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.     

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.     

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.     

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.     

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.     

Piezoelectric voltage of barium titanate with stabilized domains

In BaTiO₃ with unidirectional stabilized domains mechanical excitation causes a piezoelectric stress that is strongly asymmetrical with respect to the orientation of the electric field applied to the sample. The magnitude of the piezoelectric stress measured in the direction of polarization of the stabilized domains is usually greater than in the opposite direction. At a cyclic change in the weak electric field the dependence of the piezoelectric stress on this field is reflected in the shape of the asymmetric hysteresis loop.     

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。     

Ferroid properties and domain structure of barium titanate

Distinctive features of domain formation in ferroelectric crystals are discussed theoretically for the example of ferroelectric BaTiO₃, taking into account ferroid properties of higher order. Inclusion of ferroid properties makes it possible to refine the details of the domain formation, and in particular to explain the possible existence of charged domain walls in ferroelectric crystals. Fiz. Tverd. Tela (St. Petersburg) 39, 1634–1635 (September 1997)     

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.     

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.     

Crystal-chemical aspects of phase transitions in barium titanate

Structural aspects of phase transitions in barium titanate are analysed from a crystal-chemical point of view. The respective discussion is focused on two possible sources of ferroelectric deformation of TiO₆⁸⁻ octahedron. First, gradual changes of π-electron localisation are considered. Under an assumption of a mean field related to actual crystal symmetry, an adequate model is proposed. The values of bond orders are evaluated from resonance structures. They are compared with respective bond lengths. Another source of the ferroelectric deformation, which is taken into consideration, relates to the Ti-ion movements between eight potential minima on the cube diagonals. The analysis of the problem is grounded within adiabatic (local field) approximation and follows ideas of an eight-site model. The crystal structure is treated as a result of averaging of atomic positions according to the postulated disorder. Comparison of the X-ray interatomic distances with the values calculated from the disorder model is made. The collected data generally prove that the ferroelectric deformation of the TiO₆⁸⁻ octahedron, which is observed in barium titanate, contains two components. One is related to the changes of structural disorder degree and should be considered as a main factor. The other includes the effects attributed to the changes of π-electron localisation.     

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。