Piezoelectric performance, phase transitions, and domain structure of 0.96(K0.48Na0.52)(Nb0.96Sb0.04)O3−0.04(Bi0.50Na0.50)ZrO3 ceramics

Abstract

Demand for replacing the current lead-based piezoelectric materials with some lead-free ones becomes increasingly strong from environmental concerns. In this article, we report the piezoelectric performance, the phase transitions, and the domain configurations of highly dense 0.96(K0.48Na0.52)(Nb0.96Sb0.04)O3−0.04(Bi0.50Na0.50)ZrO3 ceramics prepared by two step-sintering through solid-state reaction. This material has outstanding piezoelectric properties of piezoelectric coefficient d33 = 512 pC/N and electromechanical coupling coefficient kp ≈ 0.56 at room temperature. While d33 exhibits a broad peak and is greater than 430 pC/N between −30 °C and 70 °C, kp depends weakly on temperature below 50 °C but decreases considerably with further increasing the temperature. In terms of thermal aging, both d33 and kp remain stable from −50 °C to 240 °C. The degradation of kp quickly stabilizes in the first thermal cycle between −50 °C and 150 °C. Furthermore, the measurement of relative dielectric permittivity ε′ upon heating indicates that rhombohedral-orthorhombic, orthorhombic-tetragonal, and tetragonal-cubic phase transitions occur at TR-O ≈ −40 °C, TO-T ≈ 54 °C, and TC ≈ 265 °C, respectively. The X-ray diffraction analysis shows that the crystalline structure at room temperature is of orthorhombic-tetragonal phase coexistence. We also investigate the domain structure with an acid etching technique. The unpoled ceramic exhibits a complicated domain pattern consisting of irregularly shaped domains of long parallel stripes separated by 180° domain boundaries from neighboring domains. In contrast, upon poling, the domain pattern becomes simpler and takes the form of long parallel stripes of diverse widths, with a hierarchical nanodomain structure appearing inside some of the broader stripes. We consider that the superior piezoelectric properties and reasonable temperature stability are closely related to the rhombohedral-orthorhombic and orthorhombic-tetragonal phase transitions and to the characteristic domain structure.