H.L.W. Chan

Electromechanical and ferroelectric properties of (Bi1∕2Na1∕2)TiO3–(Bi1∕2K1∕2)TiO3–BaTiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (0.95−x)(Bi1∕2Na1∕2)TiO3–x(Bi1∕2K1∕2)TiO3–0.05BaTiO3 (abbreviated as BNT–BKT–BT100x, with x ranged from 0 to 20mol%) have been studied. Effects of amount of BKT on the electrical properties and crystal structure were examined. BNT–BKT–BT5 ceramics give good performances with piezoelectric constant d33=148pC∕N, electromechanical coupling factor kp=34%, kt=49.2%, free permittivity e33T∕e0=700, and dissipation factor tanδ=2% at 1kHz. Accordingly, the sample shows larger remanent polarization and lower coercive field than 0.95BNT–0.05BT ceramics. X-ray diffraction analysis shows that incorporated BKT diffuses into the BNT–BT lattice to form a solid solution during sintering, but changes the crystal structure from rhombohedral to tetragonal symmetry at higher BKT amounts.

Structure and electrical properties of K0.5Na0.5NbO3–LiSbO3 lead-free piezoelectric ceramics

Lead-free piezoelectricceramics ( 1 − x ) K 0.5 Na 0.5 Nb O 3 – x Li Sb O 3 have been fabricated by a conventional ceramicsintering technique. The results of x-ray diffraction suggest that Li + and Sb 5 + diffuse into the K 0.5 Na 0.5 Nb O 3 lattices to form a solid solution with a perovskite structure. The ceramics can be well sintered at 1070 – 1110 ° C . The introduction of Li Sb O 3 into the Na 0.5 K 0.5 Nb O 3 solid solution decreases slightly the paraelectric cubic-ferroelectric tetragonal phase transition temperature ( T c ) , but greatly shifts the ferroelectric tetragonal-ferroelectric orthorhombic phase transition ( T O – F ) to room temperature. Coexistence of the orthorhombic and tetragonal phases is formed at 0.05 < x < 0.07 at room temperature, leading to a significant enhancement of the piezoelectric properties. For the ceramic with x = 0.06 , the piezoelectric properties become optimum: piezoelectric constant d 33 = 212 pC ∕ N , planar and thickness electromechanical coupling factors k P = 46 % and k t = 47 % , respectively, remanent polarization P r = 15.0 μ C ∕ cm 2 , coercive field E c = 1.74 kV ∕ mm , and Curie temperature T C = 358 ° C .

Highly efficient low-voltage cathodoluminescence of LaF3:Ln3+ (Ln=Eu3+,Ce3+,Tb3+) spherical particles

Spherical particles of rare-earth doped LaF3 are synthesized through refluxing in glycerol/water media. The low-voltage cathodoluminescence of LaF3:Eu due to D50→F71 and D50→F72 transitions was found to be sensitive to the site that Eu3+ ions occupied. The luminous efficiency of LaF3:Ce3+, Tb3+ with green emission is improved from 1.53 to 2.02 lm/W compared with LaF3:Tb3+, due to the energy transfer processes from Ce3+ to Tb3+ ions. Our results suggest that the obtained spherical particles of rare-earth doped LaF3 are promising as highly efficient low-voltage cathodoluminescent phosphors, which have received considerably less attention.

Dielectric behavior and microstructure of (Bi1∕2Na1∕2)TiO3–(Bi1∕2K1∕2)TiO3–BaTiO3 lead-free piezoelectric ceramics

(0.95−x)(Bi1∕2Na1∕2)TiO3–x(Bi1∕2K1∕2)TiO3–0.05BaTiO3 lead-free piezoelectric ceramics (abbreviated as BNT–BKT–BT100x with x varying from 0 to 20 mol %) are prepared by a solid-state reaction process. Variation of the dielectric properties and microstructure of BNT–BKT–BT100x ceramics with BKT content is studied. The results indicate that the relative permittivity er and loss tangent tanδ vary with the BKT amount. Scanning electron microscope observation also indicates that BKT in high amount affects the microstructure. X-ray diffraction analysis shows that the incorporated BKT diffuses into the BNT–BT lattice to form a solid solution during sintering.

The effect of magnetic nanoparticles on the morphology, ferroelectric, and magnetoelectric behaviors of CFO/P(VDF-TrFE) 0–3 nanocomposites

Multiferroic nanocomposite films composed of P(VDF-TrFE) copolymer and CoFe2O4 (CFO) nanoparticles have been prepared by a modified polymeric processing. Structural characterizations reveal that CFO nanoparticles with 80–100 nm diameters are well distributed in the P(VDF-TrFE) matrix. The crystalline and microstructure of P(VDF-TrFE) are strongly dependent on the volume fraction of CFO nanoparticles, which are further analyzed by Raman spectra. Consequently, the ferroelectric and magnetoelectric responses are strongly influenced by the concentration of CFO nanoparticles. A significant magnetoelectric coupling effect of around 40 mV/cm Oe is obtained from the nanocomposites. A relatively simple model has been adopted to calculate the magnetoelectric coefficient, which is also in agreement with the experimental results.

Microstructure and electrical properties of La-modified K0.5Na0.5NbO3 lead-free piezoelectric ceramics

Lead-free ceramics (K0.5Na0.5)1−3xLaxNbO3 (0 ≤ x ≤ 0.0175) have been fabricated by a conventional sintering technique. The results of XRD show that the ceramics possess a perovskite structure with orthorhombic symmetry. Moreover, doping inhibits the grain growth, decreases the ferroelectric–paraelectric phase transition temperature and induces a diffuse phase transition. At low doping levels (x ≤ 0.0075), the observed remanent polarization (Pr) and coercive field (Ec) remain almost unchanged. As x increases from 0.0075 to 0.0175, Pr starts to decrease while Ec increases. Nevertheless, due to the increase in relative permittivity, the ceramic with x = 0.0125 exhibits the optimum piezoelectric properties, giving a large piezoelectric coefficient (d33 = 135 pC N−1) and a high planar electromechanical coupling coefficient (kP = 0.40).

Structure, piezoelectric and ferroelectric properties of Li- and Sb-modified K0.5Na0.5NbO3 lead-free ceramics

Lead-free ceramics (K0.5Na0.5)1−xLix(Nb1−ySby)O3 have been prepared by an ordinary sintering technique. Li+ and Sb5+ diffuse into the K0.5Na0.5NbO3 lattices to form a solid solution with the perovskite structure. The substitution of Li+ increases the Curie temperature Tc and shifts the ferroelectric tetragonal–ferroelectric orthorhombic phase transition (TO–T) to low temperatures. On the other hand, the substitution of Sb5+ decreases Tc and has a minor effect on TO–T. The coexistence of the orthorhombic and tetragonal phases at x = 0.06 and y = 0.06 near room temperature and the strong covalence of Sb lead to significant improvements in the piezoelectric properties. For the (K0.5Na0.5)0.94Li0.06(Na0.94Sb0.06)O3 ceramic, piezoelectric constant d33 = 212 pC N−1, planar and thickness electromechanical coupling factors kP = 46% and kt = 47% and Tc = 358 °C. The donor-type doping of BaCO3, SrCO3 or Bi2O3 leads to further enhancements of the piezoelectric and ferroelectric properties.

Structure, dielectric, and piezoelectric properties of cuo-doped K0.5Na0.5NbO3-BaTiO3 lead-free ceramics

Lead-free piezoelectric ceramics 1� xK 0.5 Na 0.5 NbO 3 +xBaTiO 3 +y mol % CuO have been fabricated by an ordinary sintering technique. Our results show that the doping of CuO is effective in promoting the densification of the ceramics. With the doping of CuO, all the ceramics can be well sintered and exhibit a dense, pure perovskite structure. After the formation of a solid solution with BaTiO3, both the paraelectric cubic–ferroelectric tetragonal and ferroelectric tetragonal– ferroelectric orthorhombic phase transition temperatures decrease and a relax behavior is induced. Coexistence of the orthorhombic and tetragonal phases is formed in the ceramics with 0.04x 0.06 and y = 1.00 at room temperature. Because of the more possible polarization states arising from the coexistence of the two phases and the improved densification, the piezoelectric and dielectric properties of the ceramics are enhanced significantly. The ceramic with x = 0.06 and y = 1.00 exhibits the optimum properties: d33= 193 pC/ N, kp = 0.43, kt = 0.40, and TC = 314 ° C. On the other hand, the ceramics with 0x 0.01 and y = 1.0 exhibit excellent “hard” piezoelectric characteristics: kp 0.40, kt 0.47, Qm 1940, r 230, and tan 0.5%.

PZT ceramic/ceramic 0–3 nanocomposite films for ultrasonic transducer applications

Abstract Lead zirconate titanate (PZT) ceramic/ceramic 0–3 nanocomposite films of several micron thickness were fabricated using a modified sol–gel process. Nanosized PZT powder was dispersed in a PZT solution which was spin-coated onto stainless steel or silicon substrates to form composite films. The crystallization of the films was studied by X-ray diffraction. The dielectric permittivities and ferroelectric properties of the PZT films deposited on stainless steel substrates were also investigated.

Pyroelectric activity of ferroelectric PT/PVDF-TRFE

This paper studies the pyroelectric coefficient of 0-3 composites consisting of 27%vol lead titanate (PT) powder embedded in a vinylidene fluoride-trifluoroethylene copolymer (PVDF-TRFE) matrix. The constituent phases of the composites have been polarized in four possible ways: only the copolymer polarized; only the ceramic polarized; the copolymer and ceramic phases polarized in the same direction; the two phases polarized in opposite directions. The pyroelectric coefficient was measured by a dynamic method at 5 mHz within the temperature range 20 to 90/spl deg/C (which covers the ferroelectric to paraelectric phase transition temperature of the copolymer matrix). The composite with the copolymer and ceramic phases polarized in the same direction exhibits strong pyroelectric but relatively weak piezoelectric activity, and vice versa when the constituent phases are oppositely polarized. A theoretical model is used to analyze the pyroelectric coefficient of the composites in terms of the pyroelectric and dielectric properties of the copolymer matrix as determined from experiment, and those of the ceramic particles which are assumed to be temperature independent. The pyroelectric coefficient and dielectric permittivity of the ceramic particles are obtained as fitting parameters. The theoretical prediction is found to agree well with the experimental data.