Structure Of Y1 Research Articles

Structure of Y0.75La0.25PO4·0.67H2O rhabdophane nanoparticles synthesized by the hydrothermal microwave method

Nanopowders with a rhabdophane structure of nominal composition Y0.75La0.25PO4·0.67H2O were obtained by hydrothermal-microwave synthesis. The monoclinic structure of rhabdophane was refined by the Rietveld method within the C2 (5) space group. The nanopowders were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron microdiffraction (selected area electron diffraction, SAED), small angle X-ray scattering (SAXS), thermal analysis, low-temperature nitrogen adsorption-desorption measurements for analysis of surface area and porosity (ASAP) and pycnometric density measurements. These methods showed the formation of rod-like single-crystal rhabdophane nanoparticles with isolated pores inside the nanoparticles. To describe the formation of such nanoparticles, a mechanism of coherent-accommodative intergrowth of nanoscale clusters with rhabdophane structure is proposed.

Synthesis and characterization of the novel rare earth orthophosphates Y0.5Er0.5PO4and Y0.5Yb0.5PO4

AbstractThe new mixed rare earth (RE) orthophosphates Y0.5Er0.5PO4and Y0.5Yb0.5PO4were synthesized by a classical solid state reaction in an electrical furnace at 1200 °C. As starting materials, the corresponding rare earth oxides and diammonium hydrogen phosphate were used. The powder diffraction analyses revealed that the new compounds Y0.5Er0.5PO4and Y0.5Yb0.5PO4crystallize in a zircon-type structure being isostructural with the rare earth orthophosphate YPO4. Y0.5Er0.5PO4and Y0.5Yb0.5PO4crystallize in the tetragonal space groupI41/amd(no. 141) with four formula units in the unit cell. The structural parameters based on Rietveld refinements area= 687.27(2),c= 601.50(2) pm,V= 0.28412(1) nm3,Rp= 0.0143, andRwp= 0.0186 (all data) for Y0.5Er0.5PO4anda= 684.61(2),c= 599.31(2) pm,V= 0.28089(2) nm3,Rp= 0.0242, andRwp= 0.0313 (all data) for Y0.5Yb0.5PO4. Furthermore, the structure of Y0.5Er0.5PO4was refined from single-crystal X-ray diffraction data:a= 687.78(5),c= 601.85(4) pm,V= 0.28470(5) nm3,R1= 0.0165, andwR2= 0.0385 (all data). In both compounds, the rare earth metal ions are eightfold coordinated by oxygen atoms, forming two unique interlocking tetrahedra with two individualRE–O distances. The tetrahedral phosphate groups [PO4]3–are slightly distorted in both compounds. The individual rare earth ions share a common position (Wyckoff site 4a). The presence of two rare earth ions in the structures of the new orthophosphates Y0.5Er0.5PO4and Y0.5Yb0.5PO4was additionally confirmed by single-crystal EDX spectroscopy revealing a ratio of 1:1.

Anomalies of the Y1 − x Ca x Ba2Cu3O y crystal structure in the temperature range 80–300 K

The effect of doping on the temperature evolution of the crystal structure of the YBa2Cu3Oy high-temperature superconductor has been investigated. The crystal structure of Y1 − xCaxBa2Cu3Oy (x = 0, 0.1; y = 6.6, 6.8, 6.95) has been studied using the full-profile analysis with X-ray powder diffraction data in the temperature range 100–300K. The unit cell parameters, the bond lengths, and the calculated linear and volume coefficients of thermal expansion are characterized by a nonmonotonic behavior in the temperature range ∼160–225 K. Samples with the oxygen content y = 6.6–6.8 in both systems (with x = 0 and 0.1) have negative linear coefficients of thermal expansion at low temperatures. A possible reason for the anomalous behavior can be the change in the state of the electronic subsystem. The data analysis confirms that the doping mechanisms upon oxygen introduction, and when Y is substituted for Ca are different.

Structural study of the pseudobinary Y(Ni,Cu)2 system

The pseudobinary Y(Ni1−xCux)2 compounds have been investigated by X-ray and neutron diffraction, density measurements as well as with electron probe microanalysis. The goal was to understand the mechanism behind the structural change from the cubic structure of Y0.95Ni2 (a cubic superstructure of the cubic Laves phase with ordered vacancies on the Y site) into the orthorhombic CeCu2 type structure of YCu2. 20% of Cu can be substituted for Ni in Y0.95Ni2 accompanied by an increase of the number of Y vacancies in the cubic superstructure. On the Cu-rich side a solid solution was found from YCu2 to Y(Ni0.5Cu0.5)2. The substitution for Ni in the orthorhombic structure mainly causes a decrease of the lattice parameter a, giving rise to a 3.5% contraction of the unit cell volume. These two solid solutions are separated by a two-phase region. The thermal expansion among the cubic compounds hardly changes with the Cu concentration, whereas it increases in the orthorhombic range towards YCu2.

Mössbauer Investigation of Eu3+ Site Occupancy and Eu-O Covalency in Y2O3 and Gd2O3 Nanocrystals

Abstract Samples of nanocrystalline Y1.8Eu0.2O3 and Gd1.8Eu0.2O3 were examined by 151Eu Mössbauer spectroscopy. The degree of covalency of the Eu-O bond has been studied. The spectrum of the cubic Y1.8Eu0.2O3 sample has been resolved into 2 contributions due to europium in the C3i and C2 sites, for the first time in 151Eu Mössbauer spectroscopy. The degree of covalency and the electric field gradient of the 2 sites has been compared. The occupancy, by the lanthanide ion, of the more and less symmetric sites in the cubic structure of Y1.8Eu0.2O3 has been investigated and discussed.

Crystal structure of Y0.95Ca0.05CuO2.54: A new oxygen-deficient perovskite chemically and structurally related to the “123” superconductor

The crystal structure of Y0.95Ca0.05CuO2.54(1) has been determined by neutron powder diffraction at room temperature. The compound crystallizes with the symmetry of the hexagonal space group P63/m and lattice parameters a=6.1991(2), c=11.2059(3) A. The configuration of the atoms in the unit cell may be alternatively described as an AgFeO2-type structure with extra oxygen atoms in the copper plane, or as an oxygen-deficient perovskite of general formula ABO3-x (x=0.46) chemically and structurally related to the “123” superconductor oxide. In the unit cell the sequence of layers is …[(Y3O6 )( Cu2.43O1.62+Cu0.57 )( Y3O6 )( Cu2.43O1.62+Cu0.57 )]… . The yttrium and calcium atoms are mixed over three symmetrically independent sites. The coordination number of Y/Ca atoms is seven. The defective layer can be derived from a defective perovskite layer BO2 in which rows of oxygen atoms are interleaved with double rows of oxygen vacancies, giving an oxygen stoichiometry of O2.67. The shifts of the oxygen atoms from their original perovskite positions and the hexagonal distortion of the lattice result in tetrahedral coordination around each Cu atom. The additional oxygen vacancies in the copper layers necessary to reduce the oxygen stoichiometry to O2.54 are assumed to be randomly distributed.

Structure of Y0.95Ni2 and its hybride

The structures of Y 0.95 Ni 2 and its deuteride Y 0.95 Ni 2 D 2.6 are studied by X-ray and neutron powder diffraction analyses. Both compounds can be described in a cubic cell eight times larger than the C 15 cell, with yttrium vacancies on the 4a site in the F 4̄3 m space group. Addition of deuterium leads to a 16% cell volume increase and a reordering of the yttrium vacancies. 88% of the deuterium atoms are located in five A 2 B 2 sites.

Crystal structure of Y0.9Ba2.1Cu3O6, a compound related to the high-Tc superconductor YBa2Cu3O7

The crystal structure of the high-temperature superconductor YBa2Cu3O7 is derived from the ideal perovskite (YBa2Cu3O9) structure by the presence of ordered vacancies in the oxygen sublattice. Owing to the ordering of these vacancies, the coordination polyhedra around the copper cations are either pyramids or slightly distorted squares1–5; the one-dimensional character and the orthorhombic symmetry of the structure are due to the existence of the squares. We have synthesized single crystals of the further-reduced compound Y0.9Ba2.1Cu3O6, and we report here a structural determination using single-crystal X-ray diffraction data. Y0.9Ba2.1Cu3O6 has a tetragonal oxygen-deficient perovskite structure related to that of YBa2Cu3O7. The additional oxygen vacancies transform the CuO4 squares into O–Cu–O linear bonds, while the pyramids are not affected. As Y0.9Ba2.1Cu3O6 does not exhibit any superconducting transition down to 4.2 K, we conclude that the chains of CuO4 squares are essential for the superconductivity mechanism.