Papers by Keyword: Lead-Free Piezoelectric

Abstract: This paper presents a simulation of three different types of lead-free piezoelectric materials for energy harvesting. Polyvinylidene Fluoride (PVDF), Zinc Sulfide (ZnS), and Cadmium Sulfide (CdS) are simulated using COMSOL Multiphysics to evaluate the frequency response and electrical potential for each materials. The simulation consisted of two parts which is 3D block cantilever for simulating frequency response and total displacement. The second part is 2D block bimorph to simulate power generated by varying frequency responses. The simulated result for the first shows that frequency response for each materials is differents for ZnS, PVDF and CdS which 30.897 kHz, 8.517 kHz, and 22.118 kHz. For total displacement is 303 µm which same for each materials. Each material is simulated for various cantilever beam thicknesses ranging from 1-4 µm and result ZnS having the greatest frequency response. For 2D block bimorph model, the highest electric potential is 0.75 V at 60 Hz frequency for ZnS. Meanwhile for CdS and PVDF has less electric potential which 0.6 V and 0.4V at 60 Hz frequency response. For power disspation, ZnS generate 10% more power compare to CdS and PVDF. In the end of the paper, ZnS is excellent lead free material compared to CdS and PVDF in term of aforementioned parameter studied.

Abstract: The effects of CuO-B₂O₃ (CBO) additive on densification, microstructure, and electrical properties of (Ba_0.98Ca_0.02)(Sn_0.04Ti_0.96)O₃ (BCST) cermaics were investigated. The phase compositions, microstructure, dielectric, ferroelectric and piezoelectric properties of BCST ceramics were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), precision impedance analyzer, ferroelectric tester and quasi-static piezoelectric constant testing meter, respectively. The results show that CuO-B₂O₃ (CBO) frit can improve the densification and promote low-temperature sintering of BCST ceramics prepared by a conventional solid-state reaction method. Dense BCST ceramics with CBO can be sintered at temperatures as low as 1175 °C, which is approximately 275 °C less than the sintering temperature of pure BCST. When sintered at 1200 °C, the optimized properties of the BCST ceramics with 0.5 wt% CBO were obtain as ε = 1206, d₃₃ = 346 pC/N, k_P = 0.39, tgδ = 0.009.

Abstract: 5wt%B₂O₃-doped (Li,K,Na)NbO₃ (abbreviated as LKNN-B5)-based lead-free piezoelectric ceramics were prepared via solid state synthesis. The electrical humidity sensitive properties of LKNN-B5 ceramics were examined and compared with pure LKNN ceramics. The results revealed thatB₂O₃ doping enhanced electrical stability of LKNN-based ceramics in relative humidity (RH) range of 33-95%. The capacitance change was suppressed from 105% down to 43% when doped with B₂O₃. The average absorption time was reduced from 5.5 min to 1.5 min, and desorption time decreased from 8.5 min to 2.0 min. The enhanced electrical stability of LKNN-B5 series was attributed to the dense structure induced by liquid phase sintering.

Abstract: Piezoelectric materials have wide applications in today’s advanced technologies. However, most commercially used piezoelectric material PZT (PbZr1-xTixO3) is now strictly restricted worldwide due to hazardous nature of Pb. Research for the development of new lead free materials with properties comparable to that of PZT is in progress in recent years. In the present work, an effort has been made to synthesize low amount of rare earth gadolinium modified (Bi1-xGdx)0.5Na0.5TiO3 (BGNT) with compositions (x) = 0, 0.02, 0.03 and 0.04 by a novel Semi–Wet Technique. The structural, microstructure, phase transition and dielectric properties have been investigated. The XRD patterns have shown single phase formation for all the samples with a rhombohedral symmetry at RT. Gd3+ doping has shown a significant effect on the grain growth. The dielectric measurement has been carried out over the temperature range from RT to 400 oC at 1, 10 and 100 kHz frequency. It has been observed from the εr vs T plots that two phase transitions (i) ferroelectric to anti-ferroelectric and (ii) anti ferroelectric to paraelectric occur in all the samples. The composition with x = 0.02 has shown significantly high value of dielectric constant (εr ~ 1567) and low value of dielectric loss (Tan δ ~ 0.043) at room temperature.

Abstract: Our research investigates the correlations between domain texture and microstructural features, including crystallographic texture in bulk and thin film polycrystalline materials to understand the development of piezoelectric and other anisotropic properties in a number of rapidly evolving lead free piezoelectric materials. We investigate approaches to understanding polarization distributions by starting from polarization measurements. In addition, 2D and 3D microstructural simulations are carried out in all types of ferroelectrics to rationalize and then engineer their equilibrium and kinetic response. This paper discusses recent findings associated with bulk piezoelectricity, phase stability, and ferroelastic and ferroelectric domain motion for materials such as Ba(Ti_0.8Zr_0.2)O₃-x(Ba_0.7Ca_0.3)TiO₃ (BZT-BCT) and Bi_0.5Na_0.5TiO₃ (BNT). Conventional and synchrotron-based x-ray diffraction, electron and optical microscopy and piezoelectric characterization techniques are employed to assess texture, both as a function of poling and temperature. The coupling between microstructure and the inherent directional biases fundamental to piezoelectric and ferroelectric performance enable consideration of orientation and anisotropy in systems with unique constraints.

Abstract: In this paper, the effects of Bi2O3 addition on the electrical and physical properties of 0.98(Na0.5K0.5)NbO3-0.02(Na0.5Bi0.5)TiO3 were investigated. The 0.98(Na0.5K0.5)NbO3 -0.02(Na0.5Bi0.5)TiO3 [0.98NKN-0.02NBT] ceramics with the addition of 0~0.5 wt% Bi2O3 have been prepared following the conventional mixed oxide process. X-ray diffraction analysis revealed that, during sintering, all of the (Na0.5Bi0.5)TiO3 diffuse into the lattice of (Na0.5K0.5)NbO3 to form a solid solution, in which a orthorhombic phase with a perovskite structure was found. For 0.98NKN-0.02NBT ceramics by doping 0.1 wt% Bi2O3, the poled dielectric constant (K33T) and the electromechanical coupling coefficients of the planar mode kp reach 684 and 0.38, respectively, after sintering at 1100 °C for 3 h. Our results show that 0.98NKN-0.02NBT with the addition of 0.1 wt% Bi2O3 is a good lead-free piezoelectric ceramic.

Abstract: In this paper, Na_0.54K_0.42Li_0.4NbO3 nano-powders were prepared by the sol-gel method, Na₂CO₃, K₂CO₃, Li₂CO₃ and Nb₂O₅ as raw materials, citric acid as coordination agent, ethylene glycol as esterifying agent, polyethylene glycol as dispersing agent. From the XRD, TG-DTA and TEM analysis, powders’ size, lattice constants and surface topography were studied. The results showed that under the condition of 600°C × 2h, nano-powders showed good dispersiveness and no reuniting, with pure orthorhombic perovskite structure and various grain sizes was 40.78 nm.

Abstract: In this paper, the effects of Bi₂O₃ addition on the electrical and physical properties of 0.98(Na0.5K0.5)NbO3-0.02(Na0.5Bi0.5)TiO3 were investigated. The 0.98(Na_0.5K_0.5)NbO₃ -0.02(Na_0.5Bi_0.5)TiO₃ [0.98NKN-0.02NBT] ceramics with the addition of 0~0.5 wt% Bi₂O₃ have been prepared following the conventional mixed oxide process. X-ray diffraction analysis revealed that, during sintering, all of the (Na_0.5Bi_0.5)TiO₃ diffuse into the lattice of ((Na_0.5Bi_0.5))NbO₃ to form a solid solution, in which a orthorhombic phase with a perovskite structure was found. For 0.98NKN-0.02NBT ceramics by doping 0.1 wt% Bi₂O₃, the poled dielectric constant (K33^T) and the electromechanical coupling coefficients of the planar mode k_p reach 684 and 0.38, respectively, after sintering at 1100 °C for 3 h. Our results show that 0.98NKN-0.02NBT with the addition of 0.1 wt% Bi₂O₃ is a good lead-free piezoelectric ceramic.

Abstract: Second phase and defect formation mechanism of (Bi_0.5(Na_1-xK_x)_0.5)TiO₃ (BNKT100x) ceramics were investigated using electron microscopy, x-ray photoelectron spectroscope (XPS) and electrical properties measurements. Experimental results indicated that second phase formation induces Bi-rich regions and compositional inhomogeneity within matrix due to thermodynamic stability of potassium titanate. Ti valence transition for BNKT ceramics sintered in air might be ascribed to formation of the secondary phase, rather than simply attributed to volatilization of bismuth. Li substitution at A-site in BNKT ceramics suppresses formation of the second phase and Ti valence transition. Appropriate Li doped BNKT ceramics suppress oxygen vacancies and titanium valence transition, and therefore decrease the leakage current.

Abstract: The (Na_0.8K_0.2)_0.5Bi_0.5TiO₃ perovskite-type solid solution was prepared under mild condition at 160°C using Ti(OC₄H₉)₄, Bi(NO₃)₃•5H₂O as Bi and Ti sources by a mechanical hydrothermal method. It is suggested that mineralizer plays an important role in facilitating the crystallization of obtained products and promoting the formation of perovskite phase. The crystallized products were characterized by means of XRD, SEM and DSC-TG. The results show that the well-developed crystallite with a pure pervoskite structure has been formed. The powders with regular cubic morphology exhibit low agglomeration and narrow particles size distribution in the range of 3~6μm.