Impact of Bi doping on the structure and physical properties of LaCrO₃-based perovskite

Lanthanum-based chromite materials have become increasingly attractive for numerous types of research due to their many features. To enhance their properties, they are usually doped with divalent ions and rarely with trivalent ones. In this work, we introduced bismuth in LaCrO₃ perovskite using the solid-state reaction method and we investigated the properties of the obtained samples. The Rietveld analysis of the X-ray pattern confirms the single-phase orthorhombic structure (Pnma). The crystalline grain size increases from 46 to 77 nm when 20% of La are substituted by Bi. The analysis by energy dispersive spectroscopy confirms the incorporation of Bi atoms in LaCrO₃ matrix and the absence of other impurities. The optical band-gap energy is found to be 3.1 eV to 3.3 eV for LaCrO₃ and La_0.8Bi_0.2CrO₃, respectively. Electrical properties of prepared compounds are deduced from impedance spectroscopy in the temperature range 200–380 K and the frequency one [40–10⁶ Hz]. The ac-conductivity is well-fitted by Jonscher’s single power law for Bi-free compound and it follows double power law for Bi-doped compound. From, the analysis of the variation of the frequency exponent with temperature, we deduced that correlated barrier hopping mechanism predominates the electronic transport in the undoped compound. This mechanism is changed to the non-overlapping small polaron tunneling one when bismuth is introduced. From Nyquist plot, a non-Debye relaxation process is evidenced and the contribution of grains, grain boundaries and electrodes are deduced. These results are interesting since they show that the properties can be tuned by the bismuth amount and consequently they van be optimized according to different applications.