Structure, microstructure, magnetic and magnetodielectric investigations on BaTi(1-x-y)FexNbyO3 ceramics

Abstract

Impact of iron and niobium co-substitution in lead-free BaTiO3 ceramics on structure, microstructure, ferromagnetic and magnetodielectric behavior has been investigated. Phase pure BaTi(1-x-y)FexNbyO3 ceramic samples where x = y = 0, 0.025 and 0.05 were synthesized using solid-state reaction method. An absence of peak splitting in (200)pc reflection with an increase in x, y mole fraction indicates structural transformation. Rietveld refinement on powder diffraction data shows an existence of tetragonal (P4mm) and cubic (Pm-3m) phases in BaTi(1-x-y)FexNbyO3 ceramic samples. The cubic phase fraction is increased from 0.10 to 0.49 when the x, y mole fractions are increased from 0.025 to 0.05 respectively. An average grain size of the samples is reduced from 3.6 µm (pure BT) to submicron with Fe and Nb-substitution in the B-site of BaTiO3 ceramics. Improved ferromagnetic behavior is due to the destruction of spin cycloid with respect to tetragonal to cubic phase transformation and oxygen vacancies. Ferromagnetic order in Fe and Nb-substituted samples are confirmed from the convex curvature in ABK plot. A high value of negative Magnetodielectric constant (MDC) (%) at low frequencies (< 104 Hz) originates from extrinsic contribution which corresponds to Maxwell- Wagner polarization effect whereas strain-mediated coupling is attributed to intrinsic magnetodielectric constant above 104 Hz. The magnetoelectric coupling coefficient of 2.8371 × 10−5 mV/cm Oe is calculated for 0.025 mol fraction sample.