Influence of A/B-Site doping on the structure, lattice dynamics and optical band gap of Bi5Ti3FeO15 ceramics

BTF-xNd (x = 0, 0.5, 1.0, 1.5, 2.0) and BTF-yMn (y = 0.1, 0.2, 0.3) ceramics were synthesized via solid-phase sintering. The effects of A-site Nd3+ and B-site Mn3+ doping on the structural properties of BTF ceramics were investigated using X-ray diffraction, scanning electron microscopy, high-pressure Raman spectroscopy, and spectroscopic ellipsometry. XRD and Raman spectroscopy revealed that lattice parameters a and b initially increase, reaching maximum values at x = 1.0, before decreasing with further Nd3+ doping, while the c-axis lattice constant consistently decreases, stabilizing beyond x = 1.0. Mn3+ substitution for Ti1 ions introduced an additional phonon mode at 600 cm-1 associated with MnO6 octahedra. High-pressure Raman analysis (0-25 GPa) indicated that Nd3+ doping has minimal structural impact, whereas Mn3+ doping destabilizes the lattice. SEM showed that the average grain size of BTF-xNd ceramics first increased to x = 1.0 and then decreased with higher Nd3+ concentrations. The band gap of BTF-xNd ceramics was measured at 2.8 eV, increasing with higher Nd3+ concentrations. These findings elucidate the role of Nd3+ and Mn3+ doping in modulating the structural and electronic properties of BTF ceramics, enhancing their potential for energy storage and spintronic applications.