J.C. Champarnaud-Mesjard

New heavy metal oxide glasses: investigations within the TeO2–Nb2O5–Bi2O3 system

The TeO2–Nb2O5–Bi2O3 system was investigated by differential scanning calorimetry and temperature programmed X-ray diffraction. A large glass-forming domain was evidenced and the complex structural evolution with temperature of these glasses was followed. The glass transition and crystallisation temperatures and the nature of crystalline phases formed were determined. Moreover, this study confirmed the existence of the metastable γ-TeO2 polymorph and of a new crystalline compound, BiNbTe2O8.

Crystal structure of Nb2Te4O13

Abstract Nb2Te4O13 crystallises in the space group P1 with the unit cell parameters: a=7.535(5) A, b=12.647(7) A, c=12.702(7) A, α=116.05(4), β=90.15 (4), γ=90.03(4), Z=4). Its structure has been refined by a full matrix least-squares process to R 1 =0.029 and wR 2 =0.068 values on the basis of 5202 independent single crystal X-ray reflections recorded with an automatic diffractometer. Infinite trans chains of NbO6 octahedra are connected via TeO4 disphenoids and TeO3 pyramids, to form double UVO5 like-sheets. These sheets are cross-linked by β-TeO2-like chains of alternately corner and edge-sharing TeO4 disphenoids, and consitute a three dimensional network, in the tunnels of which are located the electronic lone pairs E of Te4+ cations.

The crystal structure of PbTe5O11

Abstract PbTe 5 O 11 crystallises with monoclinic symmetry (space group C2/c) and unit cell parameters: a = 18.959(4) A, b = 4.414(1) A, c = 25.798(6) A, β = 98.12 (1), Z = 8). Its crystal structure has been refined by a full matrix least-squares process to R 1 = 0.037 and wR 2 = 0.068 values, on the basis of 3121 independent single crystal X-ray reflections. It can be described as a Te 5 O 11 three-dimensional network of TeO 4 disphenoids (distorted TeO 4 E trigonal bipyramids) sharing corners and edges which contains three kinds of tunnels parallel to the Oy direction. The stereochemically active lone pairs E of tellurium atoms are directed towards the centre of two of them. Lead atoms are inserted in pairs in the third one.

Thermal dependence of conduction properties in the Bi2O3Pb2OF2 system

Abstract Conduction properties of bismuth-lead oxyfluorides (Bi,Pb) 2 (O,F) 3 have been investigated by complex impedance analysis. A special attention has been drawn to a hexagonal solid solution Bi (1− x ) Pb x O (1.5− x ) F x (0.45⩽ x ⩽0.741 at 770 K), which is isostructural with ALa 2 O 3 . Conductivity values range from 3 × 10 −5 to 3 × 10 −2 (ω cm) −1 at 585 K. A minimum associated with a maximum in activation energy is observed for the composition x = 0.5 i.e. BiPbO 2 F.

Glass formation study in the Bi2O3-TeO2-WO3 system

Summary Glass formation regions in the Bi 2 O 3 -TeO 2 -WO 3 system have been determined at 650 °C, 700 °C and 800 °C. Physical characteristics of some vitreous samples have been measured.

Electrical properties of new materials belonging to the Bi2O3CdOCdF2 system

Abstract The Bi 2 O 3 CdOCdF 2 system was investigated by means of X-ray diffraction at temperatures between 630 and 800 °C. Four solid solution domains were characterized, corresponding respectively to anti-α-AgI, BiSrO rhombohedral (ϵ), ALa 2 O 3 and fluorite structural types. Among these phases, the most attractive conductivity performances were evidenced in the fluorite domain ( σ = 2 × 10 −5 S cm −1 at 300°C for Bi 0.42 Cd 0.58 O 0.72 F 0.97 ) and were shown to depend on the oxygen-fluorine ratio.

Structural and single crystal conductivity characterization of fluorine pathways in a (Bi,Pb)(O,F) ionic conductor

Abstract The mechanism of F- migration in a trigonal Bi2O3-PbO-PbF2 solid solution was examined by means of structural analysis and single crystal conductivity measurements. From structural considerations, the conduction was expected to occur via a one-dimensional mechanism for the poor conductors and via a three-dimensional process as soon as the performances of the electrolyte increase. Conductivity measurements performed in selected directions on single crystals fully agree with these hypothesis.

Electrical properties and high temperature crystal structure of the bismuth lead oxyfluoride: BiPbO2F

The electrical properties of the BiPbO 2 F conductor were examined by means of impedance spectroscopy and de polarization techniques. Fluorine was shown to be the main mobile species. Crystal structure investigations were performed using X-ray single crystal and neutron powder diffractions. Cations are localized in the 2d site of the A−La 2 O 3 type structure while anions are distributed over the 1a, 2c, 6i and 6h positions of the P3ml space group. According to the fluorine location confirmed by a 19 F NMR experiment, a fluorine migration mechanism is proposed.

19F-N.M.R. study of F/O ordering in the trigonal Bi1−xPbxFxO1.5−x anionic conductor

Abstract 19 F wide-line N.M.R. experiments have been performed at 30 MHz over the temperature range 173–300 K, on three samples (x = 0.400 − 0.500 − 0.714) of the Bi 1−x Pb x O 1.5−x solid solution. Comparison of the experimental and theoretical values of the second monent M 2 , clearly indicates an ordered distribution of fluorine and oxygen atoms within the anionic subcell. The oxygen atoms are strictly located in the tetrahedral and octahedral holes of the “fluorite-like” layer of this A-La 2 O 3 -related structure. Such an order, if preserved at high temperature, should play an important role in the conduction process.

Phases stability and conduction properties in the Bi2O3-PbOPbF2 system

Abstract The Bi2O3-PbOPbF2 system was investigated by means of X-ray diffraction at temperatures between 770 and 950 K. Two solid solution domains have been evidenced. The first one exhibits a tetragonal cell (a = 7.74(1), c = 5.78(1) A for Bi(0.857)Pb(0.143)O(1.357)F(0.143)). Conductivity measurements performed by complex impedance method show that the value of σ remains lower than 10−7 (Ω.cm)−1 at 470 K. The second domain, isostructural with A La203 (hexagonal cell, a = 4.101(2), c = 6.087(2) A for Bi(0.5)Pb(0.5)0 F(0.5)) is more attractive: σ values close to 3×10 −4 (Ω.cm) −1 are reached at 470 K. The conductivity is strongly influenced by both oxygen and fluorine contents.