Lead-free perovskite piezoelectric (1 − x)(K 0.45 Na 0.5 Li 0.05 )Nb 0.95 Sb 0.05 O 3 -x(Ca 0.95 Ba 0.05 )(Zr 0.9 Sn 0.1 )O 3 ceramics were fabricated via a conventional sintering process. A microstructural study was conducted for the ceramics through a scanning electron microscope, whose grain sizes were found to gradually reduce with increasing x. The phase structure of the studied ceramics was identified by the combined analysis of X-ray diffraction data and dielectric-temperature measurements, and a rhombohedral-orthorhombic-tetragonal phase coexistence was observed to exist in the wide composition range of 0 ≤ x ≤ 0.05. The ceramics exhibited the optimal piezoelectric properties at x = 0.01, which had a piezoelectric constant d 33 of 290 pC/N and a planar electromechanical coupling coefficient of 0.43. A diffuse phase transition was induced with x increased to a relatively high value, featuring the broadening of Curie peak. In addition, the variations of ferroelectric properties with composition were investigated in this work as well. The authors believe that adding the calcium barium zirconate stannate compound (Ca 0.95 Ba 0.05 )(Zr 0.9 Sn 0.1 )O 3 into (K,Na)NbO 3 -based ceramics is a valid way for the improvement of their piezoelectric properties.
A new lead-free piezoelectric solid solution system with the formula of (1−x)(K0.45Na0.55)(Nb0.965Sb0.035)O3−xBi0.5(K0.91Li0.09)0.5(Hf0.3Zr0.7)O3 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 Bi0.5(K0.91Li0.09)0.5(Hf0.3Zr0.7)O3 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 d33 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.
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