High-pressure synthesis of SeCu1-xZnxO3 perovskites

The SeCu1-xZnxO3 solid solution, with a distorted perovskite-type structure, has been synthesized under high pressures and temperatures. X-ray diffraction analysis indicates that the zinc ions occupy the copper sites, a solid solution being formed. It seems that high-pressure stabilises a small cation such as Se4+ in the A site of the perovskite structure ABO(3) although the material is better described as formed by selenite anions SeO(3) over bar and Cu2+/Zn2+ cations

Crystal chemistry and magnetic properties of SeCu1-xZnxO3 (0-<= x <= 1) perovskites

The effects of zinc substitution in the structural and magnetic properties of the orthorhombic solid solution SeCu1-xZnxO3 have been studied. Rietveld refinements of the X-ray diffraction patterns indicate that the zinc ions occupy the copper sites. This replacement induces some changes in the Cu-O bond lengths and [Cu-O-Cu] bond angles. Magnetization vs temperature measurements show a fast decrease in the Weiss constant that reveals a direct quadratic relationship with the increase of the average [Cu-O-Cu] bond angle. Besides, the introduction of a non-magnetic cation in the B-positions in the structure of SeCu1-xZnO3 system, progressively decreases the ferromagnetic interactions. (C) 2002 Elsevier Science (USA)

The effect of Mn substitution on the structure and magnetic properties of Se(Cu1-xMnx)O-3 solid solution

The effects of Mn substitution on the structure and magnetic properties of the SeMO3 (M = Cu1-xMnx) solid solution have been studied. Rietveld refinements of the x-ray diffraction patterns of these samples indicate that the manganese ions occupy copper sites. This replacement induces significant changes in the M-O bond lengths that give rise to abrupt decreases of the [M-O-6] octahedral distortion. In contrast, the M-O(1)-M and M-O(2)-M bond angles remain essentially constant. The magnetic behaviour of this solid solution was studied in the temperature range of 2 K < T < 300 K. The temperature dependence of the inverse magnetic susceptibility is well described by the Curie-Weiss law at high temperatures, in the composition range studied. We found that the substitution of Mn for Cu induces a sharp drop in the saturation moment of SeCuO3. At about 10% of Mn there is a change from positive to negative Weiss constant theta(W) that is mainly due to the [M-O-6] octahedral distortion introduced by the substitution of the larger Mn ions in the structure. The M-H isotherms show a weak ferromagnetism at about 52 K in SeMnO3

Modulated Fluorite-Type Structure of Materials from the (1-x) Y_0.5Zr_0.5O_1.75 - x Y_0.75Nb_0.25O_1.75 (0£x£ 1) System

The microstructures of different high-temperature prepared oxides of the (1-x)Y0.5Zr0.5O1.75-xY(0.75)Nb(0.25)O(1.75) (0 less than or equal to x less than or equal to 1) system have been studied by selected-area electron diffraction and high-resolution transmission electron microscopy. The materials show a modulated fluorite-type structure mainly due to a partial or short-range ordering of the oxygen vacancies. The modulation is related to the pyrochlore-type structure in the Y0.75Nb0.25O1.75 A short-range ordering of the oxygen vacancies related to the C-type structure is observed in the Y0.5Zr0.5O1.75. Gradual transition from the pyrochlore to the C-type structures is established with the variation of the composition.</p

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