Ca1-xYxBi4Ti4O15铁电材料的结构和电性能研究

采用传统的固相反应法制备铋层结构铁电陶瓷材料Ca1-xYxBi4Ti4O15+x/2(x=0～0.1)(简称CYBT),研究了钇离子掺杂对CYBT陶瓷的烧结、晶相组成、显微形貌及电性能的影响.Y3+的A位取代,可以改善CYBT陶瓷的烧结性能,提高体积密度和瓷体致密度.Y3+的引入促进晶粒沿c轴方向生长,晶粒各向异性减小,室温介电常数增加.Y掺杂后离子半径差别和A空位浓度增加所产生的晶格畸变,使陶瓷的居里温度显著升高,当掺杂量x=0.10时,Tc升高了约80℃.Y掺杂显著降低了高温损耗,掺杂量x =0.075的样品表现出最好的压电性能,压电常数d33为15 pC/N.     

高居里点(1-x)Ba_(0.998)La_(0.002)TiO_3+xBi_4Ti_3O_(12)系统陶瓷微观结构及温度特性的研究

采用传统陶瓷制备工艺制备(1-x)Ba_(0.998)La_(0.002)TiO_3+ xBi_4Ti_3O_(12) (0≤x≤0.01)系统陶瓷.对在还原气氛(氮气)中烧成的陶瓷样品在一定温度下进行再氧化处理.研究了不同Bi_4Ti_3O_(12)掺杂浓度以及再氧化过程对BaTiO_3微观结构、介电性能及居里温度Tc的影响.结果表明:掺杂Bi_4Ti_3O_(12)后,BaTiO_3陶瓷的晶粒尺寸明显减小;Bi_4Ti_3O_(12)具有提高陶瓷居里点温度的作用,当x=1.0时,居里温度提高到T_c=150 ℃.随着BIT加入量的增加,电子与缺位混合补偿,晶格中将产生金属离子缺位,以补偿多余电子,因此随着BIT掺入量的增加,电阻率逐渐增大.     

Al-H共掺杂ZnO薄膜的形貌及光致发光性能研究

在不同衬底温度条件下采用RF磁控溅射法在石英玻璃上沉积Al-H共掺杂ZnO薄膜.对所有样品进行晶体结构、表面形貌、电学、光学以及室温光致发光性能分析.结果表明:随着衬底温度的升高,ZnO薄膜的结晶度增加,晶粒增大,薄膜致密度增加;薄膜表面起伏变化减小;同时,电阻率最低达到7.58×10-4Ω·cm,透过率保持在75;左右.所有ZnO薄膜样品都以本征发光为主,Al-H共掺杂在一定程度降低ZnO薄膜缺陷发光的强度;随着衬底温度的升高,ZnO薄膜的本征发光强度明显增大;同时在能量为3.45 eV附近观察到了一个紫外发光峰.     

Tb掺杂CaMnO3氧化物材料热电输运性能的研究

采用溶胶-凝胶法结合陶瓷烧结工艺制备了Tb掺杂CaMnO3基氧化物热电材料,系统研究了Tb掺杂材料物相组成、微观组织和和电输运性能.结果表明,Tb掺杂试样均为单一物相的CaMnO3晶体材料.随着Tb掺杂量的增加,试样晶粒逐渐细化.所得CaMnO3基材料内部晶粒互连,试样结构较为致密.所有Tb掺杂试样电阻率随温度升高而降低,呈明显的半导体传输特性,其中Tb掺杂量为0.14的试样电阻率最低.Tb掺杂试样Seebeck系数绝对值随掺杂量的增加而降低,这是由于Tb掺杂引入的电子型载流子造成的.所有试样功率因子均随温度升高而逐渐增加,并且所有Tb掺杂试样的功率因子均大于未掺杂试样.其中Tb掺杂量为0.08的块体试样功率因子在测试温度最高点973 K时达到最大值2.0×10-4 W·m-1·K-2,远高于未掺杂试样,通过稀土元素Tb掺杂可以优化CaMnO3基过渡金属氧化物材料的电性能.     

溶胶-凝胶法制备CaCu3Ti4O12陶瓷及其介电性能研究

通过溶胶-凝胶法制备CaCu3Ti4O12 (CCTO)粉体,经成型、烧结制成陶瓷,研究了烧结温度和保温时间对陶瓷显微结构和介电性能的影响.结果表明,在1050～1120℃下,随着烧结温度升高,陶瓷晶粒长大,致密度先增大后减小,经1100℃烧结所得陶瓷晶界清晰,晶粒较大且生长均匀;在1100℃下,随着保温时间的延长,陶瓷晶粒尺寸和致密度先增大后减小,经保温15 h烧结所得陶瓷具有最大的晶粒和致密度,其在1 kHz下的相对介电常数为1.77×104.     

V5+掺杂CaCu3 Ti4 O12陶瓷的 低温合成及烧结性能

采用传统固相反应法以V2O5为V5+掺杂源合成制备了CaCu3Ti4-xVxO12(CCTVO,x=0;,1;,3;,5;)陶瓷粉体,研究了V掺杂量对CaCu3Ti4O12(CCTO)物相低温合成及其低温烧结性能的影响,并对V掺杂CCTO陶瓷的低温合成机理和烧结机理进行了分析.XRD结果表明:当V掺杂量为≥1;时,在870℃煅烧20h可以完全获得CCTO物相,而未掺杂的样品则含有明显杂相,这说明V掺杂可以实现CCTO物相在低温下的合成制备.但差热分析表明,V掺杂后会提高CCTO发生固相反应的起始温度.分析认为低温下之所以实现CCTO的制备主要得益于V掺杂后会在高温煅烧过程中形成液相而增强了扩散气质和热传递效应.V掺杂量为3;的粉体在920℃相对较低温度下烧结后,具有较大的晶粒尺寸和高达92.4;的致密度,所得陶瓷在20Hz的低频率下介电常数高达2.28×105.     

Nb掺杂BaTiO%_3-Bi_(0.5)K_(0.5)TiO_3陶瓷系统PTCR性能的研究

采用固相反应法制备了Nb2O5掺杂的(1-x)BaTiO3-xBi0.5K0.5TiO3(BT-BKT,0≤x≤0.02)系统陶瓷,研究了Nb2O5和BKT掺杂量对该系统陶瓷显微结构和电性能的影响。结果表明:BaTiO3陶瓷的晶格轴率c/a值随着BKT含量的增加而变大,陶瓷具有良好的晶粒和明显的晶界。BT-BKT陶瓷的居里温度(Tc)也随着BKT的加入向高温移动,当x=0.01时,Tc提高到150℃,但室温电阻率(ρRT)随着BKT含量的增加也快速增大。     

Sr3YCo4-xMgxO10.5+δ(0≤x≤0.04)多晶的制备和热电输运性质研究

采用固相反应法制备Sr3YCo4-xMgxO10.5+δ(0≤x≤0.04)系列多晶,研究了Mg掺杂对体系结构、电输运和热电性质的影响.结果表明系列多晶为四方晶系,由于掺入的Mg2+(0.066 nm)部分替代了Co3+/4+(0.053 nm/0.061 nm),使晶格膨胀;多晶热电势在340~830 K随温度升高而下降,且Mg掺杂对热电势影响不大,表明Mg掺杂对体系载流子浓度影响不大;多晶电阻率在100~300 K随温度升高而降低,且随着掺杂量增加电阻率降低,结合扫描电镜观察到多晶的气孔数目减少、晶粒连接紧密和热电势的结果认为Mg掺杂对体系电输运性质的影响机制主要是使气孔、晶界散射作用减弱、载流子迁移率变大,而Mg掺杂对载流子浓度的影响是次要的.     

Sm掺杂Bi4Ti3O12陶瓷晶体结构及电性能的研究

采用固相反应工艺制备了Sm3+掺杂层状结构无铅Bi4-xSmxTi3O12(x=0.00,0.25,0.50,0.75,1.00,1.25)介电陶瓷.利用XRD、SEM等测试方法研究了Sm掺杂量、烧结温度和保温时间对Bi4-xSmxTi3O12 (BST) 陶瓷晶体结构及电性能的影响.结果表明:所制备的Bi4-xSmxTi3O12陶瓷均具有单一正交相结构,BST陶瓷表面晶粒的显微形貌表现为随机排列的棒状结构.样品的铁电性能测试表明,Sm3+施主掺杂明显降低了BIT的电导率,随着Sm3+含量的增加,Sm3+逐渐有部分取代B位,由于Sm3+取代Ti4+大大降低了氧空位的浓度,使得氧空位对电畴的钉扎作用减弱,并且材料的剩余极化Pr也相应提高.     

工艺参数对飞秒激光沉积硅基ZnO大面积均匀薄膜性能的影响

研究了衬底温度、真空度、激光能量、激光脉冲频率及退火处理对飞秒激光制备硅基ZnO大面积均匀薄膜的结构和性能的影响.结果表明,当激光能量为1.5mJ、脉冲频率为400 Hz、真空度为1.0 mPa、衬底温度为80℃时,所制备的薄膜质量最佳.薄膜呈高度c-轴取向,为典型的六方纤锌矿结构,晶粒沿垂直于衬底表面的方向生长;当衬底温度高于80℃时,随着温度的升高,c-轴取向度降低.80℃制备的薄膜在可见紫外区域透过率达98;,电阻率随温度升高而减小,退火后薄膜的透过率增大、电阻率升高.     

Mesomorphic Properties of the 4-(4-n-Alkoxybenzoyloxy)-Benzylidene-4-n-Alkoxyanilines and 4-(4-n-Alkoxybenzoyloxy)-3-Methoxy-Benzylidene-4-n-Alkoxyanilines

Transition temperatures, transition enthalpies and X-ray results are reported for 4-(4-n-heptyloxybenzoyloxy)-benzylidene-4-n-alkoxyanilines, 4-(4-n-nonoxybenzoyloxy)-benzylidene-4-n-alkoxyanilines and their 3-methoxy-benzylidene substituted derivatives.     

Crystallization and optical properties of CaWO4 and SrWO4

Single crystals of calcium tungstate and strontium tungstate have been grown by double decomposition flux reaction technique using lithium chloride as flux. Growth conditions are optimized to synthesize well faceted crystals. Effect of primary and secondary flux density in the growth charge has been studied. Thermogravimetric study reveals that the grown crystals are highly stable in the temperature range 25 – 1000°C. Analysis of optical absorption normal to the ab‐plane in the spectral range of 200 – 800 nm reveals the true absorption edge, the nature of transition being the allowed indirect one at 4.60 eV and 4.56 eV respectively for CaWO₄ and SrWO₄. The crystals have been characterized by determining useful pertinent optical and dielectric parameters. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vibrational Studies of Gel Grown Ferroelectric RbHC4H4O6 and SrC4H4O6 4H2O Crystals

Single crystals of Rubidium Hydrogen Tartrate (RbHT) and Strontium Tartrate Tetrahydrate (SrTT) have been grown by a gel technique using a chemical reaction method. A controlled reaction has been employed between tartaric acid and feed solution (RbCl for RbHT and Sr(NO₃)₂) at room temperature. The laser Raman and FT-IR spectra of these crystals are recorded in the frequency range 100 - 4000 cm^-1. The presence of tartrate ion, monohydrogen tartrate ion, water molecules and external mode vibrational frequencies are identified and discused. The doublet and broad nature of tartrate ion vibrational frequencies have also been observed and analysed.     

The Crystal and Molecular Structure of 4'-Cyanophenyl-4-n-Pentylbenzoate

The crystal and molecular structure of the title compound with the formula C₅H¹¹—C₆H₄—COO—C₆H₄—CN (CPPB) has been determined by X-ray diffraction methods. CPPB crystallizes in the monoclinic space group P2₁/n with eight molecules in a unit cell of dimensions a = 15.268(2) Å, b = 9.165(1) Å, c = 24.031(3) Å, β = 94.67(1)°. The structure has been solved by direct methods and refined to an R value of 0.070.

The CPPB molecules adopt a stretched form and are packed in an approximate parallel imbricated mode, the molecular long axes making an angle of about 5° with the crystal c axis. The molecular geometry and packing are discussed in relation to the mesomorphic behavior of CPPB.     

Crystal and molecular structure of 4-amino-4-carboxyl thiapyran

4-Amino-4-carboxylthiapyran crystallizes in space groupP2₁/c witha = 10.61,b = 6.55,c= 10.97 Å, =96.3 °, andZ = 4. The structure was solved by the heavy-atom method, with 897 observed reflections, and refined to anR of 0.093. The packing of the structure is found to be very similar to that in the structure of 1-aminocyclohexane carboxylic acid. The conformation of the thiapyran ring exists in the puckered chair form.Contribution No. 410 from the Dept. of Crystallography and Biophysics, Univeristy of Madras, Guindy Campus, Madras-600025, India.     

New Cluster Precursors—K5 Pyramids and K4 Tetrahedra—for Self-Assembly of Crystal Structures of Mn4(ThMn4)(Mn4)-tI26, Mn4(CeCo4)(Co4)-tI26, and MoNi4-tI10 Families

Crystallography Reports - A combinatorial and topological analysis has been performed, and the self-assembly of the crystal structures of the Mn4(ThMn4)(Mn4)-tI26 (sp. gr. I4/mmm),...     

Crystal and molecular structure of 4-amino-4-carboxyl thiapyran hydrobromide

Journal of Chemical Crystallography - 4-Amino-4-carboxylthiapyran hydrobromide crystallizes in the monoclinic space groupP21/m, witha= 9.72 Å,b= 6.60 Å andc=7.10 Å,β = 94.8...     

4H-SiC同质外延生长及Ti/4H-SiC肖特基二极管

利用台阶控制外延生长技术在偏晶向Si-面衬底上进行了4H-SiC的同质外延生长研究,衬底温度为1500℃,在厚度为32μm、载流子浓度为2～5×1015cm-3的外延材料上制备出了反向阻塞电压大于1kV的Ti/4H-SiC肖特基二极管,二极管的正向与反向电流的整流比(定义偏压为±1V时的电流比值)在室温下超过107,在265℃的温度下超过102,在20～265℃的温度范围内,利用电流电压测量研究了二极管的电学特性,室温下二极管的理想因子和势垒高度分别为1.33和0.905eV,开态电流密度在2.0V的偏压下达到150A/cm2,比开态电阻(Ron)为7.9mΩ·cm2,与温度的关系遵守Ron～T2.0规律.