The study reports structural and electrical evolution in La3+/Mn3+ cosubstituted BaTiO3, with compositions LaxBa1-xMnxTi1-xO3 (x = 0.00-0.50) in search of lead-free energy storage materials. Solid-state synthesized samples were thoroughly characterized by XRD, Raman spectroscopy, XPS, SEM, AC-impedance, and P-E measurements. Structural analysis revealed a tetragonal-to-rhombohedral (T to R) phase transition with increasing substitution, accompanied by lattice distortion and reduced tetragonality. Raman spectroscopy could clearly delineate R-type modes in otherwise single-phasic (T) La0.05Ba0.95Mn0.05Ti0.95O3. XPS confirmed mixed valence states of Mn (Mn2+/Mn3+) and O-vacancies which influenced structural and electrical behavior. Introduction of 2 mol % La3+/Mn3+ led to doubling of dielectric permittivity, K (∼1205), relative to BaTiO3. This is attributed to plausible distortion in BaO8/TiO6 polyhedra caused by occupancy of the same lattice sites by ions of varying sizes and oxidation states. The composition La0.05Ba0.95Mn0.05Ti0.95O3 showed an almost frequency-independent K (∼400) and low dielectric loss (0.05). LaxBa1-xMnxTi1-xO3 (x ≥ 0.1) yielded lossy, conduction-dominated behavior consistent with defect-facilitated ion transport. Simultaneous occurrence of ferroelectricity and visible band gap (2.23 eV) in La0.02Ba0.98Mn0.02Ti0.98O3 proposes a potential ferroelectric-photovoltaic material. These results establish La/Mn codoping in BaTiO3 as an effective strategy to yield ferroelectrics, low-loss dielectrics, and conductors by composition-driven structural tailoring.
Chahal et al. (Thu,) studied this question.