Qualitative and quantitative differences in the absorption spectra of electron-irradiated reflective coatings based on mixtures of BaTio3 powder with ZrO2 micro- or nanopowder of different concentrations

The effect of the concentration and size (micro- or nanoparticles) of zirconium dioxide powders, heated in mixtures with barium titanate powder, on the radiation resistance of reflecting coatings on their basis is analyzed during accelerated electron irradiation. It is shown that nanoparticles provide increased radiation resistance of the coatings compared to microparticles.     

Dielectric properties of perovskite ferroelectrics at the nonequilibrium concentrations of point defects

Dielectric properties of ceramic barium titanate modified by the addition of aluminum oxide are studied via impedance spectroscopy in weak electric fields in frequency range of 0.3–10³ kHz. For better separation of the properties of the inner regions of crystallites and the boundary regions by quenching, an excess concentration of point defects is created, leading to the formation of bulk charge. The experimental results are performed using the Maxwell-Wagner capacitor model and the Schottky barrier model.     

Second Harmonic Generation in Microstructured Barium Titanate

We investigate the second harmonic generation under femtosecond pulse-periodic laser radiation in barium titanate in the form of ceramics, in pores of a globular photonic crystal, and in a water colloidal suspension. We measure the dependence of the second harmonic radiation intensity on the incident laser power. Excitation of the second harmonic was carried out by powerful (10⁸ W) pulses of a solid-state Yb:KGW laser (wavelength, 1,026 nm) operating at 200 kHz. We estimate the efficiency of the second harmonic generation in various microstructured phases of barium titanate and show that the threshold of plasma formation in a suspension of barium titanate microparticles in water is substantially higher than in ceramics and in the ferroelectric photonic crystal. The second-harmonicgeneration power can be significantly increased in a water suspension of barium titanate microparticles.     

Electron microscopy of barium strontium titanate nanostructures in the aluminum oxide matrix

Electron microscopy has revealed the mechanism of formation of barium strontium titanate nanostructures during crystallization in the bulk of pores of the aluminum matrix. The nanostructures have the form of nanotubes or nanocolumns 100–200 nm in diameter and a few microns long, which are formed by barium strontium titanate crystals 3–100 nm in size.     

Synthesis,Structural and Optical Studies of Barium Strontium Titanate Borosilicate Glasses Doped with Ferric Oxide

Various barium strontium titanate borosilicate glasses were prepared by a rapid melt-quench technique. Spectroscopic studies have been carried out on investigated glasses for their structural information. Infrared and Raman spectroscopic studies showed that these glasses are formed by glass-forming network of borate and silicate as well as network modifiers in the form of cations of alkaline earth atoms. The borate and silicate networks are modified by barium, strontium, titanium, and iron cations in glass matrix. The network of triborate unit is modified in tetraborate unit by adding ferric oxide in a glassy matrix. The optical studies are performed by ultraviolet-visible spectroscopy and it confirms that the band gap decreases with increase in the concentration of ferric oxide.     

Dielectric Properties of Calcium,Strontium, or Barium Titanate Sintered with 5 mol.% of Lithium and Calcium Fluorides

Calcium, strontium, and barium titanates were previously synthesized then mixed and wet-ground with 5 mol.% of lithium and calcium fluorides. These mixtures were pressed into pellets and air-fired. The ceramics were investigated by X-ray diffraction, scanning electron microscopy, and dielectric measurements. Each sample is a perovskite single phase. The oxyfluoride deriving from calcium titanate exhibits a phase transition around 283 K. For strontium titanate, no phase transition is detected. On the other hand, the ceramic related to barium titanate displays a ferroelectric phase transition around 300 K and a dielectric relaxation at about 10 MHz. These oxyfluorides could be of interest for capacitor manufacturing.     

Specific features of the ferroelectric state in two-layer barium strontium titanate-based heterostructures

The structural properties of one- and two-layer heterostructures based on the barium–strontium titanate of various compositions deposited by the Frank–Van der Merve on a magnesium oxide substrate have been studied. The heterostructures have been prepared by the rf sputtering of the stoichiometric ceramic targets in a Plazma 50 SE deposition system. The principal difference of this method of deposition from known analogs is that the growth of single-crystal films occurs from a disperse oxide phase formed in the plasma of a high-current rf discharge during the ceramic target sputtering at the cluster level. The peculiarities of the manifestation of the ferroelectric state in the two-layer heterostructures when changing the sequence order of the films with various compositions of barium–strontium titanate.     

Nitrogen containing barium titanate: Preparation and characterisation

The purpose of this work is to study the incorporation of nitrogen into barium titanate at oxygen sites by ammonolysis. The nitrogen content of the resulting barium titanate powders strongly depends on the flow rate of ammonia and the ratio Ba/Ti. The amount of resulting oxygen vacancies is lowered by co-doping with fluoride and tantalum.By avoiding an excess of BaO and exchanging 10 mol% Ti by Ta it is possible to produce powders with nitrogen content of more than 1 wt%. Partial substitution of barium oxide by barium fluoride also increases the nitrogen content. The nitrogen containing powders are colored and show an additional absorption at 500 nm measured in the UV/vis reflectance spectrum. The concentrations of nitrogen and fluorine in the samples were determined using ion-sensitive electrodes. X-ray powder diffraction shows the composition of the powders. The thermal stability was investigated by thermogravimetric analysis, and in order to calculate the specific surface area the three-point BET method was used.     

钛酸铋钡陶瓷的介电性、铁电性及对晶格结构的依赖性

采用溶胶-凝胶工艺成功制备出BaBi₄Ti₄O₁₅微细粉料，并利用此微粉烧结出成瓷良好的BaBi₄Ti₄O₁₅陶瓷.研究了BaBi₄Ti₄O₁₅陶瓷的铁电 顺电相 变，测定了BaBi₄Ti₄O₁₅的介 电特性和饱和状态下的铁电特性.所作测量表明B 关键词： 铁电性 介电性 晶格结构 溶胶 凝胶法     

Positron annihilation in BaTiO3

The angular correlation of 2 γ-annihilation radiation has been measured in barium titanate single crystals. The effect on the angular correlation of the ferroelectricity in BaTiO₃ was not detected.     

BaTiO_3纳米粉体的制备及结构的光谱表征

采用钛酸丁脂和八水氢氧化钡为原料的溶胶-凝胶法制备了纳米BaTiO3粉体。经不同温度烧结,并利用X射线衍射和Raman光谱分析进行结构表征。实验表明,经1073K烧结后粉体粒径为26 2nm,颗粒分布均匀,还有少量BaCO3存在。在这个温度下得到的晶粒主要是立方相,并含有少量的四方相。经1273K烧结后,BaTiO3完全是四方相,粉体粒径为80 0nm,此时BaCO3已完全分解。另外探讨了溶胶-凝胶制备纳米BaTiO3粉体的反应机理,解释了BaTiO3物相的形成。     

Synthesis and characterization of highly-ordered barium-strontium titanate nanotube arrays fabricated by sol—gel method

Highly uniformed barium-strontium titanate nanotube arrays were fabricated using a porous anodic aluminum oxide template from a barium-strontium titanate sol--gel solution. Electron microscope results showed that nanotubes with uniform length and diameter were obtained. The diameters and lengths of these nanotubes were dependent on the pore diameter and the thickness of the applied anodic aluminum oxide template. High resolution transmission electron microscopy and the selected-area electron diffraction pattern investigations demonstrated the perovskite structure and the polycrystalline of the fabricated barium-strontium titanate nanotubes. The characterization of the electrical and dielectric properties had also been made. Compared to thin film material, the intrinsic leakage current density is almost the same. Besides, at 30~℃, the dielectric constant and dielectric loss of the fabricated nanotube is 80 and 0.027 at 1~MHz respectively.     

Atomic force microscopy studies of twins in yttrium-doped barium titanate

Barium titanate is the main constituent of PTC materials and their electric properties are sensitive to microstructure and defects, in atomic scale, that are significantly affected by processing parameters. The microstructure of barium titanate doped with yttrium was investigated using topographic images obtained by AFM in contact mode. The AFM images of barium titanate doped with yttrium showed the effect of large grains with double twins at different (1 1 1) planes.     

Structure and optical and dielectric properties of barium titanate nanoparticles obtained by the mechanochemical method

The parameters of mechanochemical synthesis of barium titanate nanoparticles from barium titanyl oxalate and an oxide mixture are optimized. X-ray phase analysis, infrared and Raman scattering spectroscopy, differential scanning calorimetry, and dielectric spectroscopy are applied to demonstrate that the nanoparticles contain the cubic and tetragonal crystal lattice modifications. The impurity spectra for the particles obtained by the mechanochemical method from different initial substances are identical. The ferroelectric phase volume increases as hydroxyl groups are annealed from the crystal lattice and decreases upon annealing of metal atom vacancies.     

Electron microscopy of the barium strontium titanate film structure on Pt-Ti-SiO<Subscript>2</Subscript>-Si substrates after laser annealing

The effect of laser annealing on the structure of barium strontium titanate films prepared through chemical solution deposition has been investigated. It is demonstrated that the effect of laser radiation initiates processes of crystallization and recrystallization in the films and causes amorphization of the outer surface of the film.     

Origin of semiconductng behavior in rare-earth-doped barium titanate

New explanations of the origin of semiconduction and a peculiar characteristics of resistivity vs dopant concentration in rare-earth-doped barium titanate are presented on a basis of the combined data of cation vacancy concentration, resistivity, and oxygen diffusion coefficient of the material. A limited amount of rare-earth doping into barium titanate results in the introduction of Ba-site vacancies as well as Ti-site vacancies in the lattice. The existence of Ba-site vacancies profoundly alters the chemical bonding nature of the host lattice and thereby causes some loss of oxygen as well as the formation of oxygen vacancies with captured electrons in the lattice on firing the material at elevated temperatures, the latter giving rise to n-type semiconduction. A sudden fall in conductivity for a higher rare-earth concentration occurs in accordance with the number of Ba-site vacancies being zero.     

Semiconducting ceramic barium lanthanum titanate doped with iron

The formation of semiconductive properties in polycrystalline barium titanate when doped simultaneously with lanthanum and iron is brought about by a substitution mechanism similar to that proved to work in BaTiO₃ doped with bismuth and iron. A broader validity has thus been confirmed of the substitution model previously proposed to explain the considerable change in internal electric resistance of barium titanate containing trivalent ions in barium positions when iron ions are introduced. In contrast to barium bismuth titanate, with barium lanthanum titanate an increasing addition of iron leads to the successive formation and destruction of several types of perovskite crystals differing in electrical conductivity and Curie temperature.The author thanks his collaborators from the Research Institute of Electrotechnical Ceramics for effective help: Ing. L. Plocek for the X-ray analyses and Mr. V. tefek for preparing the electron microscope pictures.     

陶瓷中的三种电响应机构

用时域和频域介电谱方法可以将晶界层陶瓷中晶粒、内边界层和阻挡层三种不同机构对外加电场的响应讯号分开。从而得出每种机构对样品的总电阻或总电抗的贡献。观察到极化子跳跃导电的弛豫效应，它使样品的阻抗呈现电感性。比较了掺杂氧化锌、钛酸锶和钛酸钡三种典型陶瓷的晶界层的异同。 关键词：     

钛酸钡瓷粉样品中多元素的X射线荧光光谱分析

本文采用四硼酸锂和偏硼酸锂混合熔剂熔样，人工合成法制备钛酸钡瓷粉XRF标样，选用Sr和Ca内标元素消除制样和仪器漂移产生的误差，建立了无须进行烧失量校正的X射线荧光光谱分析钛酸钡瓷粉样品的分析方法，分析结果的准确度和精密度符合生产要求，也适用于其它含B元素样品的分析。     

Dielectric losses in submicrometer barium titanate near the Curie temperature

Low-frequency dielectric losses (tanδ) in barium titanate ceramics with crystallite sizes of ~100 nm near the Curie temperature are studied. It is shown that the observed tanδ maximum is described by a low-frequency fluctuation mechanism of dielectric losses. An analysis of experimental data shows that the critical nucleus size in ultrafine material is smaller than the one in bulk barium titanate.