Cluster self-organization of germanate systems: Suprapolyhedral nanocluster precursors and self-assembly of the Li8GeO6, Li4GeO4, and Li6Ge2O7 crystal structures

Nanoparticles (An clusters of atoms or Kn polyhedra, where n is the number of atoms or polyhedra) corresponding to the initial stage of evolution of a chemical system have been modeled. Four series of cluster isomers K3 and K4 formed by different T tetrahedra are selected. The clusters are topologically represented by two-colored graphs. A change in their symmetry, depending on the composition and mutual arrangement of L and G tetrahedra in the chemical isomers, is established. Our model is used to search for cluster precursors in Li germanates Li₈GeO₆ (P6₃ mc, hP30), Li₄GeO₄(Cmcm, mC36), and Li₆Ge₂O₇ (P2₁/n, mP60). Three types of nanocluster precursors are identified: (A) polycyclic, with a tetrahedral arrangement of 3L + GG polyhedra (L and G are LiO₄ and GeO₄, respectively) in the Li₈GeO₆ structure; (B) monocyclic, with a sequence of L-G-L-G polyhedra in the Li₄GeO₄ structure; and (C) polycyclic, in the form of two bound monocyclic clusters with a sequence of L-L-G-G polyhedra in the Li₆Ge₂O₇ structure. Lithium atoms are found to play three different roles during structural self-assembly: they participate in the formation of nanocluster precursors, they serve as templates stabilizing the local structure of nanocluster precursors, and they act like spacers filling the voids between nanocluster precursors.     

Cluster self-organization of silicate and germanate systems: Invariant suprapolyhedral cluster precursors and self-assembly of the crystal structures of Li,TR silicates (germanates)

The initial stages of formation of suprapolyhedral clusters (containing polyhedra of different types) in an evolving chemical system are considered. The suprapolyhedral clusters of the chain and cyclic types are used for modeling two-dimensional periodic structures. The developed model is used to search for cluster precursors in the structures of Li,TR silicates (germanates) of the known structure types. The complete threedimensional reconstruction of the self-assembly of Li,TR silicates (germanates) is performed using computer methods (with the TOPOS program package) according to the following scheme: cluster precursor → primary chain → microlayer → microframework (supraprecursor) → … framework. Two types of invariant cyclic cluster precursors composed of the TR polyhedra linked by tetrahedra and the TR polyhedra joined by diorthotetrahedra are identified in five and two structures, respectively. It is revealed that the lithium atoms are located at the centers of all clusters. New types of two-dimensional nets with a hierarchical structure formed as a result of the packing of cyclic four-, six-, and eight-node clusters are described.     

新型压电晶体Sr3 Ga2 Ge4 O14的性能表征

采用坩埚下降法以及坩埚密封技术,成功生长了直径50mm的新型压电晶体Sr3Ga2Ge4O14.测试了晶体的晶格常数、热膨胀系数、密度、硬度和透过光谱等基本物理性能.测试结果表明:晶体热膨胀系数明显小于石英晶体,而且α11和α33相对比较接近,有利于该晶体用作声表面波用基片材料.在250～2500nm波段范围内,其透过率均大于80;,优于相同结构的La3Ga5SiO14晶体,是一种潜在的激光基质晶体材料.     

Simulation of self-organization processes in crystal-forming systems: Supramolecular cyclic R6 cluster precursors and self-assembly of TeO2-TEL (Tellurite) and TeO2-PAR (Paratellurite) structures

The supramolecular chemistry of oxides of sp elements (SO₂, SeO₂, and TeO₂) is considered. The self-assembly of TeO₂-TEL (Tellurite) and TeO₂-PAR (Paratellurite) crystal structures is simulated. Methods of combinatorial and topological analysis (TOPOS program package) are applied which are based on constructing a basis 3D network of the structure in the form of a graph, the sites of which correspond to the positions of centroids of TeO₂ molecules and the edges characterize bonds between them. The topological type of the basis 2D network in the TeO₂-TEL structure corresponds to graphite (C-GRA), while in the TeO₂-PAR structure the basis network corresponds to the 3D diamond network (C-DIA). A nanocluster precursor of cyclic type (R6) composed of six covalently bound TeO₂ molecules (chair conformation) is established for both structures. The desymmetrization of the cyclic structure of the R6 cluster in TeO₂-PAR is related to the formation of Te-Te bonds with lengths of 3.824 and 4.062 Å. The symmetry and topology code of the processes of self-assembly of 3D structures from nanocluster precursors is completely reconstructed into the form “primary chain → microlayer → microframework.” In both structures R6 clusters form 2D packings with a coordination number of 6. The cluster self-assembly model explains the specific features of the morphogenesis of TeO₂-TEL and TeO₂-PAR (phases with low and high crystallization temperatures, respectively): platelike shape, perfect cleavage in the (110) plane, and preferred growth in the primar-chain direction [100] in the former case and growth in the direction of the primary [001] axis with the preferred formation of tetragonal prism faces (110) in the latter case.     

Absorption spectra and circular dichroism of Sr3Ga2Ge2O14: Cr and Ca3Ga2Ge2O14: Cr crystals

Absorption spectra and circular dichroism spectra of chromium-doped Sr-gallogermanate crystals of different colors and doped and pure Ca-gallogermanate crystals have been studied. It is shown that chromium ions enter the Sr-gallogermanate crystals in two valence states—Cr³⁺ and Cr⁴⁺. It is assumed that Cr⁴⁺ ions replace Ge⁴⁺ in the tetrahedra.     

Optics and spectroscopy of a Pb3Ga2Ge4O14:Nd3+ crystal, a new representative of the langasite family

Absorption and luminescent properties of a Pb₃Ga₂Ge₄O₁₄:Nd³⁺ crystal have been studied. The refractive indices are measured in the range from 0.405 to 1.064 μm, and the molecular refraction is calculated.     

Cluster self-organization of crystal-forming systems: Suprapolyhedral cluster precursors and self-assembly of the icosahedral structure of ZrZn<Subscript>22</Subscript>(<Emphasis Type="Italic">c</Emphasis>F184)

The mechanism of self-assembly of symmetrically and topologically different chains and microlayers (in the form of planar nets) from cyclic three-node clusters A ₃ is considered in the model system. The obtained nets correspond to the uninodal Shubnikov nets N 3 12 12 and N 3 6 3 6 and the new binodal net N1 3 6 3 6 + N2 3 3 6 6 (1: 2). A complete three-dimensional reconstruction of the self-assembly of the icosahedral structure of the ZrZn₂₂ compound (cF184) is performed using computer methods (with the TOPOS program package) according to the following scheme: cluster precursor → primary chain → microlayer → microframework (supraprecursor) → ... → framework. It is revealed that the suprapolyhedral cluster precursor (nanocluster ～12 Å in size) of the AB ₂ composition is formed by three polyhedra shared by vertices in a cyclic manner: the A-ZrZn₁₆ polyhedron (sixteen-vertex polyhedron with the point symmetry \(\bar 4\)3m) and two B-ZrZn₁₂ polyhedra (icosahedra with the point symmetry \(\bar 3\) m). The AB ₂ cluster precursor in the structure retains the symmetry m. It is established that the structural mechanism of self-assembly of the two-dimensional layer in the ZrZn₂₂ structure is described by the binodal net N1 3 6 3 6 + N2 3 3 6 6 (1: 2) constructed in the modeling.     

Nd3+:Sr3Ga2Ge4O14晶体的生长及吸收光谱

采用坩埚下降法生长了Nd3+掺杂浓度分别为15;、8;和2.5;原子分数的Sr3Ga2Ge4O14晶体,所得晶体最大尺寸为φ26mm×15mm.Nd3+掺杂Sr3Ga2Ge4O14晶体的特征吸收峰波长为806nm,与Nd3+离子在YAG中的特征吸收峰相比,向短波方向发生了微小的偏离.这是Sr3Ga2Ge4O14晶格中Ga3+和Ge4+的统计分布所致.Nd3+:SGG晶体的这些特性将有助于泵浦效率的提高和泵浦阈值的降低,因此Nd3+:SGG晶体有望成为一种新型的LD泵浦固体激光材料.     

Electro‐optic,Piezoelectric and Dielectric Properties of Langasite (La3Ga5SiO14), Langanite (La3Ga5.5Nb0.5O14) and Langataite (La3Ga5.5Ta0.5O14)

Refractive indices were determined of single crystals of La₃Ga₅SiO₁₄ (langasite, LGS), La₃Ga_5.5Nb_0.5O₁₄ (langanite, LGN) and La₃Ga_5.5Ta_0.5O₁₄ (langataite, LGT) in the wavelength region between 0.36 μm and 2.33 μm. While phase‐matched optical second harmonic generation is not possible in LGS it occurs in the isotypic compounds LGN and LGT. Temperature‐dependent examination of the dielectric properties of LGS up to 600 °C showed anomalous behaviour. For all three substances the electro‐optic [r^σ_ijk] (“unclamped”) and the piezoelectric [d_ijk ] tensors were determined at room temperature. In addition, the temperature‐dependence of these properties was studied for LGS between –200 °C and +200 °C by a Jamin interferometer in combination with a modified Sénarmont compensator.     

Spectroscopy studies of pure and chromium-doped calcium gallogermanate crystals, Ca3Ga2Ge4O14

Absorption spectra, the spectra of circular dichroism and magnetic circular dichroism of pure and Cr-doped Ca₃Ga₂Ge₄O₁₄ crystals have been studied. The crystal-field parameters and the transition frequencies of Cr³⁺ ions are calculated. The location of Cr³⁺ and Cr⁴⁺ ions in oxygen octahedra and tetrahedra is confirmed. The spectra of circular dichroism show the maxima due to Cr³⁺ ions and growth-induced defects.     

Growth of Nd:Sr3Ga2Ge4O14 crystals by a modified Bridgman method

Bridgman growth of Nd:SGG (Sr₃Ga₂Ge₄O₁₄) crystals has been investigated for the first time. Pt crucible of ∅︁25mm×250mm with a seed well of ∅︁10mm×80 mm is used, and seed is SGG crystal of ∅︁10mm×50mm grown by Bridgman method in advance. The growth parameters are optimized as the furnace temperature is set to 1450∼1500°C, temperature gradient in the crystal‐melt interface is less than 25 K/cm and growth rate is less than 0.5mm/h. The Nd:SGG crystals with 25mm in diameter and 60mm in length are grown successfully from 1.5 to 8at% Nd³⁺ doped stoichiometric Sr₃Ga₂Ge₄O₁₄ melt. The distribution coefficient and concentration of Nd³⁺ in Nd:SGG crystals are obviously higher than those of Nd:YAG crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal and molecular structure of diaquabis(thiocyanato-N)bis(5-methyl-[1,2,4]triazolo[1,5-a]pyridine-N3)cobalt(II), [Co(NCS)2(C6H6N4)2(H2O)2]

The X-ray crystal structure of the title compound, [Co(NCS)₂(C₆H₆N₄)₂(H₂O)₂], has been determined. The crystals are monoclinic, space groupC2/c, with cell dimensionsa=15.6901(5),b=7.9248(10),c=16.1278(12) Å,=94.4(8)°V _c=1999.44 ų,M _r=479.18,Z=4,D _x=1.5918 Mg m³,Cu K radiation (graphite crystal monochromator, =1.54051 Å), (CuK)=39.08 cm^–1,F(000)=980.00 andT=290 K. Final conventionalR-factor=0.051, andR _w=0.053 for 1430 observed reflections and 141 variables. The structure was solved using the programsPatsys andDirdif. The Co atom is octahedrally coordinated (CoN₂O₂N₂ chromophore), with only the 5-methyl-[1,2,4]-triazolo[1,5-a]pyrimidine (5mtp) ligands in thetrans positions. The triazolo pyrimidine rings are planar and coordinated through their N(3) atoms. The H₂O ligands are also H-bond donors to N(4) (intramolecularly) and to the S atoms of the NSC anions (intermolecularly).     

新型三维配位聚合物[La(C5H4NCOO)3(H2O)2]n的水热合成和晶体结构

在水热反应条件下,设计合成了一种新型三维配位聚合物[La(C5H4NCOO)3(H2O)2]n的单晶体,对其进行了元素分析、热重分析、红外光谱表征、X射线单晶衍射测定.该配位聚合物属单斜晶系,P2(1)/c空间群,晶胞参数为a=0.9747(4)nm,b=1.9904(7)nm,c=1.1613(4)nm,α=90°,β=111.761(6)°,γ=90°,V=2.0925(13)nm3,Z=4,dc=1.718g/cm3,μ=2.090mm-1,F(000)＝1064,R1=0.0374, wR2=0.0683.X射线衍射结果显示La3+离子之间以4-氰基吡啶的羧基为桥形成一维链状结构,通过4-氰基吡啶的吡啶基与配位的水分子之间的氢键形成三维的网络结构.热重分析表明该配位聚合物在230℃下稳定.     

Crystal Growth,Thermal and Linear Optical Properties of the Non‐Centrosymmetric Hydrated Tetraborates Na2[B4O5(OH)4] . 3H2O (Tincalconite) and K2[B4O5(OH)4] . 2H2O

Large single crystals of the non‐centrosymmetric hydrated tetraborates Na₂[B₄O₅(OH)₄] . 3H₂O (Tincalconite) (point group 32) and K₂[B₄O₅(OH)₄] . 2H₂O(point group 222) were grown from aqueous solutions and the linear optical properties (refractive indices between 365 nm and 1530 nm and unpolarized absorption spectra) as a basis for nonlinear optical investigations were determined. The uniaxial positive sodium salt is not phase matchable; in the orthorhombic potassium compound type I phase matching is possible in the near infrared region. Thermal investigations indicate a phase transition at ≈285 K for Na₂[B₄O₅(OH)₄] . 3H₂O.     

Studies on the growth and defects of La3Ga5SiO14 (LGS) crystals

New and high quality piezoelectric crystals La₃Ga₅SiO₁₄ (LGS) grown by the Czochralski method in a Platinum or Iridium crucible are reported in this paper. The growth defects in the LGS crystals were investigated by Transmission electron microscopy (TEM). It was found that cracks, inclusions, grain boundary and thermal stress in the LGS crystals. Their formation mechanisms and the method of eliminating these defects are discussed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sr3Ga2Ge4O14∶Eu3+,Bi3+粉体的光谱特性及能量传递研究

研究了Eu3和Bi3+共掺锗酸镓锶粉体的合成、结构及其光谱性能.结果表明,合成粉体为纯三方相结构,掺杂没有引起新相生成,表明部分无序结构为掺杂离子提供更大的包容空间,从而实现激活离子的高浓度掺杂.高温固相合成的粉体在蓝绿光区域(570～700 nm)具有丰富的发射峰,其主峰位于618 nm,是Eu3处于非对称中心格位产生的特征峰,由此说明Eu3+取代Sr2+的位置;当Eu3+的掺杂浓度为15mol;时,在618 nm处发光强度达到最大.掺Bi3+明显增强了Eu3+的发光,是一种有效的敏化剂;当Bi3+掺杂量为5mol;时,Eu3+的相对发光强度同比提高了51.3;.     

Synthesis and crystal structure of [Nd(H2O)2]2(C2O4)3

Some crystals of [Nd(H₂O)₂]₂(C₂O₄)₃ were synthesized hydrothermally by heating at 200°C for 8 days an aqueous suspension of neodymium oxalate decahydrate in presence of terephthallic acid and guanidinium carbonate. They crystallize in the orthorhombic system, space group P2₁2₁2₁, with a = 8.6702(7) Å, b = 9.558(2) Å, and c = 17.009(2) Å. The structure of this complex is built up by two independent neodymium atoms, three bischelating oxalate ligands, and four water molecules forming a rectangle building unit of 6-membered ring, [Ln(H₂O)₂(C₂O₄)]₆. The packing of these units leads to a layer parallel to the plane (001). However, the neodymium atoms of two neighbor layers share an edge of oxalato oxygen atoms thus giving a double-layer. The three dimensionality between these double-layers is insured by hydrogen bonds of water molecules which are bound to the neodymium atoms. There is no zeolitic water molecule. The two neodymium atoms are nine-coordinated. In both cases, the coordination polyhedron can be described as a distorted tricapped trigonal prism.     

Crystal structure investigation of [Mn(3-CH3C5H4N)2(N3)2(H2O)2]

The crystal structure of the title compound has been determined by single crystal X-ray diffraction methods. [Mn(3-CH₃C₅H₄N)₂(N₃)₂(H₂O)₂] crystallizes in the space group P 1 with a = 7.444(2) Å, b = 7.691(2) Å, c = 8.926(3) Å, α = 99.82(3)°, β = 108.80(2)°, γ = 114.99(2)° and Z = 1. Least squares refinement gave a R value of R_w = 0.046 for 1414 observed reflections. The manganese atom in the title complex is octahedrally coordinated by two oxygen atoms of the water molecules and four nitrogen atoms; two N-atoms are the end atoms of azide groups and the other two nitrogen atoms belong to the 3-methylpyridine molecules. The polyhedra are linked via hydrogen bonds between the water molecules and the azide groups.