Structure evolution, dielectric, and conductivity behavior of (K0.5Na0.5)NbO3-Bi(Zn2/3Nb1/3)O3 ceramics

Abstract

(1−x)K0.5Na0.5NbO3−xBi(Zn2/3Nb1/3)O3 ((1−x)KNN−xBZN, x = 0.010, 0.015, 0.020, 0.025, and 0.030) lead-free ceramics were fabricated via a traditional solid-state method. The crystal structure, microstructure, dielectric, and conductivity behavior of this system were studied. Combined with X-ray diffraction (XRD) patterns, Rietveld refinement, and dielectric spectroscopy, an orthorhombic phase was determined for x = 0.010, an orthorhombic-tetragonal mixed phase was identified for x = 0.015, and a rhombohedral symmetry appears in 0.020 ⩽ x ⩽ 0.030. Both 0.98KNN−0.02BZN and 0.975KNN−0.025BZN ceramics exhibit stable permittivity and low dielectric loss tangent (tanδ) in wide temperature ranges owing to the combination of rhombohedral-tetragonal step-like feature and the diffuse phase transition from tetragonal to cubic. The activation energies of dielectric relaxation and conductivity behavior at high temperatures initially decrease slightly, then drop sharply, and finally decline slowly, which could be attributed to microstructure morphologies and the concentration of oxygen vacancies.