Yoshihiro Kusano

Segregation and dissolution reactions of the 2223 phase in the Bi, Pb-Sr-Ca-Cu-O system on annealing in air

Abstract Thermal behavior of the Pb-substituted Bi-2223 phase was examined by characterizing samples annealed at 500°C to 850°C in air and also those subsequently reheated at 850°C in air by XRD, SEM and magnetic measurements. Very interesting reactions occurred, which were segregation of precipitates on annealing below 830°C and dissolution of the precipitates on subsequent reheating at 850°C into the 2223 phase. The precipitates were identified as Sr 2.5 Bi 0.5 Pb 3 Ca 2 CuO 2 . The precipitation and the dissolution were clearly confirmed by morphological observations of a fixed portion of a sample before and after heat treatments. These results strongly suggest that the 2223 phase changes its composition reversibly between the relatively Pb-rich composition stabilized above 850°C and relatively Pb-poor ones stabilized in essentially the same structure below 830°C. However, T c remained almost constant at 113 K.

Microstructure and Magnetic Behaviour of Nanosized Fe3O4 Powders and Polycrystalline Films

Summary.u2002The object of investigation were the magnetic interactions in nanostructured Fe3O4 assemblies of two kinds (powder and film) where particles of similar size present nearly uniform domains in a close to planar arrangement with spacings sufficient for magnetic interactions. We discuss the use of the soft-chemistry method, i.e. the modified ‘ferrite plating’ (MFP) technique, for the synthesis of polycrystalline films of magnetite with nanosized crystallites.

A new tetragonal phase in La-rich Pr2-xLaxCuO4 (1.35 < x < 1.5)

Comprehensive X-ray diffraction study on the sub-solidus phase diagram in Pr 6 O 11 -La 2 O 3 -CuO system firstly revealed a new phase of Pr 2-x La x CuO 4 for 1.35 < x < 1.5. The phase has a tetragonal symmetry similar to the well-known T-type structure (0 < x < 0.9). However, the lattice constants of both a and c are clearly distinct between the two tetragonal phases. The new phase coexists with the T-phase for 0.9 < x < 1.3 and with the orthorhombic T-phase for 1.5 < x < 1.6. The sintered pellet of the new phase instantly transforms into fine powder (∼10 μm) upon cooling from synthesized temperature to room temperature without any compositional phase separation.

Refinement and re-formation of the Bi-2223 phase

Abstract Refining behavior of the Pb-substituted Bi-2223 phase through mechanical grinding and thermal behavior of its ground powder on heating in air have been examined for samples with a nominal composition of Bi 1.8 Pb 0.4 Sr 2 Ca 2 Cu 3.2 O z by XRD, DTA, SEM, TEM, ED and magnetic measurements. The 2223 phase easily changes into superfine powder by mechanical grinding. On annealing the ground powder below 800°C, various second phases were formed, while at 850°C the 2223 phase was reformed depending upon the amount of the superfine powder in the samples.