NbO3-LiNbO3无铅压电陶瓷的烧结特性和压电性能研究

采用传统陶瓷烧结工艺制备了（1-x）（K0．5Na0．5）NbO3-xLiNbO3无铅压电陶瓷，研究了陶瓷的结构、烧结特性及电性能特征．制备的（K0．5Na0．5）NbO3-LiNbO3陶瓷为单一的钙钦矿结构，室温下其相结构随LiNbO3含量增加逐渐由正交相向四方相转变，显微结构也由于LiNbO3含量的不同而表现出很大差异．与（K0．5Na0．5）NbO3陶瓷相比，（K0．5Na0．5）NbO3-LiNbO3陶瓷的烧结温度降低，烧结特性得到改善．（K0．5Na0．5）NbO3-LiNbO3陶瓷表现出优越的压电性能，其中0．94（K0．5Na0．5）NbO3—0．06LiNbO3（x=0．06）陶瓷的压电常数d33达到205pC／N，机电耦合系数kp为40．3％，kt达到49．8％．     

La0.5Ba0.5CoO3中的Pr掺杂效应

用固相反应法制备了La0.5-xPrxBa0.5CoO3系列化合物，系统研究了Pr不同含量时材料的磁性和电输运特性，结果表明：Pr掺杂没有改变Co的3d电子的巡游特性。随Pr掺杂量增加，材料的分子磁矩单调下降，其原因是当Pr逐渐取代La时，Co离子的3d电子逐渐由中间自旋态向低自放态转变。随Pr含量增加，材料的居里温度逐渐下降，这是由于稀土离子的尺寸效应，电阻测量表明：在所研究的温度范围内，居里温度以下，所有掺Pr材料的导电机制为热扩散型。居里点以上，导电机制为变程跳跃导电。     

Nd3+A位置换对(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷微波介电性能的影响

研究了Nd3+离子A位置换改性(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷的微波介电性能.[(Pb0.5Ca0.5)1-xNdx](Fe0.5Nb0.5)O3(PCNFN)陶瓷的微波介电性能得到改善是由于少量过剩的Nd3+与(Pb,Ca)2+的固溶能够消除氧空位.当x=0.02时,能够形成单相的钙钛矿相,随着Nd3+置换量的增加,过剩的Nd3+将导致第二相焦绿石的形成,焦绿石会恶化PCNFN的微波介电性能.PCNFN介电性能随x的增加而下降是由于焦绿石相随x增加的结果.当x=0.02-0.05,PCNFN陶瓷有很好的微波介电性能,介电常数K>100,Qf值为5385-5797GHz,频率温度系数TCF随Nd3+含量的增加从正的变为负的.     

Synthesis and Magnetic Properties of L0.5Sr0.5Mn0.5M0.5O3 (L = Y, Pr; M = Cu, Ru)

A new Mn-containing material with nominal composition L_0.5Sr_0.5Mn_0.5M_0.5O₃ (L = Y or Pr; M = Cu or Ru), as well as Y_0.5Sr_0.5MnO₃ for comparison, were synthesized. The results of the XRD and EDX analyses show that the obtained samples are single-phased and isostructural, with L_1–xA_xMnO₃. The L_0.5Sr_0.5Mn_0.5Cu_0.5O₃ material displays a PM behavior down to 8 K where paramagnetic–antiferromagnetic transition begins. The Pr_0.5Sr_0.5Mn_0.5Cu_0.5O₃ sample has a broad transition at 210 K and a magnetoresistance of 34% at 128 K. The Pr_0.5Sr_0.5Mn_0.5Ru_0.5O₃ material has a paramagnetic–ferromagnetic transition beginning at 330 K and a ferromagnetic–antiferromagnetic one at about 160 K. The obtained value of T _c is the highest for the Pr-containing manganites. The roles of Pr/Sr ratio, anisotropy, and intergranular effects in the samples are discussed.     

Mn改性Na0.5Bi2.5Nb2O9高温压电陶瓷的研究

采用固相法获得了Mn改性的Na0.5Bi2.5Nb2O9(NBN+xmol%MnCO3,0≤x≤10.0)铋层状压电陶瓷,并系统地研究了Mn(掺杂)对NBN基陶瓷显微结构与电性能的影响.结果表明,所有获得的样品都是居里点在700℃以上的单一相铁电体.加入Mn显著地提高了NBN系列陶瓷的机械品质因素Qm,明显改善了陶瓷的压电与机电性能.当MnCO3掺杂量为8.0mol%时,陶瓷获得最佳电性能:tanδ=0.749%,d33=20 pC/N,Qm=3120,kp=12.37%,kt=21.09%,Pr=7.01μC/cm2.NBN+xmol%MnCO3(x=8.0)陶瓷经700℃退极化处理后,其d33保持为原来的75%(~15 pC/N),表明该材料在高温领域下具有良好的应用前景.     

High-temperature Thermoelectric Properties of Cu-substituted Bi_2Ba_2Co_(2-x)Cu_xO_y Oxides

Cu-substituted Bi2Ba2Co2-xCuxOy(0.0≤x≤0.4) samples were prepared by conventional solid-state reaction method and the effect of Cu substitution on the microstructure and thermoelectric properties were investigated.The partial substitution of Cu for Co in Bi2Ba2Co2-xCuxOy led to an increase in the electrical conductivity because of an increase in the hole concentration and grain size of sintered bodies.In addition,Cu substitution led to an increase in Seebeck coefficients while kept the thermal conductivity unchanged.The highest thermoelectric figure of merit(ZT value) was obtained in x=0.4 sample and the value was 1.5 times as large as that of Cu-free sample at 873 K.     

非化学计量比对(K0.465Na0.465Li0.07)(Nb0.95Sb0.05)O3无铅压电陶瓷结构及性能的影响

通过传统固相合成工艺制备了(K0.465+xNa0.465+yLi0.07)(Nb0.95-zSb0.05)O3(x,y,z=-0.01～0.02)无铅压电陶瓷,研究了非化学计量比对陶瓷结构及压电性能的影响。结果表明符合化学计量比的陶瓷具有四方钙钛矿结构;在实验范围内,K和Nb的过量或少量均不会改变体系的相结构,而Na过量将会导致体系正交-四方相变温度升高到室温以上,并且正交-四方相变温度随y的增加而升高;过量添加约0.5%(摩尔分数)的K或Na便能补偿在高温烧结时的碱金属元素的挥发损失,进而提高陶瓷的压电性能;该体系陶瓷的组分在较大范围内变化时(如当y=z=0时,x=0～0.02;当x=z=0时,y=0～0.01;以及当x=y=0时,z=-0.01～0.005),仍然能保持d33>200pC/N和kP>40%这样较好的性能。上述结果不仅有利于在研究中材料制备工艺的重复,而且有利于当材料在器件应用时所面临的规模化生产。     

Ce掺杂Ca3Co4O9的高温热电性能

利用二次固相反应方法制备了Ce掺杂的Ca3Co4O9热电材料(CexCa3-xCo4O9,x=0、0.1、0.3),并测试了样品的微观结构和高温热电性能。测试结果表明,Ce替代Ca可有效调制Ca3Co4O9的热电参数;随着温度的升高,样品的电阻率和热导率降低,See-beck系数增大。在973K的温度下,Ce0.1Ca2.9Co4O9具有最高的热电性能(ZT=0.23)。     

Magnetic and crystallographic properties of Fe1−x(Cu0.5In0.5)xCr2S4 spinels

Fe_1?x(Cu_0.5In_0.5)_xCr₂S₄ spinel powders with 0 ≤ x ≤ 1 were prepared. Their lattice constant (a_o) increases linearly with x from a_o = 0.9995 nm for x = 0 to 1.0065 nm for x = 1. Cu⁺, In³⁺, and Fe²⁺ ions occupy tetrahedral A sites of the spinel lattice and Cr³⁺ ions the octahedral B sites. Spinels with 0 ≤ x ≤ 0.82 are ferrimagnets with Curie temperatures decreasing from 171 K for x = 0 to 116 K for x = 0.82. Spinels with 0.82< x≤ 1 are antiferromagnets with Néel temperatures between 31 K and 36 K. The magnetic moment of Fe_0.18Cu_0.41In_0.41Cr₂S₄ spinels was determined by susceptibility measurements to be 5.85 $\text{μ}{}_{\mathrm{<mtext>B</mtext>}}\text{molecule}$, which is equal to the calculated spin-only magnetic moment.     

Magnetoelectric and dielectric properties of Ni0.5Cu0.5Fe2O4–Ba0.5Pb0.5Ti0.5Zr0.5O3 ME composites

The (x) Ni_0.5Cu_0.5Fe₂O₄ + (1−x) Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ ME composites have been synthesized by a standard ceramic method. The presence of single phase in x = 0 and x = 1 as well as two phases in x = 0.15, 0.30 and 0.45 composites has been confirmed by XRD. The dielectric constant (ε′) and dielectric loss (tan δ) have been studied as a function of temperature and frequency. These composite materials exhibit maximum dielectric constant with a variation of frequency and temperature. The composite 15% Ni_0.5Cu_0.5Fe₂O₄ + 85% Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ had the highest magnetoelectric voltage coefficient of 0.248 mV/cm Oe at room temperature among the studied composites.     

高居里温度BaTiO3-(Bi0.5Na0.5)TiO3无铅正温度系数电阻陶瓷的制备

用传统的固相反应烧结法制备了(1-xmol%)BaTiO₃-xmol%(Bi_0.5Na_0.5)TiO₃(BBNTx)高温无铅正温度系数电阻( positive temperature coefficient of resistivity, PTCR)陶瓷。X射线衍射表明所有的BBNTx陶瓷形成了单一的四方钙钛矿结构。SEM分析结果显示随着BNT含量的增加, 陶瓷晶粒尺寸减小。空气中烧结的0.2mol% Nb掺杂的BBNT1陶瓷, 室温电阻率为~10² Ω·cm, 电阻突跳为~4.5个数量级, 居里温度为~150℃。氮气中烧结的0.3mol% Nb掺杂的BBNTx(10≤x≤60)陶瓷, 同样具有明显的PTCR效应, 居里温度在180~235℃之间。随着BNT含量的增加, 材料的室温电阻率增大, 同时陶瓷的电阻突跳比下降。     

(Na0.5K0.5)NbO3基无铅压电陶瓷的研究

由于钙钛矿结构无铅压电陶瓷具有高的压电性能，已成为无铅压电陶瓷研究的热点．本文综述了钙钛矿结构无铅压电陶瓷（Na0．5K0.5）NbO3的研究进展和趋势．重点从添加第二组元、添加助烧剂、取代改性和制备方法四个方面，归纳和分析了（Na0．5K0.5）NbO3基无铅压电陶瓷的研究开发进展，并对（Na0.5K0.5）NbO3基无铅压电陶瓷今后的研究和发展提出一些建议．     

Synthesis of (Bi0.5Na0.5)TiO3 nanocrystalline powders by stearic acid gel method

Bismuth sodium titanate (Na_0.5Bi_0.5)TiO₃ (NBT), is considered to be an excellent candidate for a key material of lead-free piezoelectric ceramics. In this study, we propose a stearic acid gel method for the preparation of nanocrystalline single phase NBT powder at relatively low treatment-temperature. Infrared (IR) spectroscopy, differential thermal analysis (DTA), thermogravimetric analysis (TG) and X-ray diffraction (XRD) were used to characterize the process of crystallization. The particle size and morphology of the calcined powders were examined by TEM. It shows that pure single phase NBT powders could be obtained at 700 °C for 1 h, and the particle size is about 20 nm. With an increase in the calcination temperature, crystallite size increased. The powders were further pressed into disk and sintered at 1120 °C for 2 h in air, and its density and microstructure were compared with traditionally prepared samples.     

Phase diagram and structure-property relationships in the lead-free piezoelectric system: Na0.5K0.5NbO3-LiTaO3

A phase-diagram for the Na(0.5)K(0.5)NbO(3)-LiTaO(3) solid solution series (NKN-LT) is presented for compositions ≤ 10 mol% LT, based on the combined results of temperaturevariable X-ray powder diffraction and dielectric measurements. In addition to the reported orthorhombic and tetragonal polymorphs of NKN-LT, a monoclinic phase is revealed. Changes to electrical properties as a function of LT substitution are correlated to phase content. Increasing the LT content from 5 to 7 mol% LT led to improved temperature stability of piezoelectric properties because of the avoidance of the monoclinic-tetragonal polymorphic phase transition during thermal cycling (at >25°C). For 7 mol% LT samples: d(33) = 200 pC/N; T(c) = 440°C; ε(r) = 550 and tan δ = 0.02 (at 20°C). Modification of this composition by solid solution with BiScO(3) led to a decrease in d(33) values. Transmission electron microscopy of a sample of 0.95[0.93 NKN-0.07LT]-0.05BiScO(3) indicated a core-shell grain structure which led to temperature-stable dielectric properties.     

Preparation and characterization of new visible-light-driven BaCo0.5Nb0.5O3 photocatalyst

A new type of visible-light-driven photocatalyst BaCo_0.5Nb_0.5O₃ was successfully synthesized via a sol-gel process in this study. After heating the precursors at 1000 °C, a pure perovskite phase was obtained. The particle size and crystallinity of BaCo_0.5Nb_0.5O₃ powders markedly increased with a rise in the calcination temperature. The band gap of BaCo_0.5Nb_0.5O₃ calculated from the UV-visible spectra was found to be less than that of titania. BaCo_0.5Nb_0.5O₃ was demonstrated to have photocatalytic activity under visible light irradiation and this activity significantly depended on the synthesis temperature. The sol-gel derived powders were found to have better photocatalytic activity than the solid-state derived powders because of the reduced particle size and increased surface area.     

新型溶胶-凝胶工艺制备La0.5Ca0.5MnO3薄膜及性能分析

鉴于以醇盐为原料溶胶-凝胶制备La0.5Ca0.5MnO3薄膜工艺中存在诸多苛刻因素,本文以无机盐为原料采用溶胶-凝胶工艺在SiO2/Si(100)衬底上制备了La0.5Ca0.5MnO3薄膜.并用XRD、SEM和TEM等分析手段对薄膜进行了表征,通过不同磁场下电阻-温度(R-T)曲线,研究了样品的磁电阻(CMR)效应...     

Magnetic and crystallographic properties of the mixed system (FeF3)1-x (KMnF3)x

The mixed system (FeF₃)_1-x (KMnF₃)_x with 0 ≤ x ≤ 1 has been prepared and investigated. The compounds with 0.19 ≤ x ≤ 0.22 are single phase hexagonal while the materials with 0.40 ≤ x ≤ 0.55 are single phase tetragonal. The powder samples are all light colored and at low temperatures become antiferromagnetic (with weak ferromagnetic moments.) The Néel temperatures are 111°K for the hexagonal compound with x = 0.20, and 160°K and 133°K for the tetragonal materials with x = 0.40 and 0.55, respectively. The reasons for the low ordering temperatures are examined using the generalized molecular field theory.     

Epitaxial growth and thermoelectric properties of TiNiSn and Zr0.5Hf0.5NiSn thin films

Due to their exceptional thermoelectric properties Half-Heusler alloys like MNiSn (M = Ti,Zr,Hf) have moved into focus. The growth of single crystalline thin film TiNiSn and Zr_0.5Hf_0.5NiSn by dc magnetron sputtering is reported. Seebeck and resistivity measurements were performed and their dependence on epitaxial quality is shown. Seebeck coefficient, specific resistivity and power factor for Zr_0.5Hf_0.5NiSn at room temperature were measured to be 63 μV K^− 1, 14.1 μΩ m and 0.28 mW K^− 2 m^− 1, respectively. Multilayers of TiNiSn and Zr_0.5Hf_0.5NiSn are promising candidates to increase the thermoelectric figure-of-merit by decreasing thermal conductivity perpendicular to the interfaces. The epitaxial growth of multilayers containing TiNiSn and Zr_0.5Hf_0.5NiSn is demonstrated by measuring satellite peaks in the X-ray diffraction pattern originating from the additional symmetry perpendicular to the film surface.     

Ag_2Te掺杂对p型Bi_(0.5)Sb_(1.5)Te_3块状合金热电性能的影响

采用真空熔炼、机械球磨及放电等离子烧结技术(SPS)制备得到了(Ag2Te)x(Bi0.5Sb1.5Te3)1-x(x=0,0.025,0.05,0.1)系列样品,性能测试表明,Ag2Te的掺入可以显著改变材料的热电性能变化趋势,掺杂样品在温度为450~550K范围内具有较未掺杂样品更优的热电性能.适当量的Ag2Te掺入能够有效地提高材料的声子散射,降低材料的热导率.在测试温度范围内,(Ag2Te)0.05(Bi0.5Sb1.5Te3)0.95具有最低的晶格热导,室温至575K范围内保持在0.2~0.3W/(m·K)之间,在575K时,(Ag2Te)0.05(Bi0.5Sb1.5Te3)0.95试样具有最大热电优值ZT=0.84,相较于未掺杂样品提高了约20%.     

Ni0.5Zn0.5Fe2O4粉末化学镀铜前后的电磁性能

本文用溶胶-凝胶自燃烧法制备了Ni0.5Zn0.5Fe2O4粉末颗粒,以甲醛为还原剂在Ni0.5Zn05Fe2O4颗粒表面进行了化学镀铜,制备了Cu/Ni0.5Zn0.5Fe2O4复合粉体.用扫描电镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)对镀铜前的Ni0.5Zn0.5Fe2O4颗粒以及镀铜后的复合纳米颗粒进行了表征.对镀铜前的Ni0.5Zn0.5Fe2O4粉体和不同镀铜量的Cu/Ni0.5Zn0.5Fe2O4复合粉体进行了电磁性能的研究,结果表明镀铜后镍锌铁氧体的吸波性能明显提高,增重量为65%的Cu/Ni0.5Zn0.5Fe2O4复合粉体在频率为11GHz处反射率可达-12dB左右.