Preparation and properties of toughened yellow zirconia ceramics

To obtain the high toughness yellow ceramic, using the Y₂O₃ (5%) stabilized ZrO₂ as main starting material, Al₂O₃ as toughen reagent, NH₄VO₃, V₂O₅ as colorant, and mixed with ball mill, molded with dry press method and two times sintered. By testing the properties and structure of the ceramic, we have optimized the best technical conditions, and the mechanism of toughness and color present has been studied. The result shows that the NH₄VO₃ as colorant is better than V₂O₅, and the color is between X = 0.396–0.412 and Y = 0.402–0.390. The highest bending strength of toughened ZrO₂ ceramics is 1138 MPa, and the fracture toughness is 14.8 MPa m^1/2. The toughen mechanism is that phase transformation of ZrO₂ and the dispersion of toughen reagents, and the color causing is by the colorful ion (V⁴⁺) entered into the zirconia crystals lattice of the ceramic. The text was submitted by the authors in English.     

Preparation and properties of cross-linked zirconia nanoparticle films on polycarbonate

Highly-crystalline zirconia (ZrO₂) nanoparticle was functionalized with 3-(N-aminoethyl) aminopropyltrimethoxysilane (AAPTMS) and dispersed in water at primary particle size level under basic condition (pH 13-14). The aqueous ZrO₂ nanoparticle dispersion was cast on a polycarbonate substrate with 1,4-butanediol digylcidyl ether as a cross-linker. Nanoparticle films with as high as 81 wt.% of ZrO₂ were obtained through heating the cast dispersion at 120 °C, which are highly transparent. The refractive index ranges from 1.70 to 1.77 at wavelength of 632 nm with the decrease of the amount of AAPTMS attached to ZrO₂ nanoparticles. Nanoindentation tests show that the hardness of the film reaches 1.7 GPa. In addition, both punched tape abrasion and nanoscratch tests reveal that the films exhibit prominent scratch resistant performance.     

Preparation and properties of orthorhombic TlInS<Subscript>2</Subscript>

A procedure is described for crystal growth of orthorhombic TlInS₂. The lattice parameters of the grown crystals are a = 6.88 Å, b = 14.04 Å, and c = 4.02 Å (sp. gr. P222₁, Z = 4, _x = 6.59 g/cm³). The dielectric permittivity of the crystals is measured from 170 to 300 K. The spectral dependence of the 300-K photocurrent through the crystals indicates that orthorhombic TlInS₂ is a wide-gap semiconductor. Its band gap, E _g = 2.52 ± 0.01 eV, slightly exceeds that of monoclinic TlInS₂.Translated from Neorganicheskie Materialy, Vol. 41, No. 2, 2005, pp. 138–142.Original Russian Text Copyright © 2005 by Nadjafov, Alekperov, Guseinov.     

Anisotropic thermal properties in orthorhombic perovskites

The structure, elastic properties, thermal expansion, and thermal conductivity of the orthorhombic-structured A³⁺B³⁺O₃ perovskites are determined using atomistic simulations with classical potentials. When considered as pseudo-cubic monoclinic systems, they show relatively small deviations in structure and properties from their cubic perovskite parent phase. The variations in properties are shown to be related to the magnitude of the tilting of the BO₆ octahedra, which in turn is related to the relative sizes of the A and B ions, as encapsulated in the tolerance factor.     

Preparation and characterization of zirconia and mixed zirconia/titania in ionic liquids

Zirconia and mixed zirconia/titania were synthesized in two different ionic liquids, namely, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide ([BMP]TFSA) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide ([EMIm]TFSA) using sol–gel methods. The synthesized oxides were characterized by means of X-ray diffraction, scanning electron microscopy with energy dispersive X-ray (SEM-EDX)), thermogravimetric and differential thermal analyses (TGA–DTA). The results show that the as-synthesized ZrO₂ powders obtained either in [BMP]TFSA or in [EMIm]TFSA show amorphous behaviour, and calcination at 500 °C yields t-ZrO₂ which is subject to further phase transformation to m-ZrO₂ at 1000 °C. The type of the ionic liquid influences the morphology of the synthesized zirconia as the sample obtained from [BMP]TFSA showed a porous morphology with very fine particles in the nanometer regime, whereas micro-rods were obtained from [EMIm]TFSA. ZrO₂-TiO₂ nanorods with an average diameter of about 100 nm were synthesized in [EMIm]TFSA. The presence of zirconia in the mixed oxides stabilizes the anatase phase and elevates the temperature at which the phase transformation to rutile occurs.     

Preparation and characterization of yttria-stabilized zirconia nanotubes

Yttria-stabilized zirconia (YSZ) nanotubes were synthesized by the sol–gel method using porous anodic alumina oxide (AAO) as the templates. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersion X-ray (EDX) spectrum and selected area electron diffraction (SAED) techniques were used to characterize the morphology and crystalline structure of the prepared YSZ nanotubes. The length and the diameter of the YSZ nanotubes are 50 μm and 200 nm, respectively, which are in good agreement with the dimensions of the template pores, while the wall thickness of the nanotubes depends on the impregnation time. XRD and SAED measurements indicate that the obtained YSZ nanotubes after sintering at 1073 K possess a polycrystalline structure and a cubic crystal phase. Brunauer–Emmett–Teller (BET) measurement shows that the YSZ nanotubes have a surface specific area of around 40.5 m² g⁻¹ that is higher than that corresponding to the YSZ nanopowders.     

软化学法合成正交结构LiMnO_2及其电化学性能

研究以氢氧化锂和三氧化二锰为原料,用软化学法制备具有正交结构的锂离子电池正极材料LiMnO2。用X射线衍射法确定了材料的结构,用扫描电镜考察了材料形貌和反应时间的关系,观察结果显示得到的LiMnO2的粒子尺寸在300~500nm。结合循环伏安法和交流阻抗分析研究了合成条件对材料组织结构、尺寸与电化学性能的影响。材料的电化学性能测试结果表明,合成的正交扭曲结构LiMnO2(o-LiMnO2)材料在电化学过程中初期表现了较好的电化学性能。但材料在电化学过程中逐步向尖晶石结构相LiMn2O4转变,容量产生衰减,其循环寿命有待更进一步改善。     

The dielectric properties of zirconia

The dielectric properties of a series of single-crystal and sintered polycrystalline zirconias have been measured at room temperature over the frequency range 1–12.5 kHz. The additive cations investigated were yttrium, magnesium, calcium and cerium. For monoclinic zirconia, it was found that the permittivity, , was 23 at 10 kHz, in agreement with previous work. The addition of stabilizing cations causes a substantial increase in which then lies in the range 32–42 depending on the nature and amount of the stabilizing cation. Analysis of the separate contributions to the overall permittivity arising from the monoclinic, tetragonal or cubic phases has been made for some mixed-phase systems. The results suggest that the permittivity is principally determined by the crystallographic form rather than by the nature or amount of the added cation.     

Synthesis and properties of zirconia thin films

Thin films of zirconia have been synthesized using reactive DC magnetron sputtering. It has been found that films with good optical constants, high refractive index (1·9 at 600 nm) and low extinction coefficient can be prepared at ambient temperatures. The optical constants and band gap and hence the composition are dependent on the deposition parameters such as target power, rate of deposition and oxygen background pressure. Thermal annealing of the films revealed that the films showed optical and crystalline inhomogeneity and also large variations in optical constants.     

Electronic structure and optical properties of zirconia

The effects of substitutional impurities and oxygen vacancies on the electronic structure and optical properties of cubic zirconia were studied using band-structure calculations. It is shown that oxygen vacancies produce additional states near the Fermi level, whereas impurity atoms make an insignificant contribution to the states in the valence band and at the bottom of the conduction band, and their effect has a predominantly electrostatic character. The mechanisms of the stabilization of the high-temperature ZrO₂ polymorphs are elucidated. The calculation results agree well with x-ray photoelectron spectroscopy and optical data     

Preparation of nanosized yttria-stabilized zirconia powders and their characterization

Yttria-stabilized zirconia (YSZ) powders have been prepared by basic hydrolysis of a solution containing zirconium isopropoxide and yttrium nitrate. Crystallization of cubic YSZ occurs near 450 °C yielding ceramic powders with high specific areas, the values of which are dependent on the ammonia and water contents of the hydrolysis solution. Sintering at 1420 °C yields ceramics with nearly theoretical density and homogeneous grain size distribution.     

Preparation of zirconia powders from molten nitrites and nitrates

Finely dispersed ZrO₂ powders with high purity have been prepared by the reactions of Zr(SO₄)₂ in molten nitrites and nitrates. The effects of the starting materials of -Zr(SO₄)₂ and -Zr(SO₄)₂, the different nitrate and nitrite melts, and reaction conditions such as temperature and time, on the structure and crystallite size of the ZrO₂ powders produced were investigated. The processing of the prepared powders was also studied under different conditions; the results showed that very fine ZrO₂ powders with soft agglomeration could be produced if the proper treatment of the powders was applied.     

Rheological properties of the aqueous zirconia/colloidal zirconia binder sol system

The slip behaviour of the zirconia/colloidal zirconia binder sol system has been characterized by rheological measurements. The effects of slip solid loading and methylcellulose polymer addition on rheology and on rheology as a function of ageing time have been examined. The optimum conditions for suitable slips used in the dip-coating process have been determined from the rheological properties of the slips.     

Preparation and characterization of chromium oxide supported on zirconia

Chromium oxide/zirconia was prepared by dry impregnation of powdered Zr(OH)₄ with an aqueous solution of (NH₄)₂CrO₄. The characterization of prepared samples was performed using Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and differential thermal analysis (DTA), and by measurement of the surface area. The addition of chromium oxide to zirconia shifted the transitions of ZrO₂ from the amorphous to the tetragonal phase and from the tetragonal to the monoclinic phase to higher temperatures due to the strong interaction between chromium oxide and zirconia; and the specific surface area of the samples increased in proportion to the chromium-oxide content. Since the ZrO₂ stabilizes supported chromium oxide, chromium oxide was well dispersed on the surface of zirconia, and -Cr₂O₃ was only observed at calcination temperatures above 1173 K. Upon the addition of only small amounts of chromium oxide (1 wt % Cr) to ZrO₂, both the acidity and acid strength of the samples increased remarkably, showing the presence of two kinds of acid sites on the surface of CrOx/ZrO₂ (Brönsted and Lewis acid sites).     

First-principles study of electronic and optical properties of Pbnm orthorhombic SrHfO3

The first-principles calculations were carried out to investigate the electronic and optical properties of Pbnm orthorhombic SrHfO₃. The equilibrium lattice constants of Pbnm orthorhombic SrHfO₃ optimized by the localized density approximation (LDA) are in good agreement with experimental values. Electronic structures of Pbnm orthorhombic SrHfO₃ have been studied throughout the calculations of band structure, densities of states (DOS) and charge densities. The band structure shows that Pbnm orthorhombic SrHfO₃ has direct band gap. The DOS and charge densities of Pbnm orthorhombic SrHfO₃ indicate that bonding between Hf and O is mainly covalent whereas bonding between Sr and O is mainly ionic. The complex dielectric function, refractive index, absorption coefficient, energy-loss spectrum, complex conductivity function and reflectivity of Pbnm orthorhombic SrHfO₃ have been predicted. The imaginary and real parts of the calculated complex dielectric function are consistent with the experimental measurements for the amorphous SrHfO₃.     

Linear electro-optic properties of orthorhombic PZN-8%PT single crystal

The optical transmittance spectra of relaxor ferroelectric 0.92Pb(Zn(1/3)Nb(2/3))O(3)-0.08PbTiO(3) (PZN-8%PT) single crystals poled along different directions have been systematically studied at room temperature. After being poled along the [011] direction, the transmittance of induced orthorhombic PZN-8%PT single crystal is more than 50% from 0.5 to 5.7 μm, which is much higher than that poled along the [001] and [111] directions. The refractive indices and linear electro-optic properties of the orthorhombic PZN-8%PT single crystal were characterized at a wavelength of 632.8 nm. Large electro-optic responses were observed, (γ33) = 220 pm/V, (γ13) = 62 pm/V, and (γ23) = 23 pm/V. Thus, orthorhombic PZN-8%PT single crystal is a promising material for high-performance electro-optic devices.     

正交钙钛矿YFeO3的磁性、介电性及磁介电效应研究

采用溶胶-凝胶法制备了YFeO3陶瓷粉末并研究了烧结温度对YFeO3结构的影响。XRD表明,当烧结温度达850℃以上,可形成具有正交钙钛矿结构的YFeO3。室温磁滞回线测量表明,YFeO3具有弱铁磁性,并在H=0kA/m处出现突变,这是由YFeO3的磁各向异性引起的。εr-T曲线和D-T曲线表明在40～300K之间YFeO3的介电常数随温度升高而增加,并表现出频率色散现象,同时YFeO3存在低温介电弛豫行为。当外加0.8T的磁场时,介电测量表明YFeO3具有磁介电效应,最大值可达35.11%。