Preparation and electrical properties of Sm-doped Bi2Ti2O7 thin films prepared on Pt (111) substrates

Crack-free Sm-doped Bi₂Ti₂O₇ (Sm:BTO) thin films with strong (111) orientation have been prepared on Pt (111) substrates using a chemical solution deposition (CSD) method. The structural properties and crystallizations were studied by X-ray diffraction. The surface morphology and quality were examined using atomic force microscopy (AFM). The insulating and dielectric properties were also evaluated at room temperature. The results demonstrate that the Sm:BTO films exhibit improved electrical performances as compared to the pure Bi₂Ti₂O₇ thin films and suggest a strong potential for utilization in microelectronics devices.     

Crystal growth,structure, infrared spectroscopy,and luminescent properties of rare-earth gallium borates RGa3(BO3)4, R = Nd,Sm–Er,Y

Crystals of the rare-earth gallium borates RGa₃(BO₃)₄, where R = Nd, Sm–Er, or Y, were grown by the flux method. The crystal structures of RGa₃(BO₃)₄ (R = Eu, Ho) were studied on the basis of single-crystal X-ray diffraction measurements. The hexagonal unit-cell parameters are a = 9.4657(1) Å, c = 7.4667(1) Å and a = 9.4394(2) Å, c = 7.4322(1) Å for EuGa₃(BO₃)₄ and HoGa₃(BO₃)₄, respectively, space group R32. Structure model was determined by “charge flipping” method and refined to R = 1.93% [EuGa₃(BO₃)₄] and R = 1.89% [HoGa₃(BO₃)₄] in anisotropic approximation. All grown gallium borates were investigated by infrared (IR) spectroscopy technique in a middle and far IR region. IR spectra of rare-earth gallium borates correspond to a pure rhombohedral (R32) polytype structure. Small inclusions of a monoclinic phase were detected only in Eu and Nd compounds. Luminescence of Eu and Ho gallium borates was studied at room temperature. The measured decay times for the most intensive emission lines of EuGa₃(BO₃)₄ (∼614 nm) and HoGa₃(BO₃)₄ (434 nm) are 940 μs and 140 μs, respectively. The scheme of crystal-field energy levels of Eu³⁺ in EuGa₃(BO₃)₄ was built on the basis of the temperature-dependent optical transmission measurements combined with the luminescence data. The measured UV absorption edge for RGa₃(BO₃)₄ is at about 300 nm.     

Structural and electrical properties of Na0.5Bi4.0RE0.5Ti4O15 (RE=Tm,Yb and Lu) thin films

In the current study, a series of lanthanide ions, Tm, Yb and Lu, were used for doping at the Bi-site of the Aurivillius phase Na_0.5Bi_4.5Ti₄O₁₅ (NaBTi) to investigate the structural, electrical and ferroelectric properties of the thin films. In this regard, Na_0.5Bi_4.5Ti₄O₁₅ and the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5i₄O₁₅ (RE=Tm, Yb and Lu, denoted by NaBTmTi, NaBYbTi, and NaBLuTi, respectively) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Formations of the Aurivillius phase orthorhombic structures for all the thin films were confirmed by X-ray diffraction and Raman spectroscopic studies. Based on the experimental results, the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5Ti₄O₁₅ thin films exhibited a low leakage current and the improved ferroelectric properties. Among the thin films, the NaBLuTi thin film exhibited a low leakage current density of 6.96×10⁻⁷ A/cm² at an applied electric field of 100 kV/cm and a large remnant polarization (2P_r) of 26.7 μC/cm² at an applied electric field of 475 kV/cm.     

The role of amorphous phase content on the electrical properties of atmospheric plasma sprayed (Ba,Sr)TiO3 coatings

(Ba,Sr)TiO₃ coatings deposited on carbon steel substrates were successfully prepared by an atmospheric plasma spray system. Three sets of samples containing different amount of both crystalline and amorphous phases were deposited and consequently studied in order to determine their electrical properties. The results show a clear correlation existing between the amorphous phase content and coating´s electrical properties. The resistivity increases with increase of amorphous phase content. Relative permittivity for low frequencies decreases and become more stable with frequency tuning when amorphous phase content increased. The maximum relative permittivity value is in the range 75–200 for frequency 1 kHz. The loss factor varies between 0.23 and 0.03 for all studied samples. The loss factor is at the lower limit of these values and frequency much less dependent when the coating contains 15 wt% of amorphous phase and more. The band gap of all samples is between 2.75 eV and 2.90 eV. Microstructure and hardness were evaluated in order to determine basic mechanical properties of deposits.     

Effects of sintering temperature and holding time on porosity and shrinkage of glass tubes

The influences of sintering temperature and holding time on porosity and shrinkage of glass tubes have been studied by optical microscope. It is evident that there exists three stages for the sintering process of glass. At the first stage, both increasing temperature and prolonging the holding time contribute to lowering the porosity and to intensifying the shrinkage greatly. At the second stage, the glass further densifies and the voids among particles become smaller and less. Finally, at the third stage the shrinkage rate almost keeps unchanged to sintering temperature and holding time.     

Significantly enhanced dc electrical resistivity and piezoelectric properties of Tb-modified CaBi2Nb2O9 ceramics for high-temperature piezoelectric applications

Bismuth layer–structured ferroelectric calcium bismuth niobate (CaBi₂Nb₂O₉, CBN) is considered to be one of the most potential high-temperature piezoelectric materials due to its high Curie temperature T_c of ∼940°C, but the drawbacks of low electrical resistivity at elevated temperature and low piezoelectric performance limit its applications as key electronic components at high temperature (HT). Herein, we report significantly enhanced dc electrical resistivity and piezoelectric properties of CBN ceramics through rare-earth element Tb ions compositional adjustment. The nominal compositions of Ca_1−xTb_xBi₂Nb₂O₉ (abbreviated as CBN-100xTb) have been fabricated by conventional solid-state reaction method. The composition of CBN-3Tb exhibits a significantly enhanced dc electrical resistivity of 1.97 × 10⁶ Ω cm at 600°C, which is larger by two orders of magnitude compared with unmodified CBN. The donor substitutions of Tb³⁺ ions for Ca²⁺ ions reduce the oxygen vacancy concentrations and increase the band-gap energy, which is responsible for the enhancement of dc electric resistivity. The temperature-dependent dc conduction properties reveal that the conduction is dominated by the thermally activated oxygen vacancies in the low-temperature region (200–350°C) and by the intrinsic conduction in the HT region (350–650°C). The CBN-3Tb also exhibits enhanced piezoelectric properties with a high piezoelectric coefficient d₃₃ of ∼13.2 pC/N and a high T_c of ∼966°C. Moreover, the CBN-3Tb exhibits good thermal stabilities of piezoelectric properties, remaining 97% of its room temperature value after annealing at 900°C. These properties demonstrate the great potentials of Tb-modified CBN for high-temperature piezoelectric applications.     

Yb∶LuScO_3晶体的超精密光学加工及其激光性能

Yb∶LuScO_3晶体作为固体激光器的新型增益介质,其面形和表面质量严重影响激光器的光束质量,因此探索Yb∶LuScO_3晶体的超精度光学加工工艺参数具有重要意义。本文系统开展了Yb∶LuScO_3晶体超精密光学加工的工艺参数研究,针对Yb∶LuScO_3晶体在加工过程中容易破裂和表面质量较差的问题,提出了拼接上盘和树脂铜盘抛光垫的关键技术。首先,使用COMSOL Multiphysics有限元软件对拼接工艺中选取的不同保护垫料的应力进行仿真。接着,研磨阶段逐步减小B_4C磨料的粒径。然后,粗糙阶段使用树脂铜盘作为抛光垫,并对树脂铜盘抛光垫的作用进行了分析。最后,使用激光二极管泵浦加工好的样品进行激光输出实验。实验结果表明:基于该技术加工后的晶体表面粗糙度RMS=0.296 nm,面形精度PV=53 nm。在1 086 nm处获得了8.3 W的连续激光输出,斜效率为58%。该加工方法可以广泛应用于Yb∶LuScO_3晶体的高精度加工。     

Electric field induced ferroelectric-surface modification for high mobility organic field effect transistors

Inherent spontaneous polarization in ferroelectric-dielectric polymer PVDF-TrFE (Poly[(vinylidenefluoride-co-trifluoroethylene]) and an external electric field induced surface modification procedure are utilized to enhance organic field effect transistor (OFET) characteristics. The increase in the carrier mobility of the electric-field (EF) treated device correlates with the EF magnitude and evolution of dielectric microstructure and exhibits an enhancement beyond 300%. The enhanced interfacial transport property appears to have its origin in the dipolar orientation and nanostructure evolution at the interface.     

High-yield production of N-doped graphitic platelets by aqueous exfoliation of pyrolyzed chitosan

Full exploitation of the properties of N-doped graphene and few-layers graphitic platelets will require a method for the mass production of this highly conductive material. Herein the preparation of few-layers graphitic platelet dispersions at concentrations up to 0.16 mg ml⁻¹ is reported. These suspensions are produced by dispersion and exfoliation of N-doped graphitic carbons obtained from the chitosan biopolymer. This high concentration derives from the morphology of pyrolyzed chitosan constituted by a graphitic carbonaceous residue with loose stacking of the graphene sheets that is prone to undergo easy exfoliation. The presence of few layers graphitic sheets was confirmed by Raman spectroscopy, transmission electron microscopy, electron diffraction and atomic force microscopy. Our method results in the formation of N-doped graphitic platelet suspensions with a yield of 40 wt.% of the initial graphitic carbon, which could potentially be improved to 90 wt.% by four consecutive sonication–centrifugation cycles of the same pyrolyzed chitosan residue. The absence of defects or oxides is confirmed by X-ray photoelectron, infrared and Raman spectroscopies. Solution processing of graphene and few-layers graphitic flakes opens up a range of potential large-area applications, from device and sensor fabrication to liquid-phase chemistry.