Na_(0.5)Bi_(0.5)TiO_3-K_(0.5)Na_(0.5)NbO_3无铅陶瓷介电性能研究

采用固相反应法制备了(1-x)Na0.5Bi0.5TiO3-K0.5Na0.5NbO3体系陶瓷,研究了KNN含量对Na0.5Bi0.5TiO3-xK0.5Na0.5NbO3陶瓷的晶体结构、显微结构和介电性能的影响。XRD分析结果表明,KNN进入NBT形成固溶体,该体系陶瓷均为钙钛矿结构。扫描电镜分析显示KNN的引入有利于细化晶粒,提高陶瓷致密度。测试了样品在不同频率(1 kHz,10 kHz,100 kHz,1 MHz)下的的介电温谱(室温~500℃),结果表明随着KNN含量的增加,介电峰逐渐变宽,弛豫性逐渐增强,铁电-反铁电相变温度Td和反铁电-顺电相变Tm都明显降低,当x≥0.25时,Td降至室温或更低;室温(1 kHz)下,KNN和NBT相对介电常数分别为675和575,而KNN和NBT形成的固溶体介电常数明显增大,当x=0.25时,达到最大值εr=1653。在NBT中掺入KNN得到了介电峰明显宽化、在较宽温度范围内具有低电容温度系数的致密弛豫铁电体。     

不同离子掺杂的钛酸铋钠基陶瓷结构与性能表征

采用传统固相反应法制备了0.94(Na0.5 Bi0.) TiO3-0.06BaTiO3-3wt; Bi2 O3-xwt; Nd2O3(x=0,1.5)陶瓷.研究了Bi3+和Nd3+掺杂对0.94 (Na0.5 Bi05)TiO3-0.06BaTiO3陶瓷结构和电学性能的影响.结果表明,Bi2O3和Nd2O3掺杂不影响0.94(Na0.5 Bi0.5) TiO3-0.06BaTiO3的钙钛矿结构.3wt; Bi2O3添加使得铁电陶瓷0.94(Na0.5Bi05) TiO3-0.06BaTiO3转变为反铁电陶瓷.反铁电陶瓷0.94(Na0.5Bi0.5)TiO3-0.06BaTiO3-3wt; Bi2O3具有更高的相转变温度Tm(～320℃).Nd2O3添加不改变0.94(Na0.5 Bi0.5) TiO3-0.06BaTiO3-3wt; Bi2O3陶瓷的反铁电态,但增强了陶瓷的介电性能和弛豫性能.     

(Na1/2Bi1/2)TiO3-(Na1/2Bi1/2)(Zn1/3Nb2/3)O3无铅压电陶瓷的介电特性研究

采用固相合成法制备了(1-x)(Na1/2Bi1/2)TiO3-x(Na1/2Bi1/2)(Zn/23Nb2/3)O3(简写为(1-x)NBT-xNBZN)无铅压电陶瓷.研究了该体系陶瓷晶体结构、弥散相变特征与介电弛豫行为.X射线衍射分析表明,所研究的组成均能够形成纯钙钛矿(ABO3)型固溶体.当x≥0.5%摩尔分数时,该体系陶瓷具有三方、四方共存的晶体结构.材料的介电常数-温度曲线显示陶瓷具有两个介电反常峰Tf和Tm.修正的居里-外斯公式较好的描述了陶瓷弥散相变特征,弥散指数随x的增加而增加.x≤0.5%摩尔分数的陶瓷仅在低温介电反常峰Tf附近表现出明显的频率依赖性,随x的增加,陶瓷材料在室温和低温介电反常峰Tf之间都表现出明显的频率依赖性.根据有序-无序转变和宏畴.微畴转变理论探讨了该体系陶瓷介电弛豫特性的机理.     

四方相区NBT-KBT无铅铁电介电弛豫与铁电相变研究

本文研究了具有四方结构的(Na1-xKx)0.5Bi0.5TiO3体系中x＝0.22,0.26和0.30陶瓷材料不同温度下的电滞回线,结合变温XRD和介电温谱分析,发现该体系四方结构的组成为反铁电体,但紧靠准同型相界的四方结构由于场诱导下引起的反铁电-铁电相变,表现出铁电体特性,材料在升温过程中由于反铁电宏畴向微畴的转变导致了介电峰的产生,且在介电温谱上表现出强烈的介电常数-频率依赖性,为弛豫铁电体特征.     

Bi0.5(Na0.82K0.18)0.5TiO3-BiFeO3 无铅压电陶瓷的介电特性

采用固相反应法制备了系列(1-x)Bi0.5(Na0.82K0.18)0.5TiO3-xBiFeO3(BNKT-BFx)陶瓷.研究了该陶瓷在室温至500 ℃范围内的介电性能.结果表明:该陶瓷的介电温谱与典型弛豫铁电体的特征不同,存在两个介电反常峰和一个介电损耗峰,只在低温介电反常峰温度附近具有明显的介电常数的频率依赖性,居里温度随频率增加基本不变.首次提出了弛豫铁电体分为本征弛豫和非本征弛豫铁电体的理论.通过分析极化前和极化后陶瓷的介电温谱,发现该体系低温介电反常峰温度附近的介电频率依赖性为空间电荷和缺陷偶极子极化引起的非本征弛豫.     

Bi(Zn0.5Ti0.5)O3对Bi0.5Na0.5TiO3基陶瓷相结构及弛豫性的影响

采用固相反应合成法制备了(1-x)(0.96Bi0.5Na0.5TiO3-0.04BaTiO3)-xBi(Zn0.5 Ti0.5)O3陶瓷(x≤0.10).通过X射线衍射,介电温度谱等对该体系陶瓷的相结构及弛豫特性进行了研究.结果发现,该陶瓷在Bi(Zn0.5Ti05)O3加入量低于0.05时呈现纯钙钛矿结构.此外,随着Bi(Zn0.5Ti0.5)O3加入量的增加,其相结构由三方-四方共存向赝立方结构转变;同时,陶瓷的弥散因子上升,偶极子取向冻结活化能下降,表明BZT的加入明显地增加了0.96Bi0.5Na0.5TiO3-0.04 BaTiO3陶瓷的弛豫性.     

Bi2O3掺杂Sr0.92Ca0.08TiO3基陶瓷结构与介电性能的研究

通过固相反应法以Ca2+、Bi3+取代Sr2+制备出Sr0.92-1.5xBixCa0.08 TiO3(0.155≤x≤0.195)固溶体,同时加入固定量的MnCO3和ZnO作为改性剂和助烧剂,并通过XRD衍射仪、SEM扫描电镜和LCR分析仪对样品的结构和介电性能进行分析.结果 表明,当x≥0.165时陶瓷样品中出现第二相;随着Bi3+含量的增加,介电常数先增大,后减小,且介质损耗先减小后增大.当x=0.16时,得到介电常数ε=1 153、介质损耗tgδ1KHz=3.5×10-4、绝缘强度Eb=9.37 kV/mm的高介低损耗的高压电容器陶瓷介质材料.     

BiMnO_3改性BNT-BKT压电陶瓷的研究

为了提高BNT基压电陶瓷的电性能,采用传统的陶瓷制备方法,制备了一种Bi基的钙钛矿型无铅压电陶瓷 (1-x)Bi_(0.5)(Na_(0.82)K_(0.18))_(0.5)TiO_3-xBiMnO_3 (简写为BNKT-BMx).研究了Bi基铁电体BiMnO_3对该体系陶瓷微观结构和压电介电性能的影响.结果表明:在所研究的组成范围内陶瓷材料均能够形成纯钙钛矿固溶体,微量BiMnO_3不改变该体系陶瓷的晶体结构,但促进晶粒生长.随着BiMnO_3含量增加,低温介电反常峰消失,高温介电峰出现频率分散性.随BiMnO_3含量增加,压电常数d_(33)和机电耦合系数k_p先增加后降低,在x=0.01时,k_p=0.333,x=0.015时,d_(33)=170 pC/N,为该体系陶瓷压电性能的最优值.     

复合烧结助剂对CSLST微波介质陶瓷的性能影响

研究了复合添加12.5wt; Li2CO3-B2O3-CuO (LBC)玻璃和不同含量(0～4.0wt;) Bi2O3对(Ca0.9375Sr0.0625)0.3 (Li0.5Sm0.5)0.7TiO3 (CSLST)微波介质陶瓷烧结特性、相组成和介电性能的影响,分析了CSLST陶瓷与银的共烧行为.结果表明:复合添加LBC玻璃和Bi2O3能有效降低CSLST陶瓷烧结温度至875℃,XRD分析结果显示添加0～ 1.0wt; Bi2O3有Cu3Ti3O和CaCu3Ti4O12新相产生,当Bi2O3的添加量大于2.0wt;,杂相消失.随着Bi2O3添加量的增加,陶瓷的频率温度系数Tf向负方向偏移.复合添加12.5wt;LBC玻璃和2.0wt; Bi2O3的CSLST陶瓷,在875℃保温5h烧结后,具有优良的微波介电性能:εr=78.9,Q×f=1852 GHz,τε=3×10-6/C.该材料与银共烧界面结合状况良好,无明显扩散,适合作为LTCC的材料.     

氧化钨掺杂NBT-6BT陶瓷的结构表征与介电弛豫特性研究

采用传统固相反应法制备了WO3掺杂(Na0.5Bi0.)0.94 Ba0.06 TiO3 (NBT-6BT)陶瓷.研究了WO3掺杂对陶瓷样品微观结构和介电弛豫特性的影响.微观结构分析表明:随WO3掺杂,三方-四方共存相逐渐转变为三方相;WO3掺杂对陶瓷的致密度和晶粒尺寸影响不大.随WO3掺杂,陶瓷的介电常数逐渐降低,介电峰变得更加平坦,陶瓷介电常数的温度稳定性提高.居里-外斯和修正的居里-外斯定律较好地描述了陶瓷的弥散相变特征,随WO3掺杂量的增加,弥散指数下降.探讨了该体系陶瓷介电弛豫特性的机理.     

Triethyl ammonium salt of O,O′-bis(p-tolyl)dithiophosphate, [Et3NH]+[(4-MeC6H4O)2PS2]−

Triethyl ammonium Salt of O,O′-bis(p-tolyl)dithiophosphate and O,O′-bis(m-tolyl)dithiophosphate have been obtained by reaction of p- and m-cresol, respectively with P₂S₅ in toluene and have been characterized by elemental analysis, IR, ¹H and ³¹P NMR spectroscopy. The molecular structure of O,O′-bis(p-tolyl)dithiophosphate has been determined. Crystal data: [Et₃NH]⁺[(4-MeC₆H₄O)₂PS₂]⁻: Monoclinic, P2₁/c, a=15.2441(9) ?, b=10.415(2) ?, c=3.9726(9) ?, β=91.709(7)°, V=2217.5(1) ?⁻³, Z=4.Supplementary materials Additional material available from the Cambridge Crystallographic Data Centre (CCDC no. 600927 for [Et₃NH]⁺[(4-MeC₆H₄O)₂PS₂]⁻ comprises the final atomic coordinates for all atoms, thermal parameters, and a complete listing of bond distances and angles. Copies of this information may be obtained free of charge on application to The Director, 12 Union Road, Cambridge CB2 2EZ, UK (fax: +44-1223-336033; email: deposit@ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk).     

First-principles coexistence simulations of supercooled liquid silicon

We perform first-principles coexistence simulations of the low-density and the high-density phases of supercooled liquid silicon and find a negative slope for the coexisting line in the temperature-pressure plane. Electron density maps and electron-localization function plots of the two phases of silicon show marked differences. The calculated differences suggest more localized electrons in the low-density liquid compared to the high-density liquid, coming from an increased population of covalent bonds, which further explain the calculated negative slope in the two phase coexistence regime. This is consistent with the presence of a pseudo-gap in low-density liquid silicon, absent in the high-density liquid which shows a metallic behavior.     

Crystal structures of thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane

Structures of both thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane, ?C₆H₄?CH₂SCH₂?C₆H₁₀?CH₂SCH₂?, have been determined, wherecis andtrans refer to the attachments to the cyclohexane ring. Thecis form crystallizes in the monoclinic space groupP2₁/c witha=8.4299(11)Å,b=21.772(2)Å,c=8.9724(13)Å, β=116.574(11)^o, andZ=4. Thetrans isomer packs into the monoclinic space groupP2₁ witha=8.159(16)Å,b=10.185(5)Å,c=9.558(2)Å, β=112.435(18)^o, andZ=2. The cyclohexane ring of thecis isomer is in the chair conformation, while the cyclohexane of thetrans isomer is found in a twisted boat conformation.     

CTAB与SDBS对碳酸锶粒子生长形态调控及机理研究

以表面活性剂CTAB和SDBS为化学添加剂,采用化学共沉淀法对碳酸锶晶体的生长形态进行调控,成功地制备出了实心的树枝状和花瓣为空心的花状碳酸锶粉体,并用X射线衍射(XRD)、扫描电子显微镜(SEM)和傅里叶变换红外光谱(FT-IR)等分析手段对样品进行了表征;最后重点对化学添加剂可能产生的影响机理进行了初步的探讨.结果表明,CTAB和SDBS在晶体生长的过程中能起到显著的影响作用,两者对粒子分散性能的作用效果相反,而且后者对晶体(013)和(213)晶面表面能降低的贡献明显大于前者.     

Crystal structure of Zn4Na(OH)6SO4Cl·6H2O

The structure of Zn₄Na(OH)₆SO₄Cl·6H₂O, a secondary mineral from Hettstedt, Germany, was determined by single-crystal X-ray diffraction. The crystals are hexagonal,a=8.413(8),c=13.095(24) Å, space group $P\bar 3$ , Z=2. The structure was refined to R=0.0554 and R_w=0.0903 for 970 reflections with I≥3σ(I). The structure can be described as zinc hydroxide layers perpendicular toc, from which sulfates and chlorides extend. The layers are held together by a system of hydrogen bonds involving hexaaquo Na⁺ ions which occupy the interlayer space.     

Synthesis and Crystal Structure of 5-[2-(6-bromonaphthalenyloxymethyl)]-3-(4-morpholinomethyl)-1,3,4-oxadiazole-2(3<Emphasis Type="Italic">H</Emphasis>)-thione

Abstract  The title compound, C₁₈H₁₈BrN₃O₃S, a derivative of 1,3,4-oxadiazole, crystallizes in the triclinic space group P-1 with unit cell parameters a = 6.8731(3), b = 8.9994(4), c = 15.7099(6) ?, α = 92.779(3)°, β = 130.575(3)°, γ = 107.868(4)°, Z = 2. The dihedral angle between the mean planes of the planar naphthyl and morpholine (chair) rings with the planar oxadiazol ring is 50.1(8) and 76.8(6)°, respectively. The planar naphthyl ring is twisted 52.2(5)° with the mean plane of the morpholine ring. A group of four intermolecular close contacts are observed between a bromine atom and hydrogen atoms from the closely packed naphthyl, morpholine and oxy–methyl groups in the unit cell. These molecular interactions in concert with an additional series of π–π stacking interactions that occur between the center of gravity of the two 6-membered rings of the naphthalene group influence the twist angles of each of these three groups. A MOPAC AM1 calculation of the conformation energy of the crystal structure [226.0128(9) kcal] compared to that of the minimum energy structure after geometry optimization [29.9744(1) kcal] reveals a significantly reduced value. The twist angles of the three groups above also change after the AM1 calculation giving support to the influence of both intermolecular C–H···Br short-range interactions and Cg π–π stacking interactions on these angles which therefore play a role in stabilizing crystal packing. Graphical Abstract  Crystal structure of 5-{[(6-bromonaphthalen-2-yl)oxy]methyl}-3-(morpholin-4-ylmethyl)-1,3,4-oxadiazole-2(3H)-thione, C₁₈H₁₈BrN₃O₃S, is reported and its geometric and packing parameters described and compared to a MOPAC computational calculation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Crystal structure of irisolidone from the flowers of Pueraia lobata

Irisolidone (5,7-dihydroxy-6,4′-dimethoxyisoflavone) was isolated from the flowers of Pueraia lobata and its crystal structure was examined by X-ray single crystal diffraction. The crystal structure of irisolidone is monoclinic, space group P2₁/c with a = 15.491(9) ?, b = 7.895(4) ?, c = 13.321(7) ?, β = 110.546(9)° and Z = 4. Hydrogen bonding and aromatic π–π stacking assemble the title compound into a three-dimensional networking structure.     

Synthesis of spinacine and spinacine derivatives: crystal and molecular structures of Nπ-hydroxymethyl spinacine and Nα-methyl spinaceamine

The natural amino acid L-Spinacine (4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid) has been synthesized following a new pathway which gives a chemically and optically pure product with an excellent yield. The crystal structures of a synthetic intermediate, N^π-hydroxymethyl-spinacine, and a spinacine derivative, N^α-methyl-spinaceamine, have been investigated through X-ray diffraction: Spi(πMeOH)·H₂O, monoclinicP2 _i,a=8.571(1),b=6.682(1),c=8.588(1) Å, and β=94.67(1)^o. Spm(αMe)·2HCl·H₂O, triclinicP l,a=7.492(4),b=10.799(3),c=7.040(2) Å, α=91.88(2), β=98.36(3) and γ=73.34(3)^o. Spi(πMeOH) crystallizes with a water molecule and displays a zwitterionic character. The carboxylate group is in equatorial position and forms a short electrostatic interaction of 2.618(2) Å between one of its oxygens and the protonated nitrogen of the tetrahydropyridine ring. The crystal packing is assured by strong O?H???O, O?H???N, N?H???N intermolecular hydrogen bonds and C?H???O close contacts. The biprotonated compounds Spm(αMe) crystallizes with two Cl^? anions and a water molecule. The positive charge on the imidazole ring is delocalized on the conjugated moiety N=C?N. The crystal is built up by clusters formed by two biprotonated Spm(αMe) molecules, four Cl^? anions and two water molecules linked together by hydrogen bonds.