Uniaxial stress dependence of the dielectric properties of barium titanate single crystals

BaTiO₃ single crystals were grown by the melt-grown method. The effect of uniaxial pressure (0–1700 bar) on the dielectric properties of these crystals has been systematically studied. The external stress showed obvious effects on these properties. An increase in the difference between the Curie T_c and Curie–Weiss T₀ temperatures induced by the applied pressure is observed. This could be ascribed to the inducing of non-ferroelectric cubic islands in the tetragonal phase by the applied compressive stress. On the other hand, the pressure behavior of thermal hysteresis and the ??/?T vs. T plot strongly suggests that the phase transition changes to second-order type with increasing pressure. The Curie–Weiss constant obtained from a modified Curie–Weiss law strongly decreases with increasing pressure, suggesting that the mechanism of phase transition is going to order–disorder type. An increase in the difference between the Curie T_c and Burn's T_B temperatures with increasing pressure is observed. This could be ascribed to the narrowing of the temperature range on which the Curie–Weiss law is valid. In general, the obtained results are in good agreement with hydrostatic pressure data. Some kind of relaxation near T_c, which is strongly coupled with strain caused by applied compressive stress, is postulated.     

钛酸钡基施主掺杂弛豫铁电体介电弥散的唯象分析

弛豫铁电体铁电相变的介电弛豫性涉及外来离子掺杂或原有离子的有序排列, 需要深入理解和有效统一的表征. 针对高浓度施主掺杂在晶粒中产生金属离子缺位, 降低居里温度并引起钛酸钡基铁电材料扩散相变的现象, 分析了高斯型的杂质分布、居里温度分布和金属离子缺位分布的等效对应关系, 得出了在介电常数峰值温区金属离子缺位浓度随温度降低而作用增大的结论, 认为金属离子缺位引起的单极电荷在电场作用下的跳跃运动有可能引起介电弥散和介电损耗. 提出了用‘弛豫度’表征铁电弛豫程度.     

3D dependence of the dielectric dispersion in a BaTiO3 single crystal

The 3D dependences ?′(log f, T) and tanδ(logf, T) of a perfect BaTiO₃ single crystal grown by the Remeika method have been studied in the ranges f = 1–2 × 10⁷ Hz and T = ?80–130°C. These dependences characterize a transition from the paraelectric phase (121.5°C) as a near-antiferroelectric transition followed by the transition to the tetragonal phase at ～79.5°C. According to a number of signs, the range 121.5–79.5°C corresponds to a metastable phase typical of first-order phase transitions. The unexpected result of this work has been discussed with invoking the hypothesis on the BaTiO₃ structure in the paraelectric phase, according to which it consists of three antiferroelectric states oriented along the crystallographic axes. Using the dielectric properties of BaTiO₃ as an example, the method of direct correct determination of the temperatures of the structural transformations from the anomaly of tanδ(logf, T) has also been demonstrated.     

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.     

Asymmetric transmission through a photorefractive crystal of barium titanate

We have investigated the feasibility of using a barium titanate crystal as a unidirectional device. The nonlinear interaction between a beam and its own reflection from the back face of the crystal causes an effective increase or decrease in the transmission through the crystal, depending on whether the incident beam propagates along or against the crystal c-axis, respectively. This effect was investigated for several wavelengths and compared with theory. It is possible to make a device that has an average transmission of ≈94% and a transmission asymmetry of 1% by using a crystal whose front and back faces are cut so that their normals are at angle of ≈30° to the crystal c-axis.     

On the problem of the permittivity dispersion of barium titanate

The complex permittivity of multidomain single crystals of BaTiO₃ was measured in the decimetre and centimetre wave bands and it was proved that in this frequency region there is dispersion of the permittivity. Apparatus for measuring the permittivity of substances with a high is described and the influence of the inhomogeneity of the field in the sample on the characteristics of the cavity resonator is calculated. Present theories of the high-frequency properties of BaTiO₃ are discussed from the point of view of the experimental results.

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BaTiO₃ , . . BaTiO₃.

     

Effect of barium titanate nanoparticles of different particle sizes on electro-optic and dielectric properties of ferroelectric liquid crystal

A comparative study of two different particle sizes of ferroelectric barium titanate (BaTiO₃) nanoparticles as a dopant on the molecular structure, spontaneous polarization and dielectric behavior of a pure ferroelectric liquid crystal 6F₆T have been studied. It has been found that there is a remarkable decrease in isotropic temperature of both doped samples as compared to the pure 6F₆T sample. The spontaneous polarization also decreases for both the doped samples and the reduction is more pronounced in case of the dopant with large particle size. The dielectric spectroscopy confirms the presence of soft mode as well as Goldstone mode and also shows the decrease in the value of dielectric permittivity ?' as a function of frequency for both doped samples. The improvised properties of liquid crystal host doped with BaTiO₃ nanoparticles mainly depend upon the synthesis method of nanoparticles and also upon the particle size of dopant.     

基于钛酸锶钡介电非线性效应的可调谐太赫兹人工电磁媒质

数值仿真研究了内嵌钛酸锶钡薄膜夹层的金属网格谐振单元人工电磁媒质的谐振行为. 垂直电磁波激励下, 电磁响应频率随着内嵌夹层钛酸锶钡薄膜介电常数的变大呈现红移, 调谐率为22.6%. 本文提出的人工电磁媒质调谐方法只需要以结构单元的上下两层金属图形本身作为电极对内嵌夹层钛酸锶钡薄膜施加电压, 极大地简化了可调谐人工电磁媒质的制备及应用, 在太赫兹人工电磁媒质调制器等方面具有潜在的应用. 关键词： 人工电磁媒质 钛酸锶钡薄膜 介电非线性 调谐     

Barium titanate single crystal electrooptic modulator

In this work, the magnitudes of the critical voltages are determined for various mutual orientations of the optical axis of the crystal, the vector of the applied electrical field intensity, and the wave vector of the optical radiation being modulated both for the linear and quadratic electrooptic effects in BaTiO₃ crystals. It is shown that the critical voltages are considerably lower for the linear electrooptic effect than for the quadratic. The minimal critical voltage which ensures a modulation depth of 100% for the linear electrooptic effect is equal to 30 V.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 7, pp. 35—38, July, 1973.     

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.     

The thickness dependence of the permittivity of barium titanate single crystals

A thickness dependence of the permittivity ofc-domain barium titanate single crystals was found. The experimental results were explained by means of a model of a dielectric with surface layers. The thickness of the layer and the permittivity of the surface layer and bulk of the crystal were determined.

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iO₃

iO₃, -. . , .

     

Fabrication and optical reflection behavior of a two-dimensional barium titanate ceramic photonic crystal

We demonstrate a method for fabricating a two-dimensional hexagonal array of nanoscale barium titanate ceramic pillars. A precursor array was prepared by introducing a sol solution into an electron-beam resist mold with air holes and subsequently dry etching the unnecessary gel layer formed on the mold. A ceramic array, consisting of barium titanate ceramic pillars with a radius of 85 nm, a lattice constant of 450 nm, and a height of 500 nm, was fabricated by sintering the precursor array at 1073 K. The reflection spectra for the ceramic array in the visible range revealed the underlying photonic band gaps, which were in good agreement with results calculated using a plane-wave method. PACS 77.84.-s; 42.70.-a; 42.70.Qs     

光折变晶体钛酸钡锶电荷传输参数的测量

报道用两波耦合技术测量光折变晶体钛酸钡锶(Ba_(1-x)Sr_xTiO-3,BST)的电荷传输参数φμτ在激光波长λ=515nm和光功率密度I—1W/cm~2下测得光折变响应时间为0.5sec.考虑到BST晶体吸收系数的光强相关性,修改了光栅形成率的函数变量,得到BST晶体的暗电导σ_a和电荷传输参数φμτ的拟合值分别为1.0×10~(-11)(Ωcm)~(-1)和2.8×10~(-10)cm~2/V.     

Self-enhanced diffraction properties of a nominally undoped barium titanate crystal with a thermally fixed grating

We describe recent studies on diffraction properties of a photorefractive barium titanate crystal having a thermally fixed grating. Buildup dynamics of diffracted signals are measured to analyze the contributions of ionic and re-created photocarrier (hole) gratings to the temperature-dependent diffraction efficiency in self-enhanced readout. An activation energy of mobile ions as nonphotoactive secondary carriers for fixing volume holograms is determined holographically. This value is compared with that of hydrogen ions estimated from polarization-dependent infrared absorption spectra in order to indentify the fixing species.     

On the compensation of heterovalent ferric ions in the lattice of barium titanate single crystals

The introduction of heterovalent ferric ions into the titanium sites of the BaTiO₃-lattice of single crystals prepared by the fluoride process is due to the formation of oxygen vacancies and to the introduction of F-ions into the oxygen sites. Experimental results obtained by physical and chemical methods show the dependence of both mechanisms of compensation on the iron content of the crystals.