Dielectric studies on Ba(NO3)2

Single crystals of Ba(NO₃)₂ were grown by slow evaporation of aqueous solution. The dielectric constant (ϵ) and loss (tan δ) have been measured in the frequency range of 100 Hz to 100 KHz at temperatures ranging from room temperature to 400 °C. A.c. conductivity (σ) is calculated from the data on ϵ and tan δ. ϵ, tan δ, and σ were found to show anomalies around 270 °C. The results are discussed in the light of order-disorder phase transition.     

Synthesis and crystal structures of nitratocobaltates Na2[Co(NO3)4], K2[Co(NO3)4], and Ag[Co(NO3)3] and potassium nitratonickelate K2[Ni(NO3)4]

The cobalt(II) and nickel(II) nitrate complexes with an island structure (Na₂[Co(NO₃)₄] (I) and K₂[Co(NO₃)₄] (II)] and a chain structure [Ag[Co(NO₃)₃] (III) and K₂[Ni(NO₃)₄] (IV)] are synthesized and investigated using X-ray diffraction. In the anionic complex [Co(NO₃)₄]^2? of the crystal structure of compound I, the Co coordination polyhedron is a twisted tetragonal prism formed by the O atoms of four asymmetric bidentate nitrate groups. In the anion [Co(NO₃)₄]^2? of the crystal structure of compound II, one of the four NO₃ groups is monodentate and the other NO₃ groups are bidentate (the coordination number of the cobalt atom is equal to seven, and the cobalt coordination polyhedron is a monocapped trigonal prism). The crystal structures of compounds III and IV contain infinite chains of the compositions [Co(NO₃)₂(NO₃)_2/2]^? and [Ni(NO₃)₃(NO₃)_2/2]^2?, respectively. In the crystal structure of compound III, seven oxygen atoms of one monodentate and three bidentate nitrate groups form a dodecahedron with an unoccupied vertex of the A type around the Co atom. In the crystal structure of compound IV, the octahedral polyhedron of the Ni atom is formed by five nitrate groups, one of which is terminal bidentate. The data on the structure of Co(II) coordination polyhedra in the known nitratocobaltates are generalized.     

Structural phase transition in CuFe2O4 spinel

A structural transition with a reduction in symmetry of the high temperature cubic phase (sp. gr. Fd3m) to the tetragonal phase (sp. gr. I4₁/amd) and the appearance of a ferrimagnetic structure occur in CuFe₂O₄ copper ferrite at T ≈ 440°C. It is established by an experiment on a high-resolution neutron diffractometer that the temperature at which long-range magnetic order occurs is higher than that of tetragonal phase formation. When cooling CuFe₂O₄ spinel from 500°C, the equilibrium coexistence of both phases is observed in a fairly wide temperature range (～40°C). The composition studied is a completely inverse spinel in the cubic phase, and in the tetragonal phase the inversion parameter does not exceed few percent (x = 0.06 ± 0.04). At the same time, the phase formed upon cooling has a classical value of tetragonal distortion (γ ≈ 1.06). The character of temperature changes in the structural parameters during the transition from cubic to tetragonal phase indicates that this transition is based on the Jahn-Teller distortion of (Cu,Fe)O₆ octahedra rather than the mutual migration of copper and iron atoms.     

Growth and characterization of ferroelectric‐ferroelastic Tb2(MoO4)3 crystals

Transparent and nearly colorless ferroelectric‐ferroelastic β′‐Tb₂(MoO₄)₃ (TMO) single crystals have been grown by the Czochralski (CZ) method. The single crystal structure was investigated by X‐ray powder diffraction and was shown to be a single phase with the structure similar as the β′‐Gd₂(MoO₄)₃ crystal. The optical transparency of the TMO crystal has been measured and the crystal is almost transparent in the visible and near infrared regions. The defects of TMO crystal were evaluated by etching technique and the ferroelectric domain structures were observed by an optical microscope. A high‐resolution X‐ray diffraction analysis demonstrates that the as‐grown TMO crystal possesses relatively high optical quality. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The growth of single crystals of langbeinites Rb2Cd2(SO4)3, Tl2Cd2(SO4)3, K2Co2(SO4)3, and their phase transitions

Single crystals of dicadmium dirubidium sulphate and dicadmium dithallium sulphate have been grown from non-stoichiometric aqueous solutions by various methods. Optical and thermal properties in the vicinity of their phase transitions have been studied. Polycrystalline samples of dicobalt dipotassium sulphate have been prepared using Bridgman method. Optical and specific heat measurements have shown a new phase transition at −148°C.     

Crystalloluminescence and Mechanoluminescence Spectra of Ba(ClO3)2 · H2O and 2 K2SO4 · Na2SO4 Crystals

Crystalloluminescence and mechanoluminescence of Ba(ClO₃)₂ · H₂O and 2 K₂SO₄ · Na₂SO₄ crystals are investigated. The crystalloluminescence spectra are almost similar to the photoluminescence spectra; however, they differ completely from the mechanoluminescence spectra. The crystalloluminescence excitations may take place due to the various processes: (i) the recombination of ions, (ii) from amorphous to crystalline transition, (iii) from the phase change during the crystallization, and (iv) from the dielectric breakdown by the electric field produced due to the creation of microfracture during the crystal growth. It is concluded that the crystalloluminescence excitation in Ba(ClO₃)₂ · H₂O and 2K₂SO₄ · Na₂SO₄ crystals may be chemical in origin.     

Ba3(VO4)2晶体的生长和拉曼性质的研究

采用提拉法生长了尺寸为φ22mm×50 mm的Ba3(VO4):晶体.室温下测试了Ba3(VO4)2晶体不同激发配置下自发拉曼散射光谱.另外测试了该晶体在532 nm、25 ps脉冲下的受激拉曼散射,观察到3阶斯托克斯线(625.5 am)和1阶反斯托克斯线(506.8 nm),并估算了Ba3(VO4)2晶体的稳态拉曼增益系数.     

Induced smectic A phase by homeotropic orientation in 4, n-octyloxybenzoic acid (OOBA) at nematic-smectic C phase transition

Using homeotropic and quasi-homeotropic orientation in thin film of 4-n-octyloxybenzoic acid, we indicated intermediate smectic A-like state during the nematic-smectic C phase transition. Pseudoisotropic and focal conic textures are characteristic for homeotropic and quasihomeotropic orientations respectively. The smectic A-like state induced by the boundary conditions exists in a very short (about 0.5 °C) temperature region.     

Crystal structure and phase transition in the compound [C6H5CH2NH(CH3)2]TlCl4

The N‐N dimethyl benzylammonium tetrachlorothallate (III) [C₆H₅CH₂NH(CH₃)₂]TlCl₄ crystallizes in the monoclinic system P2₁/n at room temperature with the following unit cell dimensions: a = 7.725(3) Å, b = 14.080(5) Å, c = 13.697(4) Å, β = 91.2(2)° with Z = 4. The structure shows a layer arrangement perpendicular to the b axis: planes of [TlCl₄]^‐ tetrahedra alternate with planes of [C₆H₅CH₂NH(CH₃)₂]⁺ cations. The cohesion of the atomic arrangement is ensured by hydrogen bonds N‐H…Cl. Differential scanning calorimetric and optical birefringence measurements reveals a phase transition at T = 339K. Raman spectroscopic study and dielectric measurements were performed to discuss the mechanism of the phase transition. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and studies of new crystals in the K3H(SO4)2-(NH4)3H(SO4)2-H2O system

To elucidate the effect of isomorphic substitution on the kinetics of phase transitions, single crystals of (K _x (NH₄)_1?x ) _m H _n (SO₄)_{(m + n)/2} · yH₂O solid solutions are grown from the K₃H(SO₄)₂-(NH₄)₃H(SO₄)₂-H₂O system, whose end members are known to undergo superprotonic phase transitions of fundamentally different kinetics. The chemical composition of the single crystals grown is determined by energy dispersive X-ray microanalysis. The thermal and optical behavior of (K,NH₄)₉H₇(SO₄)₈ · H₂O single crystals is studied in the temperature range 295–420 K and the crystal structure at 295 K is determined. A comparison of the results of the studies with data for crystal K₉H₇(SO₄)₈ · H₂O published earlier shows that the substitution of ammonium for potassium atoms lowers the temperature of the structural phase transition by 8 K.     

Crystal growth of ferroelastic K2Cd2(SO4)3 and the K2SO4-CdSO4 phase diagram

Crystals of congruently melting K₂Cd₂(SO₄)₃ (having the langbeinite structure with a ferroelastic transition temperature of 156°C) were grown by the Bridgman and Czochralski techniques. The former yielded colorless crystals when using oxygen under pressure; the latter yielded tan crystals of slightly smaller unit cell volume and are assumed to be oxygen deficient. The ferroelastic transition was studied by thermal expansion measurements. Reexamination of the phase diagram showed the existence of a previously unreported phase K₆Cd(SO₄)₄ which is stable only between 520°C and the melting point of about 890°C.     

Alkali-metal hydrogen selenate-phosphates M 2 H 3(SeO4)(PO4) (M = Rb or K) and M 4H5(SeO4)3(PO4)(M = K or Na)

Crystalline hydrogen selenate-phosphates M ₂H₃(SeO₄)(PO₄) [M = Rb (I) or K (II)] and M ₄H₅(SeO₄)₃(PO₄) [M = K (III) or Na (IV)] were obtained by reactions of Rb, K, and Na carbonates with mixtures of selenic and phosphoric acid solutions. The X-ray structure study of single crystals revealed that I and II are isostructural (sp. gr. Pn). In these structures, SeO₄ and H₃PO₄ tetrahedra are linked by hydrogen bonds to form corrugated layers. Structures III and IV (sp. gr. $P\bar 1$ ) have similar arrangements of non-hydrogen atoms but different hydrogen-bond systems. In III = K₄(HSeO₄)₂{H[H(Se,P)O₄]₂}, the HSeO₄ groups branch from the infinite anionic {H[H(Se,P)O₄]₂} chains. In IV = Na₄[H(SeO₄)₂]{H[H_1.5(Se, P)O₄]₂}, the anionic {H[H_1.5(Se,P)O₄]₂} chains are crosslinked by hydrogen bonds formed by the [H(SeO₄)₂] dimers.     

The Characteristics of the Mixed Crystals of the K2SO4-(NH4)2SO4-H2O System at 298 K

Equilibrium studies of the K₂SO₄-(NH₄)₂SO₄-H₂O system at 298 K have been conducted. The isotherm of solubility and the curve of distribution have been mathematically described. The parameters of the crystal lattice and the enthalpy of crystallization of the [K_x(NH₄)_1-x]₂SO₄ solid solutions as a function of their composition have been presented.     

A neutron diffraction study of the phase transition of fully deuterated triglycine sulphate (ND2CD2COOD)3.D2SO4

Using neutron single crystal and powder diffraction, the first thorough investigation of the structure of fully deuterated triglycine sulphate, (ND₂CD₂COOD)₃.D₂SO₄ is presented, including its evolution with T, through its structural phase transition. This includes new precise structural parameters determined at several key temperatures above and below T_C using single crystal diffraction, and for the first time a parametric study has been undertaken over a wide temperature range — from 4 to 500 K in 2 K steps. It was found that fully deuterated TGS shows a structure consistent with hydrogenous TGS and partially deuterated TGS. The evolution of several key hydrogen bond lengths suggests that weakening of the H‐bond network with T is crucial in decoupling the polarising glycine molecules from the other glycines and allowing the long‐range ferroelectric order to break down. A new parameterisation of the phase transition is demonstrated. Contrary to results of physical properties measurements, there is no evidence of a second low temperature phase transition in TGS – no low temperature anomalies were observed in the crystal structure.     

Bimetallic hydrogen sulfates K4 M II[H(SO4)2]2(H2O)2 (M II = Mn or Zn)

Hydrogen sulfate hydrates K₄{M ^II[H(SO₄)₂]₂(H₂O)₂}, where M ^II = Mn or Zn, are synthesized, and their single-crystal structures are determined by X-ray diffraction. The structural units of the orthorhombic crystals (space group Pccn) are potassium and M ^II cations, SO ₄ ^2? and HSO ₄ ^? anions, and water molecules. Strong (2.52 Å) and moderate-in-strength (2.71–2.75 Å) hydrogen bonds link the anions and water molecules into hexamers. The M ^II cations, which have the octahedral environment (Mn-O, 2.14–2.19 Å and Zn-O, 2.07–2.11 Å), link the hexamers into flat layers. The structures of bimetallic hydrogen chalcogenate hydrates with different compositions are compared.     

DC conductivity studies in K3Na(SeO4)2 single crystals

DC electrical conductivity studies were carried out along the three crystallographic axes for Tripotassium sodium diselenate (K₃Na(SeO₄)₂ or KNSe). Earlier studies of phase transition in this crystal show successive phase transitions at 334 K, 346 K, 730 K, and 758 K. In this paper we report the dc electrical conductivity measurements in the temperature region 303 K – 430 K along a, b and c – axes. An anomaly in conductivity was obtained around 341 K and another one around 333 K. These can be attributed as due to phase transitions in this crystal. A strong anomaly also has been observed along the c‐axis and comparatively week one along a and b axes around 395 K for the first time. This can be due to newly observed phase transition in the crystal. DSC taken for the sample also shows endothermic peak supporting the occurrence of newly observed phase transition. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ferroelectric and ferroelastic properties of Rb2MnCl4·2H2O

Rb₂MnCl₄·2H₂O crystal belonging to the family of tetrahalogeno‐metallates dihydrates has been subjected to thermal, optical and dielectric studies. At room temperature the optical study under a polarization microscope has revealed a ferroelastic domain structure. At 240 K a dielectric anomaly, characteristic of the week ferroelectric phase transition, has been also observed. Moreover, below the temperatures of the phase transitions dielectric dispersion has appeared. Ferroic properties of Rb₂MnCl₄·2H₂O crystal have been compared to those of other tetrachlorides dehydrates. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self-assembly in transition metal complexes: structural characterization of a copper histamine nitrate [Cu(II)(him)2(NO3)2]

A new monomeric copper (II) complex with histamine (him), [Cu(II)(him)₂(No₃)₂], has been prepared by the reaction of Cu(NO₃)₂ with histaminium dichloride and its structure was determined by x-ray crystallography. The complex crystallizes in the triclinic system, space group with a = 5.7238(4), b = 8.7094(7), c = 9.2481(11) Å, = 69.693(8), = 73.242(7), = 71.050(7)°, V = 400.84(6) ų, and Z = 1. The structure consists of discrete [Cu(II)(him)₂(NO₃)₂] molecules in which the metal atom is centrosymmetrically coordinated by two histamine ligands forming an equatorial plane with Cu–N(imidazole ring) being 2.032(2) and Cu–N(NH₂ group) being 2.023(2) Å. Two O atoms from nitrate anions coordinate on the elongated axial positions with Cu–O being 2.549(2) Å. In the crystal structure, the molecules are organized by hydrogen bonds forming a two-dimensional network.