Absorption and Circular Dichroism Spectra of La<Subscript>3</Subscript>Ga<Subscript>5</Subscript>SiO<Subscript>14</Subscript> Crystals Doped with Pr<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript>, and Er<Superscript>3+</Superscript> Ions

The absorption and circular dichroism (CD) spectra of La₃Ga₅SiO₁₄ langasite crystals doped with Pr³⁺, Ho³⁺, and Er³⁺ ions have been studied in the wavelength range of 350–700 nm. The electronic transitions of these ions, which replace La3+ ions in the 3e position with the symmetry 2, are observed in the spectra. All transitions are active in both the absorption and CD spectra. The dipole strengths D _om, rotational strengths R _om, and anisotropy factors g have been calculated for well-resolved bands. Some features are noted for the spectra that were obtained, and their relationship with the structure disorder is considered     

Athermal Directions in KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> Crystal

All orientations of the phase normal, at which the phase of a light wave propagating through a crystal is independent of its temperature (athermal phase directions), have been numerically found for a KGd(WO₄)₂ crystal. There are two sets of such directions for each isonormal wave. Their intersection with the main planes of the optical indicatrix of the crystal yields four athermal directions in the planes orthogonal to the axes with the minimum and intermediate refractive indices and two directions in the plane orthogonal to the axis with the maximum refractive index.     

Internal stress in doped NH<Subscript>4</Subscript>Cl:Mn<Superscript>2+</Superscript> crystals

The relationship of the effect of impurity on crystal growth and morphology, along with the internal stress and anomalous birefringence arising upon impurity trapping by a growing crystal, is considered. The NH₄Cl-MnCl₂-H₂O-CONH₃ model system and the heterostructural NH₄Cl:Mn²⁺ crystals formed in it are experimentally studied. It is found that up to 6.63 wt % Mn²⁺ impurity is effectively captured by growing NH₄Cl crystals at an impurity trapping coefficient only slightly below unity. The effect of Mn impurity stabilizes the full-face growth of NH₄Cl crystals with a rhombododecahedral habit in aqueous solutions and a cubic habit in water-formamide solutions. The trapping of manganese impurity by ammonium chloride crystals causes high internal stress (up to 4 GPa) in them, which manifests itself in the form of anomalous birefringence and leads to splitting, twinning, and cracking in NH₄Cl crystals.     

Refractometry of mechanically compressed RbKSO<Subscript>4</Subscript> crystals

The unit-cell parameters and the spatial symmetry of RbKSO₄ crystals are determined. The temperature and spectral dependences of the refractive indices and birefringence of these crystals are measured. Two first-order phase transitions are found to occur at 116 and 820 K, and the occurrence of isotropic points for three crystallophysical directions is established. The effect of uniaxial stresses on the optical properties of the crystal is studied. Both the birefringence and the birefringence-sign inversion points are found to be rather sensitive to the action of uniaxial mechanical stresses. The temperature-spectral and spectral-baric diagrams of the isotropic state of the RbKSO₄ crystal, as well as the baric shifts of the phase-transition temperatures, are determined.     

Instability of the local environment of Mn<Superscript>2+</Superscript> in BaF<Subscript>2</Subscript>

Excitation and luminescence spectra and luminescence lifetime of Mn²⁺ ion in BaF₂ crystals at 77 K have been investigated for the first time. Mn²⁺ ions in the crystal are coordinated by six and eight fluorine ions, have a trigonal environment, and form exchange-coupled pairs. Several types of centers of the Mn²⁺ ion are formed mainly because of the large difference in the Mn²⁺ and Ba²⁺ ionic radii, which causes instability of the local structure around the activator and its strain, and exchange striction. An increase in the impurity concentration enhances these factors, thus changing the relative concentration of various centers.     

Increase in the Fluorine-Ion Conductivity of Single Crystals of Tysonite-type CeF<Subscript>3</Subscript> Superionic Conductor by Substituting Polarized Cd<Superscript>2+</Superscript> Ions for Ce<Superscript>3+</Superscript> Ions

The fluorine-ion conductivity of single crystals with a tysonite (LaF₃) structure with heterovalent isomorphic substitutions of highly polarizable Cd²⁺ cations with a 18-electron shell for rare earth ions Ce³⁺ have been studied for the first time. Ce_0.995Cd_0.005F_2.995 single crystals have been grown from melt by the Bridgman technique in a fluorinating atmosphere. The fluorine-ion conductivity of single crystal is measured by impedance spectroscopy in the temperature range from 153 to 1073 K, where it increases by a factor of 10⁹, approaching the value σ_dc = 5 × 10^–2 S/cm at 1073 K. At T₀ = 450 ± 20 K, the dependence σ_dc(T) is split into two portions with the ion-transport activation enthalpy ΔH_σ = 0.39 ± 0.01 eV (T < T₀) and ΔH_σ = 0.23 ± 0.02 eV (T > T0). It is found that at T = 293 K the conductivity σ_dc = 3 × 10^–5 S/cm of Ce_0.995Cd_0.005F_2.995 crystal is higher by a factor of 10 than the conductivity of the tysonite matrix CeF₃ and close to the σ_dc value for Ce_0.995Sr_0.005F_2.995 crystal. This finding indicates a significant effect of the substitutions of Cd²⁺ ions for Ce³⁺ on the σdc value and the advantage of Cd²⁺ ions over Ca²⁺ and Ba²⁺ from the viewpoint of increasing σ_dc.     

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.     

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.     

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.     

Structural state of a radiation-modified Ti<Subscript>50</Subscript>Ni<Subscript>47</Subscript>Fe<Subscript>3</Subscript> single crystal

The structural state of a Ti₅₀Ni₄₇Fe₃ single crystal irradiated by fast neutrons (F = 2.5 × 10²⁰ cm⁻²) at 340 K was studied by thermal neutron diffraction at 78 and 295 K. The melt of this composition was chosen with the purpose of designing a radiation-resistant material exhibiting a shape-memory effect. It was found that the melt remains crystalline after irradiation, whereas the Ti₄₉Ni₅₁ crystal studied earlier becomes amorphous after an analogous irradiation. In spite of the fact that the main structural motif of the crystal remains unchanged after irradiation, martensitic transformations in the crystal do not occur and, consequently, the shape-memory effect is not retained. The radiation resistance of this class of crystals was estimated.     

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 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.      

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).     

Comparative analysis of the heat transfer processes during growth of Bi<Subscript>12</Subscript>GeO<Subscript>20</Subscript> and Bi<Subscript>4</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript> crystals by the low-thermal-gradient Czochralski technique

The heat transfer processes occurring in the solid and liquid phases during growth of Bi₁₂GeO₂₀ and Bi₄Ge₃O₁₂ crystals by the low-thermal gradient Czochralski method are analyzed and compared. It is experimentally found that, under similar growth conditions, the deflection of the crystallization front for the Bi₁₂GeO₂₀ crystal is considerably smaller than the deflection of the crystallization front for the Bi₄Ge₃O₁₂ crystal and the faceting of the former front is observed at the earlier stage of pulling. The results of the numerical simulation demonstrate that the different behavior of the crystallization fronts is associated with the difference between the coefficients of thermal absorption in the crystals.     

Stimulated Raman scattering by C<Subscript>12</Subscript>H<Subscript>22</Subscript>O<Subscript>11</Subscript> sugar (sucrose)

The efficient Stokes and anti-Stokes laser emissions with Raman frequency shift at about 2960 cm^?1 are excited in a food C₁₂H₂₂O₁₁ sugar (sucrose) single crystal under pulsed pumping. Other (χ⁽²⁾ + χ⁽³⁾) effects of the parametric Raman generation are also detected.     

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.     

Atomic structure and mechanism of ionic conductivity of Li<Subscript>3.31</Subscript>Ge<Subscript>0.31</Subscript>P<Subscript>0.69</Subscript>O<Subscript>4</Subscript> single crystals

The atomic structure of Li_3.31Ge_0.31P_0.69O₄ single crystals was refined based on high-precision X-ray diffraction data at 293 K. The characteristic features of the crystal structure are considered, and their influence on high ionic conductivity (Li⁺) of these crystals is discussed.     

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.     

Crystal structure of the binary complex of cobalt and zinc chlorides with carbamide [Co(OCN<Subscript>2</Subscript>H<Subscript>4</Subscript>)<Subscript>5</Subscript>(H<Subscript>2</Subscript>O)][ZnCl<Subscript>4</Subscript>]

Mixed single crystals of [Co(OCN₂H₄)₅(H₂O)][ZnCl₄] were grown by the isothermal evaporation of an aqueous solution. The crystal structure of this complex was established by X-ray diffraction (R = 0.052 based on 7003 reflections). The crystals consist of [Co(OCN₂H₄)₅(H₂O)]²⁺ cations containing Co atoms in an octahedral coordination and [ZnCl₄]²⁻] anions containing Zn atoms in a tetrahedral coordination. The carbamide molecules are involved in both intramolecular and interionic hydrogen bonds. The H₂O molecule forms hydrogen bonds with the anions.