[show abstract][hide abstract] ABSTRACT: Three new ternary copper phosphides, Sr(2)Cu(6)P(5), Eu(2)Cu(6)P(5), and EuCu(4)P(3), have been synthesized from the elements in evacuated silica capsules. Eu(2)Cu(6)P(5) and Sr(2)Cu(6)P(5) adopt the Ca(2)Cu(6)P(5)-type structure, while EuCu(4)P(3) is isostructural to BaMg(4)Si(3) and still remains the only representative of this structure type among the ternary Cu pnictides. All three materials show metallic conductivity in the temperature range 2 K ≤ T ≤ 290 K, with no indication for superconductivity. For Eu(2)Cu(6)P(5) and EuCu(4)P(3), long-range magnetic order was observed, governed by 4f local moments on the Eu atoms with predominant ferromagnetic interactions. While Eu(2)Cu(6)P(5) shows a single ferromagnetic transition at T(C) = 34 K, the magnetic behavior of EuCu(4)P(3) is more complex, giving rise to three consecutive magnetic phase transitions at 70, 43, and 18 K.
[show abstract][hide abstract] ABSTRACT: Polythermic studies of Bi2WO6–Bi2UO6 system revealed existence of a broad Bi2W1−xUxO6 solid solution with the Aurivillius-type structure. Below 750 °C, the homogeneity area is narrow (x ≤ 0.12) but extends significantly at higher temperatures (up to ca. 75% Bi2UO6 at 1025 °C). The solid solution retains orthorhombic symmetry over the entire compositional range, but substitution of U for W results in significant lowering of second harmonic intensity and Curie point suggesting, at high substitution degrees, a very close approach to the archetypic body-centered tetragonal centrosymmetric structure. The known Bi2WO6-based solid solutions are discussed in terms of thermal stability, and a general geometrical explanation is suggested. Incorporation of large cations into the B perovskitic positions of [Bi2O2][An−1BnO3n+1] Aurivillius structures seems yet to be restricted by the n = 1 case.Graphical abstract
[show abstract][hide abstract] ABSTRACT: A new synthetic approach is suggested for preparation of layered rare-earth oxide compounds containing [Ln2O2] slices and molecular anion sheets (CO32-, SO42-, and CrO42-). It is based on exchange reactions of rare-earth oxychlorides, [Ln2O2]Cl2, and alkali carbonates, sulfates, or chromates. Five new rare-earth oxychromates [Ln2O2]CrO4 (Ln=Pr-Gd) have been prepared which adopt a new, probably layered, structure type. In addition, significantly easier and more efficient synthetic pathways were found to the known compounds [Ln2O2]K2(CO3)2 and [La2O2]CrO4. The structure of the latter compound has been determined from neutron powder diffraction data. Factors affecting reaction pathways and products are discussed, as well as prospects for applying the approach to more complex layered compounds.
[show abstract][hide abstract] ABSTRACT: Several outstanding aspects of phase behaviour in the systems (Bi,Ln)2WO6 and (Bi,Ln)2MoO6 (Ln=lanthanide) have been clarified. Detailed crystal structures, from Rietveld refinement of powder neutron diffraction data, are provided for Bi1.8La0.2WO6 (L-Bi2WO6 type) and BiLaWO6, BiNdWO6, Bi0.7Yb1.3WO6 and Bi0.7Yb1.3WO6 (all H-Bi2WO6 type). Phase evolution within the solid solution Bi2−xLaxMoO6 has been re-examined, and a crossover from γ(H)-Bi2MoO6 type to γ-R2MoO6 type is observed at x∼1.2. A preliminary X-ray Rietveld refinement of the line phase BiNdMoO6 has confirmed the α-R2MoO6 type structure, with a possible partial ordering of Bi/Nd over the three crystallographically distinct R sites.
Journal of Solid State Chemistry 01/2006; 179(11):3437-3444. · 2.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: The oxyhalides Pb3TeO4X2 (X=ClX=Cl, Br, I) have been prepared from Pb3O2X2 and TeO2. All three compounds are isostructural and adopt the Nd2O2Te (PbBiO2I) structure type (I4/mI4/m, Z=1Z=1) according to single-crystal and powder X-ray and electron diffraction data. Contrary to previous results, the Pb/Te cation ordering was found to be nearly the same as Pb/I in schwartzembergite, Pb5IO4(OH)2Cl3 but not Pb/Sb in nadorite PbSbO2Cl. We discuss the factors affecting Pb/M cation ordering in layered (Sillén-type) multinary oxyhalides of lead.
[show abstract][hide abstract] ABSTRACT: The oxyhalides Pb3TeO4X2 (X=Cl, Br, I) have been prepared from Pb3O2X2 and TeO2. All three compounds are isostructural and adopt the Nd2O2Te (PbBiO2I) structure type (I4/m, Z=1) according to single-crystal and powder X-ray and electron diffraction data. Contrary to previous results, the Pb/Te cation ordering was found to be nearly the same as Pb/I in schwartzembergite, Pb5IO4(OH)2Cl3 but not Pb/Sb in nadorite PbSbO2Cl. We discuss the factors affecting Pb/M cation ordering in layered (Sillén-type) multinary oxyhalides of lead.
Solid State Sciences - SOLID STATE SCI. 01/2006; 8(9):1029-1034.
[show abstract][hide abstract] ABSTRACT: Three new bismuth oxyhalides, PbxBi2−xCuxO2X2 (X=Cl, x≈0.35–0.70; X=Br, x≈0.35–0.65; X=I, x≈0.35–0.55) have been predicted and synthesized from PbO, BiOX, and CuX. All three compounds adopt a very deficient LaOAgS (stuffed PbFCl) structure. Atomic parameters have been determined for Pb0.6Bi1.4Cu0.6O2Cl2 and Pb0.6Bi1.4Cu0.6O2Br2 (P4/nmm, Z=1) as well as for a structurally and compositionally related Pb0.6Bi1.4Cs0.6O2Br2 (I4/mmm, Z=2). Comparison of these structural data with bond distances and angles in related Pb0.6Bi1.4Q0.6O2X2 oxyhalides (Q=Rb, Cs, Tl; X=Cl, Br) reveals that replacement of CsCl-like [Q0.6X2] layers by anti-fluorite-like [Cu0.6X2] has a small effect on the Pb0.6Bi1.4–O and Pb0.6Bi1.4–X distances and a larger one on bond angles. We predict existence of isostructural compounds among multinary oxyhalides of bismuth and fluorohalides of lead. It is also likely that more complicated structures involving [CuxX2] layers can be realized.
Journal of Alloys and Compounds 01/2006; 413(1):40-45. · 2.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: The crystal structure of the Aurivillius phase Bi5TiNbWO15 has been analyzed in detail using powder X-ray and neutron diffraction. The structure can be described as a regular intergrowth of alternating single and double perovskite-like layers sandwiched between fluorite-like bismuth oxide layers, such that the layer sequence is … [WO4]–[Bi2O2]–[BiTiNbO7]–[Bi2O2] …. There is complete ordering of tungsten within the B sites of the single perovskite layer, so that the structure can be described as a direct intergrowth of the ‘component’ Aurivillius phases Bi2WO6 and Bi3TiNbO9. At 25°C the structure adopts the polar orthorhombic space group I2cm, a=5.4231(2)Å, b=5.4027(2)Å, c=41.744(1)Å.
Journal of Solid State Chemistry 01/2005; 178(1):180-184. · 2.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: Using various synthetic approaches, we have prepared over 50 new multinary bismuth oxyhalides which crystallize in four layered structure types. Most of the compounds belong to the three previously reported structure types involving fluorite- and CsCl-like metal-oxygen vs. metal-halogen layers as well as single or double halide ion sheets. The majority of Bi2-xAxQ0.6O2Z2 (A=Li, Na, K, Ca, Sr, Ba, Pb; Q=Rb, Cs; Z=Cl, Br, I) compounds crystallize in the tetragonal structure of Pb0.6Bi1.4Cs0.6O2Cl2 (Y2) while both Bi1.4Ba0.6Q0.6O2I2 (Q=Rb, Cs) oxyiodides adopt its orthorhombically distorted, partially ordered version. Due to the lower degree of substitution, the fluorite-like layers in the Y2 structure accommodate more A cations than previously known for related Bi compounds. However, very large Tl+ or Rb+ give compounds with another, as yet unknown, structure. We discuss the influence of size and charge of A cations and stoichiometry of [Bi2-xAxO2] fluorite layers on structure and stability of layered oxyhalides of bismuth. Also, we predict formation of isostructural compounds with smaller Q cations like Tl+ and K+.
Journal of Solid State Chemistry - J SOLID STATE CHEM. 01/2003; 173:83-90.
[show abstract][hide abstract] ABSTRACT: Systematic studies of LaOAgS-type alkaline earth–Cu/Ag fluoride chalcogenides revealed six new compounds SrFCuTe, SrFAgS, SrFAgSe, SrFAgTe, BaFAgS, and BaFAgSe. Crystal structures have been determined for these as well as for BaFCuS. Based on trends in the bond distances within the PbO- and FeS-type layers, a semi-qualitative approach is suggested to predict new members of the LaOAgS family.
[show abstract][hide abstract] ABSTRACT: Simultaneous substitution of WVI by UVI and Bi3+ by La3+ in the structure of ferroelectric Bi2WO6 results in stabilization of the archetypic tetragonal I4/mmm structure which is observed for the first time among [Bi2O2][BO4] Aurivillius-type oxides. Studies at the largest U content revealed a new Aurivillius-like compound Bi1.5La0.5UO6 which exhibits a novel distorted orthorhombic version of the archetypic structure. Formation of monoclinic α-(Bi,Ln)2WO6 structure is suppressed when W is partially substituted by U. Very similar tendencies are observed when proceeding to the derived structure of PbBi3WO8Cl. Besides the tetragonal PbBi3W1−yUyO8Cl (0 ⩽ y ⩽ 0.9) and orthorhombic PbBi3−xLaxUO8Cl (0.2 ⩽ x ⩽ 0.4) solid solutions, we were able to prepare PbBi3W1−yUyO8Br (0.1 ⩽ y ⩽ 0.8) and a line phase PbBi3W0.5U0.5O8I which is a yet rare example of bismuth-based perovskitic oxyiodides. We discuss the factors governing formation of complex layered intergrowth structures, in particular from simpler layer sequences.