钐掺杂对锰锌铁氧体微波电磁性能的影响

采用同相法合成了钐掺杂的锰锌铁氧体Mn0.3Zn0.7Fe2-xSmxO4,(x=0,0.01,0.02,0.04,0.06),通过XRD对合成粉末进行了晶体结构的分析,结果表明:当x≤0.02时,制得的粉体为相对较纯的尖品石型铁氧体.稀土掺杂锰锌铁氧体的晶格常数随着掺钐量的增加先增大后减少.使用Agilent8722ET网络分析仪在2～18 GHz的频率范围内对其微波电磁特性进行测试,结果显示,当掺钐量为0.02时,在9～18 GHz的频率范围内电磁参数ε'和ε"稍有增加,ε"最大值出现的位置移向低频.μ"和μ'峰值均大大增加,最大值分别达到6.2和5.5,该掺钐晕下微波电磁性能最佳.利用微波电磁理论分析了电磁参数的变化机制.     

CoSm_xFe_(2-x)O_4铁氧体纳米粉晶的制备及其电磁性能

用W/O微乳液法制备了CoSmxFe2-xO4(x=0.00,0.02,0.04,0.06,0.08,0.10)铁氧体纳米粉晶。用X射线衍射仪(XRD),透射电子显微镜(TEM)、振动样品磁强计(VSM)和阻抗/材料分析仪表征了样品的结构、形貌和电磁性能。结果表明,掺杂少量Sm3+对样品的晶体结构没有影响,但其晶粒尺寸、饱和磁化强度、矫顽力和电磁损耗性能等都有不同程度的改变。样品的晶粒尺寸随Sm3+含量的增加而减小,在35~20 nm之间变化;而饱和磁化强度随着钐掺杂量的增加呈先减小后增大的变化趋势(x=0.00→0.04→0.08,Ms=52.95→51.03→52.56emu.g-1);当钐掺杂量x分别等于0.6和0.4时,其磁损耗性能和电损耗性能在1 MHz~1 GHz的频率范围达到最大,且低频区优于高频区。     

白光用红色荧光粉Gd2SrAl2O7:Eu3+的合成及发光性能研究

用传统的固态反应法合成了新型红色Eu3+掺杂的Gd2SrAl2O7红色荧光粉。通过添加Li2CO3助熔剂,有效地降低了反应温度,获得了纯Gd2SrAl2O7相。用X射线衍射仪分析确认了产物为Gd2SrAl2O7晶相,并用光谱仪测试了光谱性能,发现当Eu3+掺杂浓度为30%时,荧光粉在623 nm处有最强发光,是Y2O3:Eu3+的两倍。(Gd0.7Eu0.3)2SrAl2O7(x=0.650,y=0.349)色度值与美国国家电视标准委员会标准值(x=0.670,y=0.330)接近。     

X射线荧光光谱法同时测定锰锌铁氧体材料的主量组分

用熔融制样法将样品在铂金坩埚中与四硼酸锂熔融,熔体倒入铂金专用模具中成型为玻璃态块样。用X射线荧光光谱法测定锰锌铁氧体样品中氧化铁、四氧化三锰及氧化锌含量。经试验求得熔融时样品和无水四硼酸锂熔剂的最佳质量比为1比17.5。采用基体参数法和理论α系数法对基体效应及谱线重叠的干扰予以校正。此法用于锰锌铁氧体材料分析,3种组分的日间和日内相对标准偏差(n=7)分别小于3.5%和4.0%;用于标准样品的分析,3种组分的测定值与标准值之间的绝对误差在-0.15%~0.02%之间。     

Ba0.98Bi0.02(Ti0.9Zr0.1)1-xCuxO3陶瓷的介电性能、弛豫行为与结晶化学特性

采用固相合成法,Bi3+作施主掺杂A位,Cu2+作受主掺杂B位,制备了Ba0.98Bi0.02(Ti0.9Zr0.1)1-xCuxO3(x=0,0.01,0.02,0.03)陶瓷样品。借助XRD、LCR等研究了该陶瓷的结构与介电性能。结果表明:当x=0.03时,陶瓷样品出现第二相。通过GULP模拟,缺陷偶极子的稳定性从低到高依次为:[2BiBa.+VBa″]、[2BiBa.+CuTi/Zr″]、[CuTi/Zr″+VO..],结合实验可知:介电弛豫程度与晶体中缺陷偶极子的存在形式相关,其中x=0.01时,晶体中以[2BiBa.+CuTi/Zr″]为主。随Cu2+掺杂量的增加,介电常数增加,介电常数与B位键价和呈反比变化、与八面体BO6的体积呈正比变化。     

白光LED用(Y_xGd_(1-x))(P,W)O_4:Eu红色荧光粉的发光性能研究

采用高温固相方法合成了(YxGd1-x)(P0.5W0.5)O4:Eu0.15粉末状发光材料,经X衍射分析结构发现,当Y3+/Gd3+≤3∶7时,样品主要由Gd2WO6相和Gd PO4相组成,当Y3+/Gd3+接近或等于1∶1时,合成的样品由Gd2WO6相、Gd PO4相和Gd0.5Y0.5PO4相三相组成,当Y3+/Gd3+≥7∶3时,合成的样品由Gd2WO6相与Gd0.5Y0.5PO4相组成。研究了样品在蓝光激发下的光谱性质,讨论了Y3+/Gd3+的掺杂对材料发光性能的影响,发现当Y3+/Gd3+=7∶3时,样品发光强度最高。在蓝光激发下,样品的发射光谱主峰在611.5 nm,对应于Eu3+的5D0→7F2电偶极跃迁。在添加助熔剂试验中发现,粉体中加入NH4NO3做助熔剂效果最好,其最佳掺入浓度为3%(质量分数)。     

稀土亚磷酸盐GdxTb2-x（HPO3）3（H2O）2（0≤x≤2）的微波合成、表征与性质研究

利用微波辅助合成法,成功地合成出一系列新颖的稀土亚磷酸盐GdxTb2-x(HPO3)3(H2O)2(0≤x≤2).X-射线粉末衍射分析结果表明,它们为同构的化合物.对Gd2(HPO3)3(H2O)2进行X-射线单晶衍射分析得出,该化合物结晶于P21/c空间群,晶胞参数为a=6.9124(6),b=12.8891(12),c=12.3692(11),β=100.1520(10)°.Gd2(HPO3)3(H2O)2是由GdO7多面体,GdO8多面体和[HPO3]假四面体通过共用氧原子相互连接而成的三维骨架.Gd2(HPO3)3(H2O)2和Tb2(HPO3)3(H2O)2的荧光光谱分别显示Gd3+和Tb3+的特征发光.Gd/Tb掺杂的样品中存在Gd3+-Tb3+的能量传递,它们的发光显示Tb3+的绿光发射(5D4→7F3-6),并且5D4→7F3跃迁的强度随着Tb3+掺杂量的增大而增强,这表明Gd2(HPO3)3(H2O)2引入不同浓度的发光中心Tb3+之后可以作为绿光发光材料.磁性研究表明,Gd2(HPO3)3(H2O)2中存在极弱的反铁磁相互作用.     

纳米荧光粉Eu_(0.12)Y_(1.88-x)Mg_xO_(3-δ)的光致发光特性

使用超声波作用下的均匀沉淀法,制备了掺杂Mg2+的纳米荧光粉Y2O3:Eu3+.考察了不同Mg2+掺杂含量下Eu0.12Y1.88-xMgxO3-δ(x=0～0.18,δ代表氧空位)的晶格常数变化,研究了掺杂含量对样品发射光谱及激发光谱的影响.结果表明,Eu0.12Y1.88-xMgxO3-δ的晶格常数在1.0604～1.062 3 nm之间,晶粒尺寸在25.9～40.7 nm之间.掺杂Mg2+后,当x=0.14时,样品Eu0.12Y1.74Mg0.14O3-δ的激发光谱中电荷迁移带(CTS)最大峰强度最高且色纯度最好.     

镨和镱掺杂Ba2 SiO4:Eu2+荧光材料的合成与发光性能

采用高温固相反应法分别合成了变价稀土镨和镱离子掺杂的绿色荧光粉[Ba(2-n-1.5x)REx]SiO4:nEu2+ (n=0.03, RE=Pr, Yb;x=0, 0.02,0.05,0.10).结果表明: 所有合成荧光粉的激发峰均为250～400 nm的宽峰, 与近紫外LED的发射光波长相匹配.发射峰位于450～550 nm之间, 是Eu2+的5d-4f跃迁的典型发射.Pr3+和Yb3+的掺入并未改变Ba2SiO4:Eu2+的相组成, 但对荧光强度的影响大, 且与掺杂元素、掺杂量和煅烧温度相关.当掺杂Pr3+和Yb3+的量为x=0.02时, 经1150 ℃煅烧所得荧光粉的发光强度分别是未掺杂时的595%和168%.证明三价稀土离子掺杂可以导致基质中的电荷缺陷而敏化Eu2+离子的发光, 而变价稀土离子的掺杂可以大大提高电荷缺陷, 导致荧光强度的进一步提高.     

Gd_xTm_(2-x)W_3O_(12)(x=0.5,1,1.5)的制备和负热膨胀性的研究

在Gd_xTm_(2-x)W_3O_(12)(x=0.5,1和1.5)系列固溶体中,当Gd的含量较低(x=0.5)时,其室温稳定相为正交相;当Gd的含量较高(x=1,1.5)时,其室温稳定相为单斜相,但在高温时转变为正交相。采用高温淬火的方法,使Gd_xTm_(2-x)W_3O_(12)(x=1,1.5)高温时的正交相保留至室温。通过TG-DSC和高温XRD研究了其吸水、相变和热膨胀性,结果表明:当x=0.5时,Gd0.5Tm1.5W_3O_(12)的吸水性较弱,而当x=1和1.5时,其吸水性增强;Gd_xTm_(2-x)W_3O_(12)(x=1,1.5)在500℃以下,其正交相是稳定的;Gd_xTm_(2-x)W_3O_(12)在200~500℃的区间均具有较大的负热膨胀性,并且其负热胀系数随着Gd的含量增加而增大。     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

Synthesis of pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles by Curtius reaction in Morita-Baylis-Hillman derivatives

Synthesis of substituted pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles from the Morita-Baylis-Hillman derivatives of acrylates via saponification followed by Curtius reaction is described.     

正丁胺对激光染料荧光谱影响的研究

用正丁胺作为碳源,采用射频辉光放电制备碳膜,选用激光染料R6G和聚乙二醇混合液作为蒸气源,采用单源热蒸发,在蒸发室与染料同时沉积得到混合膜,用拉曼光谱和红外光谱分析了碳膜的结构和键合方式,分析表明:碳膜中存在胺基团和氢原子.混合膜的荧光谱测量结果表明,认为正丁胺对染料荧光谱的影响是因为胺基和氢原子的存在.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.