Structure, thermal stability and microstructural properties of Bi4V2-x(Cu-Li)xO11-7x/4 solid solution (0.1 ≤ x ≤ 0.3)

Abstract

The structural, thermal, and spectroscopic properties of Bi₄V_2-x(Cu-Li)_xO_11-7x/4 (0.1 ≤ x ≤ 0.5) compounds were investigated to explore the effects of copper and lithium substitution on the material's crystalline structure and phase transitions. X-ray diffraction (XRD) analysis revealed that increasing the substitution level from x = 0.1 to x = 0.3 resulted in phase transitions from monoclinic to orthorhombic, and eventually to tetragonal, with the solid solution limit at x = 0.3. The crystallinity and porosity showed an inverse relationship as the substitution rate increased, with crystallite size enlarging from x = 0.1 to x = 0.2, and a defect-trapping effect at higher substitutions (x = 0.3 and x = 0.4). Differential thermal analysis (DTA) and thermogravimetric analysis (TG) indicated significant endothermic transitions, with a peak at 698°C corresponding to the melting of a secondary phase isostructural to Bi₈V₂O₁₇. High-temperature XRD (HT-XRD) analysis further supported the phase transitions, while Raman spectroscopy showed shifts in the V-O bond stretching vibrations with increasing substitution. The study concluded that substitution with copper and lithium modifies the thermal stability, crystallinity, and phase behaviour of BiCuLiVOx compounds, highlighting their potential in various applications requiring high-temperature stability and ionic conductivity.