One Dimensional Oxygen Ordering in YBa2Cu3O(7-delta)

A model consisting of oxygen-occupied and -vacant chains is considered, with repulsive first and second nearest-neighbor interactions V1 and V2, respectively. The statistical mechanics and the diffraction spectrum of the model is solved exactly and analytically with the only assumption V1 >> V2. At temperatures T ~ V1 only a broad maximum at (1/2,0,0) is present, while for ABS(delta - 1/2) > 1/14 at low enough T, the peak splits into two. The simple expression for the diffraction intensity obtained for T << V1 represents in a more compact form previous results of Khachaturyan and Morris[1],extends them to all delta and T/V2 and leads to a good agreement with experiment. [1] A.G.Khachaturyan and J.W.Morris, Jr., Phys.Rev.Lett. 64,76(1990)Comment: 13 pages,Revtex,3 figures available upon request but can be plotted using simple analytical functions,CNEA-CAB 92/04

Magnetism and the absence of superconductivity in the praseodymium–silicon system doped with carbon and boron

We searched for new structural, magnetic and superconductivity phases in the Pr-Si system using high-pressure high-temperature and arc melting syntheses. Both high and low Si concentration areas of the phase diagram were explored. Although a similar approach in the La-Si system produced new stable superconducting phases, in the Pr-Si system we did not find any new superconductors. At low Si concentrations, the arc-melted samples were doped with C or B. It was found that addition of C gave rise to multiple previously unknown ferromagnetic phases. Furthermore, X-ray refinement of the undoped samples confirmed the existence of the so far elusive Pr3Si 2 phase. © 2013 Elsevier B.V

Solution-combustion synthesis and study of ?-Fe2-xCr xO3 (0.75 ? x ? 1.25) maghemite-like materials

Maghemite-like materials containing Fe3+ and Cr3+ in comparable amounts have been prepared for the first time by a special method: the so-called solution-combustion synthesis (SCS). In this communication the conditions of synthesis, the powder X-Ray structural characterization, thermal analysis and the magnetic properties are described. These materials are ferrimagnetic and are much more stable than pure maghemite since the maghemite-hematite transformation takes place at about ?700 �C instead of ?300 �C as usually reported. � 2009 Materials Research Society

A computer simulation study of lithium diffusion in the 123 and 124 superconductors

Atomistic computer modelling has been applied to the structure of the YBCO family of superconductors, and the diffusion profiles of Li+ ions through the barium channels. The calculated structures agree well with the experimental data for both the 123 and 124 structures. However a slight modification to the 124 structure is suggested which we believe is consistent with experimental evidence. The calculated activation energy for Li+ diffusion approximate to 0.8eV in the 124 agrees well with experimental measurements. An hypothesis is suggested for the difficulty encountered in synthesising the 125 structure

Solution-combustion synthesis and study of γ-Fe2-xCr xO3 (0.75 ≤ x ≤ 1.25) maghemite-like materials

Maghemite-like materials containing Fe3+ and Cr3+ in comparable amounts have been prepared for the first time by a special method: the so-called solution-combustion synthesis (SCS). In this communication the conditions of synthesis, the powder X-Ray structural characterization, thermal analysis and the magnetic properties are described. These materials are ferrimagnetic and are much more stable than pure maghemite since the maghemite-hematite transformation takes place at about ∼700 °C instead of ∼300 °C as usually reported. © 2009 Materials Research Society