Structure, dielectric, and ferroelectric properties of (1-x)Bi0.5Na0.5TiO3 – X K0.5Na0.5NbO3 (0 ≤ x ≤ 0.1) solid solution

Abstract

The correlation of the phase structure, dielectric, and ferroelectric properties of lead-free (1-x)(Na0.5Bi0.5)TiO3–xK0.5Na0.5NbO3 (NBTKNx) (0 = x ≤ 0.1) polycrystalline ceramics, fabricated via a solid state reaction technique, were investigated. The Rietveld refinement allowed identifying the crystallographic transformation from a rhombohedral to a coexisting rhombohedral-tetragonal or tetragonal long range-ordered ferroelectric (FE) phase. The dielectric investigations showed an increase of the dielectric diffuseness (1.53 = γ ≤ 1.73) and a clear shift of the depolarization temperature (Td) to a lower temperature while increasing substitution. More importantly, the lattice disorder also generated a plateau-like dielectric anomaly, leading to a thermally stable ϵr ∼2859 ± 20% (120–500 °C) and ∼3112 ± 10% (120–420 °C) for x = 0.075 and 0.1 samples, respectively. At room temperature (RT), Raman spectroscopy investigations revealed a downshift of the frequencies as a function of the composition with an inhomogeneous broadening of the Raman lines. On heating, Raman spectra showed changes in the region where the dielectric transitions are observed. Moreover, the composition dependence of the current peaks in the I-E loops confirmed the occurrence of a phase transition from a non-ergodic polar phase to an ergodic weakly polar after the applying of an electric field of 60 kV/cm−1.