Papers by Keyword: MPB

Abstract: A new inorganic nonmetallic cementing material rather than epoxy resin was adopted in carbon fiber sheet (CFS) strengthened concrete beams and slabs in this paper. Firstly, the types of inorganic adhesive were introduced and double-shear tests and the compressive strength of specimens as a function of temperature were studied to prove the effectiveness of inorganic adhesive in CFS strengthened concrete beams and slabs was studied. The practice shows that MPB has good performance when applying at high temperature. RC beams and slabs strengthened with new inorganic adhesives sticked FRP sheets are feasible. The appearance of MPB renders an extensive prospect for carbon fiber sheet (CFS) application in building structure reinforcement.

Abstract: Pb (Zr_xTi_1-x)O₃ films at morphotropic phase boundary composition (x=0.52) were deposited on Pt/Ti/SiO₂/Si substrates by sol-gel spin on technique. Thickness of the films were varied up to 1μm by step-by-step crystallization process and annealed at 500, 600 and 700 °C. Films annealed at 500 °C had poor degree of crystallization for all the thicknesses while 600 and 700 °C annealed films were found to be well crystallized with a (111) preferential orientation. Also an enhanced degree of preferential orientation was observed on the films annealed at 600 °C compared to films annealed at 700 °C. Room temperature dielectric measurements showed higher dielectric constant values for the films annealed at 600 °C compared to films annealed at 700 °C. The remnant polarization (P_r) and coercive field (E_c) at an applied field of 160 kV/cm depicted that 600 °C annealed films had a higher P_r and lower E_c values compared with the 700 °C annealed films attributed to the higher degree of preferential orientation.

Abstract: In the present study, various quantities of Li2CO3 were added into Bi0.5(Na0.82K0.18)0.5TiO3 (abbreviated as 0.82BNT-0.18BKT) ceramics. For 0.82BNT-0.18BKT ceramics, the electromechanical coupling coefficients of the planar mode kp reaches 0.22 at the sintering of 1125 oC for 3 h. High-density samples were obtained through the addition of Li2CO3 into 0.82BNT-0.18BKT ceramics. It was found that 0.82BNT-0.18BKT with the addition of 0~0.9 wt.% Li2CO3 exhibit relatively good piezoelectric properties. For 0.82BNT-0.18BKT ceramics with the addition of 0.5 wt.% Li2CO3, the electromechanical coupling coefficients of the planar mode kp reach 0.37 at the sintering of 1125oC for 3 h. To promote the kp value, by adding low quantities of Li2CO3 is a effective method for 0.82BNT-0.18BKT solid solution ceramic.

Abstract: In this paper, end members of tetragonal phase (Na_0.535K_0.485)_0.905Li_0.095(Nb_0.94Ta0.06)O₃ (abbreviated as NKLN) and rhombohedral phase (Na_0.5Bi_0.5)TiO₃ (abbreviated as NBT) were used to fabricate dense (1-x)NKLN-xNBT (x=0, 0.005, 0.01, 0.02, 0.03, 0.04) lead-free piezoelectric ceramics. By increasing the NBT content x value, the crystalline structure changes from tetragonal phase to rhombohedral one across a morphotropic phase boundary (MPB) composition of x=0.02. In this MPB composition, enhanced electrical properties were obtained as follows: piezoelectric constant d₃₃=202 pC/N, planar electromechanical coupling coefficient k_p=39.6%, relative dielectric constant ε_r=1020 and dielectric loss tgδ=2.67%, indicating that this ceramic was a promising lead-free piezoelectric material for practical applications.

Abstract: The effect of nonstoichiometric Pb content on the properties of PZT has been studied. The samples of Pb_xBa_0.04(Li_1/4Sb_3/4)_0.02(Zr_0.52Ti_0.48)_0.98O₃ (0.94≤x≤0.98) were prepared by the solid state route and sintered at 1200
°C. The Pb content changed from 0.94 to 0.98. The result shows that when the Pb content deviates from the stoichiometric ratio (x=0.96), the grain growth and densification of ceramics are promoted. The phases analysis shows that ZrO₂ phase is detected when the amount of Pb is lower than 0.96, while when the Pb content is more than 0.96, the PbO phase is absent. The optimum composition of Pb_xBa_0.04(Li_1/4Sb_3/4)_0.02(Zr_0.52Ti_0.48)_0.98O₃ solid solution system are obtained when x is 0.95, and the ε^T33/ε0, d₃₃ and k_p of the PZT ceramics are: 2281, 516 pC/N and 0.80, respectively.

Abstract: A combination between piezoelectric (Pb(Zr1/2Ti1/2)O3; PZT) and relaxor ferroelectric (Pb(Co1/3Nb2/3)O3; PCN) materials with a formula of 0.8Pb(Zr1/2Ti1/2)O3 - 0.2Pb(Co1/3Nb2/3)O3 has been prepared with solid-state reaction (the columbite-wolframite precursor method). This specific composition was selected for investigation because it is close to a morphotropic phase boundary (MPB) between the tetragonal and pseudo cubic phases. The phase formation behavior and microstructure were studied using x-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The dielectric properties of the compound were measured and discussed. The ceramics were also heat-treated at 800 oC. The results showed that the dielectric properties of the compound depended significantly on the heat treatment conditions. Most importantly, this study showed that the addition of PCN can improve the dielectric characteristics in PZT ceramics.

Abstract: A lead-free piezoelectric ceramic binary system based on bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT)-bismuth potassium titanate (Bi0.5K0.5)TiO3 (BKT) was synthesized by conventional mixed-oxide technique. The XRD analysis showed that the rhombohedral-tetragonal morphotropic phase boundary (MPB) of the Bi0.5 (Na1-xKx)0.5 TiO3 system was in the composition range of x = 0.16 ~ 0.20. In addition, the piezoelectric properties of this system were also investigated. It was indicated that the piezoelectric properties are better with the compositions near the rhombohedral phase within the MPB than the compositions near the tetragonal phase.

Abstract: Lead-free Na1/2Bi1/2TiO3-6BaTiO3 (BNT-6BT) ceramics with different dopants were prepared by a conventional ceramic fabrication technique. The influence of doping CeO2, La2O3, Nb2O5 and Co2O3 on the structure was studied, and the mechanism of soft and hard additives with A-site or B-site substitute changing the piezoelectric properties was discussed. It was found that the rhombohedral-tetragonal morphotropic phase boundary (MPB) of the Na1/2Bi1/2TiO3-6BaTiO3 was not changed obviously.

Abstract: Ceramics with the type of 0.50Pb(Ni1/3Nb2/3)O3-0.15PbZrO3-0.35PbTiO3 were synthesized by conventional mixed-oxide technique. The dielectric and ferroelectric properties of this composition were investigated in detail. Frequency dispersion and diffuse phase transition were observed in the dielectric behaviors. The revealed electrical properties are εm = 22388, Pr = 21.449 μC/cm2 and Ec = 5.191 kV/cm. XRD experiments demonstrate that this composition is within the MPB region, which may help to explain the super electrical properties discussed in this study.

Abstract: (1-x)(0.64PNN-0.36PT)-x(0.91PZN-0.09PT) ferroelectric ceramics with different x were synthesized by the columbite precursor method. The phase structure and piezoelectric properties were investigated. XRD profiles implied that with the increasing of x, samples could no longer maintain the pure perovskite phase. All the compositions were found to lie within the region of the morphotropic phase boundaries (MPBs) with different contents of rhombohedral and tetragonal phases. The piezoelectric coefficients for compositions with x £ 0.30 were obviously better than those for the rest ones and the composition with x = 0.15 exhibited the largest value of d33 among all the samples. The relationship between the structure and the piezoelectric properties was discussed.