Search

Samples of bismuth lead vanadium oxide (BIPBVOX) (Bi2V1–xPbxO5.5–x/2)singly substituted system in the composition range 0.05 ≤x≤ 0.20 were prepared by sol–gel synthesis route. Structural investigations were carried out by using a combination of differential thermal analysis (DTA) and powder X-ray diffraction (PXRD) technique. Energy dispersive X-ray spectroscopy analysis (EDXA) of doped samples was carried out to predict the sample purity and doping concentration. Transitions, α↔β, β↔γ and γ′↔γ were detected by XRD, DTA and variation in the Arrhenius plots of conductivity. The ionic conductivity was measured by AC impedance spectroscopy. The solid solutions with compositionx≤ 0.07 undergo α↔β phase transition, at 329 °C and β↔γ phase transition at 419 °C. The highly conducting γ′-phase was effectively stabilized at room temperature for compositions withx≥ 0.17 whose thermal stability increases with Pb content. At 300 °C, the highest value of conductivity 6.234 × 10−5S cm−1was obtained for compositionx= 0.15 and at 600 °C the highest value of conductivity 0.65 S cm−1is observed forx= 0.17. AC impedance plots reveal that the conductivity is mainly due to the grain contribution to oxide ion conductivity. [ABSTRACT FROM AUTHOR]

A layered Aurivillius-perovskite-type BINIVOX system with the general formulawas developed as a novel photocatalyst for degradation of organic dyes. A series of the BINIVOX.xcatalysts in the compositional range 0≤x≤0.20 were successfully synthesized by the standard solid-state reaction and characterized using X-ray powder diffraction, differential thermal analysis, UV–vis diffuse reflectance spectroscopy and Brunauer–Emmett–Teller BET surface area. Then, the photocatalytic activities of prepared catalysts were investigated for the first time through the degradation of a new azo dye named sodium 4-[(E)-(4,5-dimethyl-1H-pyrazolo [3,4-c] pyridazin-3-yl) diazenyl] naphthalen-1-olate and denoted as 4-SPPN in aqueous solution under visible light irradiation. Adsorption efficiency and photocatalytic activity of BINIVOX.xcatalysts were correlated well with the variation in phase crystal structures stabilized at room temperature as a function of composition. The stabilized γ′-BINIVOX phases in the tetragonal crystal system with space groupI4/m mmexhibited the best photocatalytic performance which can be attributed to their higher specific surface area, narrower band-gap energy and higher oxygen-vacancy concentration in the perovskite vanadate layers. In addition, the possible photocatalytic degradation mechanism of aqueous 4-SPPN dye was proposed under visible light irradiation. [ABSTRACT FROM AUTHOR]

BICO0.20−xNIxVOX solid electrolyte in the composition range 0 ≤x≤ 0.20 was synthesized by standard solid-state reactions. The influence of Ni substitution for Co on the relationship between the phase stabilization and electrical performance was investigated by means of X-ray powder diffraction (XRPD), differential thermal analysis (DTA) and AC impedance spectroscopy. The highly conductive γ′-phase was effectively stabilized at room temperature for compositions withx≥ 0.13 whose thermal stability increases with Ni content. On the other hand, complex plane plots of impedance suggested a major contribution of polycrystalline grain interiors to the overall electrical conductivity and the fastest oxygen-vacancy diffusion in the perovskite vanadate layers atx= 0.13. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. However, a maximum ionic conductivity at lower temperatures (∼2.56 × 10−4S cm−1at 300 °C) was observed for the composition withx= 0.13. [ABSTRACT FROM AUTHOR]

Highlights: [•] Novel BINIVOX photocatalyst with Aurivillius-perovskite layers was developed. [•] Adsorption and photocatalysis were correlated with crystal structure of BINIVOX. [•] γ′-phase exhibited best photocatalytic activity under visible light irradiation. [•] photocatalytic degradation mechanism of aqueous 4-SPPN dye was proposed. [ABSTRACT FROM AUTHOR]

Abstract: Samples of Bi4Ce x V2−x O11−(x/2)−δ were prepared by the conventional solid-state reactions. The phase transition changes were studied by combining results obtained from high temperature X-ray powder diffraction (HT-XRPD), differential thermal analysis (DTA) and conductivity measurements. For x =0.15 composition, the phase transitions; α↔β and β↔γ were clearly evident in the temperature ranges 423–450 and 533–550°C, respectively. Although no subtle change in variation of the unit cell parameters was observed for x =0.25 composition, the Arrhenius plot and DTA thermogram showed evidence of γ′↔γ phase transition in the temperature range 450–500°C. [Copyright &y& Elsevier]

Abstract: A new solution series of bismuth vanadate of the molecular formula Bi4Cd x V2− x O11− δ ; 0≤ x ≤0.25 was synthesized by solid state reaction, via substitution of Cd for V in the parent compound, Bi4V2O11− δ . The sample characterization and study of the phase transition changes were performed by using XRD, FT-IR and DSC measurements. It has been found that the ionic conducting, tetragonal γ-phase could effectively be stabilized to room temperature for x =0.175 solid solution. Impedance spectroscopy (IS) measurements proved that the oxide ionic conductivity predominantly arises from the grain contribution. In addition, highest ionic conductivity (~1.30×10−4 S cm−1 at 420 °C) was observed for x =0.20 solid solution with less pronounced thermal hysteresis. [Copyright &y& Elsevier]

Abstract: A continuous series of Bi4Ba x V2–x O11–(3x/2)–δ solid solutions are prepared by conventional solid state reactions. The polymorphism and electrical properties of these samples are studied by FT-IR spectroscopy, X-ray diffraction, differential thermal analysis (DTA) and AC impedance. The solid solutions with composition 0.07≤x≤0.13 are isostructural with the monoclinic phase α-Bi4V2O11. However, orthorhombic β-phase is observed for x=0.17 and tetragonal γ-phase is stabilized for x≤0.30. X-ray and DTA results reveal the occurrence of α↔γ transition for x≤0.13, β↔γ transition for x=0.17 and γ′→γ transition for x≥0.20. AC impedance plots at 280°C for all compositions show greater contribution of grain to ionic conductivity than grain boundary. The highest ionic conductivity, σ 300°C=4.456×10–5 Scm–1 is observed for x=0.17. The ionic conductivity of the substituted compounds is higher than the parent α-Bi4V2O11, due to the increased oxygen ion vacancies generated as a result of barium doping. [Copyright &y& Elsevier]