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Lead-free has been a goal that people pursue due to the environmental pollution caused by lead in lead-based materials. K0.5Na0.5NbO3(KNN) is one of the most promising lead-free piezoelectric materials. Theoretically, the piezoelectric properties of single crystals are much better than those of polycrystalline materials. However, it is difficult to fabricate uniform KNN-based crystals by the high-temperature melt method because of volatilization of elements. This method also needs complicated equipment and is expensive. Here, a seed-free, solid-state crystal growth (SFSSCG) method was used to prepare Mn, Li, and Bi co-doped KNN crystals, which show an ultrahigh piezoelectric coefficient of about 1050 pC N−1, around one order of magnitude higher than that of pure KNN ceramics. Furthermore, the effective piezoelectric coefficient d33* of this crystal can reach 2290 pm V−1 at a unipolar electric field of 10 kV cm−1. This crystal also shows a high Curie temperature and good ferroelectricity. It is expected that the lead-free KNN-based single crystals fabricated by this simple method show promise for high performance ferroelectric and piezoelectric applications in industry and are environment-friendly. [ABSTRACT FROM AUTHOR]

High temperature lead-free piezoelectric ceramics 0.67BiFeO3–0.33BaTiO3 doped with 0.35 mol% MnO2 and xBiScO3 (x = 0, 0.005, 0.01, 0.015, 0.02) were prepared by conventional solid-state sintering method. The effects of BiScO3 doping on the crystal structure, piezoelectric, ferroelectric and dielectric properties of BiFeO3-BaTiO3 piezoelectric ceramics were investigated. The results show that the BiScO3 doping can not change the crystal structure of the ceramics and the grain size of ceramics increases first and then decreases with the BiScO3 doping content increasing. The optimum piezoelectric properties d33 = 165 pC/N, kp = 0.349 and Qm = 52.132 were obtained when x = 0.01, with the highest remanent polarization Pr = 37.1 μC/cm2. The ceramics become normal ferroelectrics determined by temperature spectrum with the increase of x, and the Curie temperature and depolarization temperature of 425 and 408 °C are respectively obtained when x = 0.01. In particular, a small amount of BiScO3 doping is beneficial to the improvement of the temperature stability. Moreover, a perovskite solid solution forms between the BiScO3 and BiFeO3-BaTiO3 ceramics, which can improve the electrical properties of BF-BT ceramic system. [ABSTRACT FROM AUTHOR]

BF-BT-xBGa (shortened for 0.67BiFeO3-0.33BaTiO3-xBiGaO3+0.0035MnO2) lead-free piezoelectric were prepared by a conventional solid-state sintering method. The phase structure, miscostructure, piezoelectric, ferroelectric and dielectric properties were investigated. BiGaO3 doping has little effect on the crystal structure of BF-BT-xBGa lead-free piezoelectric ceramics. All samples are perovskite structure. With the change of x, the structure of the sample is pseudo cubic structure. The ceramics (with x = 0.02 sintered at 990 °C) has Pr = 25 µC/cm2, Ec = 22.059 kV/cm and high depolarization temperature Td = 422 °C. It was found that the piezoelectric properties of the ceramic were improved by addition of BiGaO3. The ceramic shows excellent electrical properties when x is 0.02: d33 = 170 pC/N and Tc = 434 °C. Proper amount of BiGaO3 doping can improve the size of the crystal and promote the sintering of samples. These results show that the addition of BiFeO3-BaTiO3 based ceramics is promising lead-free piezoelectric ceramics for practical applications. [ABSTRACT FROM AUTHOR]

A new Bi and Ba co-doped K0.52Na0.48NbO3 transparent ceramics were synthesized by using solid-state reaction method. Their microstructure, optical and electrical properties were studied. The results show that the obtained compact ceramic has a perovskite polycrystalline structure with cubic phase. Refinement on the crystalline structure shows that the Bi and Ba co-doping results in forming an interstitial solid solution in K0.52Na0.48NbO3 ceramic. An appropriate amount of Bi and Ba co-doping is helpful for improving the transparency and densification of the ceramics. The most transparency of the samples reaches a high value of about 60% in the near-IR region. The dielectric constant-temperature spectrum shows that with increasing the Bi and Ba content the dielectric constant-temperature transition peaks become to be more flat. The complex impedance plots exhibit two impedance semicircles identified within the frequency range of 1 kHz-1 MHz for all samples, which is explained by the grain and grain boundary effects. The presence of non-Debye type of relaxation has been observed by a complex impedance analysis. [ABSTRACT FROM AUTHOR]

The Na0.5K0.5NbO3single crystal was successfully grown by a seed-free solid-state crystal growth method using super-low content of LiBiO3as a sintering aid. Microstructure, piezoelectric, ferroelectric and dielectric properties were investigated. The results show that well-paralleled lamellar ferroelectric ordering domains structure are present and no crack can be seen inside the single crystal. The best piezoelectric and dielectric properties (at 1 kHz) ofd33= 265 pC/N,Pr= 27.4 μC/cm2, ε = 738, tanδ = 0.04 appear atx= 0.40at% for (1-x)Na0.5K0.5NbO3-xLiBiO3single crystal. A higher remnant polarizationProf 36.3 μC/cm2were obtained atx= 0.45 at%. [ABSTRACT FROM AUTHOR]

Large Na0.5K0.5NbO3 ( NKN) piezoelectric single crystals were obtained by seed-free solid-state crystal growth method, which is a traditional sintering grain growth process, with LiBiO3 used as a sintering aid. The largest dimension of the single crystals obtained was 11 mm × 9 mm × 3 mm. In addition to the LiBiO3 doping content, temperature, and time effect of the crystal growth process was systematically investigated and considered from the kinetics point of view. With the assistance of Avrami analysis, parameters relevant to the crystal growth process were determined. Laue diffraction and transmission electron microscopy suggested an orthorhombic symmetry for the single crystalline structure. Dielectric-frequency-temperature measurements revealed an orthorhombic-tetragonal and tetragonal-cubic phase transition at 155°C and 405°C, respectively, both of which are typical of first-order transitions, and have a well-defined thermal hysteresis. Rayleigh analysis was performed regarding to the extrinsic reversible and nonreversible piezoelectric properties, and the result suggested a dominant intrinsic reversible piezoelectric contribution of 91.5% under E0 = 1 kV/cm AC amplitude. Such a single crystal growth process route is low cost and a relative simple preparation process. [ABSTRACT FROM AUTHOR]

The (Ba 0.85Ca 0.15) (Zr 0.1Ti 0.9)O 3 −  x   wt% Sr(Cu 1/3Ta 2/3)O 3 [BCZT −  x  wt% SCT, x = 0–0.3] lead-free ceramics were prepared by the conventional solid-state method. The phase structure was investigated by X-ray diffraction. The results show that only a tetragonal phase is observed in these ceramics. The sintering behavior of BCZT ceramics is also improved by using SCT as a sintering aid. The ceramic with x  = 0.2 wt% SCT demonstrates good piezoelectric properties:d 33 ~ 577 pC/N and k p ~ 59.1 %, Furthermore, the Curie temperature of the ceramics also increases and reaches 97 °C. [ABSTRACT FROM AUTHOR]

LiSbO (LS) doped 0.994KNaNbO-0.004KCuTaO-0.002BiMnO (KNN-KCT-BM) piezoelectric ceramics with excellent properties have been fabricated by conventional ceramic processing. It is found that the dopant of LS has considerable effect on the grain size, phase structure and electrical properties of KNN-KCT-BM ceramics. The KNN-KCT-BM ceramics doped with 4.5 mol% LS ceramics show good electrical properties such as d = 208 pC/N, Q = 95, k = 40.5 %, T = 335 °C, T = 55 °C, ε = 1,190 and rather low dielectric dissipation of tan δ = 1.25 % (1 kHz) and tan δ < 1 % (100 kHz). This indicates that 4.5 mol% LS-doped KNN-KCT-BM piezoceramic is an alternative lead-free piezoelectric material for the development of piezoelectric devices working at high temperature. [ABSTRACT FROM AUTHOR]