Single Crystals of HgBa₂Ca_n-1Cu_nO_x and Chain Compounds A_1-xCuO₂ (A=Sr, Ca, Ba), High Pressure Synthesis and Properties

High gas pressure up to 11 kbar has been applied for the synthesis and single crystal growth of Hg-based superconductors and one-dimensional A1-xCuO2 cuprates. We have investigated the influence of Re, Sr and Pb substitutions and oxygen content on the magnetic flux-pinning properties of single crystals of Hg-based superconductors. The best results have been obtained for Sr and Pb substituted Hg1223 single crystals. Susceptibility, neutron scattering, and torque investigations have been performed on Ca0.83CuO2, Sr0.73CuO2 and Ba0.67CuO2 compounds containing CuO2 infinite chains separated by Ca, Sr or Ba layers.