I.G. Muttik

The new family of complex copper oxides with possible superconducting properties: Pb2Sr2R1.33Ce0.67Cu3O10+δ

Abstract The new family of complex copper oxides Pb 2 Sr 2 R 1.33 Ce 0.67 Cu 3 O 10+δ ( R = La - Tm ) has been prepared. These compounds have two crystal structure types with different values of δ, which depend on the synthesizing conditions (partial oxygen pressure). The crystal structure models for the Sm-containing phases with δ =-0.2 and 1.7 have been determined on the basis of X-ray powder diffraction. The structures of these compounds are closely related to the structure of the known high- T c oxides Pb 2 Sr 2 R 0.5 Ca 0.5 Cu 3 O 8+δ but differ from them by the existence of flourite-like (R 1.33 Ce 0.67 O 2 ) blocks instead of the (Y 0.5 Ca 0.5 □) sheets which divide the (CuO 2 ) sheets. All these compounds are semiconductors on the basis of magnetization and resistivity measurements, but Eu-containing samples which were prepared in a nitrogen atmosphere exhibited a superconducting transition at 24 K with a relatively small volume of the superconducting phase (

New complex oxides in RBaThCuO systems (R = LaGd)

Abstract The new complex oxides R2Ba1.33Th0.67Cu3O8+δ (R = La, Pr) and La0.67Ba1.33R2−xThxCu3O8+δ (R = NdGd, x = 0.5, 0.67) were synthesized. These compounds have a similar structure to the Ce-223 high-Tc oxides. The oxygen content (or δ) was varied over a wide range after annealing at high oxygen pressure (up to 90 atm). Unit cell parameters and δ values for all the new phases were determined. The resistivities of these semiconducting compounds obey the law ϱ = ϱoT−α. A single crystal of Nd2Ba1.5Th0.5Cu3−xAlxO8+δ (x = 0.3, δ = 0.8) was obtained and its structure was determined by X-ray single-crystal experiment (tetragonal system, space group I4 mmm , a = 3.9057(5) A, c = 28.569(4) A, Z = 2).

New ternary superconducting germanides

Abstract We have studied the structure, electrical and magnetic properties of new ternary compounds with germanium and transition metals of IV and V groups (Ti 0.7 V 0.3 Ge 3 , Hf 2 V 3 Ge, Zr 32–36 V 32–36 Ge 30–32 , Hf 2 Nb 3 Ge 4 , HfVGe, Zr 15–17 V 39–40 Ge 44–45 , Hf 10.8–21.7 V 36.0–42.8 ). The homogeneity fields for all new phases are determined. Resistivity (T) and magnetic susceptibility χ(T) are investigated at T=4.2…300 K. Two new superconductors have been found — Zr 32–36 V 32–36 Ge 30–32 and HfVGe with T c =4.7 K and 5.7 K, respectively.

Particularities of the structure and oxygen stoichiometry in YBa2(Cu1- xFex)3O7−y

Abstract The oxygen stoichiometry, unit cell parameters and resistivity of YBa 2 (Cu 1−x Fe x ) 3 )O 7−y (x=0–0.08 samples were studied. The model of oxygen rearrangement explaining the observed effects of doping by Fe was proposed.

Metal-insulator transition in La3Ba3Cu6O14+y compounds

Abstract Resistivity at 4.2–300 K and crystal structure of La3Ba3Cu6O14+y with different oxygen content have been studied. Correlation between structure and superconductivity is analyzed. The metal-insulator transition induced by the change of oxygen content has been found. In the vicinity of the metal-insulator transition (EF≈Ec) conductivity is a linear function of T in a very wide temperature range.

Superconductivity in AgYBa2Cu3O7−y composites

Abstract The Ag YBa2Cu3O7−y composites with the different Ag-volume fraction x were studied. The critical current density jc of the Ag2O-based material decreases with x. For Ag-based material the maximum of the jc(x)_dependence at x∼20% seems to be caused by a larger sample density. Measurements of the current-voltage characteristics and the effect of magnetic field on the critical current show that the silver addition changes the type of the intergrain links.