This study investigated crystal structures, microstructures, and electric-field-induced strain (EFIS) properties of Bibased lead-free ferroelectric/relaxor composites. Bi_1/2(Na_0.82K_0.18)_1/2TiO₃ (BNKT) as a ferroelectric material and 0.78Bi_1/2(Na_0.78K_0.22)_1/2TiO₃-0.02LaFeO₃ (BNKT2LF) as a relaxor material were synthesized using a conventional solid-state reaction method, and the resulting BNKT2LF powders were subjected to high-energy ball milling (HEBM) after calcination. As a result, HEBM proved a larger average grain size of sintered samples compared to conventional ball milling (CBM). In addition, the increased sintering time led to grain growth. Furthermore, HEBM treatment and sintering time demonstrated a significant effect on EFIS of BNKT/BNKT2LF composites. At 6 kV/mm, 0.35% of the maximum strain (S_max) was observed in the HEBM sample sintered for 12 h. The unipolar strain curves of CBM samples were almost linear, indicating almost no phase transitions, while HEBM samples displayed phase transitions at 5~6 kV/mm for all sintering time levels, showing the highest S_max/E_max value of 700 pm/V. These results indicated that HEBM treatment with a long sintering time might significantly enhance the electromechanical strain properties of BNT-based ceramics.

In this paper, piezoelectric ceramics with the composition of (Na0.525K0.4425Li0.0375)(Nb0.8975Sb0.065Ta0.0375)O3 + 0.3 wt% CoO + x CuO (0.005≤x≤0.025) (abbreviated to NKL-NST) were fabricated for ultrasonic sensor application. The effects of CuO addition and sintering on the microstructure and the piezoelectric properties of the NKL-NST ceramics were systematically studied. Excellent piezoelectric properties such as electromchanical coupling factor(kp) = 0.415, piezoelectric constant (d33) =166 pC/N and piezoelectric figure of merit d33*g33= 5.47 pm2/N were obtained from the 2.5 mol% CuO doped NKL-NST+0.3 wt%CoO ceramics sintered at 1,000℃ for 3 h.

We investigated the sintering behavior and piezoelectric properties of lead-free (K0.5Na0.5)NbO3 ceramics co-doped with excess 0.01 mol ZnO and x mol MnO2, where x was varied from 0 to 0.03. Excess MnO2 addition was found to retard the grain growth and densification during sintering. However, 0.005 mol MnO2 addition improved the piezoelectric properties of 0.01 mol ZnO added (K0.5Na0.5)NbO3 ceramics. The planar mode piezoelectric coupling coefficient, electromechanical quality factor, and piezoelectric constant d33 of 0.01 mol ZnO and 0.005 mol MnO2 added specimen were 0.40, 304, and 214 pC/N, respectively.

In this paper, in order to develop excellent Pb-free composition ceramics for ultrasonic sensor. The SnO2-doped (Na0.525K0.443Li0.037)(Nb0.883Sb0.08Ta0.037)O3)(abbreviated as NKL-NST) ceramics have been synthesized using the ordinary solid state reaction method. The effect of SnO2-doping on their dielectric and piezoelectric properties was investigated. The ceramics doped with 0 wt% SnO2 have the optimum values of piezoelectric constant(d33), piezoelectric figure of merit(d33·g33), planar piezoelectric coupling coefficient(kp) and density : d33= 195[pC/N], d33·g33=5.62 pm2/N.kp= 0.40, density= 4.436[g/cm3]. suitable for duplex ultrasonic sensor application.

In this paper, in order to develop outstanding Pb-free piezoelectric composition ceramics, the (Na0.525K0.443Li0.037)(Nb0.883Sb0.08Ta0.037)O3 + 0.3 wt%Bi2O3 + 0.4 wt%Fe2O3 + x wt%CuO (x= 0∼0.8 wt%)(abbreviated as NKL-NST) lead-free piezoelectric ceramics have been synthesized using the ordinary solid state reaction method. The effects of CuO-doping on the structure and electrical properties of the NKL-NST ceramics were systematically studied. The results show that the ceramics exhibit a pure perovskite structure with orthorhombic phase at room temperature, and secondary phase was found in the ceramics. The 0.4 wt%CuO added ceramics sintered at 950℃ showed the optimum properties of piezoelectric constant(d33), planar piezoelectric coupling coefficient(kp) and mechanical quality factor(Qm) : d33= 213 [pC/N], kp= 0.43, Qm= 423,respectively.

n this paper, in order to develop outstanding Pb-free composition ceramics, the Fe2O3-doped(Na0.525K0.443Li0.037)(Nb0.883Sb0.08 Ta0.037)O3 + 0.3 wt% Bi2O3 + x wt% Fe2O3 (x= 0∼1.0 wt%)(abbreviated as NKL-NST) lead-free piezoelectric ceramics have been synthesized using the ordinary solid state reaction method. The effect of Fe2O3-doping on their microstructure and electrical properties were investigated. XRD diffraction pattern studies confirm that Fe2O3 completely diffused into the NKL-NSTlattice to form a new stable soild solution with Fe3+ entering the Nb5+, Sb5+ and Ta5+ of B-site. And, phase structure of all the ceramics exhibited pure perovskite phase and no secondary phase was found in the ceramics. The ceramics doped with 0.6 wt% Fe2O3 have the optimum values of piezoelectric constant(d33), planar piezoelectric coupling coefficient(kp) and mechanical quality factor(Qm) : d33= 233[pC/N], kp= 0.44, Qm= 95. These results indicate that the (Na0.525K0.443Li0.037)(Nb0.883Sb0.08Ta0.037)O3 +0.3 wt%Bi2O3 + 0.6 wt% Fe2O3 ceramic is a promising candidate for lead-free piezoelectric ceramics.

Lead-free piezoelectric ceramic/epoxy composites with ``0-3`` connectivity were prepared by cold-pressing with a temperature controlled curing method. A ceramic powder with a composition of (Na0.51K0.47Li0.02)(Nb0.8Ta0.2)O3 was synthesized by a conventional solid state reaction route. The dielectric and piezoelectric properties of ceramic/epoxy composites were characterized as a function of the volume fraction (φ) of piezoelectric ceramics, which was varied from 70 to 95vol%. The results indicated that the piezoelectric properties of composites were significantly affected by the volume fraction of ceramics. In terms of the piezoelectric properties, specimens showed the best performance at φ= 85vol%, resulting in the piezoelectric constant d33 of 39pC/N and the figure of merit as a piezoelectric energy harvester (d33·g33) of 1.24 pm2/N.

As lead-free piezoelectric materials, Ag2O doped 0.95(K0.5Na0.5) NbO3-0.05LiNbO3+ x mol% (where x = 0, 0.5, 1, 1.5, 2, 2.5 and 3, respectively) ceramics were fabricated by a conventional sintering process. The doping effects on the microstructure and electrical properties of the 0.95(K0.5Na0.5) NbO3-0.05LiNbO3 ceramics were systematically investigated. When the 3 mol % Ag2O doped 0.95(K0.5Na0.5)NbO3-0.05LiNbO3 samples were sintered at 1,080℃ for 5 hrs in air, these ceramics showed excellent values of density=4.20 g/cm3, piezoelectric constant (d33)=174pC/N and phase transition temperature(Tc)=421.6℃, respectively.

1 mol% Li2O excess 0.9(Na0.52K0.48)NbO3-0.1LiTaO3 lead-free piezoelectric multilayer ceramic actuators were investigated to determine their aging properties. To reduce the thermal aging behavior, we applied a rectified unipolar electric field of 5 kV/mm to the specimen to accelerate the electric aging behavior. By employing a rectified unipolar electric field for the piezoelectric actuators, we could remove undesirable heating from the relaxation current in the motion of the ferroelectric domain. To accelerate the aging test, the applied electric fields had a frequency of 900 Hz. To have enough time for charging and discharging, we employed an accurate time constant to design the equivalent circuit model for the aging tester. To extract exact aging behavior, we measured the pseudo-piezoelectric coefficient before and after the aging process. We also measured the electro-mechanical coupling coefficient, the frequency-dependent dielectric permittivity, and the impedance to compare with fresh and aged specimen.

Abstract: (K(0.5)Na(0.5)) (Nb(0.96)Sb(0.04)) O(3)+1.2 mol% K(4)CuNb(8)O(23) ceramics doped with iron oxide (Fe(2)O(3)) were prepared by a conventional mixed oxide method. And then, their piezoelectric and dielectric properties were investigated as a function of Fe(2)O(3) addition. X-ray diffraction studies reveal that Fe(3+) diffuses into the NKN lattices to form a solid solution with a pure perovskite structure at room temperature. At the sintering temperature of 1,060℃, when 0.2 mol% Fe(2)O(3) was doped, the piezoelectric constant (d(33)), electromechanical coupling factor (Kp), and mechanical quality factor (Qm) showed the excellent values of 131.67 pC/N, 0.436, and 696.36, respectively. Results show that Fe(2)O(3) deped (K(0.5)Na(0.5))(Nb(0.96)Sb(0.04))O(3)+1.2 mol% K(4)CuNb(8)O(23) lead-free piezoelectric ceramics are a promising lead free material for piezoelectric transformer applications.