Structural, optical, dielectric, and multiferroic properties of sodium and nickel co-substituted barium titanate ceramics

Abstract

Narrowing the bandgap energy of perovskite ferroelectrics is a potential task for improving PV applications. This study examined the effect of Ni2+/Na+ co-substitution on the structural, optical, electrical, and magnetic properties of Ba1-x(Nix/2,Nax)TiO3 (BTNaNi-x) ceramics, where (0 ≤ x ≤ 0.08), prepared by solid-state reaction method. X-ray diffraction along with structure refinement verifies the existence of perovskite structure with a tetragonal phase in all samples. The morphological study reveals a non-uniform grain size distribution with a decrease in grain size with an increase in co-substitution concentration. XPS study gives direct evidence of oxygen vacancies in the investigated sample. The oxygen vacancies and octahedral distortion accompanying the Ni2+/Na+ co-substitution significantly reduce the optical bandgap of BaTiO3 ceramics from 3.14 to 2.688 eV. The temperature dependence of the dielectric constant is measured in the range of 30–250 °C at the frequency of 1 kHz. The results reveal that the transition temperature gradually decreased with an increase in Ni2+ and Na+ concentrations. This phenomenon was interpreted based on reducing grain size and tetragonality with co-substitution. The ferroelectric and magnetic properties are determined by (P–E) and (M–H) hysteresis loops at room temperature. Magnetic properties are significantly enhanced with an increase in the Ni2+, Na+ contents in the system. The correlation between the ESR width parameter (ΔH) and asymmetry parameter (Pays) with concentrations (x) reveals that the sample with x = 0.08 has a strong magnetic nature compared to other samples.