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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]

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]

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]

Abstract: Lead-free (1−x)(Ba0.85Ca0.15)(Ti0.9Zr0.1)O3−xBiYbO3 [(1−x)BCTZ−xBYO] piezoelectric ceramics in the range of BYO concentrations were prepared by the conventional oxide-mixed method, and the effect of BYO content on their microstructure, crystalline structure, density and electrical properties was investigated. A dense microstructure with large grain was obtained for the ceramics with the addition of BYO. The ceramics with x=0.1% exhibit an optimum electrical behavior of d 33~580pC/N, r~10.9Ω, k p~56.4%, and tan δ~1.12% when sintered at a low temperature of ~1350°C. When the measuring electric field is 40kV/cm, the well-saturated and square-like P–E loops for the ceramics were observed with P r~12.2μC/cm2 and E c~1.83kV/cm. [Copyright &y& Elsevier]