Shuhui Yu

Nano Ag-Deposited BaTiO3 Hybrid Particles as Fillers for Polymeric Dielectric Composites: Toward High Dielectric Constant and Suppressed Loss

Nano Ag-deposited BaTiO3 (BT-Ag) hybrid particles usable as fillers for flexible polymeric composites to obtain high dielectric constant, low conductivity, and low dielectric loss were developed. BT-Ag hybrid particles were synthesized via a seed-mediated growing process by a redox reaction between silver nitrate and ethylene glycol. Nano Ag particles with a size less than 20 nm were discretely grown on the surface of the 100 nm BaTiO3. The similar lattice spacing of the (1 1 1) planes of BT and Ag led to the hetero-epitaxial growth of Ag on the BT surface. The thickness of the coherent interface was about 3 nm. The adhesion of Ag to BT efficiently prevented the continuous contact between Ag particles in the polyvinylidene fluoride (PVDF) matrix and suppressed the formation of the conducting path in the composite. As a result, with a filler loading of 43.4 vol %, the composite exhibited a dielectric constant (Dk) value of 94.3 and dielectric loss (tan δ) of 0.06 at 1 kHz. An even higher Dk value of 160 at 1 kHz (16 times larger than that of PVDF) was obtained when the content of BT-Ag was further increased, with low conductivity (σ < 10(-5) S m(-1)) and low dielectric loss (tan δ = 0.11), demonstrating promising applications in the electronic devices.

Construction of a 3D-BaTiO3 network leading to significantly enhanced dielectric permittivity and energy storage density of polymer composites

Herein, the designed 3D-BaTiO3 network in polymer composites results in enhanced permittivity and energy storage density. High permittivities of 200 (eeff/em ∼ 55.4) and 34.5 are achieved in the composites with only 30 vol% and 16 vol% 3D-BaTiO3, respectively. The latter exhibits a discharged energy density that is over 16 times larger than the polymer matrix.

Residual stress analysis in ferroelectric Pb(Zr0.52Ti0.48)O3 thin films fabricated by a sol-gel process

Ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) films were prepared by a modified sol-gel process, in which polyethylene glycol (PEG) was added to the precursor solutions. An x-ray diffraction (XRD) method that detected the d(123) variation associated with the change in the incline angle ψ of the plane (123) was developed to quantify the residual stress in the PZT films. The stress could not be determined from the wafer curvature due to the effects of both the underlying layers and interdiffusion among layers. Using our XRD method, it was found that the residual stress in the resulting PZT films was significantly reduced when PEG was added to the precursor solutions. Moreover, we observed a further reduction of residual stress with increasing molecular weight of the PEG additive. These results could explain why a thicker, crack-free film can be achieved by adding polymers to the sol-gel precursor solutions.

Dielectric dispersion behavior of Ba(ZrxTi1-x)O3 solid solutions with a quasiferroelectric state

The temperature dependence of dielectric permittivity was investigated for the barium zirconium titanate solid solution system [BZT, Ba(ZrxTi1−x)O3 0.25≤x≤0.5]. The dielectric relaxation behavior was observed in these ferroelectrics with diffused phase transition. In contrast to the canonical relaxors such as Pb(Mg1/3Nb2/3)O3, the diffused phase transition of BZT could not be well described by the popular modified Curie–Weiss law. Quasiferroelectric state theory was introduced to explain the dielectric results of the BZT relaxors.

Mechanism of high dielectric performance of polymer composites induced by BaTiO3-supporting Ag hybrid fillers

BaTiO3-supporting Ag hybrid particles (BT-Ag) with varied fraction of Ag were synthesized by reducing silver nitrate in the glycol solution containing BaTiO3 (BT) suspensions. The Ag nano particles with a size of about 20 nm were discretely grown on the surface of the BT. The dielectric performance of the composites containing the BT-Ag as fillers in the matrix of polyvinylidene fluoride (PVDF) was investigated. The relative permittivity (er) of the BT-Ag/PVDF composites increased prominently with the increase of BT-Ag loading amount, and the typical conductive path of the conductor/polymer system was not observed even with a high loading of BT-Ag. The er at 100 Hz for the three BT-(0.31, 0.49, 0.61)Ag/PVDF composites at room temperature were 283, 350, and 783, respectively. The er of the composites was enhanced by more than 3 times compared with that of the composite containing untreated BT nanoparticles at frequencies over 1 kHz and the loss tangent (tan δ) was less than 0.1 which should be attributed to the low conductivity of the composites. Theoretical calculations based on the effective medium percolation theory model and series-parallel model suggested that the enhanced permittivity of BT-Ag/PVDF composites should arise from the ultrahigh permittivity of BT-Ag fillers, which was over 104 and associated with the content of Ag deposited on the surface of BT.BaTiO3-supporting Ag hybrid particles (BT-Ag) with varied fraction of Ag were synthesized by reducing silver nitrate in the glycol solution containing BaTiO3 (BT) suspensions. The Ag nano particles with a size of about 20 nm were discretely grown on the surface of the BT. The dielectric performance of the composites containing the BT-Ag as fillers in the matrix of polyvinylidene fluoride (PVDF) was investigated. The relative permittivity (er) of the BT-Ag/PVDF composites increased prominently with the increase of BT-Ag loading amount, and the typical conductive path of the conductor/polymer system was not observed even with a high loading of BT-Ag. The er at 100 Hz for the three BT-(0.31, 0.49, 0.61)Ag/PVDF composites at room temperature were 283, 350, and 783, respectively. The er of the composites was enhanced by more than 3 times compared with that of the composite containing untreated BT nanoparticles at frequencies over 1 kHz and the loss tangent (tan δ) was less than 0.1 which should be attributed t...

Electrical modulus analysis on the Ni/CCTO/PVDF system near the percolation threshold

A type of Ni/CCTO/PVDF three-phase percolative composite was prepared, in which the filler content (volume fraction) of Ni and CCTO was set at 60?vol%. The dependence of permittivity, electrical modulus and ac conductivity on the concentration of Ni and CCTO fillers near the percolation threshold was investigated in detail. The permittivity of the composites dramatically increased as the Ni content approached 24?vol%. This unique physical mechanism was realized as the formation of conductive channels near the percolation threshold. Analysis on the electrical modulus showed that the conductive channels are governed by three relaxation processes induced by the fillers (Ni, CCTO) and PVDF matrix, which are the interfacial polarization derived from the interfaces between fillers (Ni, CCTO) and PVDF matrix, and the polarization of CCTO ceramic filler and PVDF matrix. The conductivity behaviour with various Ni loadings and temperature suggested that the transition from an insulating to a conducting state should be induced by charge tunnelling between Ni?Ni particles, Ni?CCTO fillers and Ni?PVDF matrix. These findings demonstrated that the tunnelling conduction in the composite can be attributed to the unique physical mechanism near the percolation threshold.

Preparation of perovskite Pb(Zn1/3Nb2/3)O3-based thin films from polymer-modified solution precursors

Epitaxial perovskite Pb(Zn1∕3Nb2∕3)O3 (PZN)-based ferroelectric thin films were prepared through a chemical solution approach, in which the solution precursors were appropriately modified with polyethylene glycol (PEG). The addition of PEG in the solution dramatically promoted the perovskite phase while suppressed the pyrochlore phase, although PEG was pyrolyzed before the crystallization. The interactions between PEG and metal ions were identified through examining the chemical states of the ions using x-ray photoelectron spectroscopy. The ferroelectric and piezoelectric properties of an obtained thin film sample with a composition of 0.462PZN–0.308PMN–0.23PT [PT:PbTiO3;PMN:Pb(Mg1∕3Nb2∕3)O3] were characterized, showing a very low coercive field, high dielectric constant, and strong piezoelectric effect.

Dielectric, ferroelectric properties, and grain growth of CaxBa1−xNb2O6 ceramics with tungsten-bronzes structure

Dielectric properties, microstructures, and phase transition behaviors of α and β phases of CaxBa1−xNb2O6 (x=0.22, 0.30, and 0.38) ceramics were investigated. All the three compositions had partially filled tungsten-bronze structure (TTB) and relatively high Curie temperatures (up to 345°C) compared with Sr1−xBaxNb2O6. The α phase exhibits unambiguously a diffused phase transition, while the β phase is associated with an incommensurate phase and needs to be further studied. The dielectric and ferroelectric properties of CaxBa1−xNb2O6 ceramics were strongly processing-dependent. A mechanism was proposed to explain the grain growth behavior of TTB ceramic niobates.

General synthesis of LiLn(MO4)2:Eu3+ (Ln = La, Eu, Gd, Y; M = W, Mo) nanophosphors for near UV-type LEDs

A series of Eu3+-doped double tungstate and molybdate red phosphors, LiLn(MO4)2:Eu3+ (Ln = La, Eu, Gd, Y; M = W, Mo), have been successfully synthesized by a simple Pechini method. The procedure involves formation of homogeneous, and transparent, metal–citrate gel precursors using citric acid as a chelating ligand to form metal complexes and ethylene glycol as a cross-linker for polyesterification with the complexes, followed by calcination to promote thermal decomposition of the gel precursors to yield the final LiLn(MO4)2 nanoparticles. The as-synthesized nanoparticles were characterized by thermogravimetric/differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) as well as kinetic decay. The results indicate that the obtained LiLn(MO4)2:Eu3+ samples crystallize in the isostructure with tetragonal space group I41/a (no. 88). A room temperature PL spectrum shows that Eu3+-doped LiLn(MO4)2 powders exhibit an excellent luminescent properties under a near ultraviolet excitation wavelength of 395 nm, suitable for near UV type LEDs. By comparing with other counterparts, it is found that LiEu(WO4)2 and LiEu(MoO4)2 display the highest emission intensity. In addition, the phosphor of composition LiY0.95Eu0.05(WO4)2 shows promising application for white light emission with a decay time of 0.585 ms.

Crossover from a nearly constant loss to a superlinear power-law behavior in Mn-doped Bi(Mg1/2Ti1/2)O3–PbTiO3 ferroelectrics

Mn-doped Bi(Mg1/2Ti1/2)–PbTiO3 disordered ferroelectric ceramics were studied under ac electric fields and a crossover from a nearly constant loss to a superlinear power-law behavior was observed. Our results confirmed that the nearly constant loss behavior also exists in disordered ferroelectrics. The exponent of the superlinear power-law was found to be temperature dependent. Such a behavior was related to the local movements of oxygen vacancies.