[en] M_r=142.10, trigonal, P31c, a=5.129, c=8.639 A, V=196.82 A³, Z=2, D_x=2.397 g cm^-3, λ(neutron)=1.176 A, μ_c=0.74 cm^-1, T=200 K. Refinement for the ordered structure with 593 reflections with (sinθ)/λ ≤ 0.57 A^-1 gave R(F²)=0.055. The study has revealed merohedral twinning of the crystal about (110), with twin components in nearly equal proportion, and large thermal vibration for the oxygens. Displacing the oxygens into three disordered positions gave somewhat better R factor. (orig.)

[en] The crystallographic and magnetic structures of H₂Fe_17-xAl_xC(x=4 and 7) were investigated by powder neutron diffraction at room temperature. The results indicate that both compositions are isostructural with Th₂Zn₁₇ (space group, R3m). Aluminium substitutes for iron in three of the four Fe sites (18h, 18f and 6c in the hexagonal description of the rhombohedral cell) but not in 9d, and the fractional occupancies have been determined for both compositions. The carbon atoms occupy 9e sites. The saturation magnetization and Curie temperatures of samples with x in the range 0-7 are given; in the room-temperature magnetic structure of the phase with x=4 the magnetic moments of all the atoms lie in the plane perpendicular to the 3 axis, with the Fe moments being ferrimagnetically coupled to those of Ho. (author)

[en] The crystal structure of the high-T/sub c/ superconductor Ba₂YCu₃O/sub 7+//sub x/ has been studied using neutron diffraction. This compound has an orthorhombic structure with space group Pmmm and lattice parameters a = 3.8132 A, b = 3.8774 A, and c = 11.653 A. We found an occupancy of 0.1 for oxygen atoms at the 1b site and a total number of oxygen atoms per unit cell of 7.1. The high quality of the sample used may be associated with the partial occupation at the 1b site by oxygen atoms

[en] The magnetic properties of YBa₂Cu₃O/sub z/ with different values of z in the temperature range 1.5--300 K were measured and compared with those of DyBa₂Cu₃O/sub z/ and EuBa₂Cu₃O/sub z/. The susceptibility data of YBa₂Cu₃O/sub z/ and DyBa₂Cu₃O/sub z/ followed the Curie--Weiss law above T/sub c/, while those of EuBa₂Cu₃O/sub z/ exhibited the Van Vleck and Frank behavior [Phys. Rev. 34, 1494 (1929)] with σ = 33. The paramagnetism persisted even below T/sub c/. The effective moment per copper ion increased as the oxygen content decreased. The results suggest that the paramagnetism in YBa₂Cu₃O/sub z/ originates mainly from the nonsuperconducting domains of the material which have disordered oxygen vacancies or have lower oxygen content than the superconducting ones

[en] The crystal structure of the high-T/sub c/ superconductor Ba₂YCu₃O/sub 7+//sub x/ at 124 and 71 K was refined by Rietveld analysis of neutron diffraction data. We found that at 124 and 71 K the structure is of the same space group Pmmm, but when the temperature is decreased and passes the critical temperature T/sub c/, 0.12 of the oxygen population on the one 1e site transfers to the 1b site. This remarkable change in the structure can be related to its superconductivity

[en] The crystal structure of the high-T/sub c/ superconductor Ba₂YCu₃O/sub x/ at 750 ⁰C was elucidated using Rietveld analysis of neutron powder diffraction data. We find that the phase is tetragonal at this temperature, with space group P4/mmm, and lattice constants a = 3.8823 A and c = 11.826 A. This is an oxygen deficient triperovskite, in which Ba and Y ions are ordered along the c axes in Ba-Y-Ba-Ba sequence. The occupation factors of the oxygen sites 4i, 2g, 2f are 0.97, 1.00, 0.33, respectively. The total number of the oxygen atoms per unit cell is 6.54

[en] YBa₂(Cu/sub 1-x/Fe/sub x/)₃O₇ compounds for 0 less than or equal to x less than or equal to 0.30 show a continuous orthorhombic-tetragonal phase transition at x approx. 0.05. Both the diagmagnetic onset temperature T/sub c/ and the effective iron moment decrease with increasing x. Coexistence of antiferromagnetism and superconductivity is observed only for x=0.10 and 0.12 as determined by magnetic-susceptibility measurements. The antiferromgnetic order may result from the Ruderman-Kittel-Kasuya-Yosida interaction

[en] Two samples of NdBa₂Cu₃O/sub 7+//sub x/ with zero-resistance transition temperatures of 85 K (x = 0.06) and 90 K (x = 0.18), respectively, were studied by using neutron-diffraction powder profile analysis. The compounds crystallize in the same orthorhombic, oxygen-deficient perovskite structure with space group Pmmm, in which both 1e(0,(1/2,0) and 1b((1/2,0,0) sites are occupied partially by oxygen atoms, with a majority of atoms being located in the 1e sites. The final refinements converge to weighted profile R factors, R/sub wp/, of 7.05% and 7.58% for the 90- and 85-K samples, respectively. The significant differences between the two samples are the oxygen content and the regular changes of all the Cu-O bond distances in the structures

[en] The generalized phonon density of states for the high-T_c superconductor YBa₂Cu₃O_7.1 with high Meissner effect (50%) and for its retreated sample with low Meissner effect (15%) at T=300 K and T=86 K respectively was measured by using inelastic neutron scattering method. The density of states of the superconductor YBa₂Cu₃O_7.1 at temperatures of both 300 K and 86 K shows a similar energy spectrum below 95 meV. However, above this energy there are evident softening of modes at 86 K. In addition, a large decrease of 92 meV peak in the density of states for a sample with lower Meissner effect was observed, this effect is supposed to be a result of an increase of vacancies on O₄ site

[en] Short communications only