Shixi Ouyang

Heating effect of BaTiO3 in microwave field and microstructure of BaTiO3

Microwave equipment at 2 450 MHz was employed to prepare BaTiO3. The heating effect of the system in the microwave field, which was influenced by several factors including dielectric properties of synthesis system and thermal insulate structures, was discussed in detail. The heating rates of the synthesis system were mainly determined by BaCO3 and TiO2 at low temperature and by TiO2 and BaTiO3 at high temperature. The results show that the heating effects in microwave field are greatly different from those in conventional furnace. The reaction of BaCO3 and TiO2 only lasts for 3 min at 1 100°C, and the fine, narrow-distributed and well-crystallized powders were prepared.

Mechanism of microwave synthesized BaTiO3

The difference of intermediate products, microstructure and element concentration in the particles between microwave synthesized samples and conventional samples was responsible for the existence of non-thermal effect in the microwave field. The diffusions of Ba2+, Ti4+ in the microwave field were enhanced, so that the diffusion of Ti4+ could not be neglected as in the conventional solid state reactions. The influences of the microwave field were mainly expressed as diffusion coefficient and the driving force of ionic motion. The intermediate phase Ba2TiO4 which occurred in the conventional solid reaction was not found during microwave syntheses. The quantity analyses based on XRD experimental data show that the reaction dynamics in microwave is suitable for the Carter equation. The activity energy for reaction of BaCO3 and TiO2 in the microwave field was 42.26 kj/mol, which was only one fifth of the conventional reaction.

Structure and Properties of Microwave Sintering ZnO Ceramics

In this paper, it is investigated the microwave sintering method of ZnO ceramics using pure ZnO powder as raw materials, and then it was successfully sintered with the 2.45GHz microwave sintering technique. The microscopic structure and morphology of ZnO ceramic samples were determined in XRD and SEM, I-V properties are also measured. The results show that microwave sintering method is a rapid sintering method for ZnO ceramic with homogeneous structure and good properties, microwave sintering is a promising method for ZnO ceramics.

Structural and electronic properties of SBT in FEDREAM devices

Abstract In the present study, we performed first-principles modeling of calculation on electricity behavior of ferroelectric strontium bismuth tantalate (SBT). Different cluster models were chosen for the discussion of the influence of atomic coordination on the atomic valence configuration, atomic charge, and bond order etc. in the DV-Xα calculations. This allowed us to understand size effects of cluster on the electronic structure of SBT. The results of first-principles calculations of the electronic structure in SrBi 2 Ta 2 O 9 (SBT) were reported. The electronic density distribution indicates density of states induced local levels within the gap, and finds significant hybridization between metal d states and the O 2p –Ta 5d and Ta 6s state. The charge of Sr is transferred to the oxygen atom, the bonding between them was nearly ionic bonding. The calculated electronic structure of SBT indicates that the absence of an energy gap in the vicinity of the fermi level stems from lowering of the Sr orbital energies due to its lower electro-negativity relative to Ta and Bi ions, and significant hybridization between Ta, Bi and O ions. The calculated total densities of states were in agreement with the reported X-ray photoemission spectroscopy data.

Kinetics and mechanism of the microwave synthesis of barium titanate

The formation kinetics of BaTiO{sub 3} from the solid-state BaCO{sub 3} and TiO{sub 2} powder in a microwave field was investigated. The quantitative XRD analysis and the model considered the volume change between reactant and product were used in this experiment. Results show that the formation rate of BaTiO{sub 3} in a microwave field is much faster than upon conventional heating. The activation energy of the solid state reaction for BaTiO{sub 3} was measured as 58 kJ/mol. This indicates the enhancement of diffusion by the microwave heating process.

Growth of NiAl shape memory alloy single crystals

Abstract As a potential candidate of high temperature Shape Memory Alloy (SMA), inter metallic compound NiAl has been studied for more than 30 years. In order to understand better the mechanism of the Shape Memory Effect(SME) in β -NiAl phase, its bulk single crystal have been prepared with an improved magnetic levitation cold crucible Czoehralski(CZ) technique in our lab. The crystal growth procedure and the β -NiAl phase stability are discussed in this paper.

The Synthesis and Structure of New Perovskite-type Niobate Processed in Millimeter Wave Field

In present paper a new niobate materials Ba 5 Li x Ti x Nb 10-x O 30 were synthesized by doping Li + in the system BaO- TiO 2 - Nb 2 O 5 in millimeter wave field. X-ray diffraction (XRD) quantitative and scanning transition spectroscopy (SEM) analysis were employed to study crystal structure and microstructure of reaction products. It was found that pure products could be obtained at temperature 900°, 8 min which is lower comparing with that by conventional method. The XRD data shown the crystal belongs to tetragonal tungsten bronze structure with space group P4bm. The grain size synthesized in millimeter wave field had smaller size, narrower distribution, better sinter-ability, and without hard agglomeration comparing whit that obtaining from conventional synthesis. At lower temperature Ba 5 LiTiNb 9 O 30 is a tetragonal ferroelectric phase.

Millimeter wave processing of materials in IECAS

Millimeter wave processing of materials is a method which has wide application prospect for improving material characteristics. In this paper, the investigated results of millimeter wave processing of materials in IECAS, such as millimeter wave sintering of Al/sub 2/O/sub 3/, ZnO, Nd/sub 2/Ti/sub 3/O/sub 9/, and chemical syntheses of spinels LiMn/sub 2/O/sub 4/ and LiCo/sub 0.1/Mn/sub 1.99/O/sub 3.92/S/sub 0.08/, as cathode materials of Li-ion batteries, with millimeter wave heating are presented.

Study of Boundary Free Tb-Dy-Fe Magnetostrictive Materials

As a promising candidate of advanced smart materials Tb-Dy-Fe system has been studied for many years. It is well known that the boundaries (which exist in polycrystal and grain oriented crystals of magnetostrictive materials) heavily hinder the motion of domain walls. Therefore to eliminating those boundaries will improve their magnetostrictive behaviors to a large extent. A single crystal growth method (which is called: growth with magnetic levitation cold crucible in CZ technique) has been successfully developed in our lab. since a few years ago. Now bulk cubic Laves phase RFe 2 Tb x Dy 1-x Fe 1.95–2.0 single crystals with boundary free structure can be prepared. Studies have been focused on comparing the performances of polycrystal, grains oriented crystal with a single crystal of the same composition. Some results indicate that λ s and d 33 performed by the single crystal are much higher than the two former materials under the same conditions.