Papers by Keyword: Lead-Free Ceramic

Abstract: The BNKBST30 + 3 vol% Fe₂O₃ ceramic was fabricated via a solid-state mixed oxide and sintered 1125°C for 2 h. The effects of ferric oxide nanoparticles (Fe₂O₃) additive on phase evolution, microstructure and electrical properties, i.e. dielectric, ferroelectric and electric field-induced strain, of BNKBST30 ceramic was investigated. The obtain ceramic was well sintered and densely with high density of 5.78 g/cm³. X-ray diffraction pattern and Raman spectra analysis showed a single perovskite with a mixed rhombohedral (R3c) and tetragonal (P4bm) phases. The obtained ceramic had a cubic-like grain shape with an average grain size of 0.82 µm. The dielectric constant as a function of temperature curves exhibited broad transition peaks at maximum temperature (T_m). The ceramic also showed good dielectric (e_r = 1085, tan d = 0.0496, e_r,max = 6099, T_m = 296 °C), ferroelectric (P_r = 27.18 µC/cm², E_c = 20.32 kV/cm, R_sq = 0.95), and electric field-induced strain properties (S_max = 0.22 %, S_neg = - 0.08 %, d^*₃₃ = 440 pm/V). The obtained results indicated that the studied ceramic is considered as candidate for lead-free electromechanical applications.

Abstract: Lead-free ceramic powders based on Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) were successfully fabricated by the conventional solid-state reaction method. Two kinds of sintering methods: zero-time sintering (ZTS) and conventional sintering (CS) were applied to obtain BCZT ceramics. The microstructure and dielectric properties of BCZT ceramics sintered from the ZTS and the CS method were systematically studied. It was found that the coarse-grained samples with grain sizes ~ 19-21 μm were obtained from the ZTS and the CS method. The CS method with a long time of dwelling was helpful for improving the dielectric properties of lead-free BCZT ceramics. The maximum dielectric constant of 9926 and low dielectric loss of 0.0108 were obtained at CS with 8h.

Abstract: Bismuth potassium titanate – strontium titanate (1-x)Bi_0.5K_0.5TiO₃-(x)SrTiO₃ (BKT-ST) lead-free ceramics when x = 0-0.20 were synthesized by the solid state reaction method with normal sintering. The ferroelectric phase transition was studied by X-ray diffraction (XRD). All compositions showed a single phase perovskite structure with tetragonal symmetry at room temperature and the phase structure transformed from ferroelectric tetragonal – paraelectric cubic in the range of x ³ 0.10 . Dielectric study revealed that the dielectric relaxor behavior was induced with increasing ST and transition temperature (T_m@ε_{r max}) of ST-doped BKT had a tendency to decrease with increasing ST. The Bi_0.5K_0.5TiO₃ – SrTiO₃ system was expected to be a new and promising candidate for lead-free capacitors.

Abstract: Lead-free bismuth sodium zirconate powder with formula Na_0.5Bi_0.5ZrO₃ was prepared by conventional mixed oxide method. Bismuth sodium zirconate (BNZ) powder with 10wt%Na₂CO₃ was calcined at 800 °C for 2 h dwell time. Investigation of the effects of re-calcination and dwell time on phase formation of powders was also carried out. The results revealed that re-calcination significantly affected the formation of single-phase BNZ powder. Phase characteristics were checked by X-ray diffraction (XRD). Powder Cell software was employed to simulate crystal structure of BNZ powder. It was found that BNZ powder most likely possessed an orthorhombic structure. SEM result showed its average particle size was 0.47 mm and composition measured EDX correlated with theoretical composition of BNZ.

Abstract: Li+ and Ta5+ modified lead-free piezoelectric ceramics [(K0.5Na0.5)1-xLix](Nb1-yTay)O3 have been prepared by an ordinary sintering technique. Effect of Li+ and Ta5+ on microstructure and piezoelectric properties of the ceramics was systematically studied. A morphotropic phase boundary between orthorhombic and tetragonal phases is identified in the composition range of (0.02≤x≤0.04, 0.15≤y≤0.25), which can enhance electrical properties of [(K0.5Na0.5)1-xLix](Nb1-yTay)O3 ceramics. The Curie temperature TC of these ceramics is lower than that of pure (K0.5Na0.5)NbO3 ceramics, but the temperature of orthorhombic to tetragonal phase transition TO-T of the former is higher than that of the latter. TC and TO-T both decrease as the content of Ta5+ increases. With the addition of Li+ increasing, TC increases. The optimal piezoelectric properties are obtained at (x, y)=(0.03, 0.20): piezoelectric constant d33 is 192pC/N; the electromechanical coefficient of the planar mode kp is 44%; room temperature dielectric constant εr is 1049, and the corresponding mechanical quality factor Qm is 49.

Abstract: Barium titanate (BaTiO3, BT) – bismuth titanate magnesium oxide (Bi(Mg0.5Ti0.5)O3, BMT) solid solution system ceramics were prepared by conventional sintering method in pursuit of the enhancement of the BT Curie temperature (TC, 132 °C). Normal ferroelectric polarization vs. electric-field (P-E) hysteresis loops were observed for BT-BMT ceramics with BMT contents below 20 and above 60 molar%. On the other hand, broad P-E double hysteresis loops were observed for BMT contents from 30 to 50 molar%. The origin was investigated using synchrotron XRD measurement and Rietveld analysis. The crystal structure was assigned to ferroelectric phase with domain-pinning by certain defect structures. A modified phase diagram was proposed on the basis of the temperature dependence of the crystal structure.

Abstract: Barium titanate (BaTiO3, BT) grain-oriented ceramics along [110] direction were prepared by a templated grain growth (TGG) method. The [110] oriented BT platelike particles (t-BT) were used as template particles. BT grain-oriented ceramics with higher relative density (Drel) over 95 %, high degree of orientation along [110] direction (F110) over 80 % and grain sizes around 30 µm were successfully prepared using only the template particles. The relationship between microstructures and piezoelectric constant (d33) was investigated. The higher F110 was, the higher Drel and the smaller grain size were required for enhancement of the piezoelectric properties.

Abstract: Barium titanate (BaTiO3, BT) – bismuth lanthanum zinc titanium oxide [(BiyLa1-y)(Zn0.5Ti0.5)O3, ByL1-yZT] solid solution ceramics were prepared to enhance Curie temperature (TC) of BT, 132 °C, to 200 °C. As the raw materials, nanoparticles were used to make sintering temperatures lower. Optimization of calcination and sintering conditions resulted in a formation of a perovskite single-phase, and their densities were always greater than 94 %. The synchrotron XRD measurement revealed that the crystal structures were assigned to rhombohedral 3m. Temperature dependence of dielectric property revealed that for the 0.5BT-0.5BZT ceramics, TC was 230 °C. Moreover, La-doping into BT-BZT ceramics resulted in decrease of TC significantly. Finally, their piezoelectric properties were measured by electric-field dependence of strain at room temperature, and for the 0.6BT-0.4BZT ceramics, the apparent d33 was measured at 250 pC/N.

Abstract: In this paper, 0.95K0.5Na0.5NbO3-0.05LiTaO3 ceramics were synthesized by conventional mixed-oxide technique. To clarify the optimal sintering condition, three kinds of different temperature conditions were used. It was found that the samples sintered near 1130 °C had the best piezoelectric properties (d33~155 pC/N). In addition, sintering aid such as K5.4C1.3Ta10O29 was investigated to confirm whether it really benefited to the sintering process and increased the piezoelectric property of ceramics.

Abstract: Lead-free (1-x) Bi1/2Na1/2TiO3-xKNbO3 (x=0, 0.01, 0.02, 0.04, 0.05 0.06, 0.10) piezoelectric ceramics were prepared by conventional ceramics fabrication technique. The results of x-ray diffraction (XRD) show that these ceramics possess pure perovskite structures with a symmetry transition from rhombohedral to cubic at about x = 0.05. The piezoelectric properties of these ceramics were reported and found to reach extreme values at x = 0.04 with d33 up to 113pC/N and kp up to 22%. The temperature dependence of dielectric constant and dielectric loss of these ceramics were also investigated. The Curie temperature and depolarization temperature dropped with the increase of KNbO3 amount.