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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]

Improving the electrical properties is one of the key technologies that need to be solved to promote the application of lead-free piezoelectric materials. This paper reports Li, Bi and Al co-doped (K0.5Na0.5)NbO3 lead-free piezoelectric single crystals grown via a Seed-Free Solid-State Crystal Growth (SFSSCG) method, and especially the effects of Li doping on the morphology, structure, and electrical properties of the single crystals. The results indicate that Li doping increases the crystal size and electrical performance of the crystals. When x = 0.004, the crystal obtains the best comprehensive electrical performance: d33 ~ 468 pC/N, Pr ~ 35.3 μC/cm2, Qm ~ 58, kt ~ 0.41, tanδ ~ 0.029, TO-T ~ 142 ℃, TC ~ 420 ℃. This provides an available route for the development and application of the potassium sodium niobate (KNN) system and has theoretical and practical significance for further regulating the functional properties of lead-free piezoelectric single 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]

The structure, microstructure, piezoelectric properties, ferroelectric properties and Curie temperature of (1 − x)BiFeO3–xBaTiO3–Bi(Zn0.5Ti0.5)O3 + MnO2 + Li2CO3 ceramics were investigated experimentally. The samples were prepared by the improved solid-state reaction approach. The crystalline structures were examined by X-ray diffractometry. When x = 0.3, the rhombohedral and pseudocubic phases coexist in the ceramic structure. It is considered that the morphotropic phase boundary was formed here. At this composition, the piezoelectric performance d33, Curie temperature TC, and depolarization temperature are as high as 184 pC/N, 550 °C, 530 °C at x = 0.3, respectively. It is worth noting that, when x = 0.24, the ceramics have a high TC = 580 °C and low dielectric loss tanδ = 1.9%. The results show that the BFBT-BZT ceramics with high piezoelectric properties are applicable in high-temperature fields. [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]

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 microstructures, phase structure, and electrical properties have been investigated for the SbO-modified (BaCa)(ZrTi)O lead-free piezoelectric ceramics. The grain size was strongly affected by SbO, and the solid solutions show a single phase perovskite structure. The ceramics with x = 0.1 % exhibit enhanced electrical properties of d ∼556 pC/N, k ∼52 %, ε ∼3,895, tan δ ∼1.3 %, and P ∼12.6 μC/cm when sintered at a low temperature of ∼1,350 °C. The high temperature stability of ferroelectric properties ( P ∼14.8 μC/cm) was obtained in the temperature range from −60 to 0 °C. And with the addition of small amount of SbO, Curie temperature ( T) maintains virtually unaltered. [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]

Lead-free (BaCa)TiO-Ba(ZrTi)O- xwt %CuO(BCZT- xCu) piezoelectric ceramics have been fabricated by the solid-state reaction process and the effects of CuO addition on the phase structure and piezoelectric properties of the ceramics have been studied. Our results reveal that the addition of CuO significantly improves the sinterability of BCZT ceramics which results in a reduction of sintering temperature from 1,540 to 1,350 °C without sacrificing the high piezoelectric properties. X-ray diffraction (XRD) data shows that CuO diffuses into the lattice of BCZT- xCu ceramics and a pure perovskite phase forms in the ceramic. SEM images indicate that a small amount of CuO addition affects the microstructure, obviously. Main piezoelectric parameters of these ceramics are optimized around x = 0.04 wt % with a high piezoelectric coefficient ( d = 510 pC/N), a planar electromechanical coefficient k of 45%, a high dielectric constant ( ε = 3,762) and a low dissipation factor (tan δ = 1.05%) at 1 kHz. The results indicate that the BCZT- xCu ceramics are promising lead-free practical applications. [ABSTRACT FROM AUTHOR]

Lead-free 0.95 K0.5Na0.5NbO3-0.05LiSbO3 (KNN-LS) ceramics doped with 0.2 mol% BiMnO3 (BM) have been prepared by the conventional mixed-oxide technique, with sintering temperature at 1095-1120°C. Microstructural and compositional analyses of these doped ceramics have been carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of the sintering temperature on the microstructure and piezoelectric and dielectric properties of BM-doped KNN-LS ceramics have been investigated. The results show that initially increasing the sintering temperature is very effective in improving the density and electric properties. However, the properties of the samples would be deteriorated as they are sintered over the optimum temperature. The KNN-LS-0.2% BF ceramics show excellent properties of d33 = 208 pC/N, kp = 43%, Qm = 65, tan θ = 2.78%, and Tc = 385°C with sintering temperature at 1110°C. [ABSTRACT FROM AUTHOR]

The phase relationships in the Gd-Co-Al ternary system at 500°C have been investigated mainly by X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy. The existence of two ternary compounds GdCo0.74Al1.26 and Gd2Co2Al has been confirmed. Twenty-two single-phase regions (including solid solution regions of the binary compounds), 43 two-phase regions, and 22 three-phase regions were found to exist at this isothermal section. In this work, no new binary or ternary phase was found. [ABSTRACT FROM AUTHOR]