The structure and electronic properties closely related to piezoelectricity of BaZrO₃-modified K_0.5Na_0.5NbO₃ lead-free ceramics: First-principle study

As one of the most attractive lead-free piezoelectric ceramics, K_0.5Na_0.5NbO₃ (KNN) has received widespread attention and by elemental doping or forming solid solution with other components, the electrical properties can be improved dramatically. Among which, BaZrO₃ (BZ) as a most promising solid solution for modification has been introduced in KNN to induce a phase transition and thus promote the electrical performance to further meet practical applications. However, the relationship between microscopic structural characteristics and macroscopic performance is still relatively vague and need to be clarified. Hence, in this work, the structural, elastic, and electronic properties of BZ-modified KNN were investigated using the first-principle calculations. The calculated results demonstrated that BZ entered the lattice of KNN spontaneously, strengthened the Nb–O octahedron distortion and optimized the elastic properties, which are all beneficial to improving the structural asymmetry and piezoelectric response. In addition, doping Ba resulted in the shift of Fermi surface toward the conduction band and thus decreased the band gap, while doping individual Zr increased the band gap. Under the coupling action of these two atoms, KNN-BZ illustrated more denser band structure and more wider band gap, which facilitated the promotion of electrical breakdown resistance and electric polarization of KNN. This study provides theoretical insights into improving the piezoelectricity of KNN.