Multiphase coexistence and enhanced piezoelectric properties in (1-x)(K0.45Na0.55)(Nb0.965Sb0.035)O(3-)xBi(0.5)(K0.91Li0.09)(0.5)(Hf0.3Zr0.7)O-3 lead-free ceramics

A new lead-free piezoelectric solid solution system with the formula of (1-x)(K0.45Na0.55)(Nb0.965Sb0.035)O(3-)xBi(0.5)(K0.91Li0.09)(0.5)(Hf0.3Zr0.7)O-3 were prepared using a conventional solid-phase sintering method, and we investigated the relationship between the composition, microstructure, phase structure and electrical properties of the ceramics. It was found that adding Bi-0.5(K0.91Li0.09)(0.5)(Hf0.3Zr0.7)O-3 induced the ceramics transition from a single orthorhombic structure to a coexistence of multiple phases, and a three-phase coexistence of rhombohedral, orthorhombic and tetragonal phases was present in the composition range x = 0.03 to 0.035. Enhanced piezoelectric properties were obtained for the ceramics near the three-phase coexistence region, with the largest piezoelectric constant d(33) of 253 pC/N and the highest planar electromechanical coupling coefficient of 0.36. Additionally, a rough phase diagram for the solid solution system was established by using the critical temperatures determined by the temperature-dependent dielectric properties. The authors believe that these results can provide a useful reference for the development of (K,Na)NbO3-based lead-free piezoelectric ceramics.