A systematic study of the phase stability of La(Pr)2-x-yRxSr(Ba, Ca)yCuO4 (R = rare earth) compounds reveals a broad composition range for T*-phase formation. Several members of this series of compounds show bulk superconducting transition temperatures up to Tc ∼ 20 K. These superconducting cuprates raise further questions about the relationship between structural stability and high temperature superconductivity in oxides. © 1989 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division).

Specific-heat and dc magnetic-susceptibility measurements have been performed on RBa2Cu3Ox (R denotes rare earth) compounds. These measurements show that the rare-earth atoms behave as local moments above the superconducting transition temperature of these compounds which can be as high or higher than in nonmagnetic YBa2Cu3Ox. Further, we find coexistence of superconductivity and magnetism in R=Gd,Er,andDy compounds and evidence for crystalline-electric-field splittings in these materials. © 1987 The American Physical Society.

The T{star, open}-phase is a mixed rare earth oxide phase forming at the composition R2CuO4. Its crystal structure is intermediate between the La2CuO4 and Nd2CuO4 structures. Sr-doped samples have Tc onsets as high as 37 K. We discuss the systematics of Tc of T{star, open}-phases as a function of Sr doping, rare earth mixture and oxygenation. Structural and transport data will also be presented. © 1989.

High-pressure (3 kbar) oxygenation of (La, Sm, Sr)2CuO4 compounds having the T* structure leads to bulk superconducting transitions above 30 K and the appearance of a diamagnetic response at temperatures as high as 1/437 K. With increasing oxygenation pressure, the electrical resistivity and thermoelectric power progress from hoppinglike to more nearly metalliclike transport. The similarity in Tc and transport character with those of T-phase La2-xSrxCuO4, despite significant structural differences, further constrains possible mechanisms for superconductivity in the cuprates. © 1989 The American Physical Society.

Precise measurements of the Knight shift at Cu(1) (chain) and Cu(2) (plane) sites have been made in the normal state of a YBa2Cu3O7 powder sample, for which the c axis of each grain has been aligned in a magnetic field. By combining these data with the Knight shift data in the superconducting state and the anisotropic magnetic susceptibility, it is shown that (1) the anisotropy of the magnetic susceptibility is mainly due to the orbital moment of the 3d electrons, (2) the magnitude of the spin contribution to the Knight shift is similar at both sites, and (3) the isotropic part of the Cu hyperfine field is large and positive (112 kOe/B). © 1989 The American Physical Society.

Properties of the hole-type, single-layer cuprate T*-phase superconductors are discussed. There is a strong variation of Tc with rare-earth constituent and oxygenation pressure. The magnetic properties of these materials have not yet been well investigated, but some aspects of the rare-earth ordering appear to be different from other known cuprates. © 1991.

Resistivity, thermoelectric power, Hall effect, and magnetic susceptibility measurements are reported in the normal state of the high-Tc compounds YBa2Cu3O7-y and GdBa2Cu3O7-y. The results are different from those expected for an uncorrelated metallic band. We suggest that Coulomb interactions are important and that the interaction energy is comparable to or larger than the uncorrelated bandwidth, leading to moderately heavy-fermion-like behavior in the normal state. The Sommerfeld coefficient calculated from the susceptibility indicates that the electron-phonon coupling constant at Tc is not unusually large. © 1987 The American Physical Society.