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.     

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.     

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.     

Growth of Cr<Superscript>4+</Superscript>: LiGaSiO<Subscript>4</Subscript> single crystals by floating-zone melting technique

The problems of growth of new promising laser crystals Cr⁴⁺: LiGaSiO₄ by the crucible-free floating-zone method with optical heating are considered. The use of high axial temperature gradients with intense stirring of the melt makes it possible to obtain crystals of satisfactory optical quality from stoichiometric melt, despite the incongruent character of the compound melting.     

Investigation of the optical properties of KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Nd<Superscript>3+</Superscript> crystals with allowance for absorption

The optical properties of a biaxial absorbing KGd(WO₄)₂:Nd³⁺ crystal have been investigated. The main refractive indices were measured in the visible spectral range and the absorption and transmission spectra of samples of these crystals were studied. The changes in the refractive indices were in the region of the absorption bands with the use of the Kramers-Kronig relation. Conoscopic pictures of this crystal in the regions of transparency and absorption bands were calculated and are presented.     

Temperature dependence of the crystal-optics characteristics of [N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>]<Subscript>2</Subscript>ZnCl<Subscript>4</Subscript>:Ni<Superscript>2+</Superscript> crystals with correlated motion of tetrahedral groups

The optical birefringence, optical indicatrix rotation, and residual intensity have been experimentally investigated in the parent and incommensurate phases of [N(CH₃)₄]₂ZnCl₄ crystals doped with Ni²⁺. The temperature dependences obtained are nonlinear in a wide temperature range (T _i − 360 K). It is shown that the nature of this nonlinearity is related to the presence of local spatial regions of the correlated motion of tetrahedral groups. It is established that the deformation of tetrahedral groups increases the temperature range of existence of these regions.     

Structural Studies of [Ru(1,8-naphthyridine)<Subscript>4</Subscript>]<Superscript>2+</Superscript> and [Ru(1,5-cyclooctadiene)(1,8-naphthyridine)<Subscript>2</Subscript>]<Superscript>2+</Superscript> as their Tetraphenylborate Salts

Abstract  

The previously reported [Ru(naph)₄]²⁺ complex (naph = 1,8-naphthyridine) has been prepared by a simplified route using [RuCl₂(1,5-COD)] _x (COD = cyclooctadiene) as starting material and isolated as its tetraphenylborate salt. The salt crystallizes in the monoclinic space group P2₁/n with a = 13.6531(3) ?, b = 12.5389(4) ?, c = 20.0349(5) ?, β = 96.5884(15)o, V = 3407.22(16) ?, D _calc = 1.300 at 150(1) K. The dication has crystallographically imposed inversion symmetry. Although the iron analogue has been found to have a coordination number of eight, the ruthenium complex is only six-coordinate, which is achieved by the presence of two monodentate and two bidentate 1,8-naphthyridine ligands. The observation of a higher coordination number for Fe(II) vs. Ru(II) can be explained by the high spin nature of the iron complex. A byproduct complex, [Ru(1,5-COD)(naph)₂][B(C₆H₅)₄]₂, could also be synthesized, isolated pure, and structurally characterized. The organometallic complex possesses an 18 electron configuration by virtue of the dicationic metal center being coordinated by the diene ligand and all four nitrogen lone pairs. This salt crystallizes in the triclinic space group \textP[`1] {\text{P}}\bar{1} with a = 12.9538(3) ?, b = 14.9485(3) ?, c = 17.4291(3) ?, α = 69.0649(11)o, β = 78.3211(9)o, γ = 78.5629(10)o, V = 3057.50(11) ?³, D _calc = 1.293 at 150(1) K.     

Exchange of sodium and silver ions in Na<Subscript>3</Subscript>Sc<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> single crystals

Sodium-and silver-ion exchange in single crystals of two polymorphous modifications of the Na₃Sc₂(PO₄)₃ compound has been studied. It is established that in the process of ion exchange, the samples undergo phase transitions similar to the well-known temperature transformations observed in these systems. It is shown that the phases with ferroelectric, ionic, and superionic properties may simultaneously coexist in one sample.     

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     

Hydrothermal Synthesis and Structure of Fe<Subscript>6.36</Subscript>Mn<Subscript>0.64</Subscript>(PO<Subscript>3</Subscript>(OH))<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Abstract  

Single crystals of iron and manganese phosphate Fe_6.36Mn_0.64(PO₃(OH))₄(PO₄)₂ was synthesized by hydrothermal method. The compound crystallizes in the Fe₇(PO₄)₆ structure type and is isotypic with the solid solution \textM_{7 - \textx} \textM_\textx^￠ ( \textHPO₄ )₄ ( \textPO₄ )₂ {\text{M}}_{{7 - {\text{x}}}} {\text{M}}_{\text{x}}^{\prime} \left( {{\text{HPO}}_{4} } \right)_{4} \left( {{\text{PO}}_{4} } \right)_{2} where M is Fe, Co, Mg, Mn. The compound is triclinic, P-1, a = 6.571(5), b = 7.993(3), c = 9.547(2) Ǻ, α = 103.97(1)°, β = 109.29(2)°, γ = 101.57(3)°. The structure is based on a three-dimensional framework of distorted edge-sharing MO₆ and MO₅ polyhedra, forming infinite chains, which are interlinked by corner-sharing with PO₄ tetrahedra. The formula unit is centrosymmetric, with all atoms in general positions except for one Fe atom, which has site symmetry −1.     

Electrical conductivity of Cs<Subscript>2</Subscript>CuCl<Subscript>4</Subscript> crystals

The electrical conductivity of Cs₂CuCl₄ single crystals, synthesized by crystallization from aqueous solutions in the CsCl–CuCl₂–H₂O system, has been investigated. The temperature dependence of the electrical conductivity of crystals in a temperature range of 338–584 K exhibits no anomalies. The electrical transfer activation enthalpy is ΔH_σ = 0.72 ± 0.05 eV and the conductivity is σ = 3 × 10^–4 S/cm at 584 K. The most likely carriers in Cs₂CuCl₄ are Cs⁺ cations, which transfer electric charge according to the vacancy mechanism.     

The domain structure of Cs<Subscript>3</Subscript>H(SeO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystals

The characteristics of the changes in the domain structure of Cs₃H(SeO₄)₂ crystals have been studied in a wide temperature range. An anomalous change in the domain structure in the temperature range near the superprotonic phase transition was found. The anomalies in this temperature range were also found by differential scanning calorimetry. The characteristics of the changes in the domain structure in different phases are compared.     

Structure of Cs<Subscript>4</Subscript>(HSO<Subscript>4</Subscript>)<Subscript>3</Subscript>(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>) single crystals

Single crystals of Cs₄(HSO₄)₃(H₂PO₄) are synthesized and studied for the first time. The new compound is found in the course of studies of the phase diagram of the CsHSO₄–CsH₂PO₄–H₂O triple system. Data on the atomic crystal structure of single-crystalline and powder specimens, as well as on structural phase transitions, are obtained.     

Birefringence of (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>SO<Subscript>4</Subscript> crystals under the action of uniaxial pressures

The influence of uniaxial mechanical pressure σ _m ≤ 150 bar on the spectral (300–800 nm) dependence of the birefringence Δn _i of (NH₄)₂SO₄ crystals is studied. The dispersion Δn _i (λ) is shown to be normal and greatly increases when approaching the absorption edge. Uniaxial pressure changes the value of dispersion dΔn _i /dλ but not its character. It is found that the simultaneous action of pressures σ _x ～ σ y ～ 560 bar results in the occurrence of a uniaxial isotropic state. Piezoelectric constants of the crystals are estimated.     

Piezo-optic properties of incommensurately modulated K<Subscript>2</Subscript>ZnCl<Subscript>4</Subscript> crystals

The effect that uniaxial pressures along the principal crystallophysical directions have on the dispersion and temperature dependences of the birefringence in incommensurate K₂ZnCl₄ crystals has been investigated in a wide temperature range. This parameter has been established to be fairly sensitive to uniaxial pressures. The spectral and temperature dependences of combined piezo-optic coefficients are analyzed. Significant anomalies of these coefficients are found at the incommensurate-commensurate phase transition. They are due to the change in the induced birefringence that results from spontaneous polarization and to the significant effect of uniaxial stress on the soliton structure of the crystal. The contributions that the electrooptic effect, the elasto-optic effect, and the order parameter make to the spontaneous changes in the piezooptic coefficients are separated.     

Simulation of the OH<Superscript>−</Superscript> group location in the cubic phase of BaTiO<Subscript>3</Subscript> crystals

An investigation of the isolated OH⁻ group location in the nonpolar phase of barium titanate crystals and an analysis of lattice local strains have been performed using computer simulation. It is shown that the presence of the OH⁻ group leads to the formation of a polarized cluster with a rather high electric dipole moment.     

The Fe<Superscript>2+</Superscript>/Fe<Superscript>3+</Superscript> ratio in natural and heat-treated iron-rich eudialytes

The structures of natural iron-rich eudialyte (specimen 3458 from the Khibiny massif, the Kola Peninsula) and two heat-treated samples of this mineral calcined at 700 and 800°C were determined by X-ray diffraction. The trigonal unit-cell parameters (sp. gr. R3m) are as follows: a = 14.2645(1) Å, c = 29.9635(5) Å; a = 14.1307(1) Å, c = 30.1229(3) Å; a = 14.1921(2) Å, c = 30.2417(5) Å, respectively. It was found that Fe³⁺ ions in the calcined eudialytes, as well as impurities in the starting specimen, occupy the square-pyramidal Fe³⁺(V) sites, whereas Fe²⁺ ions are in the planar-tetragonal Fe²⁺(IV) sites.     

Crystal structure of Rb<Subscript>2</Subscript>Mn<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>[P<Subscript>2</Subscript>O<Subscript>7</Subscript>]<Subscript>2</Subscript>, a new representative of the family of hydrated diphosphates

The crystal structure of Rb₂Mn₃(H₂O)₂[P₂O₇]₂, a new phase obtained in the form of single crystals under hydrothermal conditions in the MnCl₂–Rb₃PO₄–H₂O system, is determined by X-ray diffraction (Xcalibur-S-CCD diffractometer, R = 0.0270): a = 9.374(2), b = 8.367(2), c = 9.437(2) Å, ß = 99.12(2)°, space group P2₁/c, Z = 2, D_x = 3.27 g/cm³. A correlation between the unit-cell parameters and the size of cations forming the crystal structures of isostructural A₂M₃(H₂O)₂[P₂O₇]₂ diphosphates (A = K, NH₄, Rb, or Na; _M = Mn, Fe, Co, or Ni) is revealed. It is shown that, due to the topological similarity, the structures of diphosphates and orthophosphates of the farringtonite structural type can undergo mutual transformations.     

Structure and superconductivity of layered oxycarbonate Bi<Subscript>2</Subscript>Sr<Subscript>4</Subscript>Cu<Subscript>2</Subscript>CO<Subscript>3</Subscript>O<Subscript>8</Subscript> crystals

A complex study of the elemental composition, structure, and superconducting properties of single crystals of layered oxycarbonate Bi₂Sr₄Cu₂CO₃O₈ has been performed taking into consideration the growth and postgrowth annealing conditions.     

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.