Simultaneous Enhancement of Piezoelectricity and Temperature Stability in KNN‐Based Lead‐Free Ceramics Via Layered Distribution of Dopants

Abstract

The past two decades have seen a great enhancement of piezoelectric coefficients (d33) to higher than 570 pC/N in (K, Na)NbO3 (KNN) piezoelectrics, but one notoriously unresolved issue is their severe temperature instability, obstructing them toward practical applications. The present work demonstrates a facile approach to overcome this problem by introducing a layered distribution of key dopants (Li and Sb) in a monolithic ceramic, featuring stepwise varied polymorphic phase transition (PPT) temperatures along the thickness direction. The dopant‐graded ceramic exhibits an outstanding d33 of 508 pC/N and a very large piezoelectric strain (Suni, of 0.18%). More importantly, an excellent temperature stability (d33 variation within 13% over the temperature range of 25–150 °C) is achieved, which is superior to that of most state‐of‐art KNN counterparts. These are attributed to the construction of spatially diffused PPT in combination with enhanced polarization, permittivity, and piezoresponse through interfacial effect, including the Maxwell–Wagner effect and intergranular stress by gradient doping. The results offer an alternative strategy for designing high‐performance piezoelectric materials with desirable temperature reliability.

Diffuse multiphase coexistence renders temperature-insensitive lead-free energy-harvesting piezoceramics

“…27 In consequence, this type of DMC phase boundary is characterized by O–T phase coexistence together with an abundant domain configuration, which is likely to flatten the thermodynamic potential curve and thus improve the temperature stability of the piezoelectric and dielectric properties. 28…”

“…27 In consequence, this type of DMC phase boundary is characterized by O-T phase coexistence together with an abundant domain conguration, which is likely to atten the thermodynamic potential curve and thus improve the temperature stability of the piezoelectric and dielectric properties. 28 It has been experimentally identied that atomic-scale heterostructures can result in a widespread distribution of local phase transition points, thereby leading to a diffuse phase transition. 12,29,30 The normalized 3 r values for x = 0.00 and x = 0.035 in a wide temperature region are shown in Fig.…”

A critical review: the impact of electrical poling on the longitudinal piezoelectric strain coefficient

“…207 Recently, Song et al reached temperature stability in the range of 25-150 1C along with a higher piezoelectricity d 33 = 508 pC N À1 and a piezoelectric strain of 0.18% by adopting a facile approach with doping by Li and Sb in the monoclinic KNN ceramic, which is greater compared with other KNN composites. 208 The parallelism between electrical poling (DC loaded) and unipolar cycling together in lead-free and lead-based piezoelectric materials has already been demonstrated in the literature. 209,210 The notion of space charge concentration around the grain boundaries [210][211][212] can explain the unipolar cycling behaviour, which is responsible for the appearance of an intrinsic biased field (E int ) and gradual reduction of the piezoelectric characteristics.…”

“…207 Recently, Song et al reached temperature stability in the range of 25–150 °C along with a higher piezoelectricity d 33 = 508 pC N −1 and a piezoelectric strain of 0.18% by adopting a facile approach with doping by Li and Sb in the monoclinic KNN ceramic, which is greater compared with other KNN composites. 208…”

Realizing an Ultrahigh Depolarization Temperature near the Curie Point and Large d33 with Superior Temperature Stability in Lead-Free Ceramics via a Sandwich Structure Design

“…30 Despite the fact that T tc can be significantly improved through engineering the layered distribution of dopants without deteriorating d 33 , T d is still much lower than T m . 31 Therefore, there is still a severe challenge in lead-free piezoceramics for simultaneously attaining T d near the Curie point and relatively large d 33 as well as ultralow T tc in a facile and effective manner.…”