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1.
Samples of Sn4+-substituted bismuth vanadate, formulated as Bi4Sn x V2? x O11?( x /2)? δ in the composition range 0.07 ≤ x ≤ 0.30, were prepared by standard solid-state reactions. Sample characterization and the principal phase transitions (α ? β, β ? γ and γ′ ? γ) were investigated by FT-IR spectroscopy, X-ray powder diffraction, differential thermal analysis (DTA) and AC impedance spectroscopy. For composition x = 0.07, the α ? β and β ? γ phase transitions were observed at temperatures of 451 and 536°C, respectively. DTA thermograms and Arrhenius plots of conductivities revealed the γ′ ? γ phase transition at 411 and 423°C for x = 0.20 and 0.30, respectively. AC impedance plots showed that conductivity is mainly due to the grain contribution, which is evident in the enhanced short-range diffusion of oxide ion vacancy in the grains with increasing temperature. The highest ionic conductivity (5.03 × 10?5 S cm?1 at 300°C) was observed for the x = 0.17 solid solution with less pronounced thermal hysteresis.  相似文献   

2.
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 with x ≥ 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 at x = 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?4 S cm?1 at 300 °C) was observed for the composition with x = 0.13.  相似文献   

3.
Saba Beg 《Phase Transitions》2015,88(11):1074-1085
Bi4V2O11-δ has been doped with Ce and Cd to study double substitution. The system with various dopant concentrations (0.07 ≤ x ≤ 0.30) was prepared by the standard solid-state reaction method. The correlation between the polymorphism and oxide ion performance was well investigated as a function of temperature and composition with the help of thermal analysis, X-ray diffraction (XRD) and AC impedance spectroscopy. From XRD results it is seen that the high oxide ion conducting tetragonal γ-phase is stabilized for x = 0.17. For the compositions x ≤ 0.10, monoclinic α-phase is retained at room temperature with clear evidence for two successive phase transitions α ? β and β ? γ. For x = 0.13, β ? γ phase transition is seen. However, the existence of order–disorder, γ' ? γ transition was confirmed for x = 0.17. It is seen that the highest low-temperature ionic conductivity at 320 °C is 3.19 × 10?4 S cm?1 which was observed for x = 0.17.  相似文献   

4.
Saba Beg 《Phase Transitions》2016,89(2):167-179
New samples of the Bi2Zn0.1xTixV0.9O5.35+x; 0.02 ≤ x ≤ 0.08 system have been synthesized through a standard solid-state reaction route. XRD analysis and differential thermal analysis have been used to characterize the phase structure of samples. The γ′ phase is stabilized to room temperature in all investigated samples. The electrical properties of the BIZNTIVOX system have been studied by using AC impedance spectroscopy. An AC impedance response as a function of frequency (20 Hz–1 MHz) has been used to investigate the electrical conductivity and the dielectric permittivity in the temperature range of 150 °C–700 °C. In this temperature range, the phase transition γ′ to γ has been observed in all the compositions studied. AC impedance spectroscopy indicates that the resistance of samples decreases with increase of temperature. The ionic conductivity of samples appeared as a two-line region in Arrhenius dependence. At 300 °C, the highest ionic conductivity is shown by the composition x = 0.05 (σ300 = 1.35 × 10?4 S cm?1).  相似文献   

5.
Samples of Bi4Ca x V2? x O11?(3 x /2)?δ in the composition range 0.07 ≤ x ≤ 0.30 were prepared by conventional solid state reactions. The stability of different phases as a function of composition was analysed by X-ray powder diffraction, FT-IR spectra, differential thermal analysis and AC impedance spectroscopy. For the compositions x ≤ 0.10, monoclinic α-phase structure is retained at room temperature. For x = 0.13, orthorhombic β-phase is observed, whereas for x ≥ 0.17, high O2?conducting tetragonal γ-phase is stabilised. However, the highest ionic conductivity σ300°C = 3.27 × 10?4 S cm?1 was observed for x = 0.17. This higher value of conductivity of the substituted compound as compared to the parent compound can be attributed to the increased oxygen ion vacancies generated as a result of cation doping. AC impedance spectroscopy reveals the fact that this ionic conductivity is mainly due to the grain contribution.  相似文献   

6.
7.
Samples of Bi2V0.9Co0.1-xZnxO5.35, 0.02 ≤ x ≤ 0.08 with layered Aurivillius structure were synthesized successfully by sol-gel citrate method. Structural and electrical characterization of compositions has been investigated by X-ray diffraction, thermogravimetric analysis–differential scanning calorimetric (TGA–DSC) analysis and AC impedance spectroscopy. The tetragonal γ phase has been observed for all investigated samples. The AC impedance response of samples has been measured in the frequency range of 20 Hz to 1 MHz. The impedance for pellets decreases as thermal energy increases. The contribution of grain to the conduction process is more than that of grain boundary. The ionic conductivity and dielectric permittivity are found to be composition-dependent and increase with increasing Zn concentration. The maximum electrical conductivity observed for the composition x = 0.08 is σ = 4.51 × 10?4 S cm?1 at 300 °C.  相似文献   

8.
Bi2Cu0.1?xAlxV0.9O5.35?x/2?δ, 0.02 ≤ x ≤ 0.08, were synthesized by standard solid-state reaction route. Structural and electrical properties of samples are characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), Fourier transform infrared (FT-IR) and alternating current (AC) impedance spectroscopy. The tetragonal γ′ phase structure is preserved to room temperature with compound x = 0.02. The stabilization of β orthorhombic phase is observed for compositions 0.04 ≤ x ≤ 0.05. As the Al content increases, the monoclinic α phase is evidenced for materials 0.06 ≤ x ≤ 0.08. The electrical investigation of Bi2Cu0.1?xAlxV0.9O5.35?x/2?δ system has been performed in the frequency range from 20 Hz to 1 MHz using AC impedance spectroscopy. The impedance spectra indicate the two semicircle arcs associated with the bulk and grain boundary resistances at temperature below ~450 C. The conductivity generally changes when Al is substituted. The highest conductivity at 300 C (σ = 2.55 × 10?4 S cm?1) is shown for x = 0.02.  相似文献   

9.
Samples of Co–Ni double substituted bismuth vanadate, BICO0.20?x NI x VOX (Bi4Co0.20???x (III)Ni x (II)V1.8O10.8???(x/2)???δ ;0?≤?x?≤?0.20) were synthesized by standard solid state reactions. The influence of Ni substitution for Co on phase stabilization and oxide-ion performance have been investigated using X-ray powder diffraction, differential thermal analysis, and AC impedance spectroscopy. The high conducting γ′-phase was effectively stabilized at room temperature for compositions with x?≥?0.13 whose thermal stability increases with Ni content. The complex plane plots of impedance were typically represented at temperatures below 380 °C, suggesting a major contribution of polycrystalline grains to the overall electrical conductivity. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. Interestingly, the maximum ionic conductivity at lower temperatures (~2.56?×?10?4 S cm?1 at 300 °C) was observed for the composition with x?=?0.13. However, a good agreement was generally found between the values of electrical conductivity and corresponding activation energies of conduction.  相似文献   

10.
The BICO0.20–xNIxVOX solid electrolyte was synthesized by the standard solid-state reaction. The effect of Ni(II) substitution for Co(III) on phase stabilization and oxide-ion performance has been investigated in the compositional range 0?≤?x?≤?0.20 using X-ray powder diffraction, differential thermal analysis and AC impedance spectroscopy. The highly conductive γ′-phase was effectively stabilized at room temperature for compositions with x?≥?0.13 whose thermal stability increases with Ni content. The complex plane plots of impedance were typically represented at temperatures below 380?°C, suggesting a major contribution of polycrystalline grains to the overall electrical conductivity. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. Interestingly, the maximum ionic conductivity at lower temperatures (~2.56?×?10?4?S?cm?1 at 300?°C) was observed for the composition with x?=?0.13. The variation of low-temperature conductivity with Ni content was accompanied with a general drop in the corresponding values of ΔELT. However, the local minimum high-temperature conductivity, σ600?°C?~?2.26?×?10?2?S?cm?1 for x?=?0.10, coupled with a local maximum value of ΔEHT?~?0.48?eV was attributed to an increased defect trapping effect correlated with the V(V)?→?V(IV) reduction at elevated temperatures.  相似文献   

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