All-Optical Bypass-Exchange Switches

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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.     

Optical phase conjugation in nonresonant and saturable absorptive/resonant systems

Recent results obtained at Alabama A&M University on optical phase conjugation in electrically unpoled BaTiO₃, BANANA and SBN crystals are presented. The decay curves of the transient gratings and phase conjugation in these crystals indicate the involvement of more than one exponential process, possible reasons for which are indicated. Self induced gratings have been studied in electrically unpoled SBN crystal using a He−Ne Laser. The oscillations in a ring passive phase conjugator (RPPC) and in a unidirectional ring resonator using an electrically poled BaTiO₃ crystal have, been found to be bistable. It is also found that bistable oscillations are possible in a geometry in which the crystal is used simultaneously in a RPPC and as a linear passive phase conjugate (LPCC) mirror. The auxiliary oscillations pumped by the RPPC are bistable with the oscillations in LPCC. A brief review of the recent literature on phase conjugation in saturable absorptive/resonant systems along with the experiments planned to be undertaken by the authors on such systems are presented.     

Structural and Photoluminescence Studies on Nanosized Samarium-Doped Strontium Barium Niobate Ceramics

Nanosized pure and Samarium-doped Strontium Barium Niobate ceramic systems were synthesized by an aqueous organic gel route. The systems were characterized for their structure by X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) images. Photoluminescence measurements of Samarium-doped nanosized system showed emission peaks at 562, 598, and 644 nm when excited at 406 nm. These transitions are assigned to the 4f-4f transitions of Samarium ions in the host lattice. From the measured decay profiles, the lifetime of nanosized systems were calculated. The Samarium-doped Strontium Barium Niobate nanosystems are expected to find applications in the field of photonics.     

掺铑BaTiO3单晶场致应变特性的研究

系统地研究了掺铑的BaTiO₃单晶在老化后的场致应变性能.研究发现，晶体的场 致应变随老化时间的增加而增大，在老化27天后，在300V/mm的电场下，其双向场致应变可达1.11％；在较小的测试频率下（0.01Hz）也可得到0.95％的可逆的巨大的单向场致应变，在低频范围内，晶体的单向场致应变随测试频率增大而减小；研究晶体老化后的电滞回线，发现其 形状类似于蜂腰磁滞回线.实验结果表明，对BaTiO₃单晶掺杂铑元素可以大大改 善其电致伸缩性能，可能产生新的在超大应变及非线性驱动器中的应用. 关键词： 3单晶')" href="#">BaTiO₃单晶 掺铑 场致应变 老化     

外电场作用下掺杂SBN晶体的光致折射率变化

从实验上研究了不同外加直流电场作用下固液同成分的SBN:Cr和SBN:Rh晶体的光致折射率变化规律.测量结果表明:无外加电场作用时,晶体中的光致折射率变化不明显;若在光辐照晶体的同时,沿晶体c轴方向施加一定方向的外电场,则晶体中即刻出现显著的光致折射率变化.这种折射率变化随外加电场的增大而增大,并且电场方向不同,折射率变化的正负也不同.因而可以通过改变外加电场的极性和幅度控制SBN:Cr和SBN:Rh晶体中光致折射率的变化特性,这对于在该类晶体中制作动态光波导具有重要意义.     

A new method for measuring electro-optical coefficients of the optically active crystals

A new method has been proposed to measure the electro-optical coefficients of the crystals which have optical activity. By using this method, the half-wave voltage and the electro-optical coefficients of the optically active crystals La₃Ga₅SiO₁₄ (LGS), La₃Ga_5..5Nb_0.5O₁₄ (LGN), La₃Ga_5.5Ta_0.5Si₁₄ (LGT) have been determined. The resultants obtained are: γ₁₁(LGS)=1.9 pm/V, γ₁₁(LGN)=0.75 pm/V, γ₁₁(LGT)=0.57 pm/V. This method can also be used to simulate the on–off state of the electro-optical Q switch in the laser cavity, whether the switch is made of the ordinary crystals or the optically active crystals.     

Synthesis of transparent BaTiO<Subscript>3</Subscript> nanoparticle/polymer hybrid

Transparent BaTiO₃ nanoparticle/polymer hybrid was synthesized by polymerization and hydrolysis of barium titanium alkoxide modified with 2-vinyloxyethoxy ligand. Barium alkoxide, titanium alkoxide and 2-vinyloxyethanol were reacted affording a BaTiO₃ precursor, which was then hydrolyzed and polymerized to form BaTiO₃ particle/polymer hybrids below 100°C. BaTiO₃ particles increased in crystallinity with increasing water amount for hydrolysis. The absorption edge of the hybrid film on silica plates shifted to shorter wavelength with decreasing crystallite size. Nano-sized BaTiO₃ particle/polymer hybrid polymerized with methyl methacrylate (MMA) was shaped into a transparent and self-standing film with a refractive index of 1.595 at 589 nm.     

Co:BaTiO3/Si(100)纳米复合薄膜制备、微结构及其紫外光电子能谱研究

采用脉冲激光气相沉积(PLD)方法，在Si(100)晶面上制备了Co:BaTiO₃纳米复合薄膜.采用X射线衍射(XRD)结合透射电镜(TEM)方法研究了两种厚度Co:BaTiO₃纳米复合薄膜的晶体结构，当薄膜厚度约为30 nm时，薄膜为单一择优取向；当薄膜厚度约为100nm时，薄膜呈多晶结构.原子力显微镜(AFM)分析表明，当膜厚为30nm时，薄膜呈现明显的方形晶粒.采用紫外光电子能谱(UPS)研究了Co的价态和Co:BaTiO₃纳米复合薄     

Co:BaTiO3/Si(100)纳米复合薄膜制备、微结构及其紫外光电子能谱研究

采用脉冲激光气相沉积(PLD)方法,在Si(100)晶面上制备了Co:BaTiO₃纳米复合薄膜.采用X射线衍射(XRD)结合透射电镜(TEM)方法研究了两种厚度Co:BaTiO₃纳米复合薄膜的晶体结构,当薄膜厚度约为30 nm时,薄膜为单一择优取向;当薄膜厚度约为100nm时,薄膜呈多晶结构.原子力显微镜(AFM)分析表明,当膜厚为30nm时,薄膜呈现明显的方形晶粒.采用紫外光电子能谱(UPS)研究了Co的价态和Co:BaTiO₃纳米复合薄 关键词： 3')" href="#">BaTiO₃ 纳米复合薄膜 紫外光电子能谱     

过渡族元素掺杂BaTiO3-Tb1-xDyxFe2-y层状复合材料中的磁电效应

用溶胶-凝胶法制备1.0%mol Mn,Cr,Co掺杂 BaTiO₃(BTO)粉体,在1350℃下烧结成多晶陶瓷样品.X射线衍射和差示扫描量热分析表明,室温下掺杂BaTiO₃具有四方钙钛矿结构;居里点和相变潜热随Cr,Mn,Co掺杂逐渐降低.将掺杂BaTiO₃与Tb_1-xDy_xFe_2-y(TDF)胶合制成双层磁电复合材料,并研究了Cr:BTO-TDF,Mn∶BTO-TDF,Co:BTO-TDF层状复合材料中的磁电效应.实验表明,在340×80 A·m^-1偏置磁场下, Cr:BTO-TDF的横向磁电电压系数达到最大值586 mV·cm^-1·(80 A·m^-1)^-1.在400×80 A·m^-1偏置磁场下,Mn∶BTO-TDF和Co:BTO-TDF的横向磁电电压系数的最大值分别为480 mV·cm^-1·(80 A·m^-1)^-1和445mV·cm^-1·(80 A·m^-1)^-1.研究表明掺杂BaTiO₃-TDF层状复合材料中具有较强的磁电耦合.作为无铅压电材料,掺杂BaTiO₃制备的磁电效应器件颇具应用前景. 关键词： 磁电效应 双层复合材料 3')" href="#">掺杂BaTiO₃ 1-xDy_xFe_2-y')" href="#">Tb_1-xDy_xFe_2-y     

Enhanced performance of a mutually pumped phase-conjugation setup using two photorefractive crystals

A mutually pumped phase-conjugator (MPPC) consisting of two photorefractive crystals is investigated experimentally at a wavelength of about 807 nm. In addition to a Rh:BaTiO₃ crystal, which is used in a modified bridge configuration for phase-conjugation, a Co:BaTiO₃ crystal is used to amplify the phase-conjugate beam by wave-mixing. The phase-conjugate power is at least doubled compared to that using only one crystal, and the beam quality of the phase-conjugate beam is distinctly improved. Moreover, the temporal stability of the phase-conjugate output using two crystals is much higher than that using only one crystal. Received: 7 December 2000 / Revised version: 12 January 2001 / Published online: 27 April 2001     

Electro-optic properties of epitaxial Sr<Subscript>0.6</Subscript>Ba<Subscript>0.4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> films grown on MgO substrates using Li<Subscript>x</Subscript>Ni<Subscript>2-x</Subscript>O buffer layer

Textured Li_xNi_2-xO (LNO) thin films have been fabricated on (001)MgO substrates by pulsed laser deposition technique. The as-deposited LNO films shows a conductivity of 2.5×10^-3 Ω m and possess a transmittance of about 35% in the visible region. Subsequent deposition of Sr_0.6Ba_0.4Nb₂O₆ (SBN60) thin film on these LNO-coated MgO substrates resulted in a textured SBN layer with a 〈001〉 orientation perpendicular to the substrate plane. Phi scans on the (221) plane of the SBN layer indicated that the films have two in-plane orientations with respect to the substrate. The SBN unit cells were rotated in the plane of the film by ± 8.2° as well as ± 45° with respect to the LNO/MgO substrate. Besides the highly (00l)-orientation, the SBN films also exhibited a dense microstructure as shown by scanning electron microscopy. The electro-optic coefficient (r₃₃) of the SBN film was measured to be 186 pm/V. On the basis of our results, we have demonstrated that the LNO film can be used as a buffer layer as well as a transparent bottom electrode for waveguide applications. The SBN/LNO heterostructure is also a suitable candidate for integrated electro-optics devices. PACS  42.79.Gn; 42.82.Et; 78.20.Ci     

Effect of Ni doping on ferroelectric and dielectric properties of strontium barium niobate crystals

The influence of Ni doping on the ferroelectric and dielectric properties have been examined in Sr_0.61Ba_0.39Nb₂O₆ (SBN:61) relaxor crystals. The dopants introduced into SBN:61 crystals promote the switching process by reducing the value of threshold nucleation field, and thus coercive field. We present real-time studies of domain nucleation and growth processes in doped SBN:61 by the nematic liquid crystal (NLC) decoration technique. The broad phase transition and low-frequency dielectric dispersion that are exhibited by doped SBN:61 samples have a strong link to the configuration of the ferroelectrics microdomains, which in turn is strongly determined by Ni ions concentration.     

Der Einfluß des Kontaktes auf die durchα-Teilchen induzierten Stromimpulse in Cadmiumsulfid-Kristallen

The effect of the electrode contact on pulses induced byα-particles in single crystals of CdS grown by theFrerichs method was investigated to ascertain whether such crystals are suitable as particle counters. Thin, transparent metal electrodes were prepared on both sides of the crystals at room temperature, or above, by vacuum evaporation after surface cleaning by glow discharge. Crystals with Ohmic contacts (In, Ce) showed space charge limited pulse currents; the rise time of these pulses was longer than the dielectric relaxation time. When a thin sheet of an insulating material was interposed between crystal and electrode, polarization caused pulse amplitude to decrease very rapidly. It follows from the results that the polarizing charge is located at the electrodes. Saturation pulses were obtained with Cr, Mn and Au electrodes deposited on crystals at higher temperatures. Measured photovoltaic effects confirmed the existence of a surface-barrier potential at the electrodes. An energy resolution of about 20% forα-particles of 4·8 MeV was obtained for a crystal with Au electrodes. In regard to the charge carried by holes, the amount of energy required to produce an electron-hole pair was determined to 7·25±1·2 eV. The mobility range of the holes was estimated to be 2≦μ≦8 cm²/ Vsec. These results show that a CdS crystal can only be used as anα-particle detector with good time and energy resolution if there is a potential barrier immediately under the electrode.     

Domain switching in strontium-barium niobate crystals investigated by photorefractive self-focusing

The domain switching behaviour of undoped and Ce-doped Sr_0.61Ba_0.39Nb₂O₆ (SBN) crystals is investigated for different experimental conditions. For the investigation the photorefractive self-focusing technique is used. This method is demonstrated to be well suited for determining the polarization state of SBN crystals spatially resolved. We find that the repoling behaviour of nominally pure SBN is spatially inhomogeneous. The crystals are well repoled at the positive electrode, but are depolarized at the negative electrode. The larger the Ce doping concentration is, the smaller the depolarized crystal area. The domain switching depends on the switching velocity, while no influence of the electrode material is observed. This revised version was published online in March 2005. In the previous version, the published online date was missing     

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.     

由BaTiO3晶体结构相变时的介电特性研究其电场作用下的偶极子偏转路径

在不同频率和偏置电场下测量了BaTiO₃晶体从三方相到正交相再到四方相相变过程中的介电温谱.基于BaTiO₃晶体在电场作用下的偶极子偏转假设和介电特性实验结果,提出BaTiO₃各结构相在电场作用下的偶极子偏转路径可以由其相邻相的介电常数随温度的变化特性表现出来.推断出各结构相的偶极子偏转路径,以及偏置电场对偶极子偏转路径的影响. 关键词： 3晶体')" href="#">BaTiO₃晶体 介电特性 结构相变 偶极子偏转路径     

Properties of C60 thin film transistor based on polystyrene

This paper reports that the n-type organic thin-film transistors have been fabricated by using C60 as the active layer and polystyrene as the dielectric.The properties of insulator and the growth characteristic of C60 film were carefully investigated.By choosing different source/drain electrodes,a device with good performance can be obtained.The highest electron field effect mobility about 1.15 cm 2 /(V·s) could reach when Barium was introduced as electrodes.Moreover,the C60 transistor shows a negligible 'hysteresis effect' contributed to the hydroxyl-free of insulator.The result suggests that polymer dielectrics are promising in applications among n-type organic transistors.