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As members of the ABO3 family of oxides, the Ln4Cu3MoO12 family of compounds (LnLa, Pr, Nd, and Sm) all crystallize in the rare-earth hexagonal structure at ambient pressure. At 6 GPa and 1200 K they transform to layered perovskite structures which are ∼ 15% more dense than their ambient pressure variants. The high-pressure phases exhibit two-dimensional antiferromagnetic ordering above 200 K, which is indicative of pure copper-oxygen layers. The lanthanum analogue can be doped with up to 25% strontium, (La/Sr)4Cu3MoO12. A large decrease in resistivity is observed with doping but the compound does not become metallic or superconducting.

We have prepared pure YBCO (YBa 2 Cu 3 O 7− δ ) and Ni-doped YBCO (YBa 2− x La x Cu 3− x Ni x O 7− δ , x =0.1) samples and performed 63,65 Cu nuclear quadrupole resonance (NQR) measurements. La substitution introduced for charge compensation, as well as Ni doping, severely distorts the electric field gradient at the copper sites inducing extra 63,65 Cu NQR peaks other than the main peaks, for both the plane and the chain sites. 63,65 Cu NQR linewidths for the plane site increased significantly whereas those for the chain site remained similar. Furthermore, both the spin–lattice and the spin–spin relaxation times for the plane copper decreased whereas those for the chain copper increased. The Ni substitutional effects on linewidths and relaxation times confirm that Ni carrying a local moment substitutes for the plane copper.

Synthesis of the CuSr 2 YCu 2 O 7 compounds with Re, W and Mo substituted for Cu has been optimized for the highest T c . Materials prepared in air at 990°C and annealed at 650–700°C in 220 atm. O 2 are tetragonal with the transition elements substituting on the Cu-“chain” site, have oxygen content ∼ 7.3, and are superconducting with T c ∼ 70 K. The irreversibility lines show rather poor pinning characteristics when compared to Y123. Superconducting T c values were increased up to 77 K by additional substitution of small amounts of Ca for Y. Based on a.c. susceptibility and d.c. magnetization measurements, Ca substitution improves superconducting properties making chemically stabilized CuSr 2 YCu 2 O 7 materials interesting for high field applications below 30 K.

The band structure of La 2 CuSnO 6 in both its real and idealized crystal structure was determined using the local density full-potential linearized muffin-tin orbital (LMTO) method. Unlike the case for all other high- T c copper-based materials, the Fermi energy for the undoped crystal is located exactly on the van Hove saddle-point singularity, which may be the main reason for the lattice distortions observed in the real material. We suggest that a possible way, if any, to drive this compound into the superconducting state is to be achieved via electron doping. For several reasons, we do not expect a high T c value.

Crystals of REBa 2 Cu 4 O 8 (RE = Yb, Tm, Er, Ho, Dy, and Y 1− x Ca x ) were grown at 1100°C and 600 bar of O 2 pressure in a hot isostatic press furnace. Single crystal X-ray diffraction data show that all compounds crystallized in space group Ammm (#65) with the approximate lattice parameters a ≈ 3.82 A , b ≈ 3.86 A , c ≈ 27.1 A , and Z = 2 As the ionic radius of the lanthanide decreased, the lattice parameters decreased. Substitution of calcium in Y 1− x Ca x Ba 2 Cu 4 O 8 crystals ( x ∼ 0.02) increased T c to 87 K.

The microstructure of Ca doped Y 1− x Ca x Sr 2 Cu 2 GaO 7 and Ca substituted YSr 2− x Ca x Cu 2 GaO 7 have been investigated by electron microscopy. A common feature found in the Y 1− x Ca x Sr 2 Cu 2 GaO 7 superconductors is the existence of line defects, which are not observed in non-superconducting YSr 2− x Ca x Cu 2 GaO 7 . At the higher doping level, x ≈ 0.35, the line defects develop into modulated structures. The transition temperature and Meissner fraction increases with the doping level as does the defect concentration, indicating that the defects and superconductivity in these materials are interrelated. The line defects are associated with an asymmetrical distortion ( a p ≠ b p ) of the gallium-oxygen plane which plays a similar role to the copper-oxygen chains in YBa 2 Cu 3 O 7−° .

The variation in the average and local structure of the superconductor family Y 1− x Ca x Sr 2 Cu 2 GaO 7 as calcium is substituted for yttrium ( x = 0.20, 0.35, and 0.40) is presented and discussed. Electron microscopy and X-ray diffraction were the primary techniques employed. The local structure found by the use of electron microscopy and X-ray diffraction agrees with that previously derived from single crystal X-ray and neutron diffraction. The gallate can be confused with the three layer perovskite structure of YBCO (YBa 2 Cu 3 O 7 ) because of the similarity of [011] Ga ≈[100] YBCO and [010] Ga ≈[110] YBCO zones. However, the composition of all crystals examined were homogeneous on a 10–100 nm scale. It was also found that the twin structure varied as a function of the calcium content.

The anisotropic susceptibility of YBa 2 Cu 3 O x (6.46⪕ x ⪕6.98) has been measured as a function of oxygen composition. Samples were prepared by a high temperature zirconium-getter annealing technique followed by magnetic orientation in epoxy. The normal state magnetic susceptibility was found to be weakly dependent on temperature. The room temperature values of the susceptibility decrease linearly as the oxygen composition decreases, whereas the difference in susceptibilities for magnetic fields parallel and perpendicular to the c -axis is nearly constant. This suggests that in this range of oxygen composition the susceptibility anisotropy comes mostly from the anisotropic part of the Van Vleck susceptibility and the spin susceptibility remains nearly isotropic. Neutron diffraction results show a significant oxygen occupancy at the O(5) site. Nuclear quadrupolar and magnetic resonance spectra of the plane copper indicate a marked degree of electronic disorder, confirming that there are microscopic structural effects from the high temperature zirconium-getter annealing procedure.

A new homologous series of layered “pure” perovskites (ACuO 2.5 ) 2 (ARiO 3 ) m ( m = ∼ 4) was found. The distance between CuO 2 planes can be changed by simply changing the number of TiO 6 blocking layers. Among them, LaYCaBa 2 Cu 2 Ti 3 O 14 is a potential new superconductor.

The synthesis of layered cuprates with single and double octahedral SnO and TiO layers has been achieved.

The synthesis of layered cuprates with nonmagnetic and fixed oxidation state cations separating CuO planes has, until now, led to nonsuperconducting materials. Recently we were able to introduce superconductivity in YSrCuGaO system by appropriate doping and annealing.