BiCaIrO Pyrochlore Phases: Structure and Properties with Varied Ir Oxidation State from 3.9+ to 4.3.

Pyrochlore phases BiCaIrOO with x from 0.0 to 1.0 have been evaluated based on Rietveld analysis of neutron diffraction data, electrical resistivity and thermopower data from 3 to 756 K, and magnetic susceptibility data from 3 to 298 K.

From Serendipity to Rational Design: Tuning the Blue Trigonal Bipyramidal Mn Chromophore to Violet and Purple through Application of Chemical Pressure.

We recently reported that an allowed d-d transition of trigonal bipyramidal (TBP) Mn is responsible for the bright blue color in the YInMnO solid solution. The crystal field splitting between a'(d) and e'(d, d) energy levels is very sensitive to the apical Mn-O distance. We therefore applied chemical pressure to compress the apical Mn-O distance in YInMnO, move the allowed d-d transition to higher energy, and thereby tune the color from blue to violet/purple.

Influence of Structural Disorder on Hollandites A(x)Ru4O8 (A(+) = K, Rb, Rb(1-x)Na(x)).

Structural disorder can play an important role in the electrical properties of correlated materials. In this work we examine the average and local disorder in hollandites A(x)Ru4O8 (A(+) = K, Rb, Rb(1-x)Na(x)) through neutron total scattering techniques. Samples with A(+) = Rb, Rb(1-x)Na(x) exhibit the largest amount of local disorder as evidenced by higher atomic displacement parameters, and as a result, a weakened temperature dependence of the resistivity is observed upon cooling as compared to K(x)Ru4O8.

Structure and Properties of Ir-Containing Oxides with Large Spin-Orbit Coupling: Ba2In(2-x)Ir(x)O(5+δ).

In this work, the solid solution series Ba2In(2-x)Ir(x)O5+δ (x = 0-1.4, 2) was synthesized, and its structural, magnetic, and charge-transport properties were measured. With increasing Ir content, three transitions in the room-temperature structure were observed: orthorhombic to tetragonal to cubic to a monoclinic distortion of a hexagonal BaTiO3 structure.

True composition and structure of hexagonal "YAlO3", actually Y3Al3O8CO3.

The discovery of a brilliant-blue color upon the introduction of Mn(3+) to the trigonal-bipyramidal (TBP) sites in YInO(3) has led to a search for other hosts for Mn(3+) in TBP coordination. An obvious choice would be YAlO(3). This compound, which has only been prepared through a citrate precursor route, has long been considered isostructural with YInO(3).

Structural investigation of the substituted pyrochlore AgSbO3 through total scattering techniques.

Polycrystalline samples of the pyrochlore series Ag(1-x)M(n)(x)SbO(3+x[(n-1)/2]) (M = Na, K, and Tl) have been structurally analyzed through total scattering techniques. The upper limits of x obtained were 0.05 for Na, 0.

Intense turquoise and green colors in brownmillerite-type oxides based on Mn5+ in Ba2In(2-x)Mn(x)O(5+x).

Brownmillerite-type oxides Ba(2)In(2-x)Mn(x)O(5+x) (x = 0.1-0.7) have been prepared and characterized.

New layered compounds with honeycomb ordering: Li3Ni2BiO6, Li3NiM'BiO6 (M' = Mg, Cu, Zn), and the delafossite Ag3Ni2BiO6.

The new layered compound Li(3)Ni(2)BiO(6) has been prepared by a solid-state reaction. It crystallizes in the monoclinic C2/m space group; its lamellar structure is characterized by a honeycomb ordering between Ni(2+) and Bi(5+) within the slabs, while Li(+) ions occupy octahedral sites in the interslab space. Stacking defects weakly alter the XRD pattern.

Undulating layers in a new rhodate network: structure of Bi(1.4)CuORh5O10.

A new rhodate, Bi(1.4)CuRh(5)O(11), with an hitherto unknown channel structure containing undulating layers of RhO(6) octahedra sharing corners and edges has been discovered and its structure refined from single crystal X-ray diffraction data. The channels contain Bi(3+), Cu(2+), and some O strongly bound to Cu.

CsTe2O(6-x): novel mixed-valence tellurium oxides with framework-deficient pyrochlore-related structure.

Structures of CsTe₂O(6-x) phases were investigated by single-crystal X-ray diffraction and neutron powder diffraction. Stoichiometric CsTe₂O₆ is a mixed-valence Cs₂Te⁴⁺Te₃⁶⁺O₁₂ compound with a rhombohedral pyrochlore-type structure where there is complete order of Te⁴⁺ and Te⁶⁺. On heating, this compound develops significant electrical conductivity.

New oxides showing an intense orange color based on Fe3+ in trigonal-bipyramidal coordination.

Hexagonal YIn(1-x)Fe(x)O(3) phases have been prepared and characterized. The coordination for the In/Fe site in this structure is trigonal-bipyramidal. The colors of the phases change from yellow to orange to dark red with increasing Fe content.

Structural studies and electrical properties of Cs/Al/Te/O phases with the pyrochlore structure.

A series of polycrystalline and single crystal cesium aluminum tellurates with the pyrochlore structure have been prepared and characterized. The variations in cell edge for the Cs/Al/Te/O phases range from 10.06 Å for the Al rich limit to 10.

New oxides showing an intense blue color based on Mn3+ in trigonal-bipyramidal coordination.

Substitution of Mn(3+) into the trigonal-bipyramidal sites of oxides with YbFe(2)O(4)-related structures produces an intense blue color because of an allowed d-d transition. This has been demonstrated utilizing a variety of hosts including ScAlMgO(4), ScGaMgO(4), LuGaMgO(4), ScGaZnO(4), LuGaZnO(4), and LuGaO(3)(ZnO)(2). The hue of the blue color can be controlled by the choice of the host.

Mn3+ in trigonal bipyramidal coordination: a new blue chromophore.

We show that trivalent manganese, Mn(3+), imparts an intense blue color to oxides when it is introduced at dilution in trigonal bipyramidal coordination. Our optical measurements and first-principles density functional theory calculations indicate that the blue color results from an intense absorption in the red/green region. This absorption is due in turn to a symmetry-allowed optical transition between the valence-band maximum, composed of Mn 3d(x(2)-y(2),xy) states strongly hybridized with O 2p(x,y) states, and the narrow Mn 3d(z(2))-based conduction-band minimum.

Tin(II) doped anatase (TiO2) nanoparticles: a potential route to "greener" yellow pigments.

During our exploration of compounds in the Sn(II)-Ti(IV)-O system, we discovered that hydrolysis of titanium alkoxide solution in the presence of Sn(II) salts resulted in stable deep-yellow colored anatase nanoparticles. The samples were characterized by X-ray powder diffraction, electron microprobe, thermal analysis, transmission electron microscopy, and (119)Sn Mössbauer spectroscopy. Mössbauer data of the yellow colored samples showed the presence of both Sn(II) and Sn(IV) in a distorted environment as expected in the anatase structure.

New A2/3-xRh2O4 compounds with the CaFe2O4 structure where A is a rare earth or Bi.

New compounds of the type R(2/3-x)Rh(2)O(4) with the CaFe(2)O(4) structure have been prepared, where R is a rare earth. For crystals grown in a Bi/V/O flux, the rare earth was partially replaced by Bi. No evidence of ordering of the A cation vacancies is found, but the A cations are displaced from the ideal A cation site by about 0.

Structural investigation of the negative-thermal-expansion material ZrW2O8.

High-resolution powder diffraction data have been recorded on cubic ZrW(2)O(8) [a = 9.18000 (3) Å at 2 K] at 260 temperatures from 2 to 520 K in 2 K steps. These data have confirmed that alpha-ZrW(2)O(8) has a negative coefficient of thermal expansion, alpha = -9.

Compressibility, Phase Transitions, and Oxygen Migration in Zirconium Tungstate, ZrW2O8.

In situ neutron diffraction experiments show that at pressures above 2 kilobars, cubic zirconium tungstate (ZrW2O8) undergoes a quenchable phase transition to an orthorhombic phase, the structure of which has been solved from powder diffraction data. This phase transition can be reversed by heating at 393 kelvin and 1 atmosphere and involves the migration of oxygen atoms in the lattice. The high-pressure phase shows negative thermal expansion from 20 to 300 kelvin.

Colossal Magnetoresistance Without Mn3+/Mn4+ Double Exchange in the Stoichiometric Pyrochlore Tl2Mn2O7.

Structural analysis from powder neutron and single-crystal x-ray diffraction data for a sample of the Tl2Mn2O7 pyrochlore, which exhibits colossal magnetoresistance (CMR), shows no deviations from ideal stoichiometry. This analysis gives an Mn-O distance of 1.90 angstroms, which is significantly shorter than the Mn-O distances (1.

Unusual 180 degrees P-O-P Bond Angles in ZrP(2)O(7).

The structure of cubic ZrP(2)O(7) at room temperature has been solved and refined using a combination of modeling and high-resolution neutron powder diffraction data. The cell edge is 24.74 Å, the space group is Pa&thremacr;, and Z is 108.