Exploring the role of Zn doping on the structure, morphology, and optical properties of LaFeO3

The structural and optical properties of nanocrystalline LaFe1-xZnxO3 (0 <= x <= 0.3) samples, synthesized through sol-gel auto-combustion technique, have been studied. Transmission electron microscopy concomitant with Williamson-Hall analysis elucidates the nanocrystalline nature of the samples. High-resolution transmission electron microscopy in combination with selected area electron diffraction patterns reveals the interplanar spacing and poly-crystalline nature of samples, respectively. LFO being charge transfer insulator, its direct optical bandgap corresponding to O2p band, and the unoccupied Fe-3d band is determined. The red shift in bandgap is found with the increase in Zn doping and may be attributed to the formation of localized energy levels near the conduction band and also to the change in crystal field with the creation of oxygen vacancies. Higher order transition energy corresponding to multiple transitions has also been determined and is found to decrease with Zn doping. Urbach tail which measures the disorder in the system has been found in the pristine and doped samples and is found to increase with zinc doping. Optical constants including complex refractive index and optical conductivity have been determined from the reflectance data. The pristine sample has a refractive index of maximum value 3 which decreases with Zn doping making the sample more transparent and hence conductive. Zn doping enhances the conductivity of the pristine sample by creating the charge imbalance and thereby promoting the hopping motion of charge carriers, making the sample more transparent in the optical region.