应。研究发现，许多含尖氧的铜氧化物的超导转变温度随压力的增大而增大，而某些不含尖氧的铜氧化物的超导转变温度几乎不受压力的影响。结果表明，顶端氧影响的电子态对高tc超导性起重要作用。在压力下对有机超导体β -(BEDT - ttf)_2I_3中的上层结构进行了x射线衍射测量。发现上层建筑的波矢在100K以下变短。当花足够长的时间使不相称波矢量变短时，超导临界温度至少提高到7K。研究了静水压力对石墨这种典型的低维材料的磁致电子相变的影响。压力效应是通过将转变温度、费米能量的压力依赖性和态密度纳入类bcs表达式来解释的。利用高压技术研究了三维过渡金属和稀土金属及其化合物的磁性和电学性质。三维过渡金属和合金中异常小的体模量可以很好地理解为磁贡献提供了二次依赖于磁能的局部磁矩振幅。对含有Yb或Ce原子的重费米子化合物进行了电阻率测量。得到了它们的磁性和导电性与压力关系的一些基本数据。

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.