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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]

Lead-free K0.5Na0.5NbO3 (KNN)-based single crystals have been prepared by a seed-free, solid-state crystal growth method. The effects of the calcined temperature of ingredients on the growth, structure and electrical properties of the single crystals are systematically studied. Results show that increasing the calcined temperature is beneficial to the synthesis of pure orthorhombic-phase powder, but it hardly affects the phase structure of the single crystals. When the calcined temperature is in the range of 700–850 °C, it is more useful for obtaining larger KNN-based crystals. What is more, the width of the domains in the crystals first decreases and then increases with rising of the calcined temperature, which is in well agreement with the changing regularity of the structure and electrical properties. The single crystals with good electrical properties can be obtained in a wide calcined-temperature range of 700–850 °C: the piezoelectric constant d33 of 155–209 pC N−1, dielectric constant ε of 291–389, dielectric loss tanδ of 2.0–3.4%, and remnant polarization Pr of 25.4–49.1 μC cm−2. [ABSTRACT FROM AUTHOR]

K0.5Na0.5NbO3 single crystal with trace amounts of lithium addition was grown by the seed-free solid-state crystal growth method. The Li addition is helpful for the growth of the crystals and improves the properties of the K0.5Na0.5NbO3 single crystals. A small amounts (0.2–0.3 at.%) of Li addition can trigger the formation of around 25% tetragonal phase. The occurrence of the phase transition may be due to the variety of the K/Na atomic ratio after Li substitution in both the Na and K sites. The optimum amount of Li addition in the crystal is 0.2–0.3 at.% in order to obtain a well performance K0.5Na0.5NbO3-based single crystal. The best electrical performance of these K0.5Na0.5NbO3-based crystals can be achieved as follows: d33 = 255 pC/N, tanδ = 1%, d*33 = 313 pm/V, and Pr = 26.1 μC/cm2, indicating that the structure and properties of K0.5Na0.5NbO3-based crystals grown by the seed-free solid-state crystal growth method can be closely affected by trace lithium carbonate addition. [ABSTRACT FROM AUTHOR]

Abnormal grain growth (AGG) has been a common phenomenon during the ceramic or metallurgy processing since prehistoric times. However, usually it had been very difficult to grow big single crystal (centimeter scale over) by using the AGG method due to its so-called occasionality. Based on the AGG, a solid-state crystal growth (SSCG) method was developed. The greatest advantages of the SSCG technology are the simplicity and cost-effectiveness of the technique. But the traditional SSCG technology is still uncontrollable. This article first summarizes the history and current status of AGG, and then reports recent technical developments from AGG to SSCG, and further introduces a new seed-free, solid-state crystal growth (SFSSCG) technology. This SFSSCG method allows us to repeatedly and controllably fabricate large-scale single crystals with appreciable high quality and relatively stable chemical composition at a relatively low temperature, at least in (K 0.5 Na 0.5 )NbO 3 (KNN) and Cu-Al-Mn systems. In this sense, the exaggerated grain growth is no longer 'Abnormal' but 'Normal' since it is able to be artificially controllable and repeated now. This article also provides a crystal growth model to qualitatively explain the mechanism of SFSSCG for KNN system. Compared with the traditional melt and high temperature solution growth methods, the SFSSCG method has the advantages of low energy consumption, low investment, simple technique, composition homogeneity overcoming the issues with incongruent melting and high volatility. This SFSSCG could be helpful for improving the mechanical and physical properties of single crystals, which should be promising for industrial applications. [ABSTRACT FROM AUTHOR]

K 0.5 Na 0.5 NbO 3 (KNN)-based lead-free piezoelectric single crystals have been prepared by the Seed-Free, Solid-State Crystal Growth (SFSSCG) method, and the effects of MnO 2 doping on the structural and electrical properties were systematically investigated. The results showed that the MnO 2 -doping can promote the growth of K 0.5 Na 0.5 NbO 3 -BiAlO 3 (KNN-BA) single crystals and enhance its electrical properties. Furthermore, the size of the (1 - x)(KNN-BA)- x MnO 2 crystals reached the maximum value of about 18 × 17 × 2 mm3 at x = 0.005. Also, the color of the crystals did gradually change, from light yellow to dark brown, due to the addition of MnO 2. The XRD and refinement results showed that the addition of MnO 2 , in the range of 0 ≤ x ≤ 0.009, did not change the crystalline structure of the perovskite crystals. A two-phase perovskite crystalline structure was present in all crystals: an orthorhombic and a tetragonal phase. The content of the orthorhombic phase decreased, while the content of the tetragonal phase increased, with an increase in the MnO 2 content. In addition, the domains in the crystals were mainly composed of 180° ones and had a parallel lamellar structure. Also, the smallest average domain width was obtained for crystals with x = 0.003. These crystals had the largest piezoelectric constant of 568 pC/N and an excellent overall performance of d 33 = 568 pC/N, P r = 32.2 μC/cm2, Q m = 55.3, k t = 0.36, k p = 0.39, T C = 418 °C, ε r = 430, and tan δ = 0.015. • Compared with BiAlO 3 ceramics, single crystal exhibits more excellent electrical properties. • Using the Seed-Free, Solid-State Crystal Growth(SFSSCG) method, the process is simpler. • MnO 2 dopant promotes the growth of single crystal grains and the improvement of electrical properties. • The prepared KNN-BiAlO 3 single crystal has high piezoelectric properties. [ABSTRACT FROM AUTHOR]

CaZrO 3 (CZ)-doped Na 0.5 K 0.5 NbO 3 (NKN)-based single crystals with 20 mm over were prepared by a seed-free solid-state crystal growth (SFSSCG) method. The microstructure, piezoelectric and dielectric properties of the crystal were investigated. The results show that the piezoelectric constant d 33 of this crystal is evidently enhanced up to 488 pC/N with the addition of CZ. Two dielectric anomalies appear at 391 and 149 °C, corresponding to the tetragonal → cubic and orthorhombic → tetragonal phase transition, respectively. There exists two domains (90° and 180°) in the crystal. These results show that this NKN-based crystal is a promising lead-free piezoelectric material for applications. [ABSTRACT FROM AUTHOR]