Professor Paolo G. Radaelli OSI

Abstract:

The phase diagram of the title system is remarkably rich, exhibiting regions of long-range antiferromagnetic order, short-range (spin-glass-like) order, high temperature superconductivity, or none of these. Here, the phase diagram is reviewed, with an emphasis on our recent studies using 139La NQR, powder and single crystal neutron diffraction, and magnetization measurements for 0≤χ≤0.15 and 0≤δ≤0.1. © 1994.

Abstract:

Herein, we review the magnetic, superconducting and structural phase diagrams of the title systems, with an emphasis on our recent results form magnetic and structural neutron diffraction, magnetic susceptibility and system, and indicate the occurrence of frustrated phase separation on a nanoscopic length scale in the La2-xSrxCuO4 system with O < x ≲ 0.05. 139La nuclear quadrupole resonance measurements. The results clarify the miscibility gap in the La2CuO4+δ. © 1994.

Abstract:

We have extended the calcium solid-solubility limit in La2-xCaxCuO4 to x = 0.2 using synthesis at high oxygen pressure. The superconducting transition temperature increases with doping to 34 K at x = 0.15 and is suppressed for x > 0.15, similar to the Sr-substituted material. At a fixed doping level, the optimum superconducting properties (the highest Tc) are found for flat and square CuO2 planes. © 1994.

Abstract:

The first cuprate superconductor containing double (HgO)2 layers was synthesized using a high-pressure, high-temperature technique. The compound, with chemical formula Hg2Ba2Y1-xCaxCu2O 8-δ, contains a rock salt-type double HgO layer. The prototype compound Hg2Ba2YCu2O8-δ is an insulator. Superconductivity is induced in the system by partially replacing yttrium with calcium. © 1994.

Abstract:

We have studied the 1:2:4 phase of the YBaCuO compound by means of tunneling spectroscopy on single crystal based junctions. The crystals, with Tc≈80 K, have been chemically etched before the deposition of the counterelectrode in form of a thin film through a metallic mask. We have compared the tunneling spectra to those obtained on the Y123 system. The features at ±20 mV of the 1:2:3 phase are still observed in the 1:2:4 phase, while the low bias features at ±5 mV are not present in the tunneling characteristics of the Y124 compound. The experimental results are discussed in terms of the different CuO chain role in the Y123 and Y124 systems. © 1994.