Nan Cewen

Multiferroic behaviour of epitaxial NiFe2O4–BaTiO3 heterostructures

Multiferroic NiFe2O4 (NFO)-BaTiO3 (BTO) bilayered thin films are epitaxially grown on (001) Nb-doped SrTiO3 (STO) substrates by pulsed-laser deposition (PLD). Different growth sequences of NFO and BTO on the substrate yield two kinds of epitaxial heterostructures with (001)-orientation, i.e. (001)-NFO/(001)-BTO/substrate and (001)-BTO/(001)-NFO/substrate. Microstructure studies from x-ray diffraction (XRD) and electron microscopies show differences between these two heterostructures, which result in different multiferroic behaviours. The heterostructured composite films exhibit good coexistence of both ferroelectric and ferromagnetic properties, in particular, obvious mag-netoelectric (ME) effect on coupling response.

Dielectric behavior of nano-PbTiO3/PVDF nanocomposites in-situ synthesized by the sol-gel method

BaTiO3/PVDF nanocomposites were prepared via in-situ growth of nanosized BaTiO3 particles in PVDF matrix by using the sol-gel method. The present elements of BaTiO3/PVDF nanocomposites were analyzed by an electron probe X-ray microanalyser. Nanosized BaTiO3 grown in the composite films was characterized by an X-ray diffractometer and a transmission electron microscope, and the dielectric properties of the composite films were measured. The distribution of BaTiO3 nanoparticles in-situ grown in the PVDF matrix was examined using a scanning electron microscope.

Microstructure of steel fiber reinforced polymer-cement-based composites

Mercury intrusion porosimetry was used to measure the pore structure of steel fiber reinforced polymer-cement-based composite. The results indicate that the large pore volume decreases by 57.8%–51.2% and by 87.1%–88% with the addition of steel fibers and polymers respectively. When both steel fibers and polymers are simultaneously added, the large pore volume decreases by 88.3%–90.1%. As a surface active material, polymer has a favorable water-reduced and forming-film effect, which is contributed to the decrease of the thickness of water film and the improvement of the conglutination between the fibers and the matrix. Polymers could form a microstructure network. This network structure and the bone structure of cement hydration products penetrate each other and thus the interpenetrating network with sticky aggregate and steel fiber inside forms.

The dielectric properties and preparation method of BaTiO3/PVDF 0–3 composites

A series of 0–3 composites of the polyvinylidene fluoride (PVDF) and BaTiO3 was prepared. BaTiO3 was modified with titanate coupling agent. The dielectric properties and the interfacial interaction of composites by different preparation methods were examined and compared. The result shows that the relative dielectric constant ∈ of the composite prepared in solution has a maximum value at about 70% weight fraction of BaTiO3 and the dielectric loss tanδ increases rapidly when the fraction exceeds 70%. For the composite prepared in melt, the relative dielectric constant ε almost reaches a maximum value at about 60% weight fraction of BaTiO3 and the dielectric loss is comparatively lower. The dielectric properties of composites are improved by using a coupling agent.

Thermoelectric properties and electronic structure of Ca3Co2O6

The nanosized Ca3Co2O6 powder was synthesized via sol-gel process. The phase composition was characterized by means of X-ray diffraction. Polycrystalline samples of Ca3Co2O6 were prepared by a sintering procedure of nanosized power. The seebeck coefficient and electrical conductivity of the samples were measured from 450K up to 750K. The results show that the Seebeck coefficient increases with the increasing temperature. The electronic structures were calculated using the self-consistent full-potential linearized augmented plane-wave (LAPW) method within the density functional theory. The relationship between thermoelectric property and electronic structures was discussed.

Hydrothermal synthesis and dielectric properties of lanthanum titanate ceramics

Lanthanum titanate (La2/3TiO3) powders were synthesized by hydrothermal method based on the reaction of TiO2, La(NO3)3 and KOH at 160 °C for 24 h followed by the treatment of acidification. The microstructure, morphology and dielectric properties were investigated by using X-ray diffraction, scanning electron microscope, transmission electron microscope and impedance method. The results show that the La2/3 TiO3 particles consist of nearly homogenous and lamellar grains. The particles can be sintered into porous ceramics above 1150 °C. The dielectric properties of La2/3 TiO3 show that both the dielectric constant and the dielectric loss tangent decrease with the increase of frequency.

Structural Characteristics and Quantum Chemistry Calculation of Si-Doped Boron Carbides

Structural characteristics, chemical bonds and thermoelectric properties of Si-doped boron carbides are studied through calculations of various structural unit models by using a self-consistent-field discrete variation X α method. The calculations show that Si atom doped in boron carbide is in preference to substituting B or C atoms on the end of boron carbide chain, and then may occupy interstitial sites, but it is difficult for Si to substitute B or C atom in the centers of chain or in the icosahedra. A representative structural unit containing a Si atom is [C-B-Si] e+ [B 11 C] e- , while the structural unit without Si is [C-B-B(C)] δ- -[B 11 C] δ+ , and the coexistence of these two different structural units makes the electrical conductivity increases. As the covalent bond of Si-B or Si-C is weaker than that of B-B or B-C, the thermal conductivity decreases when Si is added into boron carbides. With the electrical conductivity increases and the thermal conductivity decreases, Si doping has significant effect on thermoelectric properties of boron carbides.

Effects of Li3PO4 Particles on Electrical Property in Li0.5La0.5TiO3/Li3PO4 Composite Solid Electrolyte

Abstract The ionic conductivity of Li 3 PO 4 dispersed Li 0.5 La 0.5 TiO 3 (LLTO) composite solid electrolyte was examined by complex impedance analysis. The X-ray powder diffraction (XRD), scanning electron microscope (SEM) observation and relative density measurement were also performed to study the dispersion of the second phase into the LLTO electrolyte. Results indicate that the addition of Li 3 PO 4 into LLTO matrix decreases the ionic conductivity, though the composites added by the Li 3 PO 4 particles show a high compactness. The reasons for the conductivity deterioration were clarified based on the lattice structure of LLTO, microstructures at the grain boundary regions, and the lithium content. The variation of the lithium content and microstructures in the LLTO matrix dispersed by Li 3 PO 4 particles are mostly responsible for the behaviors in the ionic conduction.

Research progress and future directions of multiferroic materials

Multiferroic magnetoelectric (ME) materials can not only consist of ferroelectric, magnetic or ferroelastic orders, but also novel effects produced by the coupling interaction between multi-order parameters. This kind of functional materials exhibit significant potential applications in the fields of novel multifunctional magnetic-electric devices, spintronics devices, and high performance information storage and processing, etc. Besides, multiferroic has become a hot topic due to its rich connotation in condensed matter physics concerning charge, spin, orbital, and lattice. In this paper, we review the history and the progress in the recent development of multiferroic compounds and composites, with the attention focused on the discussion of the key scientific challenges and the prospects of the future directions.