Wellenfelder in Interdigitalwandlern und ihre Abstrahlung
Fortschritte der Akustik – DAGA96 DEGA (1996) 434-435
The replacement of [HgO2 ]2- by the tetrahedral sulfate anion [SO4 ]2- in the Hg-1201 superconductor
Journal of Solid State Chemistry 121:1 (1996) 66-73
Abstract:
The possibility of existence of a Hg1-xSxBa2CuO4+2x+δ solid solution [(Hg, S)-1201] was studied at 18 kbar and 920°C. Monophasic samples were obtained in the range 0.00 ≤ x ≤ 0.15, where the unit cell parameters were found to vary from a = 3.8685(1) Å, c = 9.4667(2) Å for x = 0.00 to a = 3.9010(1) Å and c = 9.3048(6) Å for x = 0.15. Samples with x ≥ 0.20 were polyphasic and the unit cell parameters of the [(Hg, S)-1201] phases were found to vary up to a = 3.9072(1) Å, c = 9.2654(5) Å for a nominal composition x = 0.30. The as-prepared phases with 0.00 ≤ x ≤ 0.05 were found to be nonsuperconducting due to overdoping, while superconductivity appeared at x = 0.10 (Tc,onset = 40 K). Tc increases with the amount of sulfate substitution due to the decrease of the average copper valence. For the annealed samples, the variation is opposite to that found for the as-prepared samples, Tc,onset being higher for the sulfur-free phase. Rietveld refinements of neutron powder diffraction data has determined ≈18% of the HgO2-2 dumbbells to be substituted by SO2-4 groups. In this structure the SO2-4 anion adopts an average S-O bond length that is slightly higher than those in BaSO4. © 1996 Academic Press, Inc.A new monoclinic perovskite allotype in Pr0.6 Sr0.4 MnO3
Journal of Solid State Chemistry 127:2 (1996) 276-282
Abstract:
We report the observation, in Pr0.6Sr0.4MnO3, of a low-temperature phase transition between Pnma and the monoclinic space group I2/a. The I2/a allotype has never previously been observed in the (R1-xAx)MnO3 manganese perovskite system. Furthermore, this space group symmetry is not present in the recently published phase diagram obtained at 30% Mn+4, indicating that electronic doping has a direct effect on the phase stability. The structural and magnetic parameters for the new phase, as obtained from Rietveld refinements of neutron powder diffraction data, are also reported. © 1996 Academic Press.Structural phase diagram of Perovskite A 0.7 A′ 0.3 MnO 3 (A = La, Pr; A′ = Ca, Sr, Ba): A new Imma allotype
Journal of Solid State Chemistry 122:2 (1996) 444-447
Abstract:
The structural phase diagram of A 1-x A′ x MnO 3 (A = La, Pr, Y, ...; A′ = Ca, Sr, Ba, ...) as a function of the average A-site ionic radius 〈r A 〉 was determined from neutron powder diffraction data. In addition to the well-known Pnma and R3̄c phases, a new orthorhombic phase, with space group Imma, was found for large 〈r A 〉 at low temperatures. Refined structural parameters are reported for La 0.7 Ba 0.3 MnO 3 at 1.6 K (Imma) and at 293 K (R3̄c). The Imma → R3̄c phase transition was studied as a function of temperature for the same La 0.7 Ba 0.3 MnO 3 sample, and determined to be first order. © 1996 Academic Press, Inc.Lattice effects on the magnetoresistance in doped manganese perovskites
JOURNAL OF APPLIED PHYSICS 79:8 (1996) 4541-4541