Crystal structures and conductivity properties of MBi6V2O15 family type compounds (M = Pb, Sr, Ca, Cd, Na0.5Bi0.5)

International audienceA family of compounds was prepared as powder samples with nominal formulas MBi6V2O15 (M = Pb, Sr, Ca, Cd, Na0.5Bi0.5), as well as single crystals with closely related compositions. Single crystal structure determinations were realized using X-ray diffraction. Each sample crystallizes in a monoclinic cell related to the d-Bi2O3 fluorite-type cell, through the relationship: am = 3/2 aF + 3/2 bF + 3 cF, bm = 3/2 aF - 3/2 bF, cm = 2 aF + 2 bF - 4 cF.With M = Na0.5Bi0.5, the non-centrosymetricC2 space group was selected, while for M = Pb-Cd, the structures were determined in the centrosymetric space group C2/c. Whatever theMelement, a non-stoichiometric phase can be obtained. ForM = Sr, Ca and Cd, mixed sites were observed; from their refined M/Bi occupancy factors, a determination method of Pb/Bi ratios has been proposed. These phases adopt a layered structure related to the d-Bi2O3 fluorite structure, built from stacking slab units of cationic triple layers [(Bi, V)/(Bi, Bi/M)/(Bi, V)] where the vanadium atoms are located in the two external layers. Oxygen atoms are trapped either in cationic tetrahedrons (OBi4, O(Bi/M)4) for those within the slabs, or in VO4 vanadates for those in the inter-slab spaces, thus limiting the materials oxide conductivity

(MBi)46V8Oy-Family type (M=Pb; Sr; Ca; Cd; Na0.5Bi0.5) : Syntheses, crystal structures and conductivity properties

International audiencePhases, with nominal formulas (MBi)46V8Oy (M=Pb, Sr, Ca, Cd, Na0.5Bi0.5), were prepared as powder samples, as well as single crystals of closely related compositions. Single crystal structure determinations were realized using X-ray diffraction on a Bruker 4KCCD Apex diffractometer. In this series, the cell is related to the fluorite d-Bi2O3: it is orthorhombic, with 0=3/2 F-3/2 F, 0=3/2 F+3/2 F, 0=3 F when nominal ratio are either M10/Bi36 (M=Sr-Na0.5Bi0.5) or Pb3/Bi43. Two types of monoclinic structures can be obtained from Pb6/Bi40 nominal ratio, either with m=3/2 F+3/2 F+3 F, m=-3/2 F+3/2 F, m=-3 F-3 F (1), or m=3/2 F+3/2 F-3 F, m=-3/2 F+3/2 F, m=5/2 F+5/2 F+4 F (2). For nominal Sr-Na0.5Bi0.5 compositions, the structure refinements led to M10-ΔBi36+ΔV8Oy non stoichiometric materials. In all structures, a cationic “slab” model was identified by the stacking of [(Bi,M, V) / Bi,M / (Bi,M, V)] layers. In these slabs, vanadium atoms are located in the external layers. The systematic stacking of 2 slabs (i.e. 6 cationic layers) allows the description of all the structures, except for Pb6/Bi40 nominal composition where a stacking of either 2 or 3 successive slabs is needed. In this description, the interslab distances are systematically larger than inter layer distances within the slabs. Along with the oxygen atoms, the cations determine a long range network of OBi4 and O(Bi,M)4 anti-tetrahedrons, distributed over the whole structure, and VO4 located at the slab-interslab interfaces. The conductivity properties of materials with M10Bi36V8O84 nominal compositions are presented. They likely result from the oxide ion mobility (of the OBi4 and O(Bi,M)4 entities) within the interslab spaces

Synthesis and characterization of Bi31Cr5O61.5, a new bismuth chromium oxide, potential mixed-ionic–electronic conductor for solid oxide fuel cells

International audienc

Structures and oxide mobility in Bi-Ln-O materials: Heritage of Bi2O3

International audienc

Bismuth lead oxyfluroride ionic glass conductors

PosterMany works were published on anion conductors by ions O2 -, with good conductivities at 500-600°C. Oxyfluorides, conductors by ions F-, have the same level of performances around 300°C. For example, the oxyfluoride system containing bismuth and lead led to a crystallized phase having a conductivity of 1 Sm-1 at 300°C. Doping by silica makes it possible to stabilize a vitreous domain and extends the range of the conducting phases. The presented study relates to the stability of the vitreous phase and the variation of conductivity as well according to the temperature as versus the composition. Thermal analyses by DTA evidenced, after the temperature of vitreous transition, the recrystallization of material in one or more stages. The phases crystallized were identified by high temperature X-rays diffraction. The best conductivity, about 0,3 Sm-1 at 227°C, is obtained for the fluorine richest material

Les tétrachlorosulfatometallates M'M (SO

Cet article présente les spectres Raman des tétrachlorosulfatoborates M'B(SO3Cl)4 (M' = Li, Na, K. Rb, Cs) à l'état solide et en solution dans l'acide acétique pour les sels de sodium, de potassium et dans l'anhydride sulfureux pour ceux de rubidium a de césium. Une interprétation des spectres est proposée. Elle confirme l'existence de groupements SO3Cl liés à l'atome de bore par l’oxygène et permet de considérer tous les sels M'B(SO3Cl)4 comme des tétrachlorosulfatoborates. Les spectres Infrarouges ont été enregistrés ainsi que ceux d'autres tétrachlorosulfatométallates M'M (SO3Cl)4 (M = Al et Ga). Leur analogie suggère une structure moléculaire similaire pour l'ensemble de ces sels

Phase Transitions in the BiVO4-nPbO (n = 1, 2) System: Structural–Electrical Properties Relationships

International audienc

PREPARATION OF DENSE NANOCRYSTALLINE Bi2O3-Y2O3 SOLID ELECTROLYTE BY MICROWAVE PLASMA SINTERING

PosterBismuth based oxide ion conductors are well known for their high oxide ion conduction at moderate temperature, 400-700 °C. Bi2O3 in its delta form exhibits the highest conductivity with a value of 1S.cm-1 at 730 °C [1]. From the structural point of view, this form can be described as an oxygen deficient fluorite. In contrast to yttria stabilised zirconia which is an extrinsic oxide ion conductor, delta-Bi2O3 is an intrinsic conductor, possessing intrinsic oxide ion vacancies. However, this form is stable over a very narrow domain in temperature, limited by the material melting point at 830°C and a dramatic phase transition at 730°C. This phase transition is associated with mechanical stress which renders these materials unsuitable for practical applications. Numerous studies have been performed to stabilise this high temperature form at lower temperature [2]. The grain size of ceramics can affect the kinetics of phase transition. They can be considerably slowed when ceramics with small grain size are used [3, 4]. This opens the possibility to stabilise the high temperature form with its derived specific properties at lower temperature. In a recent paper, Zhen et al [5] reported the processing of dense nanocrystalline Bi2O3-Y2O3 solid electrolyte from powder prepared by a reverse chemical titration co-precipitation of hydroxide. Ceramics were sintered using a conventional oven. The use of a microwave plasma allows high temperature and extremely high heating rate [6, 7]; it should prevent grain growth and should allow the preparation of dense ceramic with very small grain size. It was here applied to Bi2O3-Y2O3 electrolyte