Measurements of the electrical resistivity of U1-xThxBe13 compounds as a function of pressure provide a possible explanation for the unusual behavior of these materials. © 1988.

Resistivity of (Th, U)Be13 under pressure may show the restoration of the onset of electron coherence. Unseparated rare earth elements can be used for preparation of high-Tc superconductors. © 1987.

We have determined the effect of pressure P on the resistance and superconducting transition temperature Tc of RBa2Cu3Ox (R=Gd,Er,andYb) and compare our results to those obtained on high-quality YBa2Cu3Ox. The transition temperature, which is 90 K or greater at ambient pressure for all four compounds, is enhanced by pressure in each at rates between 0.09 and 0.19 K/kbar. Interestingly, the presence of a localized moment in the rare-earth compounds appears to have no influence on the pressure response. From the positive dTcdP we infer a positive change in the thermal expansion upon entering the superconducting state. © 1987 The American Physical Society.

We have studied the x-ray-absorption near-edge spectra of EuBa2(Cu1-yZny)3O7 as a function of Zn and O content. There is clear evidence for the development of Cu1+ ions as the O content is reduced to levels sufficient to suppress superconductivity. However, there is no effect on the electronic state of the Cu ion as the Zn content is increased and superconductivity vanishes. We tentatively conclude that the suppression of superconductivity is in both cases due to the preferred occupancy of certain planes by nonmagnetic (filled d subshell) atoms, as proposed in YBa2Cu3O6 on the basis of neutron scattering. © 1988 The American Physical Society.

We report electrical resistance and magnetoresistance measurements on EuBa2(Cu1-yZny)3Ox under pressures to 17 kbar. With Zn substitution, Tc is depressed rapidly (∼19 K/ at.% Zn) and there are qualitative changes in the temperature and field response of the resistance. Pressure drives the Zn-substituted samples toward undoped EuBa2Cu3Ox behavior. Analysis of the temperature dependent resistance for y=0.05 and P=0, together with Hall effect and thermopower data, suggests that the suppression of superconductivity may arise from weak three-dimensional localization promoted by Coulomb interactions. © 1987.