Due to growing environmental concerns on the toxicity of lead-based piezoelectric materials, lead-free alternatives are urgently required but so far have not been able to reach competitive performance. Here we employ a novel phase-boundary engineering strategy utilizing the multiphase convergence, which induces a broad structural flexibility in a wide phase-boundary zone with contiguous polymorphic phase transitions. We achieve an ultrahigh piezoelectric constant (d 33) of 700 ± 30 pC/N in BaTiO3-based ceramics, maintaining >600 pC/N over a wide composition range. Atomic resolution polarization mapping by Z-contrast imaging reveals the coexistence of three ferroelectric phases (T + O + R) at the nanoscale with nanoscale polarization rotation between them. Theoretical simulations confirm greatly reduced energy barriers facilitating polarization rotation. Our lead-free material exceeds the performance of the majority of lead-based systems (including the benchmark PZT-5H) in the temperature range of 10–40 °C, making it suitable as a lead-free replacement in practical applications. This work offers a new paradigm for designing lead-free functional materials with superior electromechanical properties.

The piezoelectric and ferroelectric properties of [Bi0.5(Na1−x−yKxLiy)0.5]TiO3 (BNKLT-x∕y) lead-free piezoelectric ceramics were studied. The ceramics show excellent piezoelectric and ferroelectric properties, and the optimum properties measured are as follows: piezoelectric constant d33=231pC∕N, planar and thickness electromechanical coupling factors kP=41.0% and kt=50.5%, remanent polarization Pr=40.2μC∕cm2, and coercive field Ec=2.47kV∕mm, respectively. Polarization versus electric (P-E) hysteresis loops of the ceramics are well rectangle shaped, and the dependence of P-E loops on temperature reveals that the depolarization temperature Td of BNKLT-0.15∕0.075 ceramics, which simultaneously have good piezoelectric properties (d33=164pC∕N,kp=36.3%,kt=48.6%) and strong ferroelectricity (Pr=38.8μC∕cm2,Ec=3.73kV∕mm) at room temperature, is about 195 °C.

Articles you may be interested inInvestigation on transition behavior and electrical properties of (K0.5Na0.5)1-xLixNb0.84Ta0.1Sb0.06O3 around polymorphic phase transition region AIP Advances 4, 017125 (2014); 10.1063/1.4863200 Improved temperature stability of CaTiO 3 -modified [ ( K 0.5 Na 0.5 ) 0.96 Li 0.04 ] ( Nb 0.91 Sb 0.05 Ta 0.04 ) O 3 lead-free piezoelectric ceramics J. Appl. Phys.͑K 0.44−x Na 0.52 Li 0.04 Ag x ͒͑Nb 0.91 Ta 0.05 Sb 0.04 ͒O 3 lead-free piezoelectric ceramics were prepared by normal sintering. The effects of Ag content on the phase structure and piezoelectric properties of the ceramics were mainly studied. These results show that the phase structure undergoes a transition from orthorhombic to tetragonal phase with increasing x from 0.00 to 0.06. The optimum Ag content enhances the piezoelectric properties, and the Curie temperature increases with increasing x. The ceramics with x = 0.02 exhibit enhanced electrical properties ͑d 33 ϳ 263 pC/ N, k p ϳ 45.3%, T C ϳ 353°C, r ϳ 1478, and tan ␦ ϳ 2.3%͒ and good aging characteristics. These results show that the ceramic with x = 0.02 is a promising lead-free piezoelectric material.

For potassium-sodium niobate, poor piezoelectric properties always perplex most researchers, and then it becomes important to attain a giant piezoelectricity. Here we reported a giant piezoelectric constant in (1-x)(K0.48Na0.52)(Nb0.95Sb0.05)O3-xBi0.5Ag0.5ZrO3 lead-free ceramics. The rhombohedral-tetragonal phase boundary was shown in the ceramics with 0.04

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