Enhanced piezoelectricity and temperature stability in LaFeO₃‐modified KNN‐based lead‐free ceramics

Abstract

(0.96‐x)K0.48Na0.52NbO3‐0.04Bi0.5Na0.5ZrO3‐xLaFeO3 ceramics (abbreviated as KNN‐BNZ‐LF1000x) with enhanced piezoelectric performance and temperature stability were prepared by the conventional solid‐state sintering method. It was found that the incorporation of LaFeO3 gradually shifted the O‐T phase boundary toward room temperature, while maintaining the Curie temperature above 300°C. The optimal piezoelectricity was found at x = 0.006, with relatively high piezoelectric constant d33 of 345 pC/N as well as a high level of unipolar strain (0.126% at 3 kV/mm). Benefiting from the diffused phase transition induced by appropriate amount of LaFeO3 content, the KNN‐BNZ‐LF6 sample possessed greatly enhanced the temperature stability of d33∗, which varied less than 8% in the temperature range of 20°C‐100°C.

Feasible Way to Achieve Multifunctional (K, Na)NbO3-Based Ceramics: Controlling Long-Range Ferroelectric Ordering

“…Moreover, the splitting peaks of (110) pc and (002) pc diffractions gradually shift toward each other with increasing x , indicating the increased average crystal symmetry. However, both (001) pc and (200) pc diffractions are singlets at x = 0.10, which was widely observed in KNN-based ceramics having a high content of additives and was reported to be a pseudo-cubic phase. ,, Besides, the faster speed of the (002) pc peak shifting to higher angles than that of the (200) pc peak shifting to lower angles suggests the shrinkage of the lattice volume, which could be attributed to the smaller ion radius of Sb 5+ (0.60 Å) than that of Nb 5+ (0.64 Å). , …”

“…However, both (001) pc and (200) pc diffractions are singlets at x = 0.10, which was widely observed in KNN-based ceramics having a high content of additives and was reported to be a pseudocubic phase. 8,26,27 Besides, the faster speed of the (002) pc peak shifting to higher angles than that of the (200) pc peak shifting to lower angles suggests the shrinkage of the lattice volume, which could be attributed to the smaller ion radius of Sb 5+ (0.60 Å) than that of Nb 5+ (0.64 Å). 17,28 Temperature-dependent dielectric properties (i.e., ε′ and ε″) of unpoled and poled ceramics at different frequencies are measured to further analyze the phase structure (Figures S1, S2).…”

Utilization of Nonstoichiometric Nb5+ to Optimize Comprehensive Electrical Properties of KNN-Based Ceramics

“…While in the cooling stage, excessive Nb 5+ separates and aggregates at the GBs to form clusters inhibiting the grain growth process. 27 In addition, the number of defects in the lattice increases, and the relative density gradually decreases with Nb 5+ concentration increasing from 0.02 to 0.04, reducing the diffusion coefficient. The generation of oxygen vacancies decreases the migration rate of the GBs, inhibiting the growth of grains.…”

“…The decreasing stage can be ascribed to the limited solid solubility of Nb 5+ in KNN x T-BNZ-BFO ceramics, that is, more Nb 5+ dissolves in the lattice as the Nb 5+ concentration increases further during the sintering process. While in the cooling stage, excessive Nb 5+ separates and aggregates at the GBs to form clusters inhibiting the grain growth process . In addition, the number of defects in the lattice increases, and the relative density gradually decreases with Nb 5+ concentration increasing from 0.02 to 0.04, reducing the diffusion coefficient.…”

Subtle Structural Changes in LaFeO3 at High Pressure

“…[ 1–4 ] LaFeO 3 is the parent compound of many important perovskite series. [ 5–8 ] The technological versatility of LaFeO 3 is due to it being a multiferroic, showing ferroelectric ordering above 475 K [ 9 ] and antiferromagnetic ordering (with a small ferromagnetic canting) below ≈740 K. [ 9–16 ] The ferromagnetic canting and dielectric properties are shown to be highly tunable with the substitution of Fe with Ni or Co. [ 17,18 ] Pure LaFeO 3 theoretically shows favourable piezoelectric properties, [ 19 ] and has been demonstrated to improve the piezoelectric response when added as a dopant to K–Na–Nb ceramics. [ 8 ]…”