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Abstract: A facile hydrothermal route via high temperature mixing method was used to synthesize (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramic powders. The influence of Ta doping and K+/(K+ +Na+) molar ratios in the starting solution on the resultant powders were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscopy, and selected area electron diffraction. The Ta element was successfully doped into the alkaline niobate structure to form crystalline (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramics powder. The microstructure, piezoelectric, ferroelectric, and dielectric properties of the sintered (K, Na) (Nb, Ta)O3 ceramics from the obtained powders were investigated. The piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p), dielectric constant (ɛ r), and remnant polarization (P r) of the sample sintered at 1180°C show optimal values of 210pC/N, 34.0%, 2302, and 19.01μC/cm2, respectively. [Copyright &y& Elsevier]

Abstract: (K, Na)(Nb, Sb)O3 (KNNS) lead-free peizoceramic powders were successfully synthesized by hydrothermal treatment at 240°C for 8h using the KOH, NaOH, Nb2O5 and Sb2O3 as raw materials. Effects of Sb-doping on the crystal structure and morphology of the as-prepared powders were investigated by powder X-ray diffraction (XRD), Raman spectra (Raman), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The Sb element was successfully doped into the alkaline niobate perovskite structure to form crystalline (K0.7Na0.3)(Nb0.95Sb0.05)O3 lead-free piezoelectric ceramic powder, which has a hexagonal morphology due to the aggregation growth of small grains. Phase and morphology evolutions with the reaction time were also studied, and a possible formation mechanism was proposed. [Copyright &y& Elsevier]

Abstract: BaTiO3 (BT) powders were synthesized by the hydrothermal method for fabricating lead-free barium titanate piezoelectric ceramics. The obtained powders were washed by distilled water and 0.01N acetic acid solutions separately, and utilized to obtain piezoelectric ceramics by traditional sintering. BT ceramics with the highest piezoelectric properties (d 33 value is over 190 pC/N) was obtained from the BT powder synthesized at 250°C and washed by acetic acid solution. The influence of washing method and sintering temperature on the piezoelectric properties of BT ceramics were studied. The reasons were investigated by comparing the properties of BT powders and their compacts sintered at different temperature. [Copyright &y& Elsevier]

The investigation of fine structural evolutions around the morphotropic phase boundary (MPB) is important to understand the origin of the high piezoelectricity in ferroelectric ceramics. Here, we report a new phase boundary associated with oxygen octahedral tilt–untilt transition by exploring average and local structural evolutions in the vicinity of MPB in Bi0.5Na0.5TiO3–PbTiO3 (BNT–PT) ceramics. It is found that the local structural change of the oxygen octahedral tilt–untilt transition is decoupled with the average structural change of the rhombohedral-to-tetragonal phase transition at MPB in BNT–PT. The slight octahedral tilting distortion at MPB is responsible for the large high-field-induced electrostrain and small low-field-induced piezoelectricity in BNT–PT. The crucial difference of MPB between BNT–PT and the classical piezoelectric Pb(Zr,Ti)O3 is discussed from their local structural evolutions of octahedral tilting to the performance changes at MPB. It helps us to figure out the origin of large high-field-induced electrostrain but small piezoelectricity in BNT-based ceramics. [ABSTRACT FROM AUTHOR]

To analyze the effect of PFN content on the microstructure and electrical properties of x Pb(Fe 0.5 Nb 0.5)O 3 –(0.57− x)Pb(Ni 1/3 Nb 2/3)O 3 –0.43Pb(Zr 0.3 Ti 0.7)O 3 , the doping of x PFN–PNN–PZT) were systematically studied with 0.015 ≤ x ≤ 0.075. XRD patterns and Raman spectra analysis reveal that PFN diffuses into PNN–PZT perovskite lattice and forms new quaternary solid solution. With the increase of PFN content x , the proportion of rhombohedral (R) phase decreases gradually, whereas the proportion of tetragonal (T) phase displays a contrary trend. In particular, R – T coexistence near MPB was observed at x = 0.045. Meanwhile, optimized electrical properties of d 33 = 961 pC/N, k p = 0.716, ε r = 6298, and tan δ = 3.1% are achieved for the 0.045PFN–PNN–PZT ceramics. Moreover, the ceramics at MPB showed larger remnant polarization P r = 24.55 μC/cm2, smaller coercive field E c = 0.36 kV/mm, and lower dielectric relaxor degree γ = 1.813. All these results reveal that the enhanced electrical properties could be attributed to synergistic phase boundary motion, dielectric relaxor behavior and ferroelectric hysteresis effect. [ABSTRACT FROM AUTHOR]

(KNa)NbO piezoelectric ceramics can be sintered at a temperature as low as 750 °C for 5 h by incorporating LiCO + BiO + ZnO as the sintering aid, whereas the conventional sintering temperature is around 1,100 °C. The optimal 'soft' piezoelectric properties are obtained for ceramics sintered at 850 °C for 5 h. The dielectric permittivity ( ε), piezoelectric coefficient ( d), electromechanical coupling ( k) and mechanical quality factors ( Q) of (K, Na)NbO modified with 5.5 wt% sintering aids are 1,436, 90 pC/N, 0.3 and 10, respectively. These values are similar to the values obtained for (KNa)NbO ceramics sintered above 1,100 °C. The underlying mechanism for abrupt change of dielectric permittivity is explained. [ABSTRACT FROM AUTHOR]

K0.5Na0.5NbO3 (KNN) lead-free piezoelectric ceramics containing 1 mol% ZnO (KNNZ) were prepared by optimizing the sintering conditions using the newly developed K5.70Li4.07Nb10.23O30 (KLN) as a sintering aid. The phase structure and electrical properties of the KNNZ ceramics were investigated as a function of the KLN concentration. The results show that a small amount of KLN was incorporated into the lattice and formed a single-phase perovskite structure. The KLN modification lowered the phase transition temperature of the orthorhombic–tetragonal structure and increased the Curie temperature. Interestingly, an appropriate amount of KLN can simultaneously improve the sinterability of the KNNZ ceramics and the ferroelectric and piezoelectric properties. Good piezoelectric and dielectric properties (piezoelectric constant, d 33  =  131 pC/N; planar coupling coefficient, k p  =  0.42; dielectric constant, ϵ r  =  634; and mechanical quality factor, Q m  =  20) were obtained for the KNNZ ceramics doped with 1 mol% KLN. Therefore, KNNZ + 1.0 mol% KLN ceramics containing an appropriate amount of KLN are good candidate materials for the preparation of lead-free piezoelectric ceramics. [ABSTRACT FROM PUBLISHER]

Abstract: Two-step sintering was applied to manufacture a typical Li- and Ta/Sb-modified alkaline niobate-based lead-free piezoelectric ceramics. The sintering condition dependences of dielectric constants and piezoelectric properties were investigated. Under the optimal condition, dense specimens have an average grain size of approximately 5μm, and show good dielectric and piezoelectric properties. Significantly, the (K0.4425Na0.52Li0.0375) (Nb0.8925Sb0.07Ta0.0375)O3 ceramics sintered under the condition “1130/10/1020/15” show the peak values of the piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p), and dielectric constant (ɛ), which are 281pC/N, 50% and 1500, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Furthermore, the KNLNST ceramics maintain relatively low dielectric loss over wide temperature ranges. The result indicates that the KNLNST ceramics sintered by two-step sintering exhibit good temperature stability. [Copyright &y& Elsevier]

Abstract: Lead-free (K0.4425Na0.52Li0.0375) (Nb0.9625−x Sb x Ta0.0375)O3 piezoelectric ceramics were prepared by the conventional sintering method. The effects of the Sb content on the phase structure, microstructure, dielectric, piezoelectric, and ferroelectric properties of the (K0.4425Na0.52Li0.0375) (Nb0.9625−x Sb x Ta0.0375)O3 ceramics were investigated. The much higher Pauling electronegativity of Sb compared with Nb makes the ceramics more covalent. By increasing x from 0.05 to 0.09, all samples exhibit a single perovskite structure with an orthorhombic phase over the whole compositional range, and the bands in the Raman scattering spectra shifted to lower frequency numbers. The grain growth of the ceramics was improved by substituting Sb5+ for Nb5+. Significantly, the (K0.4425Na0.52Li0.0375) (Nb0.8925Sb0.07Ta0.0375)O3 ceramics show the peak values of the piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p ), and dielectric constant (ɛ), which are 304pC/N, 48% and 1909, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Besides, the underlying mechanism for variations of the electrical properties due to Sb5+ substitution was explained in this work. [Copyright &y& Elsevier]

• Sintering BFO-BT piezoelectric ceramics at low temperature below 900 °C. • Low-temperature sintered BFO-BT ceramics maintain superior electrical properties. • Good thermal stability of BFO-BT ceramic with high T d around 300 ℃. • High piezoelectricity of d 33 > 119 pC/N in wide temperature range. Piezoelectric ceramics usually have high sintering temperature, which cannot meet the low-temperature co-firing requirements of ceramics and metal electrodes in production of micro devices. Here, we studied the effects of CuO-B 2 O 3 binary composite sintering aids on the sintering behavior, phase composition, microstructure, and electrical properties of the bismuth ferrite-barium titanate (0.7BiFeO 3 -0.3BaTiO 3 , BFO-BT) based lead-free piezoelectric ceramics. We found that the CuO-B 2 O 3 sintering aids can effectively lower the sintering temperature of the BFO-BT ceramics to 880 ℃, which is far below the melting point of metal electrodes. The BFO-BT based ceramics with 0.5 wt% sintering aids exhibited excellent dielectric, ferroelectric, and piezoelectric properties (ε m = 83029, P m = 38.4 μC/cm2, P r = 33.8 μC/cm2, d 33 = 119 pC/N) with high Curie temperature (T C = 460 ℃). Meanwhile, this ceramic possessed high depolarization temperature (T d) near 300 ℃, demonstrating a good temperature stability of piezoelectricity. This study provides a feasible solution to improve the compatibility of lead-free piezoelectric materials and low-melting point metal electrodes for fabrication of micro piezoelectric devices. [ABSTRACT FROM AUTHOR]

Understanding the phase structure evolution is important for developing high performance lead-free piezoelectric materials. In this work, the effects of A-site ionic size of monovalent ions on the phase transition behaviors for the lead-free niobate ceramics ANbO 3 (A = Li, Na, Ag, and K) are investigated using XRD analysis and dielectric measurement. The iso-valent ionic doping restrains the relaxation behavior that usually appears in the hetero-valent ionic-doped niobate ceramics. The A-site average ionic size of R A and its ionic radius differences of ΔR A are found to be crucial influence factors on the phase transition behaviors of the ANbO 3 ceramics. Small Li+ doping stabilize tetragonal phase of the ANbO 3 ceramics with R A > 1.47 Å, but stabilize rhombohedral phase of the ones with R A < 1.47 Å. On the other hand, The ANbO 3 ceramics without Li+ doping prefer to orthorhombic phase due to indistinctive ionic size differences (ΔR A < 0.25 Å). Our results suggest that a certain phase and phase transition boundary could be designed by appropriate ionic doping for developing the niobate-based lead free piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

This paper presents an approach for acousto-ultrasonic source (passive damage or impact) localization based on metal core piezoelectric fiber (MPF) rosettes. MPF is a new type piezoelectric ceramic device with small size and has high directivity to sense Lamb waves. The response of surface-bonded MPF sensors to Lamb-wave fields is explored theoretically and experimentally. The good directional properties of MPF are used to determine the direction of propagation of the acoustic waves by mounting three MPF sensors in a rosette configuration. Two suitably spaced rosettes are used to locate the source of the ultrasound by taking the intersection of the direction given by each rosette. The performance of the rosettes for source location is validated on an aluminum plate. [ABSTRACT FROM AUTHOR]