Structural, optical, and dielectric properties of M/SnO₂ (M= Al₂O₃, NiO, Mn₃O₄) nanocomposites

The structural parameters, optical properties, and dielectric constants at a frequency (f) range of 0.1-20 MHz, and temperature (T) range of 300-400 K of hydrothermally synthesized M/SnO2 nanocomposites (for simplicity M denotes oxides of Al, Ni, or Mn) were compared. Rietveld refined X-ray powder diffraction (XRD) analysis demonstrated the formation of hexagonal, cubic, or spinel crystal structures of Al2O3, NiO, or Mn3O4 phases, respectively, besides the tetragonal rutile crystal structure of SnO2. The impact of Al addition on the optical band gap of SnO2 is negligible while it decreased or increased by incorporation of Ni or Mn, respectively. The residual lattice dielectric constant of SnO2 was increased, while the real part of the dielectric constant and the ac conductivity of SnO2 were decreased by M incorporation. The dielectric parameters are remarkably affected by selected M, T, and f values and their changes agree with the Maxwell-Wagner model. The Q-factor of SnO2 was increased by M addition while decreased with increasing T. The Ni/SnO2 obeys the hole conduction at T <= 330 K, while Mn/SnO2 and Ni/SnO2 obey the electronic conduction at T > 330 K. The binding energy is independent of the chosen T for SnO2, whereas it sharply increases for Ni/SnO2 and slightly decreases for Al/SnO2 and Mn/SnO2. The F-factor of SnO2 was slightly decreased by M addition, but it was increased with T for SnO2, Al/SnO2, and Mn/SnO2 while was decreased for Ni/SnO2. The Cole-Cole plots for M/SnO2 composites were analyzed, and the components of the equivalent circuit were determined. The electrical impedance, resistance of grains, resistance of grain boundaries, and equivalent resistance of SnO2 were increased by M incorporation, whereas equivalent capacitance was decreased. The findings recommend the SnO2-based nanocomposites for applications in optoelectronics, lithium batteries, supercapacitors, and solar cell devices.