Thanks to its peculiar structural properties, the high temperature ä-phase of Bi 2 O 3 is considered as the best oxide ion conductor. Many efforts to stabilize this structure at room temperature have been deployed. In the present study, we have successfully stabilized the ä-phase by chemically introducing tetra-Te 4+ and pentavalent Ta 5+ cations into the structure. A series of compounds with different percentage of Te 4+ / Ta 5+ were obtained. Their structural and vibrational properties were investigated. From the Rietveld refinement of X Ray diffraction pattern we show that the composition x = 0.2 crystallizes in the cubic symmetry, space group Fm 3m (ITA No. 225) with a lattice parameter a =5.49 Å. The reliability factors are: R F =2.151 % and R Bragg =2.545 % confirm the goodness of the refinement. From the evolution of Raman bands, we confirm the existence of the solid solution features. Furthermore, comparing the spectra of ä-Bi 2 O 3 with the alpha phase, we comfortably suggest that the decrease of the number of Raman bands is a consequence of an increase in the lattice symmetry. Similarly to other fluorite compounds, we show that the structure presents oxygen defects clearly identified in the Raman spectra.

The anion and cation deficient phase Bi0.95 In0.05 O1.5 (Bi1.9 In0.1 O3) was synthesized and experimentally investigated using X-ray diffraction and vibrational spectroscopy (Infrared and Raman). The non-stoichiometric phases are similar to sillenite family type γBi2O3 and crystallize in the I23 space group. The crystal structure was determined by full profile Rietveld analysis of the powder diffractogram. It is formed by a sequence of BiO5E polyhedra (E lone pair of bismuth) and MO4 polyhedra (M = In, Mg). The set of MO4 polyhedra are localized in cavities generated by BiO5E polyhedra. The vibrational spectroscopic study revealed the existence of three regions; low, intermediate and high-frequency region. They are attributed to Bi-O stretching mode, In / Mg-O vibrations and cationic displacements respectively.

Synthesis and crystal structures are described for the Bi 1−x Sb 1−x Te 2x O 4 solid solution with 0 ≤ x ≤ 0.1. It crystallizes in the monoclinic system, space group I2/c. Rietveld refinements of X-ray powder diffraction data indicate that the atomic positions are: Bi/Te (2) (4c), Sb/Te (1) (4d). The oxygen occupied two sites, 8f and 8b, respectively. The reliability factors are: R p = 7.45%, R wp = 10.6% and R b = 3.88% for x = 0.1. The structure contains [(Sb/Te (1))O 4 ] n layers formed by (Sb/Te (1))O 6 octahedra sharing corners, which are parallel to (001) plan and held together by bismuth and tellurium atoms. The Raman study of this solid solution shows the bands which are assigned to O-Bi 3+-O, O-Sb 5+-O and connects (Bi/Te (2))O 8-(Sb/Te (1))O 6 vibration in the crystal.

This work reports the investigation of the ternary system Bi 2 O 3-TiO 2-MgO. Some compositions have been synthesized by solid state reaction at 800 °C and characterized by powder X-ray diffraction. The doping of (α-Bi 2 O 3) allowed us to stabilize three compositions isotype of sillenite structure phase with formulas Bi 0.

In this study, Sb2O3 (Sb2O5) and Ta2O5 are used as co-dopants with TeO2 to stabilize the delta phase of bismuth oxide (δ-Bi2O3). Some compositions with formula (1 − x) BiO1.5-(x/4) Sb2Te2O9 and (1 − x) BiO1.5-(x/4) Ta2Te2O9 (x = 0.1, 0.2, 0.3, 0.6, and 0.9) have been synthesized by solid state reaction at 850• C and characterized by powder X-ray diffraction. The Bi0.9Sb0.05Te0.05O1.575, Bi0.9Ta0.05Te0.05O1.575 and Bi0.8Ta0.1Te0.1O1.65 retain a cubic fluorite structure of δ-Bi2O3 phase. The electric properties were studied by impedance spectroscopy. All samples were evaluated by calculating conductivities and activation energies. Various impedance model including constant phase element and the Warburg impedances have been used to interpret the Nyquist representations of electrical analyses.