Specific features of structure and ferroelectric properties of BaTiO<Subscript>3</Subscript> phases

Analysis of the interatomic Ti-O distances in the asymmetric Ti-O?Ti bridges in the ferroelectric barium titanate phases showed that the rhombohedral, orthorhombic, and tetragonal BaTiO₃ phases consist of TiO ₃ ^2? , TiO₂, and TiO²⁺ groups, respectively. The groups show strong electrostatic interaction and, so, orient along one direction, which gives rise to spontaneous polarization of these phases. In each phase, polarization switching under the action of a rather strong electric field proceeds via transfer of the oxygen atoms from one titanium atom to another with simultaneous change of the group orientation to the opposite one.     

Electronic structure and magnetooptical properties of an La<Subscript>0.7</Subscript>Ca<Subscript>0.25</Subscript>Ba<Subscript>0.05</Subscript>MnO<Subscript>3</Subscript> single crystal

The spectral and temperature characteristics of the magnetooptical Kerr effect and the optical properties of an La_0.7Ca_0.25Ba_0.05MnO₃ single crystal are studied. The data obtained are used to calculate the components of the permittivity tensor, whose behavior is interpreted within the framework of the known models of the electronic structure of manganites.     

New isoformula iodates In(IO<Subscript>3</Subscript>)<Subscript>3</Subscript> and Sm(IO<Subscript>3</Subscript>)<Subscript>3</Subscript> with different crystal structures: Specific structural features of I<Superscript>5+</Superscript> compounds

New iodates, namely, In(IO₃)₃ (space group R \(\bar 3\)) and Sm(IO₃)₃ (space group P2₁/a), are synthesized under hydrothermal conditions. The original crystal structure of the In(IO₃)₃ compound is determined without prior knowledge of the chemical formula. The Sm(IO₃)₃ compound is isostructural to the Gd(IO₃)₃ compound. The [IO₄]^3- tetrahedra with three short I-O bonds have an umbrella coordination, which is characteristic of pentavalent iodine, and form anionic radicals, such as a ring radical in the In(IO₃)₃ iodate, a triple helix in the isoformula compound Fe(IO₃)₃, a complex chain in the Sm(IO₃)₃ iodate, and a linear triortho group in the Sm(IO₃)₃·H₂O compound. All radicals contain triortho groups. The structural differences are determined by different ionic radii and shapes of the coordination polyhedra of the cations (indium and iron octahedra and an eight-vertex samarium polyhedron).     

Single-crystal growth of trigonal DyFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> and study of magnetic properties

Fluxes with a wide stability range of trigonal DyFe₃(BO₃)₄ were selected by the successive-approximation method using direct phase probing in the Bi₂Mo₃O₁₂-B₂O₃-Dy₂O₃-Fe₂O₃ system. Crystallization parameters of the fluxes were determined. The conditions for single-crystal growth were recommended using both spontaneous crystal nucleation and seeded growth according to the Kyropoulos method. An analysis of the measured temperature and field dependences of magnetization of crystals in fields parallel or perpendicular to the threefold axis led to the conclusion that DyFe₃(BO₃)₄ undergoes a phase transition to an ordered easy-axis state and is characterized by a field-induced spin-reorientation transition with the predominant alignment of Dy³⁺ spins along the applied field.     

The crystal and molecular structure of a trifluoroacetylacetonate complex of scandium,Sc(CH<Subscript>3</Subscript>COCHCOCF<Subscript>3</Subscript>)<Subscript>3</Subscript>

The crystal and molecular structure of Sc(CH₃COCHCOCF₃)₃ has been determined by X-ray diffraction. The compound crystallizes as pure mer-isomer in the orthorhombic space group Pbca with lattice parameters a=15.166(8) ?, b=13.560(7) ?, c=19.327(10) ?, α=β=γ=90°, V=3974(4) ?³, Z=8. The complex at 100 K is partially disordered in the crystal structure in an approximate 5:1 ratio with 83% fluorine population at C-11 and 17% at C-15. NMR data is compared to that previously reported.     

Refinement of the crystal structure of rhombohedral KU<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> as a representative of orthophosphates with the NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> structure

The crystal structure of the high-temperature β modification of synthetic orthophosphate KU₂(PO₄)₃ was refined from powder X-ray diffraction data by the Rietveld method: sp. gr. \(R\bar 3c\), the unit-cell parameters a= 9.113(1) Å and c= 24.997(1) Å. The isotropic refinement converged to R _wp = 6.15, R _B = 2.14, R _F = 3.52, and S = 0.42. It was confirmed that β-KU₂(PO₄)₃ belongs to the structure type of sodium zirconium phosphate containing an actinide atom in a sixfold (octahedral) coordination formed by oxygen atoms, which is unusual for orthophosphates. The principal interatomic distances and bond angles in the structure are reported.     

Crystal and magnetic structure of the Sm<Subscript>0.45</Subscript>Sr<Subscript>0.55</Subscript>MnO<Subscript>3</Subscript> manganite studied by neutron powder diffraction

Neutron diffraction investigation of the ¹⁵²Sm_0.45Sr_0.55MnO₃ manganite is performed. The diffraction data are compared with the magnetic and transport properties of this compound. The parameters of the crystal and magnetic structures are determined. Manganite belongs to the orthorhombic system (sp. gr. Pnma) and has a perovskite-like structure in the entire temperature range under study (1.5–260 K). The ground state of the ¹⁵²Sm_0.45Sr_0.55MnO₃ manganite at low temperatures is a single-phase A-type antiferromagnetic insulator with T _N ～ 180 K.     

Accurate crystal structure refinement of La<Subscript>3</Subscript>Ta<Subscript>0.25</Subscript>Ga<Subscript>5.25</Subscript>Si<Subscript>0.5</Subscript>O<Subscript>14</Subscript>

An accurate X-ray diffraction study of an La₃Ta_0.25Ga_5.25Si_0.5O₁₄ single crystal has been performed using two data sets obtained independently for the same sample in different orientations on a diffractometer with a 2D CCD detector. This structure was refined with an averaged set of these data (a = 8.1936(15) Å c = 5.1114(6) Å, sp. gr. P321, Z = 1, R/wR = 0.75/0.71%, 4030 independent reflections). This analysis was aimed at determining the character of the occupancies of the cation position in the structure. The octahedra at the origin of coordinates turned out to be statistically occupied by gallium and tantalum ions of similar sizes, whereas the tetrahedra on the threefold symmetry axes are occupied by gallium and silicon whose ionic radii differ significantly. The latter circumstance caused the splitting of oxygen positions and made it possible to reliably establish the structural position of statistically located [SiO₄] and [GaO₄] tetrahedra of different sizes.     

Synthesis and crystal structure of Pb<Subscript>3</Subscript>[IO<Subscript>3</Subscript>]<Subscript>2</Subscript>Cl<Subscript>4</Subscript>, a representative of a new iodate-chloride class of compounds

Compound Pb₃[IO₃]₂Cl₄ (space group C12/c1), representing a new iodate-chloride class of compounds, is synthesized under hydrothermal conditions. Only two minerals, schwartzembergite Pb₃[IO₃]Cl₂O(OH) and seeligerite Pb₃[IO₃]Cl₃O, the structures of which are unknown, are close in composition to this compound. In the iodate-chloride studied, the pentavalent iodine atom has an umbrella-like coordination, which is typical of iodates and consists of three O atoms at short distances and the fourth O atom at a longer distance. [IO₄]³⁻ tetrahedra share edges to form pairs. Lead ions form layers parallel to the ab plane. Along the c axis, these layers alternate with layers of iodate groups. Pb atoms are coordinated by O atoms of iodate groups and Cl atoms. The coordination sphere of the Pb(1) atom contains a free sector which is directed to more distant halogen atoms and possibly accommodates the lone electron pair.     

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.     

Structural features of the KH<Subscript>2</Subscript>PO<Subscript>4</Subscript>: Cr single crystal

The precision X-ray structural investigation of KH₂PO₄ (KDP) crystal samples from different growth sectors of a single crystal containing chromium impurities is performed. It is demonstrated that the structure of the sample from the prismatic growth sector is more perfect than the structure of the sample from the pyramidal growth sector. The impurity trapping can lead to the formation of at least four different types of structural defects on the face of the pyramid, whereas only two of them can be formed on the face of the prism. A comparison with the relevant data for the “pure” KDP crystal shows that the number of defects and their character are approximately identical for all samples. The analysis of the IR spectra indicates that nitrate ions are contained in the samples from both growth sectors. Moreover, structurally bound water molecules and OH groups are revealed in the sample from the prismatic sector.     

Synthesis and crystal chemical characteristics of the structure of <Emphasis Type="Italic">M</Emphasis><Subscript>0.5</Subscript>Zr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> phosphates

Double phosphates of zirconium and metals with an oxidation degree of +2 of the composition M_0.5Zr₂(PO₄)₃ (M = Mg, Ca, Mn, Co, Ni, Cu, Zn, Sr, Cd, and Ba) are synthesized and characterized by X-ray diffraction methods and IR spectroscopy. The crystal structures of all the compounds are based on three-dimensional frameworks of corner-sharing PO₄-tetrahedra and ZrO₆-octahedra. Phosphates with large Cd²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ cations octahedrally coordinated with oxygen atoms form rhombohedral structures (space group R3), whereas phosphates with small tetrahedrally coordinated Mg²⁺, Ni²⁺, Cu²⁺, Co²⁺, Zn ²⁺, and Mn²⁺-cations are monoclinic (space group P2₁/n). The effect of various structure-forming factors on the M_0.5Zr₂(PO₄)₃ compounds with a common structural motif but different symmetries are discussed.     

Specific features of the substitution of Fe<Superscript>3+</Superscript> impurity ions for Zr<Superscript>4+</Superscript> in NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> single crystals

The EPR spectra of Fe³⁺ impurity ions in NaZr₂(PO₄)₃ single crystals at 300 K are investigated, and the spin Hamiltonian of these ions is determined. A comparative analysis of the spin-Hamiltonian and crystal-field tensors is performed using the maximum invariant component method. It is demonstrated that Fe³⁺ impurity ions substitute for Zr⁴⁺ ions with local compensator ions located in cavities of the B type. It is revealed that the invariant of the spin-Hamiltonian tensor B₄ and the crystal-field tensor V ₄ ⁴⁴ depend substantially on the mutual arrangement of ions in the first and second coordination spheres. The corresponding dependences are analyzed.     

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 of Rb<Subscript>2</Subscript>[Ti(VO<Subscript>2</Subscript>)<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>]

The crystal structure of the new compound Rb₂[Ti(VO₂)₃(PO₄)₃] obtained by hydrothermal synthesis in the RbCl-TiPO₄-V₂O₅-B₂O₃-H₂O system (a = 13.604(2) Å, c = 9.386(2) Å, sp. gr. P6cc, Z = 4, ρ_calcd = 3.32 g/cm³) has been studied by X-ray diffraction (Xcalibur-S-CCD diffractometer, R = 0.038). It is shown that the isotypism of Rb₂[Ti(VO₂)₃(PO₄)₃] and Cs₂[Ti(VO₂)₃(PO₄)₃] is caused by the flexibility of a mixed anionic framework composed of phosphorus tetrahedra, vanadium five-vertex polyhedra, and titanium octahedra (bases of the crystal structures of these compounds). The topological correlations between the structures of titanium-vanadyl phosphates and benitoite and beryl silicates are analyzed.     

Growth and crystal structure of binary molybdate CsFe(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript>

CsFe(MoO₄)₂ single crystals have been grown by solution-melt crystallization with a charge-to-solvent ratio of 1: 3 (with Cs₂Mo₃O₁₀ used as a solvent). The crystal structure of this compound has been refined by X-ray diffraction (X8 APEX automatic diffractometer, MoK _α radiation, 356 F(hkl), R = 0.0178). The trigonal unit cell has the following parameters: a = b = 5.6051(2) Å, c = 8.0118(4) Å, V = 217.985(15) ų, Z = 1, ρ_calc = 3.875 g/cm³, and sp. gr. P \(\bar 3\) m1. The structure is composed of alternating layers of FeO₆ octahedra (with MoO₄ tetrahedra attached by sharing vertices) and CsO₁₂ icosahedra.     

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.     

Synthesis and structure of (Rb<Subscript>0.50</Subscript>Ba<Subscript>0.25</Subscript>)[UO<Subscript>2</Subscript>(CH<Subscript>3</Subscript>COO)<Subscript>3</Subscript>]

A new compound (Rb_0.50Ba_0.25)[UO₂(CH₃COO)₃] is synthesized and its crystal structure is studied by X-ray diffraction. The compound crystallizes in the form of yellow plates belonging to the cubic crystal system. The unit cell parameter a = 17.0367(1) Å, V = 4944.89(5) ų, space group I \(\bar 4\)3d, Z = 16, and R = 0.0182. The coordination polyhedron of the uranium atom is a hexagonal bipyramid with oxygen atoms of three acetate groups and the uranyl group in the vertices. The crystal chemical formula of the uranium-containing group is AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B ⁰¹ = CH₃COO^?). The oxygen atoms of the acetate groups that enter the coordination polyhedron of uranium are bound to barium and rubidium atoms.     

Slip and cleavage systems in the new crystal Li<Subscript>6</Subscript>YB<Subscript>3</Subscript>O<Subscript>9</Subscript>

The structure of single crystals of the double lithium-yttrium borate Li₆YB₃O₉ is investigated. It is shown that the cleavage planes are parallel to the layers that are located at the largest distance from each other and characterized by the weakest electrostatic interaction. Thus, cleavage of a crystal occurs through the longest Li-O bonds in the lithium five-vertex polyhedra and the bridge Y-O bonds. It is ascertained that slip in Li₆YB₃O₉ occurs in the planes that are most close packed with respect to oxygen ions, while the reason for the absence of plastic deformation at room temperature is that \((10\bar 2)\) B triangles impede the motion of \((\bar 301)\) B triangles.     

Growth,structure, and magnetic properties of CuFeTe<Subscript>2</Subscript> single crystals

CuFeTe₂ single crystals were grown and the temperature dependence of their magnetic susceptibility in the temperature range 1.8–400 K was investigated. It is found that the magnetic susceptibility shows anomalies at temperatures T _s = 65 and T _N = 125 K. At T > 125 K, the crystal is in the paramagnetic state controlled by Fe²⁺ and Cu²⁺ ions with an effective magnetic moment of 1.44 μB.