Effect of type of fuel used and calcination temperature on the disorder-order transformation of zinc aluminate spinel during combustion synthesis

Order-disorder transition for zinc aluminate samples synthesized via auto combustion synthesis method using different fuels (Citric acid, Glycine and Urea) were determined. The synthesized powders with various fuels are showing abnormal X-ray diffraction intensities, specifically in (331) and (400) reflections are too sensitive because of a significant amount of cations (Zn2+ -tetrahedral site and Al3+- octahedral site) displaced from their ideal positions. With increase in calcination temperatures disorder to order transformation achieved through the diffusion of cations into the respective tetra and octahedral sites. Complete ordered structure attained at 750 degrees C for the sample synthesized with citric acid. However, powders synthesized with glycine requires high calcination temperature (1000 degrees C) due to the diffusion of the metal cations is severely impeded in powders of foam morphology. XRD and Raman results are corroborate with each other. Further, the UV-Vis and Photoluminescence studies for a sample with glycine as fuel is studied which shows the variation in band gap and narrowing of the emission band respectively.