Study of the relationships among the crystal structure, phase transition behavior and macroscopic properties of modified (K,Na)NbO 3 -based lead-free piezoceramics

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(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.

Section: Resultsmentioning

confidence: 99%

“…Moreover, electrical properties with an excellent stability were obtained in these ceramic systems. The addition of the La 2 O 3 or Fe 2 O 3 also served as a sintering aid to improve the density and enhance the electrical performance in the KNN‐based ceramics …”

Section: Introductionmentioning

confidence: 99%

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

Wang

Xing

et al. 2019

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“…Therefore, many studies have been carried out to synthesize novel NKN‐based piezoelectric ceramics with the rhombohedral‐tetragonal PPB structure . Furthermore, NKN‐based materials with the orthorhombic‐tetragonal PPB structure exhibited high d 33 values (300‐450 pC/N) . An orthorhombic NKN‐based material also displayed excellent piezoelectric properties ( d 33 of 512 pC/N and an electromechanical coupling factor ( k p ) of 0.54) …”

Section: Introductionmentioning

confidence: 99%

Thermally stable high strain and piezoelectric characteristics of (Li, Na, K)(Nb, Sb)O₃‐CaZrO₃ ceramics for piezo actuators

Lee

Kim

et al. 2019

The 0.97(Na0.5K0.5)(Nb1−xSbx)O3‐0.03CaZrO3 ceramic with x = 0.09 exhibits a high d33 of 518 pC/N and a strain of 0.13% at 4.0 kV/mm owing to its orthorhombic‐pseudocubic polymorphic phase boundary (PPB) structure. However, these values decreased considerably above 90°C owing to its low Curie temperature (TC), indicating that its thermal stability is not sufficient for practical applications. Li2O was added to the specimen with x = 0.11 to improve its thermal stability of the strain and d33 by increasing the TC without degrading the actual d33 and strain values. The 0.97(Li0.04Na0.46K0.5)(Nb0.89Sb0.11)O3‐0.03CaZrO3 ceramic, having an orthorhombic‐tetragonal PPB structure, exhibits a d33 of 502 pC/N and a strain of 0.16%. This large strain was maintained up to 150°C and the d33 slightly decreased to 475 pC/N at 130°C. Therefore, this lead‐free ceramic displays excellent piezoelectric characteristics with improved thermal stability, indicating that it can be applied to piezoelectric actuators.

“…In order to detect the evolution of tetragonality induced by Nb nonstoichiometry, the tendency of c/a ratio and lattice parameters as the function of Nb content were shown in Figure E. Increased c/a ratio results from the suppression of vacancies can be observed with the increase in Nb content, which may partly contribute to the improvement of piezoelectric constant, as excess Nb 5+ can incorporate into crystal lattice and result in more distortions of oxygen octahedron along with higher tetragonality …”

Section: Resultsmentioning

confidence: 99%

Defect engineering electrical properties of lead‐free potassium sodium niobate‐based ceramics

Sun

Zheng

et al. 2019

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Defect engineering plays an important role in property modification for piezoelectric materials. In this work, we pay much attention to the effect of Nb nonstoichiometry on structure and properties of typical 0.95(K0.45Na0.55)Nb1+xO3–0.05Bi0.5Na0.5HfO3 ceramics. Large piezoelectric constant (d33 ~ 425 pC/N and d33∗ ~482 pm/V) together with high Curie temperature (TC ~ 315°C) have been achieved in the ceramics with excess Nb content (x = 0.01). However, the ceramics with deficient Nb element have seriously suppressed cryogenic εr‐T curves and deteriorated electrical properties. Multi‐scale characterizations including phase structure, microstructure, defect structure and domain structure have been adopted to explain the corresponding phenomenon. Defect complex VNb″″′-VnormalO·· caused by deficient Nb induces clamped domain wall motion, leading to blocked polarization vector and poor electrical properties. On the contrary, the enhanced properties for the ceramics with excess Nb are attributed to easier domain switching due to the suppressed vacancies. We believe that defect engineering, for example nonstoichiometry, cannot only modulate electrical properties but also help us to understand some fundamental and critical problems about KNN‐based ceramics.