[en] Single crystals of niobium-substituted α-Fe₂O₃ were grown by using chemical vapor transport with tellurium tetrachloride and were characterized by using bulk methods (X rays, resistivity, magnetism) and surface techniques (low-energy electron diffraction (LEED), Auger, X-ray photoelectron spectroscopy (XPS)). Niobium-substituted α-Fe₂O₃ crystallizes with the corundum structure, and is an extrinsic n-type semiconductor with a room temperature resistivity of approximately 85 Omega cm, and an activation energy for conductivity of 0.22 eV. Low-temperature susceptibility measurements suggest that the substitution of niobium(V) in octahedral sites leads to reduction of iron(III) to iron(II) without spinel phase inclusions. The main face of the single crystal platelets is the (001) basal plane of α-Fe₂O₃. The surface is very well ordered as shown by LEED. These crystals show good potential for application in both photoelectrochemistry and surface science studies. 23 references, 5 figures

[en] A new nine-coordination geometry has been discovered. Monazite-type compounds, such as LnPO₄ (Ln = La, Ce, Pr, Nd, Sm, Eu, and Gd), LnAsO₄ (Ln = La, Ce, Pr, and Nd), α-PbSeO₄, (Rooseveltite), BiPO₄, PbCrO₄ (Crocoite), α-PbSeO₄, LaVO₄, SrCrO₄, and ThSiO₄, exhibit this new nine-coordination geometry. The new geometric form is best described as a pentagonal interpenetrating tetrahedral polyhedron (PITP)

[en] Attempts have been made to prepare the solid-solution La/sub 1-x/Pb/sub x/Co/sub 1-x/O₃ for 0 < x < 1. X-ray diffraction indicates the formation of single-phase materials over the entire range. Compositions with 0 < x ≤ 0.20 are rhombohedral, those with x in the range 0.2 to 0.8 are cubic, and those with x ≥ 0.9 are tetragonal. Chemical analysis shows that all these samples are lead deficient. This is due to volatilization of PbO during preparation. Conduction is mainly due to 3d electrons of cobalt ions. All the samples except x = 0.05 show p-type conduction at and above 300 K. Samples with x ≥ 0.5 exhibit dielectric anomaly at a particular temperature which increases the increasing x

[en] Attempts to prepare and to characterize new catalysts belonging to the (V-P-Mo-O) system selective in the mild oxidation of butane or butene to maleic anhydride lead to the conclusion that molybdenum can be substituted up to 7% in VOPO₄ phases. Thermal analysis of the hydrated precursor, XRD, ESR spectroscopies, UV-visible and IR spectroscopies of both hydrated and anhydrous solid phases obtained show that the solid solutions isostructural with VOPO₄ 2H₂O and α₁-VOPO₄, respectively, can be formulated: [(VO)/sub 0.07/²⁺(VO)/sub 0.93/^3-(MoO₄)/sub 0.07/^2- nH₂O] (n = 1 to 2) and [(VO)/sub 0.93/³⁺(VO/sub 0.07/^3-(MoO₄)/sub 0.07/^2-]

[en] A wide variety of electropositive elements of the periodic table can be inserted into the vacant sites in the host framework structure of hexagonal NbTiP₃O₁₂ (an analog of nasicon) to give rise to isostructural phases. Synthesis, characterization, and preliminary data on the structure, IR spectra, and electrical resistivity are presented. Possible areas for further exploration are delineated

[en] Solid solutions of Bi₂O₃ and Nb₂O₅ encompassing the compositional range from pure Bi₂O₃ to 5Bi₂O₃ x 3Nb₂O₅ exhibit a range of complicated ordered structures which are extremely difficult to study by X-ray diffraction methods. High resolution electron microscopy, using previously outlined methodologies, has proved capable of elucidating the structural principles upon which the so-called Type III phase, with a composition of approximately 7Bi₂O₃ x 3Nb₂O₅, is based. The structure of this phase is a composite one, built up of limited fluorite, pyrochlore, and perovskite units

[en] Rb₂PuCl₆ and K₂PuCl₆ were prepared by heating mixtures of anhydrous PuCl₃ and the respective alkali metal chlorides under high Cl₂ pressures. Their crystal structures were determined by powder X-ray crystallography. Rb₂PuCl₆: hexagonal, space group P6₃mc, a = 7.377 +- 0.002, c = 11.880 +- 0.007 A, Z = 2, V = 279.9 +- 0.3 A³ (per formula), D/sub x/ = 3.69 gcm³. K₂PuCl₆: monoclinic, space group P2m, a = 7.218 +- 0.005, b = 7.611 +- 0.006, c = 10.208 +- 0.007 A, β = 91.59 +- 0.04⁰, Z = 2, V = 280.3 +- 0.3 A³ (per formula), D/sub x/ = 3.14 gcm³. The variable atom parameters were obtained by means of electrostatic calculation to have the maximum Madelung constant. Raman spectra showed two lines corresponding to v₁(A/sub 1g/) and v₅(F/sub 2g) for both compounds. The difference of stability in M₂PuCl₆ (M = K, Rb, Cs) is discussed

[en] The authors extend P.W. Anderson's idea of real-space pairing to correlated and hybridized systems. The pairing is provided by the antiferromagnetic exchange interaction between the electrons which form resonating hybrid bonds. In the solid state an ensemble of such pairs may condense into either superconducting or Kondu-lattice states

[en] Magnetic susceptibilities of Ca/sub y/U/sub 1-y/O/sub 2+x/ solid solutions with fluorite structure were measured from 4.2 K to room temperature. An antiferromagnetic transition was observed for all the solid solutions examined in this study (y ≤ 0.33). The Neel temperature of the oxygen-hypostoichiometric solid solutions (x < 0) decreased with increasing calcium concentration, which shows that magnetic dilution proceeds with calcium concentration. The variation of the Neel temperature with uranium concentration was similar to that of (U,Y)O₂ solid solutions, but different from that of (U,Th)O₂ solid solutions. The effective magnetic moment decreased with increasing calcium concentration, which indicates the oxidation of uranium in the solid solutions. From the analysis of the magnetic susceptibility data, it was found that the oxidation state of uranium was either tetravalent or pentavalent. The Neel temperature of the hyperstoichiometric solid solutions (x > 0) did not change appreciably with calcium concentrations. From the comparison of the magnetic susceptibility data of the hypostoichiometric solid solutions with those of the hyperstoichiometric solid solutions, the effect of oxygen vacancies is more significant than that of interstitial oxygens on the decrease of magnetic interactions between uranium ions

[en] A new process for the production of high surface area, high reactivity ceramic oxide powders involves the bonding of metal cations to polymeric polyacrylate chains. This process results in the formation of a gelatinous metal polyacrylate precipitate which can be easily removed from the mother liquor, and then calcined to form a high density ceramic oxide. Using FTIR spectroscopy, the nature of the structural arrangements has been studied for metal complexes in the yttrium, lanthanum, aluminum, cerium, copper, and iron polyacrylates. Interpretation of the infrared spectra indicates that two types of metal complex formation occur in these precipitates, involving bidentate or bridging interactions. The type that is observed for a particular metal ion is dependent on its metal ion size