Why Is Iron-Copper Co Doped Bismuth Vanadate?

Iron-Copper co doped bismuth vanadate, has led to the formation of the BIFECUVOX solid solution in the composition range 0.05≤x≤0.20 were synthesized by standard solid state reactions. Fe and Cu substitution effects on the phase stabilityand electrical performance in the parent bismuth vanadate and was investigated by combining results obtained fromPowder X-ray diffraction (PXRD), Differential Thermal analysis (DTA), Thermogravimetric analysis (TGA),Scanning Electron Microscopy(SEM) and AC impedance spectroscopy. The PXRD results show that the composition x= 0.05 and 0.07 have monoclinic while for x= 0.10 orthorhombic symmetry. Composition x ≥ 0.15 presents a tetragonal symmetry. The thermal analysis revealed the existence of polymorph γ′ phase,
A single endothermic peak is observed in the temperature range 400 – 550 oC for all investigated compositions. However, the relatively large endothermic peaks seen in the DTA thermograms for x=0.17 and x = 0.10 are assigned to α→β and→ transitions respectively, while the occurrence of order → disorder('→) transition is detected in the composition range 0.15 ≤ x ≤ 0.20. This assignment is in a good agreement with the results obtained from the XRPD analysis. It can be noted that the onset phase temperature, Tt initially increases as a function of Fe and Cu substitution, reaching a maximum for the composition x=0.15 (Tt =510 oC) and thereafter it is substantially decreased in the composition range with stabilized γ'– BIFECUVOX phase. However, the maximum Tt accompanied with increased heat flow for x=0.15 might be attributed to a subtle ordering in some oxygen sublattice positions located in the perovskite–layered polyhedra [5–7].
3.3. Scanning electron microscopy analysis
The SEM micrographs of as–calcined samples of BIFECUVOX system for different compositions are shown in Figure 4. It is clearly seen that all the sample calcinated at 550 oC are generally composed of the agglomerated particles with different shapes varying from uniform spherical to disc– like. The disc– like particles might be formed by splitting of spherical particles due to thermal effect during the prolong calcination applied. From these images it is estimated that
4. Conclusion
In this work the new oxide ion conductor related to BIMEVOX family BIFECUVOXhas been successfully synthesized using solid state reaction routein the composition range 0.05 ≤ x≤ 0.20. The tetragonal γ′-phase is stabilized at room temperature in the compositionx = 0.17.
In α–Bi4V2O11,double substitution of V by Fe and Cu stabilizes the high temperature tetragonal γ′-phase at room temperature for composition x≥ 0.15. While the stabilization of orthorhombic β- phase is observed for composition x=0.10. It was found that the x = 0.17 composition has pronounced ionic conductivity of 05.28×10-3 S.cm-1at 300oC.The micrographs clearly distinguished between the grain and grain boundary area. AC impedance shows that the main conductivity is due to the grain contribution of the