Dielectric properties of Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> garnet crystals in the IR range

The dielectric properties of a series of yttrium-iron garnet single crystals of different structural and optical quality are investigated in the IR range (400–1000 cm^?1). Some regularities of the dependence of the permittivity ε_∞ of the garnet samples on the charge-carrier fraction (the parameter k/nk) are revealed. The maximum values of ε_∞ are found for the samples containing magnetoactive Sm and Mn ions as dominant impurities, which increase the concentration of conduction electrons and, therefore, provide large values of k/nk. A correlation between ε_∞ of the Y₃Fe₅O₁₂ samples and the concentration of oxygen ions is established.     

Relationship between the imperfection of Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> garnet samples of different crystallographic orientations and their physical properties

The kinetic, optical, and dielectric properties of Y₃Fe₅O₁₂ garnet single crystals of different structural quality have been investigated. It is established that the ratio of the intensities of coherent and incoherent scattering characterizes the conduction electron concentration in inhomogeneous magnetic samples. A correlation between the physical properties of the samples and the character of their structural inhomogeneity is revealed.     

Structure of amorphous oxide Al<Subscript>2</Subscript>O<Subscript>3</Subscript>: Results of a molecular-dynamics experiment

The structure of amorphous aluminum oxide was simulated by the molecular-dynamics method. A random distribution of Al³⁺ and O^2? ions over the volumes of cubes with sides of 21 and 24 Å was used as a starting configuration. The character of the distribution of cations in the anion subsystem was analyzed. It was shown that formation of voids in model clusters is possible when the average electron density is underestimated     

Invar effect in PbFe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>O<Subscript>3</Subscript> ceramics

High-density lead ferroniobate PbFe_1/2Nb_1/2O₃ (PFN) is prepared by conventional ceramic technology. Its structural properties are studied in a wide temperature range (293 ≤ T ≤ 973 K). The following chain of phase transitions is established in the vicinity of the transition to the polar phase: Rh (rhombohedral phase) (T < 363 K) → Psc (pseudo-cubic phase) (363 < T < 387 K) → C (cubic phase) (T > 387 K). The paraelectric range contains five ranges of constant unit-cell volume (invar effect): I (387 ≤ T ≤ 413 K), II (433 ≤ T ≤ 463 K), III (553 ≤ T ≤ 613 K), IV (743 ≤ T ≤ 773 K), and V (798 ≤ T ≤ 823 K). It is shown that the anomalous behavior of the PFN dielectric characteristics above the Curie temperature, which was revealed previously, is associated with the specific features of its real (defect) structure, which is caused by the crystal-chemical specificity of the main structure-forming agents: α-Fe₂O₃ and α_ht-Nb₂O₅.     

Structure of phases of the sillenite family in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript> system

X-ray diffraction studies of sillenite Bi₂₄V₂O₄₀ single crystals grown by the hydrothermal method are performed for a separate crystal and powdered crystals. It is found that the composition of the two specimens is described by the (Bi_{24 − x} ▭ _x )[Bi _y ³⁺V_1−y ⁵⁺]₂ O₄₀ general formula with completely populated oxygen sites but differs in the content of vacancies at the bismuth site (this was established for the first time) and the Bi: V ratio at the tetrahedral site. The structural models of all the vanadium-containing sillenites reported in the literature are considered, and the possibility that Bi atoms are located at the centers of BiO₄ tetrahedra is established.     

Synthesis and Structure of Ba<Subscript>5</Subscript>(V<Subscript>2</Subscript>O<Subscript>7</Subscript>)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>

Abstract  A new barium chlorovanadate, Ba₅(V₂O₇)₂Cl₂, was isolated by a high-temperature (850 °C) reaction employing a CsCl/RbCl flux. The structure was determined by single crystal X-ray diffraction methods. This compound crystallizes in an orthorhombic crystal system, Pmmn (No. 59), with a = 11.558(2) ?, b = 15.164(3) ?, c = 10.023(2) ?, Z = 4 and V = 1756.7(6) ?³. The structure of Ba₅(V₂O₇)₂Cl₂ was determined by full-matrix, least-squares methods with R ₁ = 0.0398, wR ₂ = 0.1069 and GOF = 1.048 for all data. This new structure can be described as a composite lattice made up of mixed covalent and ionic moities. The extended framework is orchestrated by stacked [Ba(V₂O₇)Cl]³⁻ slabs that are interconnected by Ba²⁺ cations through Ba–O bonds to the [V₂O₇] units. The Ba²⁺ and Cl^- ions form BN-type “[BaCl]” sheets with pseudo-hexagonal windows that are centered by [V₂O₇]⁴⁻ pyrovanadate units. Graphical Abstract  The structure of a new chlorovanadate, Ba₅(V₂O₇)₂Cl₂, exhibits an interesting BN-type salt lattice that consists of an extended [BaCl] sheet containing pseudo-hexagonal windows that are centered by [V₂O₇] pyrovanadate units.      

On the nature of fracture of SrB<Subscript>4</Subscript>O<Subscript>7</Subscript> and PbB<Subscript>4</Subscript>O<Subscript>7</Subscript> single crystals

The crack resistance and peculiarities of the internal structure of isostructural SrB₄O₇ and PbB₄O₇ single crystals of the framework type have been studied. It is shown that the cleavage of these crystals, which is atypical of this type and inherent in strontium and lead tetraborates, is due to the presence of boron-oxygen layers (bound by a relatively small number of covalent bonds) in their 3D boron-oxygen frameworks; crystals are cleaved along these layers. It is established that cracks propagate in SrB₄O₇ and PbB₄O₇ single crystals as a result of breakage of both the bonds between bridge atoms and the bonds in B₃O₃ boron-oxygen cycles—the main elements of the boron-oxygen framework. The break of bonds in the boron-oxygen cycles is explained by the presence of an unusual oxygen position in these cycles, which is shared by three boron-oxygen tetrahedra and whose B-O bonds are much weaker in comparison with the bonds typical of BO₄ groups.     

Crystal Structure of a New Quinternary Oxide: NaTl<Subscript>3</Subscript>Cu<Subscript>4</Subscript>Te<Subscript>2</Subscript>O<Subscript>12</Subscript>

Abstract  

A new quinternary oxide, NaTl₃Cu₄Te₂O₁₂, has been synthesized and characterized by single crystal X-ray diffraction. The reported material was synthesized by hydrothermal techniques using TlNO₃, CuO, TeO₂, and NaOH as reagents. The material exhibits a two-dimensional layered structure consisting of edge-shared CuO₆ and TeO₆ polyhedra separated by Na⁺ and Tl⁺ cations. NaTl₃Cu₄Te₂O₁₂ crystallizes in space group C2/m with a = 12.9800(17) ?, b = 9.3455(12) ?, c = 5.2335(7) ?, β = 104.276(2)°, V = 615.24(14) ?³, and Z = 2.     

Synthesis and an X-ray diffraction study of Rb<Subscript>2</Subscript>[(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>3</Subscript>]

The synthesis and X-ray diffraction study of compound Rb₂[(UO₂)₂(C₂O₄)₃], which crystallizes in the monoclinic crystal system, are performed. The unit cell parameters are as follows: a = 7.9996(6) Å, b = 8.8259(8) Å, c = 11.3220(7) Å, β = 105.394(2)°, and V = 770.7(1) ų; space group P2₁/n, Z = 2, and R ₁ = 0.0271. [(UO₂)₂(C₂O₄)₃]^2? layers belonging to the AK _0.5 ⁰² T ¹¹ crystal chemical group of uranyl complexes (A = UO ₂ ²⁺ , K ⁰² = C₂O ₄ ^2? , and T ¹¹ = C₂O ₄ ^2? ) are uranium-containing structural units of the crystals. The layers are connected with outer-sphere rubidium cations by electrostatic interactions.     

Crystal structure refinement of Sr<Subscript>3</Subscript>TaGa<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>14</Subscript>

An accurate X-ray diffraction study of Sr₃TaGa₃Si₂O₁₄ (STGS) crystal (a = 8.3023(10) Å, c = 5.0853(2) Å, sp. gr. P321, Z = 1, R/wR = 0.59/0.52%, 4004 independent reflections) is performed. The use of two independent data sets obtained on diffractometers with point and 2D detectors made it possible to determine the model structure characterized by the best reproducibility of parameters. The ordered distribution of atoms over crystallographic positions and the anharmonic character of displacements of all cations and one oxygen atom are established.     

Crystal structure of the Ca<Subscript>3</Subscript>TaGa<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>14</Subscript> compound

The absolute crystal structure of the Ca₃TaGa₃Si₂O₁₄ piezoelectric compound is refined using X-ray diffraction analysis. The unit cell parameters and final R factors are as follows: a = 8.112(1) Å, c = 4.9862(6) Å, space group P321, Z = 1, R = 0.98%, and R _w = 1.42%. It is shown that the configuration of the absolute crystal structure inherited from the seed material determines the positive sense of the optical activity of the crystal under investigation. The structural and acoustical characteristics of the Ca₃TaGa₃Si₂O₁₄ crystals are compared with those of the La₃Ga₅SiO₁₄ crystals.     

The cubic space group of tungstogallate acid,H<Subscript>5</Subscript>GaW<Subscript>12</Subscript>O<Subscript>40</Subscript>

The space group of tungstogallate acid, H₅GaW₁₂O₄₀, reported by Niu et al. (J. Chem. Crystallogr. 2003, 33, 799) should be I–43m instead of Cm; the monoclinic C-centered cell is transformed to the I-centered cubic cell by (1 0 0; ,– , 1; – , – , –1).     

Characteristic of spontaneous polarization in Pb<Subscript>5</Subscript>Ge<Subscript>3</Subscript>O<Subscript>11</Subscript> crystals

The temperature behavior of the spontaneous polarization of lead tetragermanate, a uniaxial ferroelectric, is studied in the range from 4.2 to 300 K. The results obtained along with the data from the literature make it possible to reconstruct a complete pattern of the behavior of P _s (T) both in the vicinity of the phase transition and at lower temperatures. In the range from 290 K to T_C, the crystal behavior is found to change from the dipole type (β = 1/2) to the pseudoquadrupole type (β = 1/4). This specific crossover manifests itself in the change in the behavior of P _s ^1/β as a function of (T_C-T). In the low-temperature range, weak anomalies in the dependenceP _s >(T) are found, which point to the occurrence of contributions from the dipole moments of separate structural fragments of Ge₂O₇ and GeO₄, which have internal degrees of freedom and are weakly bound to the dynamics of the crystal lattice.     

Structure and some properties of [UO<Subscript>2</Subscript>(C<Subscript>5</Subscript>H<Subscript>12</Subscript>N<Subscript>2</Subscript>O)<Subscript>5</Subscript>](ClO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Compound [UO₂(C₅H₁₂N₂O)₅](ClO₄)₂ is synthesized and characterized by thermogravimetry, IR spectroscopy, and X-ray diffraction. The compound crystallizes in the monoclinic crystal system; a = 15.2985(9) Å, b = 26.9676(15) Å, c = 20.6962(11) Å, β = 100.697(1)°, space group P2₁/c, Z = 8, and R = 0.0445. Discrete [UO₂(C₅H₁₂N₂O)₅]²⁺ groups belonging to the AM ₅ ¹ crystal chemical group of uranyl complexes (A = UO ₂ ²⁺ and M ¹=C₅H₁₂N₂O) are uranium-containing structural units of the crystals.     

Synthesis and Structure of [Fe<Subscript>3</Subscript>O(O<Subscript>2</Subscript>CCH<Subscript>2</Subscript>OMe)<Subscript>6</Subscript>(H<Subscript>2</Subscript>O)<Subscript>3</Subscript>][FeCl<Subscript>4</Subscript>]

Abstract  The structure of [Fe₃O(O₂CCH₂OMe)₆(H₂O)₃][FeCl₄] · 2.5H₂O has been determined. The three iron atoms and the μ₃-oxo are coplanar. Each carboxylic ligand is bidentate and links two iron atoms in the cluster. The clusters are linked by intra-trimer hydrogen bonding to form a zigzag motif that forms sheets via hydrogen bonding involving disordered waters of hydration. The [FeCl₄]⁻ anion is intercalated between the hydrogen-bonded sheets. Crystal data: space group P2₁/n, a = 10.276(2), b = 22.793(5), c = 17.091(3) ?, β = 96.66(3)°, V = 3976(1) ?³, Z = 4, R = 0.0837, wR ₂ = 0.1836. Graphical Abstract  The structure of [Fe₃O(O₂CCH₂OMe)₆(H₂O)₃][FeCl₄] · 2.5H₂O has been determined in which the clusters are linked by intra-trimer hydrogen bonding to form a zigzag motif that forms sheets via hydrogen bonding involving disordered waters of hydration.      

Accurate structural study of langasite-family Ca<Subscript>3</Subscript>TaGa<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>14</Subscript> crystal

An accurate X-ray diffraction study of Ca₃TaGa₃Si₂O₁₄ single crystal has been performed using two datasets obtained on a diffractometer equipped with a CCD area detector (a = 8.1056(2) Å, c = 4.9800(1) Å, sp. gr. P321, Z = 1, R/wR = 0.486/0.488%). A model structure is determined which is characterized by a high degree of reproducibility of structural parameters. Each site in Ca₃TaGa₃Si₂O₁₄ is occupied by atoms of only one type. Nevertheless, its structural feature is asymmetric disordering of sites of Ca, Ta, Ga, and two out of three oxygen atoms occupying special and general sites. A transition of some part of Ca atoms (~3%) from 3e sites on the twofold symmetry axis to general 6g sites is revealed.     

Crystal-structure refinement of Sr<Subscript>3</Subscript>Ga<Subscript>2</Subscript>Ge<Subscript>4</Subscript>O<Subscript>14</Subscript>

The accurate X-ray diffraction study of a Sr₃Ga₂Ge₄O₁₄ crystal was performed based on two X-ray diffraction data sets collected on a diffractometer equipped with a CCD area detector (a = 8.2776(2), c = 5.0415(1) Å, sp. gr. P321, Z = 1, R/wR = 0.78/0.69%, 3645 independent reflections). The structure of Sr₃Ga₂Ge₄O₁₄ is characterized by the presence of two mixed cation sites, which is accompanied by the anharmonic motion not only of cations, but also of two oxygen atoms in general positions. The structures and electromechanical characteristics of Sr₃Ga₂Ge₄O₁₄ and Sr₃TaGa₃Si₂O₁₄ were compared. The Sr₃Ga₂Ge₄O₁₄ structure is characterized by a larger elongation of the Sr polyhedron along the a axis and, simultaneously, by the smaller unit-cell parameter a compared with Sr₃TaGa₃Si₂O₁₄, which correlates with the ratio of the piezoelectric coefficients d ₁₁. The absence of thermally stable directions in the crystals of Sr₃Ga₂Ge₄O₁₄ and Sr₃TaGa₃Si₂O₁₄ is consistent with the absence of the anomalous temperature dependence of the dielectric constant ?₃₃.     

X-Ray Structure Investigation of Sr<Subscript>3</Subscript>NbGa<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>14</Subscript> Langasite Family Crystal

An accurate structure analysis of Sr₃NbGa₃Si₂O₁₄ single crystals, belonging to the langasite family, has been performed. Two datasets are obtained on an Xcalibur S diffractometer equipped with a CCD detector. The structure is been refined using an averaged dataset: sp. gr. P 321, Z = 1, 295 K, sin θ/λ ≤ 1.35 Å^–1, a = 8.2797(3) Å, c = 5.0774(5) Å; the agreement factors between the model and experiment are found to be R/wR = 0.76/0.64% and Δρ_min/Δρ_max =–0.21/0.17 e/ų for 3820 independent ref lections. The Sr₃NbGa₃Si₂O₁₄ and Sr₃NbFe₃Si₂O₁₄ structures are compared, and the role of magnetic ions in the predicted P321 → P3 phase transition is analyzed.     

Flux crystallization of trigonal GdFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> competing with the crystallization of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The formation of trigonal GdFe₃(BO₃)₄ crystals in the Bi₂Mo₃O₁₂-B₂O₃-Li₂MoO₄-Gd₂O₃-Fe₂O₃ system was studied. The flux compositions for which GdFe₃(BO₃)₄ is the high-temperature phase with a wide range of crystallization were determined. The features of nucleation of these crystals and their growth near the phase boundary with α-Fe₂O₃ were analyzed. The growth of GdFe₃(BO₃)₄ single crystals involving preliminary nonequilibrium crystallization of α-Fe₂O₃ is described.     

Growth and structure of La<Subscript>3</Subscript>Zr<Subscript>0.5</Subscript>Ga<Subscript>5</Subscript>Si<Subscript>0.5</Subscript>O<Subscript>14</Subscript> crystals

The complete X-ray structure determination of Czochralski grown La₃Zr_0.5Ga₅Si_0.5O₁₄ single crystals with the Ca₃Ga₂Ge₄O₁₄ structure is performed (sp. gr. P321, a = 8.226(1) Å, c = 5.1374(6) Å, Z = 1, Mo K_α1 radiation, 1920 crystallographically independent reflections, R = 0.0166, R_w = 0.0192). The absolute structure is determined. It is shown that possible transition of some of La atoms (～1.2%) from the 3e to 6g position may give rise to the formation of structural defects.