Topology and symmetry analysis of the Sr2VO(VO4)2 family exhibiting magnetic properties and prediction of structures with different orderings of vanadyl bonds

A topology and symmetry analysis of structures of the Sr-vanadyl-vanadate family Sr₂VO(VO₄)₂ with a quasi-one-dimensional spin system, which is responsible for magnetic properties, is performed. Based on the known structure with space group I2/a, structures belonging to its subgroups with ordered vanadyl bonds in octahedra containing the magnetic V⁺⁴ ion are derived. Structures with a polar orientation of vanadyl bonds in chains of octahedra correspond to space groups P2₁/c, P2/c, and Pc, and structures with a nonpolar orientation of vanadyl bonds correspond to space groups P2/a, P2, and P2/n. Variants of disordering of vanadyl bonds over two directions, namely, along the b and a axes, are considered for all structures. The predicted structures can be used for the diagnostics of phases obtained in this family and as initial information necessary for studies of magnetic properties of crystals.     

Symmetry and topological analysis of the OD nenadkevichite-labuntsovite-zorite family

The symmetry and topology of the structures of nenadkevichite, labuntsovite, and zorite minerals are analyzed within the Dornberger-Schiff OD theory. The common “layers,” their symmetry, and the symmetry variants of their stacking determining their diversity and close structural characteristics are considered, which allowed us to relate these minerals to one family. According to the fundamental theorem of the OD theory, the number Z of possible combinations of aperiodic blocks inserted between the layers in zorite equals two simultaneously along two axes of the structure, which explains the structural disorder. Some hypothetical structures are also considered.     

Prediction of the structures in the family of La(IO<Subscript>3</Subscript>)<Subscript>3</Subscript> iodates based on topology and symmetry analysis within the OD theory

Topology and symmetry analysis of the structures of the La (IO₃)₃ family is performed within the Dornberger-Schiff OD theory. Two-dimensional periodic blocks (“layers”) of two types are found in the monoclinic La (IO₃)₃ iodate; the local symmetry of one of these blocks is higher than the symmetry of the structure as a whole. This feature defines the possibility of varying the relative position of the pairs of “layers” and the existence of structures other than the structure studied. Three hypothetical polytypes with the maximum degree of ordering that belong to different crystal systems (triclinic, monoclinic, and trigonal) and disordered structures are predicted by the OD theory. This example demonstrates the possibilities of the OD theory for predicting structures.     

Structure and properties of crystals in the potassium titanyl phosphate family: A review

This paper presents an overview of the data available in the literature and the results obtained by the authors in the study of the influence of the chemical composition on the structure and properties of crystals in the potassium titanyl phosphate family. The structure and properties of phosphates in which univalent cations are substituted for potassium cations, as well as of crystals with isovalent or heterovalent substitutions for tetravalent titanium cations in the structure of potassium titanyl phosphate crystals, are considered.     

Topology and symmetry analysis of rare earth borocarbides structural family,analogy to hexaferrites and relation to properties

The topology and symmetry analysis was applied to a series of rare earth borocarbide compounds, which have been gaining increasing interest due to their magnetic and thermoelectric properties. Using principles of OD theory, the crystal structures were deconvoluted into L(1) (B₁₂ icosahedra and C‐B‐C chain) layers and L(2) (rare earth and B₆ octahedral) layers. The arrangement of B₁₂ icosahedra in the L(1) layer is equal to close packed spheres, however, symmetry of the B₁₂ block lowers symmetry of the resulting layer from P 6/mmm to P 3m1. Both layers, L(1) and L(2) possess symmetry P 3m1 and the conjugation of L(1) with L(2) layers occurs in accordance with the symmetry elements. No disorder may appear here because of equal symmetry of single layers and layer pairs and it is not a classical OD family. Only the increasing of the amount of one type of layers, namely L(1), provides the structural variations. Close analogy to the hexagonal ferrites family has been found. Topology and symmetry analysis reveals principles in the building up of the structural family, gives an insight into the particular order‐disorder formation mechanism/criteria of these homologous borocarbide compounds and as the result relation to the properties (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

3D printed models of small and large molecules,structures and morphologies of crystals,as well as their anisotropic physical properties

Three‐dimensional (3D) physical models of atomic structures of crystals, their anisotropic properties and morphologies as well as models of small and large molecules were printed with support from 3D Systems Corporation. Structural information in Crystallographic Information Framework (CIF) files from the Crystallography Open Database and the Protein Data Bank was utilized. Computer programs were either newly developed (Cif2VRML) or enhanced by 3D print file export functions (WinXMorph and WinTensor) in order to design most of these models. Current 3D printing technologies are briefly reviewed. The literature on the impact on students’ comprehension and retention of structural information with access to such models is assessed. Our taking of a historical perspective in this paper illustrates that the usage of models has for more than 200 years been an integral component of crystallography.     

Molecular structures of chalcone podands: A prognosis of photoinduced transformations in the crystals

A series of chalcone podands with the propenone group in the ortho position of the bridging aryl substituent with respect to the oxyethylene fragment is synthesized. The influence of the preorganization of the chalcone podand molecules in crystals on their ability to participate in topochemical reactions is investigated. From analyzing the X-ray structural data, the highest probability of the solid-state photochemical [2 + 2]cycloaddition is predicted for podands with phenyl substituents and the oxyethylene fragment containing two or three oxygen atoms. The X-ray structural data for the chalcone podand C₃₂H₂₆O₄ (3a) are as follows: a = 7.904(9) Å, b = 14.92(2) Å, c = 21.30(3) Å, β = 91.7(1)°, monoclinic system, space group P2₁/c, Z = 4, V = 2510(5) ų, ρ = 1.26 g/cm³, and R = 0.046; C₃₄H₃₀O₅ (3b): a = 15.738(9) Å, b = 11.889(2) Å, c = 15.0830(15) Å, β = 105.47(14)°, monoclinic system, space group C2/c, Z = 4, V = 2720.0(9) ų, ρ = 1.266 g/cm³, and R = 0.0418; C₃₂H₂₄N₂O₈ (4a): a = 17.9416(18) Å, b = 10.9703(8) Å, c = 41.699(2) Å, β = 105.970(11)°, monoclinic system, space group P2₁/c, Z = 4, V = 2781.4(5) ų, ρ = 1.348 g/cm³, and R = 0.0426; C₃₆H₃₂N₂O₁₀ (4c): a = 7.6286(5)Å, b = 17.9398(10) Å, c = 11.5890(3)Å, β = 95.287(4)°, monoclinic system, space group P2₁/n, Z = 2, V = 1579.27(14) ų, ρ = 1.372 g/cm³, and R = 0.0377; and C₂₈H₂₂O₆ (5a): a = 15.6032(10) Å, b = 8.1131(5) Å, c = 17.7334(11) Å, β = 91.381(5)°, monoclinic system, space group C2/c, Z = 4, V = 2244.2(2) ų, ρ = 1.345 g/cm³, and R = 0.0309.     

Growth, structure, and properties of KTiOPO4 crystals doped with iron

A series of iron-doped KTiOPO₄ (KTP: Fe) single crystals in which iron substitutes for 0.1–0.3% titanium was grown. The structure of the KTP: Fe crystals was determined, and their dielectric and conducting properties were studied. An X-ray diffraction analysis failed to reveal such asmall amount of Fe⁺³ ions in titanium octahedral positions of the structure. It was found that an increase in the iron concentration results in a lowering of the symmetry of Ti(1)O₆ and Ti(2)O₆ octahedra. The splitting of the dielectric anomaly due to the ferroelectric phase transition was explained by the mechanism of incorporation of an impurity into different growth pyramids of the crystals. It was established that the aging of the KTP: Fe crystals leads to changes in the permittivity and electrical conductivity during long storage.     

X-ray diffraction from ideal mosaic crystals in external fields of certain types, part III: Changes in space symmetry and symmetry of diffraction pattern

The change in the space symmetry and the symmetry of the corresponding diffraction pattern occurring under the effect of uniform electric and magnetic fields applied to a crystal have been analyzed. The tables of point symmetry groups for various directions of applied magnetic fields are constructed. It is shown that in the absence of an external field, the diffraction patterns are described by nine possible point groups; in an electric field, they are described by eleven point groups; and in a magnetic field, by only five point groups. The theoretically calculated diffraction parameters are compared with the corresponding experimental values.     

Self-assembly of a Cd(II) coordination polymer with the 3,5L2 topology: Synthesis,structure, and properties

A new cadmium(II) coordination polymer, [Cd(ntdc)(dps)·H₂O]_n, was synthesized using 3-nitro-thiophene-2,5-dicarboxylic acid (H₂ntdc) and 4,4´-dipyridylsulfide (dps) as organic linkers. In the complex, adjacent Cd²⁺ ions are linked by ntdc^2? anions adopting a new coordination mode to form a one-dimensional (1D) [Cd(ntdc)]_n chain. Then dps ligands further expand the 1D chain into a corrugated two-dimensional (2D) layer network by linking neighboring Cd²⁺ ions. Topologically, the 2D network can be rationalized to a 3,5-connected 3,5L2 topology. Moreover, solid state properties such as thermogravimetric analysis and photoluminescent property were also investigated.     

Doping of KDP single crystals with cerium: Growth and optical properties

The features of doping of KDP crystals with cerium ions and organocerium complexes with alizarin complexon and arsenazo III have been investigated. It is established that “direct” doping by introducing cerium salts into the initial solution cannot be implemented. The effect of organometallic complexes of cerium on the crystal growth has been studied. Organocerium complexes predominantly enter the prismatic or pyramidal growth sectors. It is shown that the complex arsenazo III + Ce blocks the growth of the prismatic sector. Cerium-doped KDP crystals exhibit a photoluminescence band peaking at the wavelength λ_max= 350 nm.     

Dielectric,piezoelectric, elastic properties and internal friction of TGSe crystals with large unipolarity

In this work we have studied influence of temperature and external electric field on dielectric, elastic, piezoelectric properties and internal friction of D, L-α-alanine doped triglycine selenate crystals. Experimental result analysis allows to conclude that ferroelectric materials with stable physical properties may be created on doping crystals foundation.     

Synthesis,properties, and structure of potassium titanyl phosphate single crystals doped with hafnium

Single crystals of potassium titanyl phosphate doped with hafnium are grown by spontaneous flux crystallization. Their physical properties are studied, and the structure of three KTi_{1 − x} Hf _x OPO₄ crystals (x = 0.01, 0.03, and 0.12) is determined. In the crystals studied, hafnium mostly occupies the second titanium position. The doping of KTP crystals with hafnium results in an elongation of K-O bonds in the potassium polyhedra and, as a consequence, in a considerable (by approximately 180°C) decrease in the temperature of ferroelectric phase transition. The magnitude of anomalous permittivity substantially decreases. The electrical conduction in the specimens studied decreases by approximately half an order of magnitude in the low-temperature region but remains almost unchanged in the high-temperature region. Even at minor concentrations, the presence of a hafnium additive in the specimens considerably (by 35%) enhances the intensity of the second harmonic generation of laser radiation.     

PbS crystals with clover‐like structure: Preparation,characterization, optical properties and influencing factors

A new and simple route to synthesize Lead sulfide (PbS) crystals with the clover‐like structure was described in the current paper. PbS was prepared in a simple aqueous solution employing (CH₃COO)₂Pb and thiourea as the initial materials under 130 W microwave irradiation. No any surfactant or template including organic polyamines with N‐chelation property was needed. The phase and composition of the product were identified by X‐ray powder diffraction (XRD) and X‐ray photoelectron spectra (XPS). TEM observation showed that the product with the six‐petal flower‐shaped structures was obtained, but SEM observation confirmed the clover‐like structure of the product; and the six‐petal flowers were formed via the overlap of two clovers revolved 60° around the center of the flower. Some factors affected the shape of the final product were studied and the optical properties of PbS crystals with the clover‐like structure were measured. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anisotropic properties of Nd:ReCOB (Re=Y,Gd):A low symmetry self-frequency doubling crystal

The anisotropy of low symmetry Nd:YCOB and Nd:GdCOB crystals, including their linear and nonlinear optical properties, as well as their laser and SFD properties, are discussed in detail, for the first time, in this paper. We have found the optimum directions of doubling-frequency for these crystals are not in the principle planes.     

Synthesis, crystal structures, and properties of copper complexes with tripodal ligands and azide anion

Two new Cu^II complexes, (CuL¹N₃)ClO₄ (1) and (CuL²N₃)ClO₄ (2), have been synthesized and characterized in the presence of NaN₃, where L¹ = tris[2-(6-methylpyridyl)methyl]amine and L² = tris[(3,5-dimethylpyrazol-l-yl)methyl]amine, and their crystal structures have been determined by X-ray diffraction methods. Compound 1 crystallizes in the triclinic space group P–1, with a = 8.258(2) Å, b = 11.481(2) Å, c = 14.158(3) Å, = 72.30(3)°, = 79.05(3)°, = 86.08(3)°, V = 1255.4(5) ų. Compound 2 crystallizes in the monoclinic space group C2/c, with a = 26.752(2) Å, b = 10.561(2) Å, c = 21.059(4) Å, = 120.51(3)°, V = 5126(3) ų. In both compounds, each Cu^II center is in a distorted trigonal–bipyramidal coordinated environment with four nitrogen atoms from the tripodal ligand and one nitrogen atom from the azide group. The coordination geometry around Cu^II center of 1 is axially compressed trigonal bipyramid, while that of 2 is an axially elongated trigonal bipyramid. The coordinated azide group is in the axial site in both complexes. A quasi-dimeric structure of 1 has been formed in the unit cell through hydrogen bonding. The electronic spectra of two complexes in solution have been further studied by UV–vis technique, and the coordination properties have been discussed.     

Synthesis, atomic structure, and properties of crystals in the RbTiOPO4-CsTiPO5 system

The subsolidus region of the phase diagram of the RbTiOPO₄-CsTiPO₅ system has been studied in the temperature range 700–1000°C, and the boundaries between the stability fields of the orthorhombic phase with the KTiOPO₄-type structure and the cubic phase with the pyrochlore-type structure have been determined. Single crystals of the RbTiOPO₄ and CsTiPO₅ based solid solutions were synthesized by crystallization from flux. The crystal structure and the physical properties of the first members of the series were studied.     

Synthetic Na,Sr-carbonatoborate with a new type of pentaborate layer: The OD nature of the structure and its correlation with volkovskite,veatchites, and hilgardites

A new carbonate borate, Sr(Na_0.4Sr_0.1)Na₂[B₅O₈(OH)₂] · (CO₃)_{1 ? x} , space group B2/b, is synthesized under hydrothermal conditions. A new layered anionic boron-oxygen radical based on the 5[3T + 2Δ] block, which is a component of the framework of the subgroup of triclinic hilgardites, is found in the structure. The structure of the new carbonatoborate is compared with the structures of veatchites, volkovskite, and other layered borates that are based on the 5[2T + 3Δ] block. The OD nature of their structure is shown. The regions responsible for the slight acentricity and disorder along the baxis are revealed in the centrosymmetric model of the new borate.     

Influence of impurities,irradiation and temperature on the mechanical and electrical properties of LiF crystals

On the basis of study of the temperature dependence of mechanical and electrical properties of LiF crystals with different impurities an evident interaction between radiation defects and impurities is revealed. As a result of trapping of radiation defects (F- and H-aggregate colour centres) by impurity centres the reconstruction of impurity centres takes place, causing a change of mechanical and electrical properties.     

A theory for elastic properties of single crystals with microstructure and its application to diffusion induced segregation

In this article a general theory for elastically stressed single crystals in the presence of microstructure is presented and an explicit formula for the resulting non‐linear stored mechanical energy is obtained. The optimal microstructure under applied stress is characterised and the optimal laminates are identified in 2D. The analysis is based on a sharp lower estimate of the energy that relies on relaxation. The new theory is then used to extend existing models for diffusion induced segregation (DIS) in the case of (Zn,Fe)S single crystals. Numerical simulations based on finite elements are carried out and the results are compared with former computations of the homogeneous case. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)