Piyi Du

Percolative conductor/polymer composite films with significant dielectric properties

A percolative film with conductive acetylene black introduced into β-polyvinylidene fluoride was prepared by dip-coating method. Percolation theory was employed to explain the dielectric behavior of polymer/conductor composite films. Experimental results showed that the dielectric constant of polymer/conductor composite films can reach 56 and the dielectric loss is below 0.15 when acetylene black concentration is in the neighborhood of percolation threshold (fc). The experimental results are in good agreement with classic percolation power law, with fc≈1.3% and exponent q≈0.53. Such composite films have a potential to become capacitors and can be easily fabricated due to its flexibility.

Sol-gel preparation of bioactive apatite films

The surface of biomedical metallic implants covered by a bioactive apatite film can create bioactivity of the implant and shorten healing time. In this work, apatite films on Ti6Al4V were prepared by sol–gel route using Ca(NO ) , P O and HPF as 32 2 5 6 the precursors, in vitro evaluations of the resulting hydroxyapatite (HA) and fluorapatiteyhydroxyapatite solid solution (FHA) films were done in Kokubo’s simulated body fluid and citric acid modified phosphate buffer solution (CPBS). HPF showed a 6 good reagent for the incorporation of fluorine into apatite films. The FHA film demonstrated to have good bioactivity, and to have better stability in CPBS and higher adhesion strength than the HA film. When fluorine is incorporated into the film, an increase in crystallinity of the apatite film and a decrease in intrinsic solubility of the FHA film could make significant contributions to the improvement in the stability; the thermal expansion coefficient of the FHA film getting closer to that of Ti6Al4V could be responsible for the increase in adhesion strength. 2002 Elsevier Science B.V. All rights reserved.

Ag-Ba0.75Sr0.25TiO3 composites with excellent dielectric properties

The percolative ceramic composites of Ba0.75Sr0.25TiO3∕Ag (BST/Ag) with dense microstructure were sintered at a low temperature of 960°C. Excellent dielectric properties, such as high dielectric constant (er∼24000), low dielectric loss, and high dielectric tunability, were reported. The dielectric constant is found to be nearly temperature and frequency independent. It is essential to introduce the low-melting-point metal of silver into BST ceramics for significantly enhancing the dielectric properties of the composites. The superproperties make it potential to be used for electronic devices such as high charge-storage capacitors and tunable filters.

PbTiO3 nanofibers with edge-shared TiO6 octahedra.

A new tetragonal phase of PbTiO(3) was discovered, in which each TiO(6) octahedron pair shares an edge and stacks over following pairs in an interlaced manner to form a one-dimensional (1D) columned structure along the c-axis. This new tetragonal phase of PbTiO(3) transforms into a normal perovskite phase in air at elevated temperature.

The effect of citric acid addition on the formation of sol-gel derived hydroxyapatite

In order to improve the gelation in sol–gel preparation of hydroxyapatite by using Ca(NO3)2 and PO(OH)3−x (OEt)x precursors, citric acid was selected as an enhancing gelation additive. Hydroxyapatite derived from the mixed precursor solutions (Ca/P molar ratio of 1.67) with citric acid showed a different reaction path from that without citric acid. The addition of citric acid led to formation of amorphous as-prepared powder, the powders calcined at 650 ◦ C contained three phases: hydroxyapatite, carbonated hydroxyapatite and a small amount of -tricalcium phosphate. The powders calcined at 800 ◦ C contained only a single phase of oxy-hydroxyapatite. It is suggested that citric acid plays a role in enhancing gelation through a strong coordination ability of Ca ions with citrate groups.

Ag nanoparticle dispersed PbTiO3 percolative composite thin film with high permittivity

Ag nanoparticle dispersed PbTiO3 percolative composite thin films were prepared in situ by sol-gel method using Pb(NO3)2, Ti(C4H9O)4, and AgNO3 as raw materials and lactic acid along with citric acid as complexing agent. The size of the Ag nanoparticles measured by ultraviolet-visible spectra is about 3nm. The percolation effect occurs in composite thin films. The composite exhibits relatively high dielectric constant which is about five times higher than that of PbTiO3 thin film and comparatively low dielectric loss comparable to pure PbTiO3 system. It is highly attractive in application of high quality dielectric devices and miniaturization.

Enhanced Luminescence of Eu-Doped TiO2Nanodots

Monodisperse and spherical Eu-doped TiO2nanodots were prepared on substrate by phase-separation-induced self-assembly. The average diameters of the nanodots can be 50 and 70 nm by changing the preparation condition. The calcined nanodots consist of an amorphous TiO2matrix with Eu3+ions highly dispersed in it. The Eu-doped TiO2nanodots exhibit intense luminescence due to effective energy transfer from amorphous TiO2matrix to Eu3+ions. The luminescence intensity is about 12.5 times of that of Eu-doped TiO2film and the luminescence lifetime can be as long as 960 μs.

Ferroelectric/ferromagnetic ceramic composite and its hybrid permittivity stemming from hopping charge and conductivity inhomogeneity

Exploring the nature of multiferroic ceramic composite with dual high performances is much important to take full advantage of its novel dielectric properties. In this paper, Ni0.5Zn0.5291Fe2O4/BaTiO3 ceramic composite is proposed and successfully prepared from BTO and NZFO powders which are obtained by sol-gel process and citric acid combustion method, respectively. Results show that with increasing BTO content from 0 to 25 vol. % in the matrix of NZFO, the permittivity of the composite decreases from 220 k to 100 k at low frequencies (∼40 Hz) and contrarily from 20 to 100 at high frequencies (∼100 MHz). It is mainly ascribed to the instant polarization in NZFO at low frequencies and the polarization in the perovskite phase of BTO at sufficiently high frequencies. The permittivity of the ferrite and composite is shown to be compatible with a hybrid model proposed, which concerns hopping charges between Fe2+ and Fe3+, conductivity heterogeneity at the grain boundaries of the ferrite, and changes in the co...

Highly sensitive hydrogen peroxide biosensors based on TiO2 nanodots/ITO electrodes

Uniformly dispersed and size-controllable TiO2 nanodots (TN) were directly synthesized on indium-tin-oxide (ITO) electrodes and were further utilized to immobilize horseradish peroxidase (HRP) enzyme and facilitate direct electron transfer for construction of a hydrogen peroxide (H2O2) biosensor. The enzyme adsorption ability of TN/ITO electrodes were investigated using a UV–vis spectrometer, and the results indicated that TiO2 nanodots possess better enzyme adsorption ability than TiO2 film, and this ability could be further improved by varying the mean diameter of the nanodots from 30 nm to 79 nm. The sensitivity of the H2O2 biosensors based on Nafion/HRP/TN/ITO electrodes was significantly increased by adjusting the dimension of TiO2 nanodots on the modified electrode and the sensitivity differences among these electrodes are in accord with their enzyme adsorption ability. TiO2 nanodots with the largest diameter (79 nm) on a ITO electrode had the best enzyme adsorption ability and biosensor performance with a high sensitivity of 1176 μA mM−1 cm−2 as well as a wide linear range of 1–780 μM. These results show that well-dispersed, high surface area and high curvature TiO2 nanodots could be a promising material for protein adsorption and fabrication of electrochemical biosensors.

Ferrite with extraordinary electric and dielectric properties prepared from self-combustion technique

Nickel-zinc ferrites (Ni0.5Zn0.5Fe2O4) with extraordinary electric and dielectric properties were prepared by self-combustion technique. The resistivity of ferrite in the ferric citrate system is on the order of 1010Ωcm, which is about four orders higher than that of ferrite in the ferric nitrate system as well as that of ferrite prepared by the conventional method. The dielectric loss of sample in the ferric citrate system is only 0.008. The amorphous phase and its encapsulation well around the grains have played most important roles in both high resistivity and low dielectric loss of ferrite in the ferric citrate system.