Insight into structural, optical, electrical, dielectric, and photovoltaic behaviour of cerium-doped strontium titanate by a modified combustion method

Compounds with the general formula SrTi (1-x) Ce O-x(3) (x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05) were synthesized through an auto-ignition solution combustion process. XRD analysis revealed that all the samples have cubic structures. The lattice parameters increased with doping because the titanium ions with smaller ionic radii were replaced with cerium ions of comparatively large ionic radii. The crystallite size of the compounds decreased with an increase in cerium concentration in the system because the presence of cerium inhibits crystallite growth. Transmission Electron Microscopic investigation of the samples revealed that they have irregular cubic-like structures. The optical studies carried out using UV-visible absorption spectra confirmed that the bandgap of the samples was reduced by cerium doping because cerium introduces additional energy states in the forbidden energy gap of strontium titanate. The intensity of photoluminescence signals decreased in the cerium-doped compounds, indicating that the recombination rate of the photo-induced charge carriers has been reduced. Dielectric characterization revealed that all compound's dielectric constants and dielectric losses followed a similar trend: they were larger in the low-frequency region and immediately decreased when frequency increased, where they eventually stabilized. Also, the dielectric constant and loss factor decreased with the doping of cerium. The decrease in the dielectric constant was attributed to the decrease in the cation 'rattling effect'. Impedance spectroscopic studies were also carried out on the ceramic materials, which showed an increase in the total impedance with the doping of cerium atoms into the host material. The frequency dependence of the conductivity satisfied Jonscher's power law. Also, the total electrical conductivity of dense ceramics increased in line with the Arrhenius relation when temperature increased. The electrical conductivity decreased with doping due to the reduction in the number of charge carriers for conduction according to the results obtained from the Arrhenius plot. The newly doped samples were used as photoanode in dye-sensitized solar cells. The open-circuit voltages and short circuit current varied with an increase in cerium content.