Temperature dependent phase structure and enhanced electrical properties of CaZrO3-modified (K,Na,Li) (Nb,Ta)O3 lead-free piezoelectric ceramics

Abstract

A series of lead-free (K0·49Na0·49Li0.02) (Nb0·8Ta0.2)O3 (KNLNT) piezoelectric ceramics modified by CaZrO3 (denoted as KNLNT-xCaZrO3, x = 0–0.05) were synthesized using a conventional solid-state approach. Herein, the influence of CaZrO3 doping on the crystal structure, ferroelectric properties, dielectric properties as well as piezoelectric properties were systematically investigated. The XRD analysis shows that all the proposed samples present pure perovskite phase, revealing the phase structure transition from an orthorhombic to a pseudocubic phase at a threshold value of x is 0.01 and 0.03. Moreover, the in-situ XRD characterization was applied to investigate the transformation process of phase structure: the pseudocubic-tetragonal (TP-T) phase transition temperature has been decreased to room temperature at x = 0.04. In addition, the results were further confirmed by the temperature-dependent dielectric properties. For the microstructure, the typical strip-like domains and nanoscale domains can be found in transmission electron microscopy (TEM) images. Due to the coexistence of orthorhombic and pseudocubic with x = 0.03, the remnant polarization has an anomaly, and large strain value and large signal d33* value is obtained under a 20 kV/cm electric field, which is about 0.106% and 532 pm/V.