一种新的非线性光学材料—Na3Sm2（BO3）3

本文采用固相反应法合成了一种新的硼酸盐化合物Na3Sm2(BO3)3,以Na2CO3-H3BO3为助熔剂,用悬挂铂丝法获得了3mm×2mm×0.5mm的透明单晶,X射线粉末衍射分析表明,该化合物属正交晶系,晶胞参数a=0.50585nm,b=1.10421nm,c=0.70316nm.红外光谱测量证实晶体结构中含有BO33-基团,粉末倍频效应测试表明该化合物具有非线性光学效应,粉末倍频信号强度接近KDP.     

硫属卤化物红外二阶非线性光学晶体材料的研究进展

对二阶红外非线性光学晶体材料的研究是当前激光及非线性光学领域研究的重点、难点和热点之一.由于满足应用需求的材料比较缺乏,很有必要从源头上探索潜在的新型红外非线性光学晶体材料.硫属化合物和卤化物是红外非线性光学晶体新材料探索的主要体系,前者一般表现出大的倍频效应和宽的红外窗口,后者则多具有大的光学带隙,即高的抗激光损伤阈值.结合两者的优势,有望获得综合非线性光学性能优异的新材料.在此背景下,本文综述了近期硫属卤化物红外非线性光学晶体材料的研究现状,包括含S8单元的卤化物、包盐硫属卤化物和钡基硫属卤化物.这些硫属卤化物的粉末样品大都表现出优异的非线性光学性能.最后,本文讨论了该方向未来研究的机会和重点.     

层状化合物La0.26Bi0.74OOH光学性能的研究

构建非中心对称结构及研究材料的构效关系对于探索新型非线性光学晶体具有重要意义.La0.26Bi0.74OOH是一种具有PbFC1型结构的层状化合物,结晶在非中心对称的正交晶系空间群Pmm2,其主体结构由[La0.26Bi0.74O2]-层和H+阳离子组成.本文采用水热法合成了La0.26Bi0.74OOH晶体,并首次测试了该化合物的非线性光学性能.粉末倍频实验显示La0.26Bi0.74 OOH的倍频响应为KH2PO4的0.6倍.紫外-可见-近红外漫反射光谱表明该化合物的截止波长为335 nm.此外,第一性原理计算显示该化合物为直接带隙半导体,其内部的Bi-O和La-O基团对La0.26Bi0.74 OOH的非线性光学性能起主要作用.     

福建物构所碘酸盐二阶非线性光学晶体的设计与合成获进展

二阶非线性光学材料广泛应用于激光及光通讯领域,而金属碘酸盐晶体因具有较强的倍频效应、较宽的透过波段、较高的热稳定性和光学损伤阈值,在二阶非线性光学晶体材料领域占有非常重要的地位。设计二阶非线性光学材料的关键是如何诱导无心结构的形成及如何增加化合物的极化率。中科院福建物质结构研究所结构化学国家重点实验室毛江高研究员领导     

CaB_8O_(11)(OH)_4晶体的水热生长、表征与非线性光学效应研究

本文研究了含水硼酸盐非线性光学晶体CaB_8O_(11)(OH)_4的生长方法及其基本性质.以H_3BO_3和CaO为原料,采用水热法在280～350 ℃生长了二水八硼酸钙(CaB_8O_(11)(OH)_4),并对其进行了XRD、TG-DSC、FT-IR、SHG、透过光谱测试;从结构上分析了其产生较大非线性光学效应的原因,其粉末倍频效应相当于同等粒度KDP的1～2倍,透过率在350～750 nm达到80;.     

非线性光学原子响应理论及最新进展

二阶非线性光学晶体材料通过倍频效应转换激光频率，并且调制激光的振幅和位相，在现代制造、激光医疗、光通信，以及基础科学研究领域都有重要用途。本文简要介绍了近年来在部分响应泛函方法的基础上发展起来的非线性光学原子响应理论。该理论使人们能够在第一性原理计算的基础上定量评估单个组成原子及轨道对非线性光学晶体材料倍频效应的贡献。在此基础上，本团队还发展了一套普适的以物理性能为标准的基团划分方案，为确定倍频效应的功能基元提供了概念基础。本工作对该理论方法的最新进展及其带来的一些新观点，如导带的作用、原子负贡献、静态偶极矩的作用、非共价基团的压倒性贡献、线性规律等进行解释和阐述，并给出了在新材料设计中的应用实例。     

Ba7AgGa5S15:一种新型混合金属硫化物的非线性光学性能研究

采用高温熔融-自发结晶法成功获得一种新型混合金属硫化物Ba7AgGa5S15.该化合物结晶于非中心对称的P31c空间群(No.159),晶胞参数为a=0.964 53(10) nm,c=1.805 9(4) nm,Z=2.其结构是由[Ga4 S10] T2超四面体与[AgS4]四面体共顶点连结形成的含有18元环孔道的三维网状框架,孤立的[Ga(2)S4]四面体填充在孔道中,Ba2+填充在该三维框架结构的空隙当中.第一性原理计算研究了该化合物的电子结构、态密度、双折射率、二阶非线性光学系数,以及倍频密度.结果 表明,该化合物具有大的光学带隙(3.76 eV),其带隙主要由S3p,Ba5d和Ga4s轨道决定;其d33方向上的倍频系数约为AgGaS2的0.4倍,主要倍频贡献来源于[AgS4]和[GaS4]四面体.该研究表明在Ag-Ga-S体系中引入Ba2+,形成的Ba7 AgGa5S15表现出比AgGaS2更宽的带隙,有利于产生高的激光损伤阈值(LDT).     

A7MIIRE2(B5O10)3系列紫外非线性光学晶体的研究进展

稀土硼酸盐非线性光学(NLO)材料由于其在激光技术领域的重要应用而备受关注,这主要是因为三价稀土离子如Y³⁺、Sc³⁺、Lu³⁺等可以有效抑制d-d和f-f电子跃迁从而扩宽化合物的透过范围,同时稀土原子与氧原子结合成畸变的多面体可增强材料的非线性光学效应。A₇M^IIRE₂(B₅O₁₀)₃系列(RE为稀土金属,A为碱金属、M为二价金属)化合物是稀土硼酸盐中一类重要的材料,其A、M以及RE位点具备灵活的占据方式,近年来得到了广泛关注。通过化学元素取代法,研究者们对该类化合物的种类进行拓展,目前已经合成出数十种属于该体系的化合物。这些化合物的截止边大多处在紫外甚至是波长小于200 nm的深紫外波段,非线性光学效应为0.4~2.1倍KDP,在紫外以及深紫外波段非线性光学领域中展现出了应用潜力。本文对其研究现状进行了总结,分析了其微观结构与光学性能之间的关系,并指出不同位点组分对材料非线性光学性能的影响,以期对此类化合物今后的发展提供参考。     

具有倍频效应的硼酸盐Pb2 [B5O9]Br化合物的合成、晶体生长及其性质研究

利用高温固相反应法合成出Pb2 [B5O9]Br硼酸盐粉末.采用PbO-NaF做复合助熔剂,利用顶部籽晶法获得了3 mm ×3 mm ×1.5 mm的透明单晶,X射线粉末衍射数据显示,该晶体属正交晶系,Pnn2空间群,晶胞参数为a=1.1524(1) nm, b=1.1431(1) nm, c=0.65399(3) nm. 红外光谱测量证实晶体结构中含有BO3-3和BO5-4基团.反射光谱表明Pb2 [B5O9]Br的紫外吸收边在250 nm左右.Pb2 [B5O9]Br粉末倍频效应(SHG)测试表明该化合物具有非线性光学效应,信号强度约等同于β-BaB2O4.     

一种全新的非线性光学材料-金属有机配合物硫氰酸汞镉合乙二醇一甲醚(GCMTC)

本文报道了在水和乙二醇-甲醚体积比为1∶1的混合液中,用低温溶液法生长出金属有机配合物型非线性光学晶体硫氰酸汞镉合乙二醇一甲醚(GCMTC)晶体.该晶体具有较强的粉末倍频效应,用半定量的方法测定了其SHG强度约为尿素的10倍.透光范围为366～2770nm,比氰酸汞镉(CMTC)紫移了14nm.具有较稳定的物理化学性能.是一种具有潜在的应用前景的非线性光学晶体.     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

A SAXS study of kinetics of aggregation of silica sols

SAXS in situ experiments on the evolution of TMOS solutions during hydrolysis and polycondensation lead to power laws with scaling exponents ≈ 2. It is suggested that this could be the result of the polydispersity of the samples and that only an apparent fractal dimension can be obtained in this way. Kinetic studies tend to indicate that agglomeration in the sol is the result of a diffusion-controlled process.     

Study of the possibility of interactive control of the surface profile of X-ray optical elements

We investigate the possibility of controlling the curvature parameters of parabolic mirrors that are modular elements of two types consisting of a base and thin inserts placed at the opposite side of the work surface. In the first type of modular elements, bending is controlled by the difference in the coefficients of the thermal expansion of the base and inserts. In the second type of elements, the profile is changed by the piezoelectric straining of the inserts under an electric field. A correlation is established between the parameters of modular elements and their surface curvature profile.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Mechanism of thermal expansion of structural modifications of zinc pyrovanadate

Crystal chemical characteristics of the α and β modifications of Zn₂V₂O₇ are calculated based on in situ high-temperature X-ray measurements. The expansion of the structure is found to be strongly anisotropic up to the negative volumetric thermal expansion of the α-Zn₂V₂O₇ unit cell in the temperature range of 300–600°С, α _V =–17.94 × 10^–6 1/K. The transformations of the “hard” and “soft” sublattices with an increase temperature and at the phase transition are considered in detail. It is shown that the negative volumetric thermal expansion of α-Zn₂V₂O₇ is due to the degeneracy of the zigzag-like shape of zinc–oxygen columns at constant distances between their vertices.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

Investigation of the Mechanism of Influence of Stress Corrosion on the Development of Macroplastic Instabilities of Aluminum–Magnesium Alloy

Crystallography Reports - Macroscopic jumps of plastic deformation (few percent in amplitude) on creep curves of aluminum–magnesium alloy, caused by a local effect of concentrated solution of...