Professor Paolo G. Radaelli OSI

Abstract:

A cuprate superconductor containing double mercury layers was synthesized with a high-pressure, high-temperature technique. The compound, with chemical formula Hg(2)Ba(2)-Y1-xCaxCu(2)O(8-delta), contains a double HgO layer with structure similar to that of rock salt. The prototype compound Hg(2)Ba(2)YCu(2)O(8-delta) is an insulator. Superconductivity is induced in the system by partially replacing yttrium with calcium.

Abstract:

63Cu(1) NQR signals and their relaxation have been measured in YBa2Cu3O6.1 and ErBa2Cu3O6+x at temperatures between 10 K and 300 K. In YBa2Cu3O6.1 a peak is observed in the spin-lattice relaxation, T1-1, around 140 K. An explanation in terms of doped-hole motion is presented and alternative O(4)-O(5) diffusion mechanisms are critically discussed. In ErBa2Cu3O6+x the low-temparature T1-1 is dominated by magnetic fluctuations of Er; quantitative agreement is found when the correct ground state and magnetic dynamic properties of the rare earth are taken into account. © 1994.

Abstract:

The crystal structures of superconducting HgBa2CuO4+δ and HgBa2CaCu2O6+δ have been investigated with a pressure up to 0.6 GPa and HgBa2Ca2Cu3O8+δ to 9.2 GPa by neutron powder diffraction. The compressibility along the c-axis is nearly the same for the three compounds and up to two times larger than the compressibility along the a-axis. The one-layer compound, HgBa2CuO4+δ, shows the largest a-axis compressibility, while HgBa2Ca2Cu3O4+δ shows the smallest compressibility. The bond compressibilities of HgBa2CuO4+δ and HgBa2CaCu2O6+δ are significantly different from HgBa2Ca2Cu3O8+δ bond compressibilities. In the one- and two-layer compounds the largest bond compressibility was the Cu-O2 (apical) bond distance, while for the three-layer compound it was the Hg-O2 bond distance. © 1994.