Spectroscopic investigation of morphotropic phase control in BNKT-BBN relaxor ferroelectrics

Abstract

Today, lead-free dielectric ceramics are drawing tremendous interest for its use in energy storage applications. We have studied bismuth layer structured relaxor BaBi2Nb2O9 (BBN) into 0.78(Bi1/2Na1/2TiO3)-0.22(Bi1/2K1/ 2TiO3) (BNKT). BNKT-BBN, a composite of a ferroelectric and relaxor, exhibits versatile energy conversion efficiency and morphotropic phase controllability. Thus, precise quantification on the ferroelectric phase and the detailed evolution mechanism of the dielectric/ferroelectric properties in the controlled BNKT-BBN ceramics, are scrutinized by analyzing chemical and local structural information gathered from X-ray spectroscopies. The results demonstrate that not only the tetragonal-to-rhombohedral phase evolution but also the formation of conductive grain boundaries are observed, and both are responsible for lowering the remnant polarization to enhance the energy conversion efficiency. Therefore, controlling the grain boundaries in the mixed ceramics can be a novel tuning knob to tailor the dielectric properties to secure reliable ferroelectrics-based energy materials.