Room temperature constructing rhombohedral-tetragonal phase boundary in novel (Bi, Na)(Zr, Ti)O3 modified (K, Na)(Nb, Sb)O3 ceramics: Phase structure, defect and piezoelectric performance

Abstract

Lead-free (1-x)(K0.5Na0.5)(Nb0.96Sb0.04)O3-x(Bi0.5Na0.5)(Zr0.8Ti0.2)O3 ceramics (abbreviated as (1-x)KNNS-xBNZT, x = 0, 0.01, 0.02, 0.03, 0.035 and 0.04) were synthesized by the solid-state method, and the dependence of phase evolution, microstructure, oxygen vacancy defect and electrical properties on compositions were carefully investigated. All ceramics had a pure perovskite structure and a dense microstructure. The phase transition temperatures (TR-O and TO-T) of the ceramics were adjusted by adding BNZT, and the rhombohedral-tetragonal (R-T) phase coexistence boundary was successfully constructed at room temperature when x = 0.03, the excellent piezoelectric performance (d33 ∼ 323 pC/N, kp ∼ 0.372) and high Curie temperature (TC ∼ 276 °C) have been achieved at this time. The grain size of the ceramics showed a strong difference on x content, and the maximum relative density value of 95.42% was obtained. The domain structure characterized by PFM confirmed that the ceramics possess small-sized nano-domains and complex domains at x = 0.03, which are the origin of enhanced piezoelectric properties. Moreover, the oxygen vacancy defect that can pin the domain walls was increased with the addition of (Bi0.5Na0.5)(Zr0.8Ti0.2)O3. As a result, the doping with BNZT can significantly affect the phase structure and electrical properties of the ceramics, indicating that the (1-x)KNNS-xBNZT ceramics system with a R-T phase boundary is a promising lead-free piezoelectric material.