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K0.5Na0.5NbO3 (KNN) crystals have great application prospects due to their excellent piezoelectric properties, high Curie temperature, and environmental friendliness. Currently, KNN crystals grown by the seed-free solid-state crystal growth (SFSSCG) method exhibit relatively high dielectric loss. In order to reduce their dielectric loss, Cu, Bi and Mn co-doped KNN lead-free piezoelectric single crystals were prepared by the SFSSCG method. The effects of the CuO doping content on the structure and electrical properties of (1 − x)(0.996KNN–0.004BiMnO3)–xCuO crystals were systematically studied. The results show that an appropriate doping amount of CuO is beneficial for the growth of the crystals and the improvement of electrical properties. When the diameter of the billets is 40 mm, the maximum crystal size of 25 × 21 × 2 mm3 is obtained. All crystals have a typical perovskite structure almost with a single orthorhombic phase and are very compact almost without holes. The minimum average domain width of 276 nm is obtained for the crystal at x = 0.005. The KNN crystals exhibit normal ferroelectric characteristics and a space-charge-limited-conduction (SCLC) mechanism. The introduction of Cu2+ ions reduces the dielectric loss of the crystal and increases its piezoelectric and dielectric properties. The Cu, Bi and Mn co-doped KNN crystals achieve excellent comprehensive properties: d33 = 314 pC N−1, Pr = 29.9 μC cm−2, Ec = 10.1 kV cm−1, = 869 pm V−1, Qm = 56.8, Kt = 0.38, tan δ = 0.013 and TC = 409 °C. This provides a route to improve the electrical properties of KNN-based crystals. [ABSTRACT FROM AUTHOR]

KNN crystals and solid-state crystal growth method have great application prospects due to their, respectively, outstanding advantages. However, at present there are also some problems that need to be solved urgently. In this work, both of BiCoO3 and CuO were chosen as dopants to further improve the size and piezoelectric properties of KNN-based crystals prepared by seed-free solid-state crystal growth (SFSSCG) method. In particular, the effects of CuO-doping on the growth, structure, and electrical properties were investigated systematically. The results show that Co, Cu, and Bi co-doping can promote the growth of KNN-based single crystals and enhance their electrical properties. The addition of CuO does not change the perovskite crystalline structure of the crystals. When the content of CuO is less than 0.5 at.%, the crystals have a single orthorhombic perovskite structure. And when the content of CuO is 0.7 at.%, a two-phase coexisting structure consisting of orthorhombic and tetragonal phases is present in the crystal. The domains in the crystals are mainly composed of 180° ones and have a parallel lamellar microstructure. The average domain width in the crystals first decreases and then increases with increasing the CuO content. When the content of CuO is 0.3 at.%, the crystals obtain an excellent overall electrical properties of d33 = 498 pC/N, Pr = 28.3 μC/cm2, Qm = 64.9, kt = 0.37, TC = 418 °C, εr = 373, and tanδ = 0.015, implying that they have a promising applications in piezoelectric and ferroelectric devices. [ABSTRACT FROM AUTHOR]

A trace of Zn doped 0.997K0.37Na0.63NbO3-0.003BaBiO3 based lead-free piezoelectric single crystals were prepared by a seed-free, solid-state method. The effects of Zn doping on the growth, microstructure and electrical properties of the single crystals were systematically studied. The results show that the Zn doping does not change the perovskite crystalline structure of the crystals. Compared with many other dopants, Zn doping can effectively reduce or even avoid crystal cracking, and bending/warping deformation during the growth process. With the increase of Zn content, the volume of the grown crystal first increases and then decreases, while the roughness of the crystal exposed surface first decreases and then increases. When the Zn-doping content is 0.8at.%, the size of the crystal reaches the maximum value of 12 × 10 × 2 mm3. The influence of Zn-doping content on the main electrical properties of the crystals also shows a similar changing relationship. For the crystal doped with 0.8at.% Zn, excellent electrical properties can be obtained as below: d33 = 354 pC/N, Pr = 47.2 µC/cm2, Tanδ = 0.6%, kt = 0.68, εr = 515, Tc = 402 °C. The results imply that the crystal has promising development and application prospects. [ABSTRACT FROM AUTHOR]

K0.5Na0.5NbO3(KNN)-based piezoelectric single crystals have relatively high Curie temperature and piezoelectric properties. Seed-free solid state crystal growth (SFSSCG) method has many advantages, such as simple process, low cost, easy composition control and no seed crystal required, etc. In this work, (1 − x)[0.997(0.996K0.5Na0.5NbO3–0.004MnBiO3)–0.003B2O3]–xLi2CO3 (x = 0, 0.001, 0.003, 0.005, 0.007) single crystals were prepared by the SFSSCG method with B2O3 used as a sintering aid. And the effects of Li doping on the growth, morphology, structure and electrical properties of the crystals were investigated. The investigation results indicate that Li-doping is beneficial to the growth of the crystal. The formation of tetragonal phase, a secondary phase, is promoted by the addition of appropriate amount of Li, especially at 0.3at.%. The electrical properties of the crystals are enhanced obviously after Li-doped. When doped with 0.3at.% Li, the crystal has excellent piezoelectric properties as follows: d33 = 422 pC/N, tanδ = 0.034, TC = 429°C, and Qm=166, etc. These results suggest that the obtained crystals have potential and promising application prospects in the field of environmental-friendly piezoelectric devices. [ABSTRACT FROM AUTHOR]

As we all known that the piezoelectric single crystals exhibit unique and outstanding performance and therefore have been used widely in many electronic devices, including sensors, actuators, and transducers. Recently, large lead-free K0.5Na0.5NbO3(KNN)-based piezoelectric single crystals were prepared using a seed-free solid-state crystal growth (SFSSCG) method. However, there are some defects in the crystals prepared by this method. The defects would inhibit the domain-wall movement and increase the leakage currents in the crystals and then prevent the improvement of performance of the crystals. Here, an approach to considerably enhance the piezoelectric properties of the KNN-based crystals by annealing treatment is reported. The effect of the annealing temperature on the structure and electrical properties of the crystals was studied. The results show that the annealing temperature has a little effect on the crystalline structure but great effect on the natural surface morphology, domain structure, and electrical properties of the single crystals. When the annealing temperature is in the range of 550 ~ 800 °C, it can enhance significantly the piezoelectric, ferroelectric, and dielectric properties of the crystals and decrease their dielectric loss. The crystal annealed at 700 °C shows excellent properties: d33 = 591pC/N, εr = 580, tanδ = 0.01, kt = 0.715, and Tc = 417 °C. The effects of the annealing treatment on the leakage current density and conduction mechanism in the crystals were also studied. The results indicate that the annealing treatment enables the crystals to far outperform the unannealed crystals and comparable to the lead-based materials. [ABSTRACT FROM AUTHOR]