Bi2Pb2V2O10的晶体结构

使用X射线单晶衍射法测定了Bi₂Pb₂V₂O₁₀的结构。该晶体属三斜晶系,空间群为C₁¹-P1,单位晶胞内化学式数Z=1,晶胞参数为:a=7.084(4)?,b=7.278(3)?,c=5.587(3)?,α=111.91(5)°,β=95.01(6)°,γ=108.86(4)°,V=245.70?³,D_x=7.35g/cm³,μ(MoK_α)=678,94cm^-1,F(000)=456。用Patterson函数分析及Forier技术测定了结构,对原子坐标、各向同性及各向异性热参数进行了最小二乘方修正,R=0.079。结构分析表明,Bi₂Pb₂V₂O₁₀的Pb原子与O原子形成八角十二面体,Bi原子与O原子形成六角多面体。两个共棱的Pb—O多面体与两个共棱的Bi—O多面体相连,并沿bc平面无限延伸。讨论了吸收的影响。最后,将Bi₂Pb₂VO₁₀的结构与Pb₂SO₅的结构进行了比较。 关键词：     

Eu2+掺杂CaSi2O2N2荧光粉发光性能

采用固相反应法合成了组成为Ca_1-xEu_xSi₂O₂N₂的Eu²⁺掺杂CaSi₂O₂N₂荧光粉.通过荧光光谱对样品的发光性能进行了研究,发现Eu²⁺掺杂CaSi₂O₂N₂荧光粉发射光谱为宽波段的单峰结构,主要包含绿光和黄光区,发射峰在556~568 nm.从发射光谱的宽带特征来看,CaSi₂O₂N₂:Eu²⁺的发射主要对应着Eu²⁺离子4f⁶5d→4f⁷跃迁.从激发光谱所覆盖的范围还可以看到,样品可以有效的被UV蓝-光激发,这意味着该类荧光粉在白光LED方面有可能得到广泛的应用.另外,样品的发光性能与激发离子的浓度有着很大关系.激发离子浓度增大时,发射光谱会发生明显红移.利用这一性质,可以通过改变Eu²⁺浓度来调节荧光粉的发光范围,从而满足不同场合的需要.同时,Eu²⁺浓度提高,样品发射光谱的强度也会随之增强,在x=0.06时发射强度达到最大值,之后继续增加Eu²⁺浓度,强度不仅没有增加反而降低,即出现浓度猝灭现象.     

BaB2O4-K2O和BaB2O4-K2B2O4赝二元系相图的研究

用X射线衍射和差热分析方法研究了BaB₂O₄-K₂O和BaB₂O₄-K₂B₂O₄赝二元系的相平衡关系。BaB₂O₄-K₂B₂O₄属共晶体系,共晶温度为850±3℃,共晶点成分为45mol％K₂O。在Ba 关键词：     

Eu2+掺杂P2O5-BaO-Na2O-K2O与Na2O-TeO2-ZnO系统玻璃的制备与光谱性质

用高温熔融法,把Eu₂O₃掺入到P₂O₅-BaO-Na₂O-K₂O与Na₂O-TeO₂-ZnO系统玻璃中。测定了玻璃的荧光光谱与激发光谱。结果表明,Eu离子在P₂O₅-BaO-Na₂O-K₂O玻璃中呈现出Eu³⁺态。然而在Na₂O-TeO₂-ZnO系统玻璃中,尽管在空气气氛下,大部分的Eu离子在玻璃中以二价的状态存在。从玻璃的结构及化学组分解释了产生Eu²⁺的原因。在磷酸盐玻璃配料中加入适量的硅粉(Si)作还原剂,能有效地把玻璃中的极大部分Eu³⁺还原成Eu²⁺,获得含Eu²⁺的优质透明磷酸盐玻璃。     

BaO-Li2O-B2O3三元系中BaB2O4-Li2B2O4和BaB2O4-Li2O截面相平衡关系的研究

本文用X射线和差热分析方法对BaO-Li₂O-B₂O₃三元系中的两个截面:BaB₂O₄-Li₂B₂O₄和BaB₂O₄-Li₂O作了研究。在BaB₂O₄-Li₂B₂O₄赝二元系中发现了一个新的化合物4BaB₂O₄·Li₂B₂O₄。化合物在930±3℃由包晶反应形成,并与Li₂B₂O₄形成共晶反应。共晶温度为797±3℃,共晶点组分为79mol％Li₂B₂O₄。在BaB₂O₄-Li₂O截面中也存在化合物4BaB₂O₄·Li₂B₂O₄,其包晶反应温度从930±3℃随Li₂O含量增加下降到908±3℃。在组分60mol％Li₂O处形成另一个新的化合物2BaB₂O₄·3Li₂O。该化合物在630±3℃也是由包晶反应形成,并与Li₂O和Li₂CO₃分别形成共晶反应,共晶温度分别为400±3℃和612±3℃。在BaB₂O₄-Li₂B₂O₄和BaB₂O₄-Li₂O体系中都没有观察到固溶体。用计算机程序分别对化合物4BaB₂O₄·Li₂B₂O₄和2BaB₂O₄·3Li₂O的X射线粉末衍射图案进行了指标化,其结果:4BaB₂O₄·Li₂B₂O₄的空间群为Pmma,a=13.033?,b=14.630?,c=4.247?,每个单胞包含两个化合式单位;2BaB₂O₄·3Li₂O的空间群为Pmmm,a=4.814?,b=9.897?,c=11.523?,每个单胞也含有两个化合式单位。 关键词：     

Ga2O3组分对Tm3+掺杂GeO2-Ga2O3-Li2O-BaO-La2O3玻璃的光谱性能影响

制备了Tm³⁺(8.0mol%)掺杂(77-x)GeO₂-xGa₂O₃-8Li₂O-10BaO-5La₂O₃(x=4,8,12,16)系列玻璃.系统地研究了Ga₂O₃从4mol%变化到16mol%时,玻璃的光谱性质与热学性质的变化规律.差热分析表明,随着Ga₂O₃含量的增加,锗酸盐玻璃的热稳定性增加.运用Judd-Ofelt(J_O)理论计算得到了Tm³⁺在不同Ga₂O₃含量的GeO₂-Ga₂O₃-Li₂O-BaO-La₂O₃玻璃中的J-O强度参数(Ω₂,Ω₄,Ω₆)及Tm³⁺各激发能级的自发跃迁概率、荧光分支比以及辐射寿命等光谱参量.在808nm激光二极管的激发下,测试并分析了Ga₂O₃对Tm³⁺荧光光谱特性的影响.随着Ga₂O₃从4mol%增加到16mol%,Tm³⁺在1.8μm处的荧光强度呈现先减弱后增强的特性.当Ga₂O₃含量大约在12mol%时,Tm³⁺在1.8μm处的荧光强度最弱,受激发射截面达到最小.还初步讨论了Ga₂O₃对玻璃结构与光谱参数的影响规律. 关键词： 3+掺杂锗酸盐玻璃')" href="#">Tm³⁺掺杂锗酸盐玻璃 光谱性能 Judd-Ofelt参数 热稳定性     

Bi2Sr2CaCu2O8单晶中的反常尖锋效应

使用牛津震动样品磁强计(VSM)研究了Bi₂Sr₂CaCu₂O₈单晶的磁滞回线.在20到40K温度之间发现了反常的尖锋效应,随样品O含量的增加,发生尖锋效应的外场也相应提高.可以认为在尖峰效应处发生了由涡漩物质的有序固态到无序固态的相变,在有少量点缺陷存在的BSCCO单晶相图上,B_sp线终止于20K温度处,在20K以下温区没有发生准格子到涡漩玻璃的相变,涡漩固相始终以准格子形式存在;可以认为尖峰效 关键词： 2Sr₂CaCu₂O₈单晶')" href="#">Bi₂Sr₂CaCu₂O₈单晶 磁滞回线 尖锋效应 相变     

GaAs表面不同运动状态H2SO4-H2O2-H2O液滴的红外辐射特性

利用红外热像实时监测系统,研究了GaAs表面不同运动状态(包括静止状态、缓慢运动状态、快速运动状态)下H₂SO₄-H₂O₂-H₂O液滴的红外辐射特性,并对实验结果和研究价值进行分析.主要的实验结论包括：静止状态时,反应生成热在液滴内部向上对流,液滴顶部为红外辐射灰度峰值,并向液滴边缘陡降,同时,生成热将沿GaAs基片向周边扩散;缓慢运动时,液滴后存在类似于“彗尾”的热残留现象,表现为温度降低、灰度峰值与液滴运动同向的“双重运动特性”,灰度峰值位移曲线与液滴实际位移存在差异,温度最高点有可能位于“慧尾”中;快速运动时,液滴未与GaAs反应便脱离基片,表现为“液膜轨迹”现象,辐射灰度从液膜边缘到液膜中心为半椭圆面的平缓过渡,并分析了轨迹中心灰度值的分布与变化特性.液滴运动热行为红外监测方法的提出,在推动液滴自身研究的同时,也将进一步推动红外技术与材料科学、化学科学等交叉学科的融合. 关键词： 红外热像 实时监测 液滴 砷化镓     

掺镱TeO2-Al2O3-Cs2O玻璃的光谱性质

采用熔融法制备了一种组分为80TeO2-10Al2O3-10Cs2O-xYb2O3(x=0～1.6)(mol%)的掺镱碲酸盐玻璃材料,测试了该玻璃材料的密度、热膨胀系数和折射率随波长的变化关系,分析了其吸收光谱、荧光光谱和荧光寿命随Yb3+浓度的变化性质.利用McCumber理论计算了该玻璃系统中Yb3+离子从2F5/2到2F7/2能级跃迁的受激发射截面.实验表明:当Yb2O3掺杂量为1mol%时,Yb3+在1 004nm波长处的发射截面为1.06×10-20 cm2,荧光有效线宽为89.6nm,荧光寿命达到最大值为0.80ms.激光性能评价结果表明,该掺镱碲酸盐玻璃是实现超短脉冲激光的候选材料之一.     

PbBi2Nb2O9的晶体结构

PbBi₂Nb₂O₉晶体属正交晶系,空间群为D_2h²³-Fmmm。晶胞参数为a=5.4806(7)?,b=5.4791(7)?,c=25.416(3)?,α=β=γ=90.0(0)°,V=763.2(2)?³。单位晶胞内化学式数z=4,D_obs=7.91g/cm³,D_x=8.26g/cm³ 关键词：     

Orbital ordering in Mott-insulators La2O3Fe2Se2 and La2O3Co2Se2

The electronic structure and magnetic properties of new layered oxyselenide compounds La₂O₃Fe₂Se₂ and La₂O₃Co₂Se₂ are studied by first-principles calculations. Our results indicate that both compounds are Mott-insulators with orbital ordering. The ground states of both compounds are the checkerboard antiferromagnetic states, which are different from the iron pnictide superconductors, although their structures are similar to those of the Fe-As-based superconductors.     

Incommensurate modulations in Ba2TiSi2O8, Sr2TiSi2O8, and Ba2TiGe2O8

Incommensurate modulations in Ba₂TiSi₂O₈, Sr₂TiSi₂O₈, and Ba₂TiGe₂O₈ are compared based on their corresponding electron diffraction patterns. The dependence of the modulations on chemical composition provides a suitable model system for the investigation of incommensurations in framework structures using high-resolution transmission electron microscopy (HRTEM). A widening of quantitative HRTEM utilising the concept of rigid units is proposed allowing for a determination of atomistic displacements responsible for the formation of incommensurately modulated structures.     

Magnetic properties of NdCo2Ge2, ErCo2Ge2 and PrFe2Ge2 compounds

Magnetometric and neutron diffraction studies of polycrystalline NdCo₂GE₂, ErCo₂Ge₂ and PrFe₂Ge₂ compounds were carried out in the temperature range between 4.2 and 300 K. All samples are antiferromagnetic with Néel temperature 26.5, ～ 4.2 and 13 K, respectively. The RECo₂Ge₂ compounds have collinear antiferromagnetic order of +?+? type. For PrFe₂Ge₂ a sinusoidal magnetic structure is observed. Magnetic moment is localized on RE atoms only and is equal to that of RE³⁺ free ion value. In ErCo₂Ge₂ the magnetic moment of Er atoms is perpendicular to the c-axis, whereas for remaining compounds it is parallel to the c-axis.     

Neutron diffraction study of magnetic ordering in PrCu2Si2, PrCu2Ge2, PrFe2Ge2 and NdFe2Ge2

A neutron diffraction study of polycrystalline PrCu₂Si₂ [1], PrCu₂Ge₂ [2], PrFe₂Ge₂ [3] and NdFe₂Ge₂ [4] intermetallics carried out at liquid helium temperature shows the presence of a collinear antiferromagnetic order below T_N = 19 ± 1 K [1], T_N = 16 ± 1 K [2], T_N = 9 ± 1 K [3] and 13 ± 1 K [4]. Magnetic moment, parallel to the c-axis is localized on RE ions only. The magnetic structure of these compounds consists of ferromagnetic layers perpendicular to the c-axis coupled antiferromagnetically with sequence +-+- for PrCu₂Si₂ and PrCu₂Ge₂ and +--+ for PrFe₂Ge₂ and NdFe₂Ge₂. The RE moments amount close to the free ion values for Fe containing compounds but are smaller in those containing Cu suggesting a fairly strong influence of crystal field.     

Structural study of the Lu2Si2O7-Sc2Si2O7 system

Different compositions in the Lu₂Si₂O₇-Sc₂Si₂O₇ system have been synthesized following the ceramic method. All XRD patterns are compatible with the thortveitite structure (β-RE₂Si₂O₇ polymorph). Unit cell parameters change linearly with composition, which indicates a complete solid solubility of Sc₂Si₂O₇ in Lu₂Si₂O₇. ²⁹Si MAS NMR spectra show a decrease of the ²⁹Si chemical shift with increasing Sc content. A correlation reported in the literature to predict ²⁹Si chemical shifts in silicates is applied here to obtain the theoretical variation in ²⁹Si chemical shift values in the system Lu₂Si₂O₇-Sc₂Si₂O₇ and the results compare favourably with the values obtained experimentally. The FWHM values of the ²⁹Si MAS NMR curves indicate a random distribution of Lu and Sc in the structure of the intermediate members. Finally, the IR study of the system confirms the solubility of Sc₂Si₂O₇ in Lu₂Si₂O₇, showing the splitting of several modes in the intermediate members and a linear shift of the frequency on going from one end-member to the other.     

Emission analysis of Dy and Pr:Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses

In this paper, we present the spectral results of Dy³⁺ and Pr³⁺ (1.0 mol%) ions doped Bi₂O₃-ZnF₂-B₂O₃-Li₂O-Na₂O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy³⁺:glass has shown two emission transitions ⁴F_7/2→⁶H_15/2 (482 nm) and ⁴F_7/2→⁶H_13/2 (576 nm) with an excitation at 390 nm wavelength and Pr³⁺:glass has shown a strong emission transition ¹D₂→³H₄ (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy³⁺ and Pr³⁺ glasses have shown bright yellow and reddish colors, respectively, from their surfaces.     

Electrical and electrochemical properties of glass-ceramic electrolytes in the systems Li2S-P2S5-P2S3 and Li2S-P2S5-P2O5

Electrical and electrochemical properties of the 70Li₂S·(30 − x)P₂S₅·xP₂S₃ and the 70Li₂S·(30 − x)P₂S₅·xP₂O₅ (mol%) glass-ceramics prepared by the mechanical milling technique were investigated. Glass-ceramics with 1 mol% P₂S₃ and 3 mol% P₂O₅ showed the highest conductivity of 5.4 × 10^− 3 S cm^− 1 and 4.6 × 10^− 3 S cm^− 1, respectively. Moreover, these glass-ceramics showed higher electrochemical stability than the 70Li₂S·30P₂S₅ (mol%) glass-ceramic. From the XRD patterns of the obtained glass-ceramics, trivalent phosphorus and oxygen were incorporated into the Li₇P₃S₁₁ crystal. We therefore presume that the Li₇P₃S₁₁ analogous crystals, which were formed by incorporating trivalent phosphorus and oxygen into the Li₇P₃S₁₁ crystal, improve the electrical and electrochemical properties of the glass-ceramics. An all-solid-state cell using the 70Li₂S·29P₂S₅·1P₂S₃ (mol%) glass-ceramic as solid electrolyte operated under the high current density of 12.7 mA cm^− 2 at the high temperature of 100 °C. The cell showed an excellent cyclability of over 700 cycles without capacity loss.     

Triply hydrogen bonded van der Waals complexes: CH2F2?CF2CH2 and CH2F2?CF2CHF

The results of molecular beam Fourier transform microwave (FTMW) investigations of the van der Waals complexes of difluoromethane with 1,1-difluoroethene (DFE) and trifluoroethene (TFE) are reported. The rotational parameters of the complexes have been interpreted in terms of a C_s geometry with the two H or F atoms of CH₂F₂ lying out of the σ_v symmetry plane of the complexes. The complexes are bound by three hydrogen bonds, of which one is the stronger C-F?H-C type, and two are the weaker C-H?F?H-C or C-F?H?F-C types for DFM-DFE or DFM-TFE, respectively. The most notable difference in the two complexes is that the out of plane atoms are two hydrogens for DFM-DFE, but are two fluorines for DFM-TFE. Additional information on the structure and hydrogen bonding has been obtained from ab initio calculations.     

EPR and magnetic properties of MgO-CaO-SiO2-P2O5-CaF2-Fe2O3 glass-ceramics

Glass-ceramics have been derived from 4.5MgO(45−x)CaO34SiO₂16P₂O₅0.5CaF₂xFe₂O₃ (x=5, 10, 15, 20 wt%) glasses by heat treatment. Room temperature electron paramagnetic resonance (EPR) spectra and temperature-dependent magnetic susceptibility (χ) of the glass-ceramics have been obtained. The EPR absorption line centered at g≈4.3 disappeared at higher concentrations of iron oxide. The intensity and line width of the EPR absorption line centered at g≈2.1 increased as the iron oxide concentration was increased. Temperature-dependent magnetization of samples with low iron oxide content revealed ferrimagnetic as well as paramagnetic contributions. Information about the structural changes involving iron ions, their valence state and the type of magnetic interactions between the Fe ions as a function of composition was obtained using EPR and χ studies.