Investigation of the structural and microstructural properties of copper and tantalum substituted BiMeVOx compounds with enhanced oxygen ion conductivity: Bi4V2-xCux/2Tax/2O11-3x/4 (0.1≤ x ≤ 0.5)

Abstract

In this study, the objective was to improve the performance of bismuth vanadium oxide Bi4V2O11 by synthesizing double substituted compounds using copper ions Cu2+ and tantalum ions Ta5+. Bi4V2-xCux/2Tax/2O11-3x/4 (0.1 ≤ x ≤ 0.5) polycrystalline samples of were prepared via the solid-state route. XRD patterns measured at room temperature revealed the stabilization of the monoclinic α-Bi4V2O11 type structure for x = 0.1 and the tetragonal γ or γ' -Bi4V2O11 for x > 0.2. This result has been confirmed by thermogravimetric analysis (DTA), FT-IR spectroscopy and Raman scattering measurements. The influence of the composition on the microstructure and grain size of the prepared samples was explored through dilatometric study, density measurements, and scanning electron microscopy (SEM). Thermal Raman spectra evolution was also investigated. The temperature-dependent Raman spectroscopy analysis of the compound α-BiCuTaVOx (x = 0.1) demonstrated variations in the position, intensity, and width of the Raman mode around 850 cm−1, indicating temperature-assisted structural modifications. One defining feature of the tetragonal-dominated phase of the BiMeVOx systems is the increasing merging of the weak band at 930 cm−1 with the dominating band at 850 cm−1. This behavior was also observed for our samples. The V–O bond lengths were calculated using an empirical relation based on the diatomic approximation. Electrochemical impedance spectroscopy (EIS) was used to investigate the changes in electrical conductivity with the substitution rate across the temperature range of 300–720 °C. The sample with x = 0.3 exhibited the highest electrical conductivity at both high and low temperatures. However, the optimal substitution rate to achieve the best conductivity in this series of copper and tantalum-substituted BiCuTaVOx was found to be x = 0.3 (σ = 4 × 10−3 S cm−1 at 600 °C).