Effect of rare earth substitution on properties of barium strontium titanate ceramic and its multiferroic composite with nickel cobalt ferrite

Highlights: • Rare earth ions Dy³⁺, Gd³⁺ and Sm³⁺ have been substituted in Ba_0.95Sr_0.05TiO₃ (BST). • Ni_0.8Co_0.2Fe₂O₄ has been used as ferrimagnetic phase to obtain composites. • Substitution of these ions increases dielectric constant of BST and composites. • Magnetoelectric coefficient of composites increases on substitution of these ions. - Abstract: Effect of substitution of rare earth ions (Dy³⁺, Gd³⁺ and Sm³⁺) on various properties of Ba_0.95Sr_0.05TiO₃ (BST) i.e. the composition Ba_0.95−1.5xSr_0.05R_xTiO₃ (where x = 0.00, 0.01, 0.02, 0.03 and R are rare earths Dy, Gd, Sm) and that of their multiferroic composite with Ni_0.8Co_0.2Fe₂O₄ (NCF) has been studied. Shifting of peaks corresponding to different compositions in the X-ray diffraction pattern confirmed the substitution of rare earth ions at both Ba²⁺ and Ti⁴⁺ sites in BST. It is clear from scanning electron microscopy (SEM) images that rare earth substitution in BST increases its grain size in both pure and composite samples. Substitution of rare earth ions results in increase in value of dielectric constant of pure and composite samples. Sm substitution in BST significantly decreases its Curie temperature. Dy substituted pure and composite samples possess superior ferroelectric properties as confirmed by polarization vs electric field (P–E) loops. Composite samples containing Dy, Gd and Sm substituted BST as ferroelectric phase possess lower values of remanent and saturation magnetizations in comparison to composite sample containing pure BST as ferroelectric phase (BSTC). Rare earth substituted composite samples possess higher value of magnetoelectric coefficient as compared to that for BSTC