Dielectric tunability and magnetoelectric coupling in LuFe2O4 epitaxial thin film deposited by pulsed-laser deposition

C-axis orientated LuFe₂O₄ thin films on (001) sapphire substrates are epitaxially deposited by pulsed-laser deposition. Temperature-dependent resistance characterization reveals the ferrimagnetic transition at 237 K and charge-ordering transition at 340 K in the film. Importantly, the dielectric constant of the film can be significantly changed by both electric and magnetic fields. The dielectric tunability reaches 35% when an electric field of 5 V is applied, while this value reduces to 20% and 15%, respectively, when a magnetic field of 0.83 T is applied perpendicular and parallel to the film normal direction. This suggests a magnetically controlled dielectric tunability and strong magnetoelectric coupling, and is therefore promising for tunable device applications in film form.     

激光二极管泵浦Yb：YAG激光器特性的研究

本文从YbYAG的晶体光谱特性出发,系统地介绍了YbYAG激光器的运转特性。着重阐述了自吸收效应、空间烧孔效应对激光器输出特性的影响，以及YbYAG激光器可调谐特性和自调Q特性.     

氟化钙掺杂对钛酸锶钡陶瓷结构和介电性能的影响

研究了Ca F2掺杂对钛酸锶钡(Ba0.6Sr0.4Ti O3,BSTO)陶瓷的结构和介电性能的影响。采用传统烧结工艺制备了Ca F2掺杂的BSTO陶瓷,对其晶体结构、微观形貌和介电性能进行了研究。XRD结果显示,Ca F2掺杂BSTO陶瓷为钙钛矿结构,当掺杂量≥3%(质量分数)时,基体中出现第二相Ba Ca Ti O4。添加少量Ca F2(0.5%)可明显减小晶粒尺寸,随掺杂量继续增加,晶粒尺寸变化不明显。Ca F2掺杂降低了BSTO陶瓷的介电常数和介电可调性,减小了其介电损耗,提高了材料的综合使用性能。     

低锐度F—P干涉具调谐TEA CO2激光器理论分析

从理论上计算了低锐度F-P干涉具有直接输出耦合调谐TEA CO2激光器的输出特性，结果表明：通过改变干涉具的间距，激光器的输出波长可在9μm带和10μm带之间切换；而且，输出一般为多波长，每个波长包含精细纵模结构，纵模的数目和谱线展宽有关，理论计算还给出了输出脉冲波形和脉冲能量随波长的分布。     

氧化铝掺杂对Ba0.6Sr0.4(Zr0.2Ti0.8)O3陶瓷介电性能的影响

Zr4+取代Ti4+的Ba0.6Sr0.4(Zr0.2Ti0.8)O3固溶体在降低介电常数的同时,保持了BST固溶体优异的可调性。为降低BST材料的介电损耗和介电常数,以氧化铝为改性剂对Ba0.6Sr0.4(Zr0.2Ti0.8)O3材料(BSZT材料)进行了掺杂。随着氧化铝掺杂质量分数从1%到10%增加,BSZT材料的介电常数从5000降低到了1550(100kHz),介电损耗降低到0.001(100kHz)以下,而材料的介电可调性保持在35%左右(1.5kV/mm)。X射线衍射图谱表明,烧结后得到的BSZT材料具有典型的钙钛矿结构。扫描电子显微镜观察表明,氧化铝的掺杂使得陶瓷致密度较高,晶粒均匀。     

BSTO/MgO复相铁电陶瓷的调谐性分析

基于目前的实验数据,构建了复合材料模型解释Ba0.55Sr0.45TiO3/MgO复相铁电陶瓷的调谐性。结果表明,所分析的三种模型中,球状填充模型能较好的解释Ba0.55Sr0.45TiO3/MgO体系中介电常数的调谐性与偏压电场的关系,特别当Ba0.55Sr0.45TiO3的质量分数小于50%时,模型分析结果与实验数据吻合较好。     

Conservation of Permittivity and Tunability of Ferroelectrics Over Temperature

The existence of an intersection point of electric field strength dependencies of permittivity of ferroelectrics at different temperatures is theoretically described by Ginzburg-Devonshire (GD) theory and experimentally confirmed by studying (Ba_0.3Sr_0.7)TiO₃ (BSTO) and SrTiO₃ (STO) thin film varactors. GD analysis enables one to propose a way to improve the thermal stability of ferroelectric microwave devices. In particular, parameters of a L-band digital (0°/180°) phase-shifter fabricated from thick BSTO film varactors were stabilized in the temperature range T = (210–310) K by application of variable to DC control voltages.     

Growth and Dielectric Properties of Ferroelectric BaTiO3 Thin Films for Cantilever-Type Microsensors

ABSTRACT

Ferroelectric BaTiO₃ (BTO) thin films were deposited on Si, silicon-on-insulator (SOI) and MgO substrates by pulsed laser deposition. The orientations of the films, polycrystalline and epitaxial phase, were controlled by the lattice mismatch between the BTO film and substrates. The structural properties and surface morphologies were examined using X-ray diffractometer and atomic force microscope. The dielectric properties of BTO films were investigated using metal-ferroelectric-metal (MFM) and interdigital co-planar capacitors. Conductive oxide layers, SrRuO₃(SRO) and La_0.5Sr_0.5CoO₃ (LSCO), were grown on Si and SOI substrates as bottom electrodes. For MFM capacitors based on Au/BTO/SRO/Si and Au/BTO/LSCO/SOI layer structures, a little asymmetric capacitance-voltage curves were obtained with about 36% capacitance tunability. The remanent polarizations were about 21 μC/cm² and the coercive fields were about 71 kV/cm. For an interdigital capacitor based on Au/BTO/MgO layer structure, a little lossy capacitance-voltage curve was obtained with about 64% capacitance tunability.     

BST-BT4/13复合陶瓷介电调谐性能的研究

通过固相反应法制备了高介电相含量和高温度稳定性的介电可调Ba_(0.6)Sr_(0.4)TiO_3-Ba_4Ti_(13)O_(30)(BSTBT_(4/13))复合陶瓷,研究了介电相BT_(4/13)含量和烧结温度对其显微结构、介电性能和调谐性能的影响。结果表明,BT_(4/13)含量的增加有利于BST-BT_(4/13)复合陶瓷烧结性能的提高、介电常数的下降及其温度稳定性的增强,但会降低其调谐率。随着烧结温度的升高BST-BT_(4/13)复合陶瓷的介电常数增大。当BT_(4/13)相的体积分数高达92%时,BSTBT_(4/13)复合陶瓷在20～160℃内具有优异的温度稳定性及其介电常数在20～65℃之间几乎不变,且表现出明显的介电非线性,在10kV/cm的直流偏置场强下调谐率仍可达1%。     

Novel multi-wavelength excitable single-component phosphor system for application in white-LEDs

A novel color-tunable phosphor of BaZnO₂:xEu³⁺ (x = 0–20 mol%) has been successfully prepared via high-temperature calcination method using alkaline earth metal as the charge compensator. Uncommonly, BaZnO₂:Eu³⁺ is a multi-wavelength excitable phosphor due to its wide absorption spectrum ranging 250–550 nm. It shows broad white (400–700 nm), orange (∼580 nm) and red (∼611 nm) photoluminescence (PL) under 370 nm, 395 nm and 467 nm excitations, respectively and were assigned to one or more ⁵D₀→⁷F_J (J = 1 to 4) transitions of Eu³⁺ ion. An efficient energy transfer between Zn²⁺ and Eu³⁺ has been observed upon systematically increasing the concentration of Eu³⁺ ion. Scanning Electron Microscopy images indicated elongated rod-like structures with an average diameter of ∼20 nm. The chromaticity coordinates (x, y) were found to be positioned at white (0.33, 0.42), orange (0.51, 0.42) and red (0.65, 0.34) regions correspond to 370 nm, 395 nm and 467 nm excitations, respectively. The temperature-dependent luminescence spectrum of BaZnO₂:Eu³⁺ under the excitation of 467 nm was also studied. It exhibited good thermal stability and a marginal drop in photoluminescence intensity by 4.29% at 150 °C was observed. The mathematical calculation of the activation energy was approximately 0.20 eV. The results indicate the suitability of the phosphor for LEDs applications, which is otherwise difficult to obtain in single-component system.