CaSnO₃ perovskite oxide: influence of Bi doping on structural, optical, and magnetic properties

In the present study, the structural, optical, and room-temperature magnetic properties of undoped and Bi-doped CaSnO₃ (CSO) perovskite samples were systematically investigated. The samples were synthesised via a chemical precipitation method. X-ray diffraction (XRD) analysis revealed the crystal structure and variations in lattice parameters, with a significant reduction in crystallite size from 60 nm in the undoped sample to 21 nm in the Bi-doped CSO, indicating the inhibitory effect of Bi incorporation on crystal growth. Metal oxide vibrations and defects such as oxygen vacancies (V_O) arising from bismuth doping were characterized through Fourier-transform infrared (FTIR) and Raman spectroscopy. Ultraviolet-visible (UV-Vis) absorption studies demonstrated a decrease in the optical band gap from 4.25 eV (undoped) to 3.73 eV (Bi-doped), while photoluminescence (PL) measurements confirmed the presence of defect-induced states. Electron paramagnetic resonance (EPR) spectra further corroborated the existence of defect sites and F-centers within the lattice. Undoped CSO exhibited a weak ferromagnetic component superimposed on a dominant diamagnetic response. Upon Bi doping, subtle magnetic interactions emerged, with 3% of Bi doped CSO demonstrating a ferromagnetic behaviour of 2.6 × 10^-3 emu g^-1, which can be explained based on an F-centre exchange mechanism.