Zn2SnO4 and Zn2TiO4 inverse spinels: influence of the temperature on structural, microstructural and luminescent properties

Despite different works deals with the synthesis of Zn2SnO4 and Zn2TiO4 spinels, no aspect of their thermal and structural evolution upon heating has been reported yet. Herein, Zn2SnO4 and Zn2TiO4 spinels were synthesized by modified-Pechini method and the dependence of heating temperature and the lattice former (Sn and Ti) on the materials properties were investigated. Thermal analysis (TG/DTA), in situ high temperature and conventional X-ray diffraction (HT-XRD and XRD), infrared spectroscopy (IR), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), UV-Visible spectroscopy (UV-Vis), and Photoluminescence (PL) analysis were used for such objectives. HT-XRD and TG/DTA reveal that intermediate phases are formed during the precursor powders heating prior final crystallization of the spinels in Fd-3 m cubic phase that occurred at different temperatures. Direct calcinations at pre-determined temperature led to single-phase materials as indicated by conventional XRD patterns and Raman spectra. FE-SEM analysis indicate the presence microaggregates formed by smaller nanoparticles, whose diameter is interfered significantly by the lattice former Ti4+ and Sn4+ cation. The change in the morphological characteristics according to the temperature and to the lattice former is consistent with the structural analysis. As established by UV-Vis and PL, optical and electronic properties of the spinels were strongly influenced by simultaneous changes in short- and middle-range structural disorder (associated with the exchange cations in coordination sites and with the elimination of electronic defects) and long-range structural order (attributed to the changes in crystallinity). Our work demonstrate that the characterization techniques are complementary in understanding structural, microstructural, and optical/luminescent properties of materials.