Observation of ferroelectric domains on barium titanate by X-ray diffraction microscopy

Ferroelectric domains in single crystals of BaTiO₃ are observed by the Lang method. It is shown that this method is suitable for studying ferroelectric domain structures. Using different reflections the visibility of 90 ferroeletric domains is studied and stresses accompanying the domain walls are discussed.The authors thank H. Arend, C.Sc, for preparing suitable BaTiO₃ crystals and J. Fousek, C.Sc., V. Janovec, C.Sc., and B. esták C.Sc., for valuable discussions which contributed towards the interpretation of the experimental results.     

Electrorheological effects in carbon, barium titanate, and nickel coated with barium titanate suspensions

Effects of the electric field on the rheology, electrorheological (ER) effects, are investigated on carbon, barium titanate (BaTiO₃) and BaTiO₃-coated nickel (BT-Ni) suspensions. Among some electroreological properties, electric field frequency dependence of the induced shear stress (yield stress) observed for three suspensions shows a contrasting behavior. With increase in the electric field frequency, the yield stress decreases above 100 Hz in the carbon suspension, monotonously increases in the BaTiO₃ suspension, and is almost constant in the BT-Ni suspension. The difference in the frequency dependence and magnitude of the yield stress is discussed on the basis of the magnitude and relaxation time of the interfacial polarization and the effect of the particle rotation under the shear flow.     

Raman study of barium titanate with oxygen vacancies

Barium titanate (BaTiO₃) crystal samples with different distribution of oxygen vacancies were prepared through different thermal treatment processes. The influences of oxygen vacancies on the Raman spectra and X-ray photoelectron spectroscopy (XPS) spectra of BaTiO₃ single crystals were studied comparatively. Raman measurements of fast-cooled BaTiO₃, which annealed in vacuum and then cooled in air showed many different spectroscopic results comparing with as-received BaTiO₃ sample. Raman measurements of slow-cooled BaTiO₃, which annealed in vacuum and then cooled in tube furnace exhibited few spectroscopic differences. XPS measurements of as-received BaTiO₃ sample and fast-cooled BaTiO₃ sample confirmed that this discrepancy resulted from the surface phase of oxygen vacancy in BaTiO₃.     

The growth of single crystals of barium titanate from melts with barium chloride

On the basis of experiments carried out on the growing of barium titanate, single crystals (BaTiO₃) it is shown that the data given by B. T. Matthias [1] are incomplete and insufficient thus leading in certain cases to negative results. This paper gives the conditions for growing crystals which are suitable for fundamental physical research.     

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.     

Coloring and breakdown of barium titanate

Spontaneous increase in current in strong fields is found to be related to motion of color centers. Electron injection increases the number off, centers, which reduces the electrical strength.Read at the All-Union Conference on Recent Insulator and Semiconductor Techniques, Leningrad.     

Elastic compliances of barium titanate crystal

The elastic compliances of barium titanate have been calculated on the basis of the point dipole model taking account of the dipole-dipole interactions and the proper interatomic forces. The results obtained are discussed.     

Ultrasonic de-agglomeration of barium titanate powder

BaTiO3 (BT) powder, with average particle size of 1.4 microm, was synthesized by solid-state reaction. A high-intensity ultrasound irradiation (ultrasonication) was used to de-agglomerate micro-sized powder to nano-sized one. The crystal structure, crystallite size, morphology, particle size, particle size distribution, and specific surface area of the BT powder de-agglomerated for different ultrasonication times (0, 10, 60, and 180 min) were determined. It was found that the particles size of the BT powder was influenced by ultrasonic treatment, while its tetragonal structure was maintained. Therefore, ultrasonic irradiation can be proposed as an environmental-friendly, economical, and effective tool for the de-agglomeration of barium titanate powders.     

Improving electret properties of PP filaments with barium titanate

Barium titanate (BaTiO₃) containing polypropylene (PP) composite filaments were melt spun to modify polymer electrostatic charging characteristics. Sample filaments were charged with a corona instrument and their surface potentials were measured. Initial surface potential as well as potential stability was monitored through an accelerated decay procedure. It was found that both BaTiO₃ concentration and charging temperature influence the charging characteristics of the fibers. When BaTiO₃/PP composite filaments were charged at 130 °C, significant enhancements were observed when compared to samples charged at room temperature. The distribution of BaTiO₃ particles within the filaments and changes in the crystal structure were also examined.     

Electrical phenomena in barium titanate ceramics

We have studied the current voltage curves of BaTiO₃ ceramics, with fired silver electrodes, between 110–400°C. We have observed a current controlled negative resistance between low conductivity and high conductivity states. The passage from the low to the high conductivity state is accompanied by a brown coloration starting from the anode. Once the high conductivity state is reached it is impossible to return to the low conductivity state unless one anneals the sample for several hours at 400°C. We have measured the voltage distribution along the sample and the short circuited currents after applying a voltage. We interpret our results, assuming carriers injection, by means of the Rose and Lampert models of injection. In the low conductivity state the conduction is ohmic or due to electron injection, and in the high conductivity state there is a double injection regime. However the agreement of the results with the theoretical prediction is good only qualitatively. We think that a more elaborate model is necessary.     

Lead zirconate titanate–barium titanate by mechanical activation of mixed oxides

For the first time, the perovskite phase in 0.9Pb (Zr_0.52Ti_0.48)O₃-0.1BaTiO₃(0.9PZT-0.1BT) is triggered to form in an oxide matrix consisting of PbO, ZrO₂, BaO, and TiO₂. Unlike in the solid-state reaction activated by calcination at an intermediate temperature, intermediate phases, such as PbTiO₃, were not observed with increasing degree of mechanical activation prior to the formation of perovskite 0.9Pb(Zr_0.52Ti_0.48)O₃-0.1BaTiO₃ phase. This suggests that the nucleation and subsequent growth of perovskite crystallites in the activated oxide composition are not a result of the interfacial reactions that normally occur in the temperature-driven solid-state reaction. The mechanical activation-derived powders can be sintered to a relative density of >97% theoretical at 1100 °C. Sintered 0.9Pb(Zr_0.52Ti_0.48)O₃-0.1BaTiO₃ derived from mechanical activation of constituent oxides exhibits a maximum dielectric constant of 775 and a minimum dielectric loss of <2% at room temperature when measured at 1.0 kHz. Received: 3 December 1998 / Accepted: 18 March 1999 / Published online: 24 June 1999     

Fluctuations and Landau-Devonshire expansion for barium titanate

The experimentally observed temperature dependence of the quartic coefficients in the Landau-Devonshire expansion for BaTiO₃ is naturally accounted for within a proper fluctuation model. It is explained, in particular, why one of the quartic coefficients varies with temperature above T _c , while the second is constant. It is argued that the tetragonal phase in BaTiO₃ exists essentially due to thermal fluctuations, while the true Landau-Devonshire expansion with temperature-independent coefficients favors the rhombohedral ferroelectric phase.     

掺杂钛酸钡薄膜的合成及性能研究

通过化学溶液沉积法制备的BiFeO3-BaTiO3薄膜在室温下能够同时显现铁电性及铁磁性。在600-700℃的条件下,以Pt/TiOx/SiO2/Si为载体,能够成功得到钙钛矿单相0.7BiFeO3-0.3BaTiO3薄膜。随着结晶温度上升,晶粒持续增长,最终在700℃到达更高的结晶度。由于0.7BiFeO3-0.3BaTiO3薄膜的绝缘电阻较低,它所显现的极化（P）-电场（E）磁滞回线较弱。尽管如此,由于在0.7BiFeO3-0.3BaTiO3薄膜铁的位置上添加锰,高作用场的漏电流有效地减少,最终铁电性质得到了提高。在室温下,添加了摩尔分数5%的锰的0.7BiFeO3-0.3BaTiO3薄膜同时显现铁电极化和铁磁磁化磁滞回线。