Effect of solvents on the morphology and structure of barium titanate synthesized by a one-step hydrothermal method

Tetragonal barium titanate was synthesized from barium hydroxide octahydrate and titanium tetrachloride through a simple one-step hydrothermal method.The effect of different solvents on the crystal structure and morphology of barium titanate nanoparticles during the hy-drothermal process was investigated.Except for ethylene glycol/water solvent,impurity-free barium titanate was synthesized in pure water,methanol/water,ethanol/water,and isopropyl alcohol/water mixed solvents.Compared with other alcohols,ethanol promotes the formation of a tetragonal structure.In addition,characterization studies confirm that particles synthesized in methanol/water,ethanol/water,and isopropyl al-cohol/water mixed solvents are smaller in size than those synthesized in pure water.In the case of alcohol-containing solvents,the particle size decreases in the order of isopropanol,ethanol,and methanol.Among all the media used in this study,ethanol/water is considered the optimum reaction media for barium titanate with high tetragonality(defined as the ratio of two lattice parameters c and a,c/a=1.0088)and small aver-age particle size(82 nm),which indicates its great application potential in multilayer ceramic capacitors.

Preparation and Mechanical Properties of Zirconia Ceramics Doped with Different Y_(2)O_(3)Contents

The sintering behavior and mechanical properties of zirconia doped with 2.0mol%-3.0mol%Y_(2)O_(3)were studied by pressure-less sintering.The experimental results show that the densification temperature of zirconia ceramics increases gradually with the decrease of Y_(2)O_(3)doping content by which decreases the sintering driving force due to the lower oxygen vacancy concentration of the systems.Furthermore,the bending strength and fracture toughness of the prepared zirconia ceramics increase with the decrease of Y_(2)O_(3)doping content.It can be attributed to the fact that the phase stability of tetragonal zirconia decreases with the decrease of Y_(2)O_(3)doping content,which is easier to induce"phase transformation toughening"and dissipate impact energy.The relative density,bending strength and fracture toughness of 2.0 mol%Y_(2)O_(3)doped zirconia ceramics(2.0Y-ZrO_(2))sintered at 1525℃are 99.00%,1256.65±20.82 MPa and 9.85±0.13 MPa·m^(1/2),respectively.

相变的激光光散射研究进展

本文简述地评述了相变的激光非弹性光散射研究取得的进展。其内容包括光散学研究相变的历史,铁电相变、非公度相变以及高温钇钡铜氧超导体结构相变等晶格动力学方面。

Crystallinity, Microstructure and Mechanical Strength of Yttria-Stabilized Tetragonal Zirconia Ceramics for Optical Ferrule

Yttria-stabilized zirconia ceramics were prepared by using different raw materials in order to compare commercially available optical ferrule. Injection-molded cylindrical green compacts were sintered in air at 1350°C, 1400°C and 1450°C for 2 hrs, followed by furnace cooling. Crystallinity, microstructure and mechanical strength of the sintered body were evaluated by using an X-ray diffraction analyses, a field emission-scanning electron microscope, a universal tester, and a micro-hardness tester, respectively. For practical usage, the sample B sintered at 1350°C was favorable because of high tetragonality and good mechanical strength.

Phase Transitions and Dielectric Properties of Lead-Free Bi0.5K0.5TiO3-BaTiO3 Piezoelectric Ceramics

Abstract： Lead-free piezoelectric ceramics of （1 - x） Bi0.5K0.5TiO3-BaTiO3 （BKT-BT） were fabricated by the solid state reaction method with normal sintering. The influence of BT addition on the crystal structure, phase transition and dielectric properties was investigated. The crystal structure and ferroelectric phase transition were studied by XRD （X-ray diffraction） and dielectric measurements. The complete solid solution of BKT-BT was observed for all compositions. In XRD results, all compositions showed a single phase perovskite structure with tetragonal symmetry at room temperature. With increasing BT content, the separation between diffraction peaks corresponded to increasing tetragonality. The phase transition temperature of ferroelectric tetragonal-paraelectric cubic （Tc） decreased with increasing BT content. As the amount of BT concentration increased, the ceramic became denser, and almost no porosity was finally obtained.

Spark plasma sintering of high-toughness ZrO_2 materials doped with yttrium

Zirconia powders doped with yttrium prepared by special liquid-phase precipitation method were sintered by spark plasma sintering （SPS） to obtain high performance samples. The microstructure, phase composition, and mechanical properties of the samples were studied. The results of X-ray diffraction （XRD）, Raman spectrum, and transmission electron microscope （TEM） show that the phase is tetragonal. The powders with large surface area and high sintering activity, due to small crystallite size, could be densified at 1100℃. The highest relative density of the sample obtained at 1300℃ is higher than 99% （the tetragonal phase is 6.08 g/cm^3）. The Hv and KIC are 13.76 GPa and 15.4 MPa.m^1/2, respectively.

Morphological Change and Its Mechanism of Eutectic Silicon for Strontium-Modified Alloy A357

The Y 2O 3-CeO 2-ZrO 2 powders were prepared using a co-precipitation process and the corresponding coatings were prepared by plasma spraying. The results show that an optimal composition exists in Y 2O 3-doped CeO 2-ZrO 2, but not in CeO 2-doped Y 2O 3-ZrO 2. The powders mainly contain tetragonal phase and a trace amount of monoclinic phase. The homogeneity in composition, large agglomerate size, ideal particle size distribution and high flowability were obtained. The as-sprayed coatings are composed of non-transformable tetragonal phase, tz′structure, and resistant to transformation under thermal or mechanical stresses.

Evaluation of zirconia–porcelain interface using X-ray diffraction

The aim of this study was to determine if accelerated aging of porcelain veneering had an effect on the surface properties specific to a tetragonal-to-monoclinic transformation（TMT） of zirconia restorations. Thirty-six zirconia samples were milled and sintered to simulate core fabrication followed by exposure to various combinations of surface treatments including as-received（control）,hydrofluoric acid（HF）, application of liner plus firings, application of porcelain by manual layering and pressing with firing, plus accelerated aging. The quantity of transformed tetragonal to monoclinic phases was analyzed utilized an X-ray diffractometer and one-way analysis of variance was used to analyze data. The control samples as provided from the dental laboratory after milling and sintering process had no TMT（X m5 0）. There was an effect on zirconia samples of HF application with TMT（X m5 0.8%） and liner plus HF application with TMT（X m5 8.7%）. There was an effect of aging on zirconia samples（no veneering） with significant TMT（X m5 70.25%）. Both manual and pressing techniques of porcelain applications reduced the TMT（manual, X m5 4.41%, pressing,X m5 11.57%）, although there was no statistical difference between them. It can be concluded that simulated applications of porcelain demonstrated the ability to protect zirconia from TMT after aging with no effect of a liner between different porcelain applications.The HF treatment also caused TMT.

Biomolecule-assisted Solvothermal Synthesis and Enhanced Visible Light Photocatalytic Performance of Bi2S3/BiOCl Composites

Novel Bi2S3/BiOCl photocatalysts were successfully synthesized via a facile biomoleculeassisted solvothermal method and biomolecule L-cysteine was used as the sulfur source.The structures,morphology,and optical properties of the synthesized samples were characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,Raman spectroscopy,transmission electron microscopy（TEM）,and UV-vis diffuse reflectance spectroscopy（DRS）.The presence of Bi2S3 in the Bi2S3/BiOCl composites could not only improve the optical properties but also enhance the photocatalytic activities for the degradation of Rhodamine B（Rh B） under visible-light irradiation（λ〉420 nm） as compared with single Bi2S3 and BiOCl.Especially,the sample displayed the best performance of the photodegradation when the feed molar ratio of BiCl3 and L-cysteine was 2.4：1,which was about 10 times greater than that of pure Bi OCl.The enhanced photocatalytic activities could be ascribed to the effective separation of photoinduced electrons and holes and the photosensitization of dye.Moreover,the possible photodegradation mechanism was also proposed,and the results revealed that the active holes（h＋） and superoxide radicals（·O2-） were the main reactive species during photocatalytic degradation.

Synthesis and electrical conductivity of nanocrystalline tetragonal FeS

A convenient method for synthesis of tetragonal FeS using iron powder as iron source, is reported. Nanocrystalline tetragonal FeS samples were successfully synthesized by reacting metallic iron powder with sodium sulfide in acetate buffer solution. The obtained sample is single-phase tetragonal FeS with lattice parameters a = 0.3767 nm and c = 0.5037 nm, as revealed by X-ray diffraction. The sample consists of fiat nanosheets with lateral dimensions from 20 nm up to 200 nm and average thickness of about 20 nm. We found that tetragonal FeS is a fairly good conductor from the electrical resistivity measurement on a pellet of the nanosheets. The temperature dependence of conductivity of the pellet was well fitted using an empirical equation wherein the effect of different grain boundaries was taken into consideration. This study provides a convenient, economic way to synthesize tetragonal FeS in a large scale and reports the first electrical conductivity data for tetragonal FeS down to liquid helium temperature.

Young’s modulus surface and Poisson’s ratio curve for tetragonal crystals

This paper gives the general expressions for the compliance s′ijkl, Young＇s modulus E（hkl） and Poisson＇s ratio v（hkl, θ） along arbitrary loading direction [hkl] for tetragonal crystals. The representation surface for which the length of the radius vector in the [hkl] direction equals E（hkl） and representation curve for which the length of the radius vector with angle θ deviated from the reference directions [001^-], [100], [001^-], [101^-] and [112^-] equals v（100, θ）, v（001, θ）, v（110,θ）, v（101,θ） and v（111, θ） respectively, are constructed for nine tetragonal crystals （ammonium dihydrogen arsenate, ammonium dihydrogen phosphate, barium titanate, indium, nickel sulfate, potassium dihydrogen arsenate, potassium dihydrogen phosphate, tin and zircon）. The characteristics of them are analysed in detail.

Dielectric Properties of Unfilled Tetragonal Tungsten Bronze Ba4PrFe(0.5)Nb(9.5)O(30) Ceramics

In order to found new dielectrics ceramics in tungsten bronze structure, unfilled tungsten bronze（TB） ceramics with nominal formula Ba4PrFe（0.5）Nb（9.5）O（30） were prepared by the solid state reaction method. The microstructure and dielectric properties were studied using powder X-ray diffraction, field emission scanning electron microscope, and variable temperature dielectric test system. The results show that the ceramics have a single phase and belong to the space group of P4bm with the cell of a = b = 12.4839（3） ？, c = 3.9409（5） ？, V = 614.192（2） ？3. The frequency dependent dielectrics properties show that the ceramics have a Debye-like relaxation at room temperature, while the temperature dependent dielectrics properties indicate that the ceramics are a relaxor and the relaxation is due to the nanopolars and oxygen vacancies. The ceramics have a potential application in electronic ceramics as temperature-stable multilayer ceramic capacitors.

EFFECTS OF TRACE ELEMENTS ON THE MICROSTRUCTURE FOR ZrO_2 SYSTEM CERAMICS

Under the sintering condition of normal pressure, the su-perfine, high density tetragonal zirconia polycrystalline ceramics were prepared by means of doping 3 mol% Y2O3 and other trace oxides which act as the grain stabilizing agent and the grain growing in-hibitor. By the density measurements and analyses of XRD, SEM and TEMj etc. it was studied that the microstructure of ZrOz system poly-crystalline ceramics is affected by doping trace oxides of CuO. FezO3 and SiO2.

Coulombic interaction in the colloidal oriented-attachment growth of tetragonal nanorods

In this report, the analytical expression of Coulombic interaction between a spherical nanoparticle and a tetragonal nanorod is derived. To evaluate the Coulombic interaction in the oriented attachment growth of tetragonal nanorods, we analyze the correlation between the Coulombic interaction and the important growth parameters, including： nanoparticle- nanorod separation, aspect ratio of the nanorods, and surface charge density. Our work opens up the opportunity to investi-gate interparticle interactions in the oriented attachment growth of tetragonal nanorods.

Tetragonal Domain Switching via Reversible tm Phase Transformation

Grinding-induced tm phase transformation and the resultant texture in ceria-yttria-doped tetragonal zirconia polycrystals with varied tetragonality have been studied by XRD. It is observed that the reversible tm phase transformation occurs during grinding and the intensity ratio of I(002)t/I(200)t increases with the transformability. The author proposes that the texture induced by grinding at low temperatures is due to the tetragonal variant reorientation via cyclic,reversible tm phase transformation, termed 'transformational domain switching', instead of the ferroelastic one

Temperature Dependence of the Raman Spectra and Phase Transition of Zirconia

A newly constructed high-temperature Raman spectrometer was used to study the temperature-dependence Raman spectra(up to 2023 K)and transformation of zirconia crystal.High-temperature Raman scattering is a useful tool in characterizing the different structures of zirconia and offers the possibility to identify the phase transformation.It shows that monoclinic zirconia transforms to tetragonal phase at about 1440 K during the process of increasing temperature,but shows a lower transformation temperature from tetragonal to monoclinic phase at about 1323 K while the temperature decreased.

Domain Patterns and Phase Transitions in Ferroelectric Crystal KNbO_(3)

We have studied the domain configurations and structures of KNbO_(3) crystal in orthorhombic and tetragonal phases by polarizing microscopy.The phase transition processes among orthorhombic,tetragonal and cubic phases and thermal hysteresis during phase transitions are observed directly.Domain-pattern changes and the stable domain patterns during the phase transitions are discussed.

INFRARED REFLECTANCE FROM ORIENTED FILM SAMPLES OF Y-Ba-Cu-O

We have studied infrared reflectivity from epitaxial films of YBaCuO,in which the c axes are oriented either perpendicular or parallel to the film surface.We classified phonons in superconducting phase to be two modes including E⊥C and E//C modes.The strong coupling between the phonons and free carriers reduces the infrared activity of phonons.The infrared activity of phonons increases in the process that the orthorhombic phase changed into tetragonal phase.The important role of phonon in superconductivity is shown.

Theoretical Study of Carrier Mobility in Two-Dimensional Tetragonal Carbon Allotrope from Porous Graphene

The carrier mobility of two-dimensional tetragonal carbon allotrope （T-CA） from porous graphene is investigated by first-principles calculations. T-CA can be constructed from divacancy and Stone-Thrower--Wales defects from graphene. T-CA is a direct semiconductor with a band gap of 0.4 eV at F point. T-CA possesses a high carrier mobility of the order of 104 cm2V-ls-1. As our study demonstrates, T-CA has potential applications for next-generation electronic materials.