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

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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.