Structure and dielectric dispersion in cubic-like 0.5K0.5Na0.5NbO3- 0.5Na0.5Bi0.5TiO3 ceramic

TL;DR

This study investigates the cubic-like state and dielectric properties of a lead-free piezoelectric ceramic, revealing complex structural features and relaxor behavior with significant dielectric dispersion.

Contribution

It provides detailed structural analysis combining multiple diffraction techniques and compares relaxor behavior with other known relaxors, highlighting the unique dielectric dispersion of KNN-50BNT.

Findings

Pure perovskite structure with pseudocubic symmetry

Superlattice reflections indicate tetragonal symmetry

Strong dielectric dispersion observed

Abstract

The nature of the cubic-like state in the lead-free piezoelectric ceramics 0.5K0.5Na0.5NbO3-0.5Na0.5Bi0.5TiO3 (KNN-50BNT) has been examined in detail by synchrotron x-ray diffraction (SD), selected area electron diffraction (SAED), neutron diffraction (ND), and temperature dependent dielectric characterization. The SD pattern of KNN-50BNT presents a pure perovskite structure with pseudocubic symmetry. However, superlattice reflections were observed by SAED and completely indexed by tetragonal symmetry with P4bm space group in ND pattern. The relaxor behavior of KNN-50BNT is compared with Pb-based and Ba-based relaxors and discussed in the framework of the Vogel-Fulcher law and the new glass model. The KNN-50BNT ceramic exhibits the strongest dielectric dispersion among them.