Magnetic susceptibility and neutron diffraction measurements prove the 3D rather than the 2D or 1D character of magnetic interactions in Bi2CuO4. It has been shown that, at TN=44.6+or-0.3 K, Bi2CuO4 undergoes a transition to an antiferromagnetic state. The magnetic unit cell coincides with the chemical cell (k=0) and is of type I. The value of magnetic moment is either (0.53+or-0.1) mu B or (0.75+or-0.1) mu B depending on whether the magnetic moments are oriented parallel or perpendicular, respectively, to the c axis. The effective magnetic moment of the Cu2+ ion is (1.80+or-0.2) mu B. The results of theoretical susceptibility calculations for the BCT lattice model and for the SQ lattice model together with the molecular-field interactions have been presented and compared with the experiment.

Abstract. Phase relations in the Bi,O,SrO-CuO system at 800°C are presented. Several binary and ternary phases existing within this system have been identified and characterised by x-ray powder diffraction and denslty and overall oxygen content determination. Among them, particular 'A' and 'B' phases (both of variable composition) represent potential interest from the point of view of superconductivity. Evidence of the actual stoichiometry of the 2201-type superconductor (T, = 9-20 K) and of the most probable distribution of structural component atoms within its elementary unit subcell is given. A new interpretation of the general formula for the Bi-based superconducting cuprates has been proposed.

No abstract

Analytical explanation of an unexpected behaviour of sample densities is given. Three different types of construction of the investigated solid solutions have been recognised: normal for Z=constant versus increasing contribution of Sr substituent (X); atom-deficient for Z decreasing with X; atom-overcrowded for Z increasing with X. The mechanism of mutual transformation of the 2201-type matrix to that of the 2212-type is proposed.

The domains of existence of the 2201- and 2202-type structures in solid solutions of the Bi2O3-SrO-CaO-CuO quaternary system are investigated from the powder X-ray diffraction, density and resistive transition measurements. It is shown that the general formula of Torardi (1988) should not be identified as describing fixed stoichiometry of Bi-based compounds but as a code according to which the unit cells are to be constructed. The authors have also shown that the composition of the investigated phases can vary within some region of homogeneity. The 2201-type structure acts as a matrix for the formulation of new phases by addition of some quantities of calcium and copper, which are known as 80 K and 110 K superconductors. The influence of oxygen on the properties of Bi-based compounds is also evaluated.