A. I. Goldman

Synthesis and characterization of ceramic (Sr1−xCax)2 CuO3

Ceramic (Sr{sub 1{minus}{ital x}}Ca{sub {ital x}}){sub 2}CuO{sub 3} samples have been prepared with {ital x}=0.00, 0.25, 0.50, 0.55, 0.75, and 1.00 in order to study the change in lattice constants with the ratio of Sr/Ca. This phase is frequently an impurity phase in the fabrication of Bi--Sr--Ca--Cu--O superconductors, and it is important to be able to connect the lattice constants with stoichiometry. The behavior of the lattice constants closely follows Vegards law.

An approximant to the Al--Cu--Ru icosahedral phase

The crystal structure and space group of an approximant phase to the face-centered icosahedral (FCI) phase in the Al--Cu--Ru system is reported. The crystal structure is simple cubic, with [ital a]=12.38 A. The space group has been determined to be [ital Pm][bar 3], which is the same space group as [alpha][minus]AlMnSi, an approximant to the simple-icosahedral (SI) phase. With isostructural phases, the SI and FCI alloys in Al-transition metals also are structurally similar. We also report the crystal structure and space group of a tetragonal phase which is apparently not an approximant phase.

Dynamical properties of the AlPdMn icosahedral phase

Abstract A centimetre-sized single grain of the perfect AlPdMn icosahedral phase can be grown by slow cooling from the liquid. This phase has been shown to have perfect icosahedral symmetry, i.e. without any frozen phason strain. The dynamical properties of this icosahedral phase have been studied by mean of inelastic measurements on triple axis spectrometers. The dispersion relations around several Bragg reflections were measured. Pseudo-zone boundaries can be defined, similarly to those previously obtained in the AlLiCu phase. A dispersionless optic mode was identified around 4 THz.

Crystallization of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ superconducting filaments produced by gas-jet fiberization

X-ray diffraction and differential thermal analysis techniques have been used to investigate the recrystallization products obtained from various heat treatments of glassy Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ filaments produced by the gas-jet fiberization process. In both Pb-doped and Pb-free samples, the 85 K superconducting phase appears after the formation of a disordered Bi/sub 2/Sr/sub 2/Cu/sub 2/O/sub x/-like intermediate phase at lower temperature. The c-lattice parameter of this phase is substantially smaller than the published values for Bi/sub 2/Sr/sub 2/Cu/sub 2/O/sub x/ and increases as the temperature of the heat treatment increases. After heat treatment at 600 degrees C, a Pb-rich second phase is found together with the 2201-like intermediate phase in the Pb-doped material.

Environmental contamination of amorphous Bi-Sr-Ca-Cu-O fibers

A study of the environmental contamination of amorphous YBa2Cu3O7-δ fibers has been undertaken in order to determine the best method to handle these materials during the fabrication of superconducting wire. The fibers often need to be handled in organic solvents as part of the cleaning and manipulating process. In organics that are free of water, the fibers retain their mechanical strength with little carbon contamination or other ill effects. Water, however, causes premature crystallization and destroys the mechanical strength of the fibers.

Dynamics of the AlPdMn icosahedral phase

Dynamics of the icosahedral phase AlPdMn has been investigated with a centimetre size single grain and using inelastic neutron scattering measurements. Well defined acoustic modes have been observed close to strong Bragg reflections. Phonons broaden significantly as wavevectors exceed 0.35 A−1. Broad (1 THz) dispersionles excitations also show up with energies close to 1.8, 3.4 and 5.8 THz, some of them being associated to crossing with quasi-Brillouin zone boundaries.