High Pressure Crystal Growth and Properties of Hg-Based Superconductors and One-Dimensional A_(1-x)CuO_2 (A=Sr, Ca,Ba) Cuprates

摘要

High gas pressure up to 11 kbar has been applied for the synthesis of cuprates. Both single crystals and polycrystalline samples of Hg-based superconductors and quasi-one-dimensional A_(1-x)CuO_2 (A = Sr, Ca, Ba) compounds have been obtained. The influence of substitutions and oxygen content on the magnetic flux-pinning properties of single crystals of Hg-based superconductors has been investigated. The irreversibility field of almost optimally doped, unsubstituted BgBa_2Ca_2CuO_(8+#delta#) crystal (T_c = 130 K). As a result of Re substitution for Hg a significant improvement of the irreversibility line position for a Hg_(0.77)Re_(0.23)Ba_2Ca_2Cu_3O_(8+#delta#) crystal is observed only at low temperatures (below 80 K). Neutron irradiation of HgBa_2Ca_2Cu_3O_(8+#delta#) crystal enhances the flux pinning, while also leading to a decrease of the effective mass anisotropy. The magnetic properties of infinite-chain cuprates Ca_(0.83)CuO_2, Sr_(0.73)CuO_2 and Ba_(0.66)CuO_2 have been studied. Susceptibility measurements give some evidence for a singlet ground state. However, all these compounds order antiferromagnetically at T<10K. Specific heat, elastic neutron scattering of polycrystalline material and magnetic torque on single crystals have been measured. These measurements give clear evidence that the AF ordered state is of long-range 3D character.