Hanxing Liu

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.

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.

The Effect of ZnO–B2O3–SiO2 Additive on Sintering and Dielectric Properties of Ba0.3Sr0.7TiO3 Ceramics

ZnO–B2O3–SiO2 additive with 0.55: 0.35: 0.10 molar ratio was added to Ba0.3Sr0.7TiO3 ceramics in order to lower the sintering temperature. The densification behavior, crystalline structure, microstructure, dielectric properties and breakdown strength of ceramics were studied. When 9 wt.% additive was mixed with pure Ba0.3Sr0.7TiO3 powder, the densification temperature of samples decreased from 1350°C to 1100°C compared with no additive system, and the sintered ceramics revealed dielectric properties at room temperature as follows: dielectric constant ϵr = 413, dielectric loss tanδ = 0.00231 under 1 kHz and the breakdown strength Eb = 9.2 kV/mm.

Effect of B-Site Bond Valence on Microwave Dielectric Properties of Ca[(Zn1/3Nb2/3)(1 − x)Ti x ]O3 Ceramics

The relationship between B-site bond valence and microwave dielectric properties of Ca[(Zn 1/3 Nb 2/3 ) 1 − x Ti x ]O 3 ceramics with a perovskite structure prepared by solid reaction method was investigated. As the bond valence of B-site increased with increasing of Ti, the dielectric constant (K) and quality factor (Q ƒ) varied from 42 to 115 and 13030 to 5030 GHz, respectively. The temperature coefficient of resonant frequency (TCF) increased from ∼ -28 to ∼ 336 ppm/°C. The theoretical polarizabilities (α theo ) from additivity rule were compared with the measured polarizabilities (α mea.) from Clausius-mosotti equation. Therefore, the microwave dielectric properties can be controlled with the change of bond valence.

Effects of CeO2 doping on electrical properties of lead metaniobate based ceramics

Pb 0.97 Ca 0.03 Nb 2 O 6 + xwt% CeO2 (x = 0, 0.3) bulk ceramics were fabricated by conventional solid state reaction route. The structures of the specimen were investigated by XRD and SEM. The dielectric, piezoelectric properties were also measured, the results indicate that CeO 2 doping can improve the piezoelectric properties. The specimen of x = 0.3 showed the main electrical properties as follows: K p = 0.06, K t = 0.40, Q m = 25, tanδ = 0.36%, ϵ 33 T /ϵ0 = 243 and d 33 = 71 pC/N. The Curie temperature of the specimen x = 0.3 is 526°C, it can be potentially applied for high temperature and high frequency wideband ultrasonic transducers and detectors.

Microstructures and Microwave Properties of Alkali Cations Displacement of 0.4ATiO3-0.6La (Mg0.5Ti0.5)O3(A = Ca, Sr, Ba) Ceramics

Microstructures and microwave dielectric properties of Alkali cation displacement of 0.4ATiO 3 -0.6La(Mg 0.5 Ti 0.5 )O 3 (A = Ca,Sr,Ba) ceramics were investigated. With the alkali cation displacement, namely the increase of the A-site cation radii, the bulk density increased with the rise of sintering temperature obviously while the higher temperature caused the decrease of bulk density. As the increase of radii, diffraction peaks shifted to low angle by XRD which illuminated the volume of unit cell reduced. The 0.4ATiO 3 -0.6La(Mg 0.5 Ti 0.5 )O 3 (A = Ca, Sr, Ba) ceramics showed a dense microstructure without the presence of second phases by XRD and SEM. The relationship of properties and tolerance factor were discussed.

Phase Transition and Thermochromism of the Hybrid (C12H25NH3)2FeCl4

This paper focuses on the structural change and the thermochromism of the phase transition of the hybrid (C12H25NH3)2FeCl4. The temperature and the structures of the phase transition is investigated by a thermal gravimetry (TG) and differential scanning calorimetry (DSC), an infrared spectra (IR) and X-ray diffraction (XRD) patterns. The UV adsorption spectra account for the thermochromism. The results suggest that the reversible phase transition arises from the structural changes of the organic chains. The thermochromism is presumably due to the electrons redistribution on the levels and to the energy transition to translational and rotational motions of the organic chains.

The Influence of the Interactions between the Organic and Inorganic Species on the Structural Stabilities of Hybrids (CnH2n+1NH3)2 MCl4

This paper focuses on the influence of interactions between different species in hybrids (CnH2n+1NH3)2MCl4 (M = Mn, Cu; n =2,4,6,8,10) on the structural stabilities. DSC-TG curves were used to find out the onset and the end decomposition temperatures. The results show that the hybrids of M =Cu start to decompose at about 210 centigrade degrees, average 25 centigrade degrees lower than that of M=Mn. The end temperatures of M=Cu are also lower. This suggests that in this case the thermal stabilities of the hybrids would be governed by the interactions between the organic and inorganic species and are little affected by weak Van de Waals interactions between the organic and organic species.