Guifen Fan

Phase transition behaviour and electromechanical properties of (Na1/2Bi1/2)TiO3–KNbO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)(Na1/2Bi1/2)TiO3–xKNbO3 (abbreviated as NBT–KN100x, x = 0–0.12) were synthesized by the conventional ceramic sintering technique. The phase transition behaviour in NBT–KN100x ceramics with respect to changes in composition and temperature was investigated using x-ray diffraction analysis, dielectric and ferroelectric characterizations. At x = 0.04–0.06, the rhombohedral and pseudo-cubic morphotropic phase boundary (MPB) occurs in NBT–KN100x ceramics. Near MPB, the NBT–KN5 ceramics exhibit the optimum piezoelectric properties: kp = 0.22 and d33 = 125 pC N−1. The curves of permittivity versus temperature show that NBT–KN100x ceramics exhibit the diffuse phase transition and are characterized by a strong frequency dispersion of the permittivity. The hysteresis loops at different temperatures indicate that there is no existence of antiferroelectrics above the depolarization temperature Td. The depolarization reason is that the tetragonal nonpolar phase occurs and leads to the macro–micro domain transformation at about Td.

Morphotropic phase boundary and piezoelectric properties of (Bi1∕2Na1∕2)TiO3–(Bi1∕2K1∕2)TiO3–KNbO3 lead-free piezoelectric ceramics

The crystal structure and piezoelectric properties of ternary ceramics x(Bi1∕2Na1∕2)TiO3–y(Bi1∕2K1∕2)TiO3–zKNbO3 (abbreviated as BNT-BKT-KN100x∕100y∕100z) system have been investigated. Effects of BKT and KN on the crystalline structure were examined. The morphotropic phase boundary (MPB) phase diagram of BNT-BKT-KN ternary system was determined by x-ray diffraction patterns from sintered specimens. Near the MPB, BNT-BKT-KN82∕16∕2 ceramics had good performances with piezoelectric constant d33=215pC∕N which reached a maximum value in this ternary system and planar electromechanical coupling factor kp=35%. Besides, BNT-BKT-KN87∕10∕3 ceramics had good performances with piezoelectric constant d33=138pC∕N and electromechanical coupling factor kp=38% which attained a maximum value in this ternary system.

Dielectric performance of polymer-based composites containing core-shell Ag@TiO2 nanoparticle fillers

This paper reports composites prepared by embedding core-shell Ag@TiO2 fillers into polytetrafluoroethylene. Ag nanoparticles were homogeneously coated with TiO2, to give a shell thickness of approximately ∼8–10 nm. The composite containing Ag@TiO2 nanoparticles with rutile shells exhibited better dielectric properties than the composite containing Ag@TiO2 nanoparticles with anatase shells. The relative permittivity (er) of the composite containing 70 vol. % filler was approximately 240 at 100 Hz, which was more than 100 times higher than that of pure polytetrafluoroethylene (er = 2.1). An effective medium percolation theory model is used to account for the dielectric constant of the composite.

Dielectric and ferroelectric behavior of an incipient ferroelectric Sr(1−3x/2)CexTiO3 novel solid solution

Phase formation, chemical structure, microwave (MW) dielectric properties, and relaxor-to-ferroelectric phase transition behavior of a novel solid solution with Ce-doped, A-site SrTiO3 (Sr(1−3x/2)CexTiO3) ceramic sintered in nitrogen have been investigated. X-ray diffraction (XRD) showed that the samples with x ≤ 0.3 appeared cubic but exhibited splitting and superstructure reflections consistent with tetragonal (0.4 ≤ x ≤ 0.45) and orthorhombic (0.5 ≤ x ≤ 0.6) structures. Chemical structure analysis revealed that the addition of small amounts of ceria (x ≤ 0.3) promoted Ti3+ cation and oxygen vacancy . By contrast, the addition of large amounts of ceria (x ≥ 0.4) inhibited this process. Sr(1−3x/2)CexTiO3 ceramics displayed frequency-dependent relaxor dielectric anomalies and frequency-independent normal ferroelectric behaviors. The relaxor/dielectric properties were strongly dependent on structure-chemical factors. The value of er decreased several times when Sr was subsequently substituted with Ce, and induced a relaxor-to-ferroelectric phase transition. A good combination of the following microwave dielectric properties was obtained for the Sr0.1Ce0.6TiO3 orthorhombic solid solution at an optimum temperature of 1300 °C for 3 h: er = 50, Q × f = 11 311 GHz, and τf = +3 ppm per °C.

Dielectric and Piezoelectric Properties of [Bi0.5(Na1-xLix)0.5]TiO3 Lead-Free Ceramics

The structural, dielectric and piezoelectric properties of [Bi0.5(Na1-xLix)0.5]TiO3 ceramics were studied in the compositional range of x=0–0.30. The samples were fabricated by a conventional sintering technique. X-ray diffraction results showed that the ceramics possessed a pure perovskite structure with a rhombohedral symmetry in the range of x=0–0.2. The scanning electron microscope (SEM) micrographs indicated that the sintering temperature of the ceramics decreased with an increase in the amount x of Li+. The optimum piezoelectric constant d33 and planar electromechanical coupling factor kp were 110 pC/N and 0.18 at x=0.15, respectively.

Improved dielectric properties of Ag@TiO2/PVDF nanocomposites induced by interfacial polarization and modifiers with different carbon chain lengths

In this study, poly(vinylidene fluoride) (PVDF)-based nanocomposites filled with surface-functionalized Ag@TiO2 core-shell nanoparticles were fabricated in order to achieve high dielectric permittivities. Using two phosphonic acid surfactants with differing carbon chain lengths, octyl and octadecyl phosphonic acid, the filler surfaces were modified to improve the dispersion of the core-shell filler in PVDF. The experimental results showed that the dielectric constant of the composite with fillers modified using octyl phosphonic acid (148 at 1 kHz) was almost three times that of the material with fillers modified using octadecyl phosphonic acid (58 at 1 kHz) at the same filler loading. The mechanisms of interfacial polarization between the modified core-shell filler and the polymer matrix were analyzed by introducing a circuit model based on AC impedance spectroscopy.In this study, poly(vinylidene fluoride) (PVDF)-based nanocomposites filled with surface-functionalized Ag@TiO2 core-shell nanoparticles were fabricated in order to achieve high dielectric permittivities. Using two phosphonic acid surfactants with differing carbon chain lengths, octyl and octadecyl phosphonic acid, the filler surfaces were modified to improve the dispersion of the core-shell filler in PVDF. The experimental results showed that the dielectric constant of the composite with fillers modified using octyl phosphonic acid (148 at 1 kHz) was almost three times that of the material with fillers modified using octadecyl phosphonic acid (58 at 1 kHz) at the same filler loading. The mechanisms of interfacial polarization between the modified core-shell filler and the polymer matrix were analyzed by introducing a circuit model based on AC impedance spectroscopy.

Well-dispersed Nd:Y2O3 nanopowders fabricated by a modified solution-combustion method

ABSTRACT Ammonium polyacrylate was adopted for the first time to fabricate nanosized Nd:Y2O3 powders with good dispersity through solution-combustion method. Results indicate that cubic Y2O3 can be synthesized at a relatively low temperature (300°C) and that the crystallinity of powder increases with increased calcination temperature. TEM observations reveal that the influence of improve with increased organic-fuel dosage. Well-dispersed Nd:Y2O3 particles with a narrow size distribution of 20–40 nm can be obtained when the mass ratio of ammonium polyacrylate to yttrium nitrate is 0.5:1. Therefore, ammonium polyacrylate is a new fuel that can be used to prepare well-dispersed Nd:Y2O3 nanopowders.

Preparation of Ni/PZT core-shell nanoparticles and their electromagnetic properties

The Ni nanoparticles coated with Pb(Zr,Ti)O3 (PZT) were synthesized by a sol-gel method and in situ reaction. And their structure, oxidation resistance, and electromagnetic properties were investigated. The X-ray diffraction patterns (XRD) exhibited that a small amount of impure phase characterized to Ni(OH)2 was detected from the ammonia-treated Ni nanoparticles and the ammonia-treated Ni nanoparticles coated with PZT. After being pre-treated with aqueous ammonia, the PZT coating layer was more uniform and about 10 nm in thickness. The oxidation resistance of the ammonia-treated Ni nanoparticles coated with PZT, compared with that of the non-treated ones, was improved by about 66 °C. The PZT shell layer prepared by in-situ reaction can greatly reduce the dielectric constant and improve the natural resonance loss at high frequency, so as to obtain the optimal impedance matching performance of the electromagnetic wave transmission.

High field dielectric property and piezoelectric response in PMS-PZT piezoelectric ceramics modified with BiFeO3

ABSTRACT The piezoelectric ceramic Pb0.98Sr0.02(Mn1/3Sb2/3)0.05Zr0.48Ti0.47O3+0.25 wt%CeO2 modified with BiFeO3 was synthesized by conventional ceramics technology and the high field dielectric property was investigated. The XRD patterns show that BiFeO3 can be commendably dissolved into the PMS-PZT solid solution. Bi3+ replacement for A-site Pb2+ and Fe3+ replacement for B-site Ti4+ or Zr4+ cause BiFeO3 to act as “soft” and “hard” dopant. Therefore, an appropriate amount of BiFeO3 enhances the piezoelectric properties and high field dielectric properties simultaneously. The ceramic modified with 0.2 mol% BiFeO3 exhibited the following optimal properties: d33 = 359pC/N, kp = 0.622, Qm = 1519, ϵr = 1760, tanδ = 0.46% (1 kHz, 1V/mm), and tanδ = 3.26% (1 kHz, 500V/mm).