Improved structural and electrical properties of nickel and aluminum co-doped Bi4V2O11 solid electrolyte

Abstract

A layered Aurivillius-type solid electrolyte, formulated as BiNi0.20 − x Al x VOX (Bi4Ni 0.2 − (II) Al (III) V1.8O10.7 + (x/2); 0 ≤ x ≤ 0.20) was synthesized by the standard solid-state reaction. The influence of Al substitution for Ni on the relationship between the phase stability and electrical performance in the parent bismuth vanadate was investigated by combining results obtained from X-ray powder diffraction (XRPD), FT-IR spectroscopy, differential thermal analysis (DTA), and AC impedance spectroscopy. The orthorhombic β-phase (Acam) was seen for very low Al content up to x = 0.10, while in the composition range 0.10 < x ≤ 0.20, the conducting γ′-phase (I4/mmm) was effectively stabilized at room temperature. For all the studied compositions, three contributions were shown in the complex plane plots of impedance response below 400 °C. It was found that the electrical conductivity is mainly due to the grain interior contribution. However, the γ′-phase stabilized at x = 0.15 exhibited a maximum short-range diffusion of oxygen vacancies. Two linear regions were observed in Arrhenius plots of conductivity with abrupt discontinuity for the compositions x ≤ 0.10 and subtle discontinuity for x ≥ 0.13, clearly discriminating the thermal stability of β→γ and γ′→γ transitions, respectively. The electrical parameters were also correlated with the stabilization of the various phases within the system. The low-temperature conductivity, $$ {\sigma}_{30{0}^{\mathrm{o}}\mathrm{C}} $$ , exhibited a maximum (∼6.56 × 10−5 S cm−1) for x = 0.15. Moreover, a maximum value of $$ {\varepsilon}_{300^{\mathrm{o}}\mathrm{C}} $$ was also observed for x = 0.15, while the variation of $$ {\varepsilon}_{600^{\mathrm{o}}\mathrm{C}} $$ showed a maximum at x = 0.07, followed by a minimum at x = 0.15.