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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.

(1 − x)(0.95K0.5Na0.5NbO3–0.05LiSbO3) − xAl(Fe0.9Mn0.1)O3 (KNN–LS–AFM) lead-free piezoelectric ceramics have been fabricated by a traditional ceramic technique. The structure and piezoelectric properties of this system have been studied. The result of X-ray diffraction analysis shows that LS and AFM diffuse into the KNN lattices to form a new solid solution with a perovskite structure. The phase structure of the ceramics has a transition from the coexistence of tetragonal and orthorhombic phases to single tetragonal phase, with increasing the AFM content. The orthorhombic–tetragonal phase-transition peaks in the temperature-dielectric constant (e r ) plots first shifts to the room temperature and then almost disappears, while the Curie temperature does not change evidently with the addition of AFM. The ceramic at x = 0.004 exhibits the best piezoelectric properties: d 33 = 285 pC/N, k p = 53.9 %, Q m = 22.64. The Curie temperature is about 350 °C. Below the Curie temperature, all samples show a temperature-stable piezoelectric constant, indicating the possibility of applications from the room temperature to high temperature.

The (1 − x)K0.5Na0.5NbO3–xAlFeO3 ((1 − x)KNN–xAF) (x = 0.01–0.08) lead-free piezoelectric ceramics were prepared at low temperature of 1,000 °C by conventional ceramic processing. And AF was used as a sintering aid in order to improve the sintering behavior of KNN. The effect of AF addition on the microstructure, dielectric and piezoelectric properties of the ceramics have been investigated. The results indicate that a small amount of AF can improve the sintering performance and piezoelectric properties of the ceramics effectively. The KNN–AF ceramics for x = 0.03 show the best piezoelectric properties: d 33 = 116 pC/N, k p = 32.9 %, Q m = 114.8, T C = 382 °C, P r = 21.8 μC/cm2. This also indicates that (1 − x)KNN–xAF ceramics are a promising lead-free piezoelectric candidate material because of its good properties, low-temperature sintering characteristics and plenty of Al2O3 and Fe2O3 resources with low cost.

(1 − x) (0.95K0.5Na0.5NbO3–0.05LiSbO3)–xBiScO3 lead-free piezoceramics have been fabricated by an ordinary pressure-less sintering process. The relationship between the BS content, phase structure, density, and piezoelectric properties and their temperature stability was discussed particularly. All compositions show a main perovskite structure, showing room-temperature symmetries of orthorhombic at x = 0, of tetragonal at 0.002 ≤ x ≤ 0.01. When 0.002 ≤ x ≤ 0.008, the ceramics have excellent electrical properties of d33 = 265–305 pC/N, kp = 45–54%, ɛr = 1346–1638, Curie temperature Tc = 315–370 °C and depolarizing temperature Td = 315–365 °C, comparable to that of other KNN-based piezoceramics. The results indicate that the ceramics are promising lead-free piezoelectric materials.