Papers by Keyword: Lead-Free Ceramics

Abstract: Lead-free MnO doped 0.955K_0.5Na_0.5NbO₃-0.045Bi_0.5Na_0.5ZrO₃ (abbreviate as KNN-0.045BNZ) ceramics have been prepared by a conventional solid-state sintering method in a reducing atmosphere. The addition of MnO suppresses grain growth and eliminates the liquid phase. MnO dopant changes the crystalline structures of KNN-0.045BNZ ceramics from the classical Morphotropic Phase Boundary (MPB) with rhombohedral phase (R) and tetragonal phase (T) to the suppressed MPB with R/T phase. The 0.4% MnO doped KNN-0.045BNZ ceramics show an excellent electrical properties with quasi static piezoelectric constant d₃₃=300 pC/N, Curie temperature T_C = 350 °C, insulation resistivity ρ=4.83 × 10¹¹ (Ω・cm), and high field piezoelectric constants =438 pm/V (at E_max = 25 kV/cm). The results indicate that the 0.4%Mn doped KNN-0.045BNZ ceramic is a promising lead-free piezoelectric candidate material for commercial applications.

Abstract: In this research, the effect of electrode type on electrical i.e. dielectric and ferroelectric behavior of 0.94BNT-0.06BT ceramics was studies. The ceramics were prepared by conventional mixed oxide method. The sample exhibited a pure perovskite structure with rhombohedral phase. For dielectric measurement, the ceramics with Ag pasted electrodes exhibited very high dielectric constants and good responding with low frequency than Au sputtered electrode.

Abstract: A solid-state reaction method is generally used to fabricate ceramics. This work studies the influence of heterogenous nano-crystallites on electrical properties of lead free Na_0.47K_0.47Li_0.06NbO₃ (NKLN) ceramics by adding SrTiO₃ nano-crystals as the initial phase of reaction. The lead-free piezoelectric ceramics were synthesized by the seed-induced method. The SrTiO₃ nano-crystals used as seeds were prepared by molten salt technique. The seed content was varied from 0 to 10.0 mol%. The investigation reports microstructure and electrical properties of ceramics. The XRD showed a mixed tetragonal and orthorhombic phase structure. T_c decreasing with increased SrTiO₃nano-crystal concentration.

Abstract: The study was conducted to find out the effect of particle sizes of BaTiO₃ (BT) seed on the microstructure and electrical properties of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) ceramics. The BT seeds were prepared by the molten salt method. Results indicated that the BT seed powder showed a single pure perovskite phase when using a low temperature of ~750°C. The particle sizes of BT seeds increased from ~381 to ~600 nm with increasing heating temperatures from 750 to 900°C. After that, the different BT seeds were mixed with BaCO₃, CaCo₃, ZrO₂ and TiO₃ via the solid state reaction method. The mixed powder was calcined and sintered at 1200 °C for 2 h and 1450 °C for 4 h, respectively. The microstructure, phase formation and electrical properties were investigated. All ceramic samples showed a pure perovskite phase. The density and average grain size values of ceramics were in the range of 5.36-5.47 g/cm³ and 9.83-11.86 μm, respectively. The highest values of dielectric constant (ε_r), piezoelectric constant (d₃₃) were 3393 and 452 pC/N, respectively which obtained at the sample of BT-seed size 372 nm doped.

Abstract: Material research and development on piezoelectric ceramics, especially lead-free ceramics, was proposed from a viewpoint of relationships between piezoelectricity and elastic constants such as Young’s modulus and Poisson’s ratio. We developed a method to be convenient to measure acoustic wave velocities by an ultrasonic thickness gauge with high-frequency. From the change in longitudinal and transvers wave velocities before and after DC poling, it was found that the ceramic bulk density was important to improve the piezoelectricity in lead-free ceramics. As a result, the candidates of lead-free ceramic compositions with higher piezoelectricity were proposed. Furthermore, the ratio of transvers wave velocity to longitudinal wave velocity was clarified to estimate compositions with higher piezoelectricity. The measurement of sound velocities was an effective method for researching and developing piezoelectric materials, and it was possible to design the material compositions of lead-free piezoelectric ceramics as well as lead-containing ceramics by the novel measuring method.

Abstract: Lead-free piezoelectric 0.97 K_0.5Na_0.5NbO₃-0.03 AlFeO₃ (KNN-AF) ceramics were prepared at low temperature of 980 °C to 1020 °C by the conventional ceramic process. The effect of sintering temperature on the crystal structure, density and electrical properties of the ceramics was investigated. The results indicate that KNN-AF ceramics sintered at an low temperature of 1000 °C exhibit high electrical and piezoelectric properties, with piezoelectric constant d₃₃=116ρC/N, and electromechanical coupling factor k_p = 32.9%, polarization (P_r) was P_r =21.8 μC/cm² and curie temperature T_C=382°C. This also indicates that KNN-AF ceramics are promising candidate materials for lead-free piezoelectric applications.

Abstract: (Na,Bi)TiO₃-BaTiO₃ lead free piezoelectric ceramics were fabricated with modification of CaCu₃Ti₄O₁₂ additives. The phase structure, morphology, dielectric and piezoelectric properties of prepared samples were investigated, respectively. It was found that CaCu₃Ti₄O₁₂ additives evidently improve the polarization properties of (Na,Bi)TiO₃-BaTiO₃ lead free ceramics and the obtained samples exhibit an excellent piezoelectric properties (electromechanical coupling factor K_p=31%, mechanical quality factor Q_m=151 and piezoelectric constant d₃₃=160pC/N). According to results, the effect of CaCu₃Ti₄O₁₂ additives on electrical properties of (Na,Bi)TiO₃-BaTiO₃ lead free piezoelectric ceramics is discussed.

Abstract: Lead-free (Bi_0.5K_0.5)TiO₃)-Bi (Mg_0.5Ti_0.5)O₃-BiFeO₃ (BT-BMT-BF) ceramics were prepared by a conventional solidstate synthesis. Synchrotron x-ray diffraction studies indicated two compositional phase boundaries. An increased strain of 0.070% was obtained at 50 kV/cm, 1 Hz, 25 °C for one of the phase boundary compositions of 0.45BKT-0.1BMT-0.45BF with the temperature of the dielectric maximum of 331 °C.

Abstract: Bismuth potassium titanate ((Bi_1/2K_1/2)TiO₃: BKT) powder were prepared using bismuth oxide (Bi₂O₃), potassium hydrogen carbonate (KHCO₃) and titanium oxide (TiO₂) raw materials. Barium titanate (BaTiO₃: BT) platelike particles oriented along [110] direction were used as template particles. Barium titanate-bismuth potassium titanate (BT-BKT) ceramics had a tetragonal phase at -100 °C. The main composition was fixed to BKT 30 molar% because the Curie temperature (T_C) was well above 200 °C at BKT 30 molar%. The orientation of [110]-oriented BT-BKT ceramics (BKT 30 molar%) was 54.6 %.

Abstract: (Na0.5K0.5)NbO3 with Bi0.5(Na0.97K0.03)0.5TiO3 with x≤0.05 has been prepared by the conventional mixed oxide process. X-ray diffraction analysis revealed that, during sintering, all the Bi(Na0.97K0.03)TiO3 diffuses into the lattice of (Na0.5K0.5)NbO3 to form a solid solution with a perovskite structure. A morphotropic phase boundary (MPB) between orthorhombic (O) and rhombohedral (R) was found at the composition 0.98(Na0.5K0.5)NbO3-0.02Bi0.5(Na0.97K0.03)0.5TiO3 [abbreviated as 0.98NKN-0.02BNKT] with correspondingly enhanced dielectric and piezoelectric properties. For 0.98NKN-0.02BNKT ceramics, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.33 and 0.49, respectively, after sintering at 1100 oC for 3 h. The ratio of the thickness coupling coefficient to the planar coupling coefficient is 1.48. With suitable Bi0.5(Na0.97K0.03)0.5TiO3 concentration, a dense microstructure and good electrical properties are obtained.