Demko-Sharpless合成稀土四唑化合物的结构及性质

使用Demko-Sharpless法,用氰基吡啶(4-氰基吡啶和3-氰基吡啶)与稀土硝酸盐(Ln=La,Gd,Er)在水热条件下反应,安全有效地合成了四个稀土四唑离子型化合物:[Ln(H2O)8·3(p-TPD)·2(p-HTPD)·7H2O],(Ln=La(1),Gd(2),Er(3),p-TPD=4-四唑吡啶),[...     

PVT法生长4H-SiC晶体及多型夹杂缺陷研究进展

作为第三代半导体材料的典型代表,碳化硅因具备宽的带隙、高的热导率、高的击穿电场以及大的电子迁移速率等性能优势,被认为是制作高温、高频、高功率以及高压器件的理想材料之一,可有效突破传统硅基功率半导体器件的物理极限,并被誉为带动“新能源革命”的绿色能源器件。作为制造功率器件的核心材料,碳化硅单晶衬底的生长是关键,尤其是单一4H-SiC晶型制备。各晶型体结构之间有着良好的结晶学相容性和接近的形成自由能,导致所生长的碳化硅晶体容易形成多型夹杂缺陷并严重影响器件性能。为此,本文首先概述了物理气相传输(PVT)法制备碳化硅晶体的基本原理、生长过程以及存在的问题,然后针对多型夹杂缺陷的产生给出了可能的诱导因素并对相关机理进行解释,进一步介绍了常见的碳化硅晶型结构鉴别方式,最后对碳化硅晶体研究作出展望。     

化学气相传输法生长ZnO单晶及性质研究

利用化学气相传输法生长了ZnO单晶.在无籽晶自发成核的条件下,使用碳辅助增强质量传输方法,得到了晶粒尺寸达4mm×10mm的ZnO晶体.利用长有GaN层的蓝宝石晶片作为衬底,得到了直径为30mm、厚2mm左右的ZnO单晶体.比较了不同温度条件下晶体生长的结果并进行热力学过程和现象了分析.用光荧光谱和X射线双晶衍射研究了ZnO晶体的性质.     

Investigation of One‐Dimensionally Disordered Structures of AIIBVI Crystals by Monte Carlo Technique. I. The 3C Disordered Structure and the 3C Structure with Different Kinds of Stacking Faults

The Monte Carlo computer simulation technique is applied to investigate one‐dimensionally disordered (ODD) structures in A^IIB^VI compounds. Computed diffracted intensities for 3C disordered structure (3C/DS) with various frequency functions of fault to fault distances have shown a strong intensity distribution dependence upon the frequency function. Distinctive features of the diffraction patterns along the 10.L reciprocal lattice row corresponding to different kinds of faults in 3C structure are discussed. In particular, both random as well as non‐random distribution of stacking faults (SFs) are considered.     

Investigation of One‐Dimensionally Disordered Structures of AIIBVI Crystals by Monte Carlo Technique. II. 2H Structure with Different Kinds of Stacking Faults

To investigate 2H disordered structures in A^IIB^VI compounds, the Monte Carlo computer simulation technique has been applied. Calculations of diffraction intensity distributions along the 10.L reciprocal lattice row from 2H structure with four different kinds of stacking faults (SFs) are presented. In particular, both random and non‐random distributions of SFs are considered. The chosen examples of transformations from the parent 2H structure into another small‐period polytypes due to simple frequency function of fault to fault distances are discussed in detail.     

水热合成钛酸盐纳米管的晶型结构及光催化活性

以锐钛矿相为主的氧化钛粉体为原料,在强碱条件下采用水热合成法制备出外径约10nm的钛酸盐纳米管.采用TEM、XRD和EDS对产物进行表征,并对其热稳定性、光催化活性进行测试,研究结果表明:制得的纳米管的结晶程度很低,主要成分为钛酸钠,含少量锐钛矿二氧化钛;煅烧温度对钛酸盐纳米管的晶型结构和光催化活性有显著影响.未煅烧及400℃煅烧的纳米管光催化活性较低, 500℃煅烧后具有较高的光催化活性,但煅烧温度高于600℃后,由于锐钛矿晶体减少,纳米管的光催化活性降低.     

Complexes formed by the reactions of fluorinated and non-fluorinated organonitriles with [Zn(SO2)2][AsF6]2: A structural study

[Zn(SO₂)₂][AsF₆]₂ (1) has been prepared from zinc metal and AsF₅ in liquid sulfur dioxide, and crystallized from sulfur dioxide giving crystals of [Zn(SO₂)₄(AsF₆)₂] (1a). The compound 1 forms the homoleptic complexes [Zn(NCR)₆](AsF₆)₂ (R: CH₃ (2a), C₆H₅ (3a), C₆F₅ (3b)) with the corresponding nitriles. In these complexes, the metal center is octahedrally surrounded by six ligands (average Zn–N 2.13 ?). Reaction of 1 with the weaker ligand F₃CCN results in dicoordination at the metal center complemented by a two-dimensional polymeric network (2b) containing bridging AsF₆ ⁻ anions. [Zn(SO₂)₄(AsF₆)₂] (1a): monoclinic, P2₁/c, a=8.5176(8) ?, b=13.5787(14) ?, c=14.7661(15) ?, β=99.296(2)°; [Zn(NCCH₃)₆][AsF₆]₂ (2a): rhombohedral, R-3, a=11.2225(8) ?, b=11.2225(8) ?, c=16.9393(14) ?; [Zn (NCCF₃)₂][μ-FAsF₅)₂( (2b): monoclinic, P2₁/c, a=11.226(3) ?, b=6.6147(19) ?, c=10.460(3) ?, β=104.028(5)°; [Zn(NCC₆H₅)₆][AsF₆]₂ (3a): monoclinic, P2₁/n, a=13.7968(10) ?, b=19.8861(15) ?, c=16.1692(12) ?, β=91.563(2)°; [Zn(NCC₆F₅)₆][AsF₆]₂·2SO₂ (3b): monoclinic, P2₁/n, a=10.8448(9) ?, b=154456(13) ?, c=17.5206(15) ?, β=104.158(1)°.     

钙钛矿型层状化合物K_2Ln_2Ti_3O_(10)(Ln=La,Pr,Sm,Eu,Gd)X射线衍射晶体结构分析

固相反应法合成了具有钙钛矿型层状的化合物K_2Eu_2Ti_3O_(10) 和K_2Gd_2Ti_3O_(10) ,利用X射线粉晶衍射仪对镧系元素的钙钛矿型层状化合物K_2Ln_2Ti_3O_(10) (Ln=Eu,Gd)进行结构分析,获得其X射线粉晶衍射数据.X射线衍射分析结果表明:K_2Ln_2Ti_3O_(10) (Ln= La,Pr,Sm,Eu,Gd )为四方晶系,空间群I4/mmm.并得到其晶胞参数及其镧系元素的钙钛矿型层状化合物K_2Ln_2Ti_3O_(10) 晶体结构变化规律.     

基于Rietveld精修方法解析Bi2O3的原子热振动

三氧化二铋(Bi2 O3)是氧离子导电体,为了获得它的原子热振动各向同性温度因子,对该粉末晶体进行X射线衍射实验,建立了晶体结构模型,利用Rietveld精修方法的RIETAN-2000程序对所得实验结果进行了晶体结构精修,通过最大熵方法(MEM)解析得到了粉末晶体的等高电子密度分布三维(3D)和二维(2D)可视化图谱...     

溶胶-凝胶自燃烧法制备Ba(NiMg)0.2AlxFe11.4-xO19的结构与磁性能

以柠檬酸为络合剂,利用溶胶-凝胶自燃烧法制备了Ni、Mg、Al掺杂的M型钡铁氧体粉体(Ba(NiMg)0.2AlxFe11.4-xO19,x=0~0.4),利用X射线衍射仪、透射电子显微镜、综合物性测量系统等对样品结构与室温磁性能进行研究.结果表明,样品的物相组成与Al掺杂量有密切关系,当Al掺杂量x超过0.2时,产物中出现杂相α-Fe2O3,且杂相α-Fe2O3的含量随x值的增大而增加.在10kOe的外加磁场下,样品的饱和磁化强度(Ms)随x值的增大而降低,矫顽力(Hc)则随x值的增大先增大后减小,当x=0.2时,矫顽力达到最大值5644Oe,对应的饱和磁化强度为46emu/g.     

PVT法氮化铝晶体铝面、氮面生长对比分析

在氮气环境下用PVT方法生长氮化铝过程中,氮面和铝面由于表面化学性质不同,生长的主要化学反应速度存在差异。原子在生长表面的迁移能力不同造成单晶表面生长方式差异较大。在基本相同条件下(生长温度、生长温差、生长气压、类似的籽晶、同一台生长设备)进行了铝、氮面氮化铝单晶晶体生长。为了更明显地表现铝氮面的差异,将同一片籽晶分为两半,翻转其中一半让铝氮面同时生长。铝面生长较好的区域形成了明显的晶畴,而氮面生长时生长较好的部分出现了明显的生长台阶,并出现了晶畴边界被生长台阶湮灭的生长现象,进一步通过AFM观测到铝面生长台阶平整但被缺陷所阻隔,晶畴发育明显为各晶畴独立生长。氮面生长台阶没有铝面规则但连续性较强,在原来晶畴边界位置也出现了连续的生长台阶(或台阶簇)。所以籽晶质量不高时氮面生长更容易提高晶体质量,后续的XRD测量结果也证明了氮面生长后的晶体质量明显高于铝面生长的晶体质量。     

Conformational variability exhibited by mellitic acid anions (MA?n) with organic amine cations: Structures with an abundance of NH ?s OC hydrogen bonds and a paucity of hydrogen bonds

Benzenehexacarboxylic acid (mellitic acid) is an ideal substrate for the study of radially arranged ionic interactions with organic bases. Earlier work has shown that the net charge in MA (−4, −3, or −2) influences its assembly, respectively, either as ribbons or sheets. In the former case the cations intersperse the ribbons forming a tight network. In the MA sheets from the latter, the cations are arranged in orthogonal stacks. In the MA-phenanthroline complex such stacks are arranged exactly parallel resulting in significant π–π interactions. The present work relates to the modification of the phenanthroline motif to flexible structures. The reported ability of 2,3-bis-(2′-pyridyl) pyrazine (P2), prepared from 2,2′-pyridyl by reaction with ethylenediamine (EDA) followed by dehydrogenation of the resulting 2,3-bis-(2′-pyridyl)-5,6-dihydropyrazine, to form helical structures made it an obvious choice for complexation studies with MA. These resulted not only in the formation of the desired 7 MAP2 complex but also, surprisingly, with the dihydroprecursor complex with EDA 3 (MAEDA), a compound that eluded direct preparation with MA and EDA. The crystal structure of MAEDA reports the first complex of MA where MA⁻⁵ ions are encountered. The 15 hydrogen bonds, three for each N, result in hard packing. The complex with P2 7 (MAP2) showed the common features of MA⁻² sheets. Unlike phenanthroline, the nonplanar disposition of the pyridine rings made it possible for both pyridine protons to be available for salt formation, resulting in the arrangement of the cations in layers interposed between the sheets of MA⁻² ions. The pyrazine ring does not participate in hydrogen bonding or stacking in the crystal.