The role of structural and nonstructural water in oxyfluoride K<Subscript>2</Subscript>WO<Subscript>2</Subscript>F<Subscript>4</Subscript> · H<Subscript>2</Subscript>O

X-ray structural and polarization optical investigations have been performed, and birefringence and rotation angles of the optical indicatrix φ _b and φ _c of the K₂WO₂F₄ · H₂O crystal have been measured in the temperature range of 100–600 K. The structure and symmetry of compounds at room temperature have been refined. It has been established that the layered crystal K₂WO₂F₄ · H₂O can exist in two states (A and B) depending on the atmospheric humidity and undergoes the sequence of reversible and irreversible phase transformations G ₃ ↔ G ₂ → G ₁ → G ₀. The sequences of changes in the phase symmetry P [`1]\bar 1 ↔ C2/m → P4/nmm for samples A and m ↔ C2/m → P4/nmm for samples B have been found. The second-order proper ferroelastic phase transition (P [`1]\bar 1 ↔ C2/m) at T ₀₃ = 270–290 K (G ₃ ↔ G ₂) is accompanied by twinning and appearance of the shift deformation x ₆. The crystal system of the substance for the B crystals remains invariable after the second-order phase transition G ₃ ↔ G ₂. The irreversible first-order phase transition G ₂ → G ₁ occurs in a temperature range T ₀₂ ≈ 350–380 K; it is accompanied by the loss of the crystallization water, which then is reduced easily from the atmosphere for a day. The substance decomposes at T ₀₁ ≈ 510 K (G ₁ → G ₀). The distinction between the A and B crystals has been explained by the presence or absence of free water in interlayer spacings.     

Preparation and characterization of organic–inorganic hybrid compound [N(C<Subscript>4</Subscript>H<Subscript>9</Subscript>)<Subscript>4</Subscript>]<Subscript>2</Subscript>Cu<Subscript>2</Subscript>Cl<Subscript>6</Subscript>

Organic–inorganic hybrid sample [N(C₄H₉)₄]₂Cu₂Cl₆ was prepared via the reaction between copper chloride and tetrabutylammonium chloride. The compound was characterized by X-ray powder diffraction, IR, Raman, differential scanning calorimetry (DSC), DTA-TGA analysis and electrical impedance spectroscopy. DSC studies indicate a presence of one-phase transition at 343 K. The complex impedance of compound [N(C₄H₉)₄]₂Cu₂Cl₆ have been investigated in temperature and frequency ranges 300–380 K and 200 Hz–5 MHz, respectively. The Z′ and Z″ versus frequency plots are well fitted to an equivalent circuit model. The circuits consist of the parallel combination of bulk resistance R _p and constant phase elements CPE. The frequency dependence of the conductivity is interpreted in term of Jonscher's law: s(w) = s_dc + Awⁿ \sigma (\omega ){ } = {\sigma_{\rm{dc}}} + { }A{\omega^n} . The conductivity follows the Arrhenius relation. The variation of the value of these elements with temperatures confirmed the availability of the phase transition at 343 K detected by DSC and electrical measurements.     

Magnetic structure of molecular magnet Fe[Fe(CN)<Subscript>6</Subscript>]·4H<Subscript>2</Subscript>O

We have studied the magnetic structure of Fe[Fe(CN)₆]·4H₂O, prepared by precipitation method, using neutron diffraction technique. Temperature dependent DC magnetization study down to 4.2 K shows that the compound undergoes from a high temperature disordered (paramagnetic) to an ordered magnetic phase transition at 22.6 K. Rietveld analysis of neutron diffraction pattern at 60 K (in its paramagnetic phase) revealed a face centred cubic structure with space group Fm3m. The structure contains three-dimensional network of straight Fe³⁺-C≡N-Fe³⁺ chains along the edges of the unit cell cube. Fe³⁺ ions occupy 4a (0, 0, 0) and 4b (1/2, 1/2, 1/2) positions. Fe³⁺(0, 0, 0) is surrounded octahedrally by six nitrogen atoms and Fe³⁺ (1/2, 1/2, 1/2) is surrounded octahedrally by six carbon atoms. Magnetic Rietveld refinement of neutron diffraction data at 11 K shows a ferromagnetic coupling between the two inequivalent Fe³⁺ sites. Refinement yielded an ordered moment of 4.4(6) and 0.8(6) μ_B per Fe ion located at (0, 0, 0) and (1/2, 1/2, 1/2), respectively. Ordered moments are found to align along the face diagonal. The observed net moment from low temperature neutron diffraction study is consistent with DC magnetization results.     

Calculation of refractive indices for the (NH<Subscript>2</Subscript>CH<Subscript>2</Subscript>COOH)<Subscript>2</Subscript> · HNO<Subscript>3</Subscript> crystal

The refraction R of the diglycine nitrate (DGN) crystal, (NH₂CH₂COOH)₂ · HNO₃, in the para-and ferroelectric phases has been calculated in the model of noninteracting diatomic chemical bonds of the elementary unit cell of the crystal on the basis of the longitudinal and transversal polarizabilities of these bonds. The calculated magnitudes of the principal refractive indices n _p , n _m , and n _g and the orientations of the optical indicatrix of the crystal agree satisfactorily with experimentally observed values. Introducing the coefficient of Lorenz-Lorentz interaction x into the corresponding formula permits better agreement of the calculated and experimental refractive indices of DGN crystal to be obtained. The temperature changes of these x coefficients upon the ferroelectric phase transition in the DGN crystal have been analyzed.     

Effect of the humidity on the uptake of NO<Subscript>3</Subscript> on coatings composed of MgCl<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O and MgBr<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O and mixtures thereof with NaCl

The reactive uptake of NO₃ radicals on the surface of wetted individual X salts and of wetted X-NaCl salts (X = MgCl₂ · 6H₂O and MgBr₂ · 6H₂O) at [H₂O] = 2 × 10¹²−2 × 10¹⁵ cm⁻³ and NO₃ (4.8 × 10¹² cm⁻³) was studied using a reactor with a movable insert covered with a salt coating in combination with a mass spectrometer for monitoring the initial reactant and products. The probabilities of NO₃ uptake γ on X-NaCl binary salts as functions of the content of doping salt were determined. A parametric approximation of the experimental data was proposed, which makes it possible to quantitatively predict the extent of surface enrichment of a wetted binary salt coating in doping salt and its dependence on the humidity and the content of this salt in the binary mixture. It was established that the relative surface density σ_X of X doping salt depends on its mole fraction μ_X in the X-NaCl binary salt as σ_X = aμ_X (a = 2.2 for MgBr₂ and 13.1 for MgCl₂) over the entire humidity range covered. The contributions of the X salts to the overall uptake of NO₃ at NO₃ concentration typical of the tropospheric conditions ([NO₃] ∼ 10⁷ cm⁻³ and relative humidities of RH ≤ 20%) were estimated.     

Long-range magnetic order in copper nitrate monohydrate Cu(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> · H<Subscript>2</Subscript>O

The magnetic phase diagram of copper nitrate monohydrate Cu(NO₃)₂ · H₂O and the basic parameters of its magnetic subsystem have been determined by measuring the thermodynamic properties of this compound. This compound becomes antiferromagnetically ordered at T _N = 3.6 K, undergoes the spin-flop and spin-flip transitions at H _C1 ～ 0.06 T and H _C2 ～ 1.1 T, respectively, at low temperatures. The magnetization of Cu(NO₃)₂ · H₂O at T _SR = 2.7 K exhibits an additional anomaly, which is likely attributed to the spin-reorientation transition.     

Synthesis and characterization of oxide cathode materials of the system (1-x-y)LiNiO<Subscript>2</Subscript>·xLi<Subscript>2</Subscript>MnO<Subscript>3</Subscript>·yLiCoO<Subscript>2</Subscript>

Composite cathode materials produced by integrating isostructural (2D-layered) compounds LiNiO₂, LiCoO₂, and Li₂MnO₃ (Li(Li_1/3Mn_2/3)O₂) have been investigated utilizing a compositional phase diagram. The samples were characterized by multiple techniques to establish structure–property relationships. Specifically, for structural characterization, powder X-ray diffraction, scanning electron microscopy, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy were carried out. For properties, electrochemical characterization was carried out. The best composition showed a discharge capacity of 244 mAh/g (C/15 rate) in the testing range of 4.6–2 V, with good coulombic efficiency and cyclability.     

Fluorescent Property of the Gd<Superscript>3+</Superscript>-Doped Terbium Complexes and Crystal Structure of [Tb(TPTZ)(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>]Cl<Subscript>3</Subscript>·3H<Subscript>2</Subscript>O

The complex of Tb(TPTZ)Cl₃·3H₂O was synthesized by adding the ethyl alcohol solution of TbCl₃ (1 mmol) to the solution of 2,4,6-tris-(2-pyridyl)-s-triazine(TPTZ,1 mmol) with constant stirring. The solution which had been filtered was kept at the room temperature for 4 weeks, and then a kind of transparent crystal was formed. Besides, nine kinds of solid complexes in the different molar proportion of terbium to gadolinium had been synthesized by adopting the similar method mentioned above. It was inferred from the elemental analysis and rare earth complexometry that the composition of these complexes is (Tb_xGd_y)(TPTZ)Cl₃·3H₂O (x : y = 0.9 : 0.1, 0.8 : 0.2, 0.7 : 0.3, 0.6 : 0.4, 0.5 : 0.5, 0.4 : 0.6, 0.3 : 0.7, 0.2 : 0.8, 0.1 : 0.9). The absorption spectra and photoluminescence of the complexes were determined in dimethylsulfoxide (DMF), which showed that the excitation of the complexes is mostly ligand based. The triplet state energy level of TPTZ was measured, indicating that the lowest excitation state energy level of Tb(III) and the triplet state energy level of TPTZ match well each other. The fluorescent data indicated that the fluorescent emission intensity of Tb³⁺ ions would be enhanced in the complexes after terbium was doped with Gd³⁺ ion. When x : y was 0.5 : 0.5, the fluorescent emission intensity was the largest. The result obtained by testing the X-ray diffraction of the monocrystal revealed that the molecular formula of the mono-crystal complex is [Tb(TPTZ)(H₂O)₆]Cl₃·3H₂O. The number of metal ion coordinates is nine, and the tridentate TPTZ and six water molecules are bonded with terbium respectively. Besides, it also revealed that the monocrystal belongs to the monoclinic system, and space group Cc with the following unit cell parameters is a = 1.4785 (3) nm, b = 1.0547 (2) nm, c = 1.7385 (4) nm, β = 94.42 (3)°, V = 2.7028 (9) nm³ and Z = 4.     

Synthesis and characterization of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>·LiMn<Subscript>0.33</Subscript>Fe<Subscript>0.67</Subscript>PO<Subscript>4</Subscript>/C cathode materials

A new polyanionic cathode material, Li₃V₂(PO₄)₃·LiMn_0.33Fe_0.67PO₄/C for lithium-ion batteries, was synthesized using a sol-gel method and with N,N-dimethyl formamide as a dispersion agent. The analysis of electron transmission spectroscopy and X-ray diffraction revealed that the composite contained two phases. The material has high crystallinity with a grain size of 20–50 nm. The valence states of Mn, V, and Fe in the composite were analyzed by X-ray photoelectron spectroscopy. The electrochemical kinetics in Li₃V₂(PO₄)₃ is effectively enhanced by the incorporation of LiMnPO₄ and LiFePO₄, via structure modification and reduced Li diffusion length. The Li₃V₂(PO₄)₃·LiMn_0.33Fe_0.67PO₄/C materials displayed high rate capacity and steady cycle performance with discharge capacity remained 148 mAh g^?1 after 50 cycles at the rate of 0.2C. In particular, the composite exhibited excellent reversible capacities, with the values of 157, 134, 120, 102, and 94 mAh g^?1 at charge/discharge 0.2, 0.5, 1, 2, and 5C rates, respectively.     

<Superscript>2</Superscript>H NMR investigation of the transition to the proton glass state in the Cs<Subscript>5</Subscript>H<Subscript>3</Subscript>(SO<Subscript>4</Subscript>)<Subscript>4</Subscript> · 0.5H<Subscript>2</Subscript>O crystal

A crystal of the Cs₅H₃(SO₄)₄ · xH₂O (x ≈ 0.5) (PCHS) compound, which belongs to the family of proton conductors with a complex system of hydrogen bonds, is investigated by ²H NMR spectroscopy. The temperature and orientation dependences of the ²H NMR spectra are measured and analyzed. It is established that, upon transition to the glassy phase at the temperature T _g = 260 K, the parameters characterizing the proton exchange between positions in hydrogen bonds remain unchanged to within the limits of experimental error. The protons in the two-dimensional network of hydrogen bonds in the (001) plane are dynamically disordered over possible positions down to temperatures considerably lower than the glass transition point T _g . However, water molecules are fixed at particular structural positions in the phase transition range. In PCHS crystals with a nonstoichiometric water content, this circumstance can be responsible for the frustration that leads to the formation of the glassy state.     

Atomistic simulation of sodium–gadolinium molybdate of stoichiometric (Na<Subscript>1/2</Subscript>Gd<Subscript>1/2</Subscript>MoO<Subscript>4</Subscript>) and cation-deficient (Na<Subscript>2/7</Subscript>Gd<Subscript>4/7</Subscript>MoO<Subscript>4</Subscript>) compositions

Crystals of sodium–gadolinium molybdates of two compositions: stoichiometric (Na_1/2Gd_1/2MoO₄) and cation-deficient (Na_2/7Gd_4/7MoO₄) composition in which 1/7 of the corresponding cation positions are not occupied are simulated by the method of interatomic potentials. For cation-deficient crystals, two kinds of cation position distribution are considered: the statistical distribution of sodium, gadolinium, and unoccupied cation positions in the I4₁/a structure and their partial ordering in the I space group. As a result of the simulation, structural characteristics of sodium–gadolinium molybdates agreeing well with the known experimental data are obtained. In addition, a number of important elastic and thermodynamic properties of these compounds are predicted. The results obtained in the partial-occupancy approximation and by constructing a 7 × 2 × 2 supercell are compared. The local structure of sodium–gadolinium molybdates are analyzed in detail. The influence of the deviation from the stoichiometry as well as cation ordering on the properties of these crystals is discussed.     

O<Subscript>2</Subscript> photodesorption from AuO<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and Au<Subscript>2</Subscript>O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>

Using time-resolved photoelectron spectroscopy, the decay channels of AuO₂⁻ and Au₂O₂⁻ following photoexcitation with 3.1-eV photons have been studied. For AuO₂⁻, a state with a rather long lifetime of 30 ps has been identified. Its decay path could not be determined but photodesorption can be excluded. For Au₂O₂⁻, the spectra indicate O₂ desorption after 3.1-eV photoexcitation on a time scale of 1 ps. While comparing these results on Au _n O₂⁻ with analogous data on Ag _n O₂⁻ clusters, a discernible pattern emerges: for dissociatively bound O₂(AuO₂⁻, Ag₃O₂⁻), there are long-living excited states which do not decay by oxygen desorption, while for molecular chemisorption (Au₂O₂⁻, Ag₂O₂⁻, Ag₄O₂⁻, Ag₈O₂⁻), the 3.1-eV photoexcitation triggers fast O₂ desorption with a high quantum yield.     

Antiferromagnetic inclusions in organic semiconductor (DOEO)<Subscript>4</Subscript>[HgBr<Subscript>4</Subscript>] · TCE

The systematic studies of the electronic state of surface layers in organic semiconductor (DOEO)₄[HgBr₄] · TCE by X-ray photoelectron spectroscopy and UV photoelectron spectroscopy are performed. At temperatures below 50–70 K, a transition to the antiferromagnetic state is observed in inclusions having a different structure compared to the crystal bulk. According to transmission electron microscopy, there are two types of antiferromagnetic inclusions in the samples, with sizes of 2–5 and 100–400 nm. The contributions of antiferromagnetic inclusions and the spins of localized and free charge carriers (holes) to the total magnetic moment of the crystal are separated.     

Electrical conductivity and dielectric relaxation studies on microwave synthesized Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>·NaPO<Subscript>3</Subscript>·MoO<Subscript>3</Subscript> glasses

Electrical conductivity and dielectric relaxation studies on SO₄ ^2? doped modified molybdo-phosphate glasses have been carried out over a wide range of composition, temperature and frequency. The d.c. conductivities which have been measured by both digital electrometer (four-probe method) and impedance analyser are comparable. The relaxation phenomenon has been rationalized using electrical modulus formalism. The use of modulus representation in dielectric relaxation studies has inherent advantages viz., experimental errors arising from the contributions of electrode-electrolyte interface capacitances are minimized. The relaxation observed in the present study is non-Debye type. The activation energies for relaxation were determined using imaginary parts of electrical modulus peaks which were close to those of the d.c. conductivity implying the involvement of similar energy barriers in both the processes. The enhanced conductivity in these glasses can be attributed to the migration of Na⁺, in expanded structures due to the introduction of SO₄ ^2? ions.     

Elastic properties of TeO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Ag<Subscript>2</Subscript>O glasses

A series of glasses [(TeO₂) _x (B₂O₃)_1−x ]_1−y [Ag₂O] _y with x = 70 and y = 10, 15, 20, 25 and 30 mol% were synthesised by rapid quenching. Longitudinal and shear ultrasonic velocity were measured at room temperature and at 5 MHz frequency. Elastic properties, Poisson's ratio, microhardness, softening temperature and Debye temperature have been calculated from the measured density and ultrasonic velocity at room temperature. The experimental results indicate that the elastic constants depend upon the composition of the glasses and the role of the Ag₂O inside the glass network is discussed. Estimated parameters based on Makishima–Mackenzie theory and bond compression model were calculated in order to analyse the experimental elastic moduli. Comparison between the experimental elastic moduli data obtained in the study and the calculated theoretically by the mentioned above models has been discussed.     

Specific features of spin-variable properties of [Fe(acen)pic<Subscript>2</Subscript>]BPh<Subscript>4</Subscript> · <Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O

The [Fe(acen)pic₂]BPh₄ · nH₂O compound has been synthesized and studied in the temperature interval of 5–300 K by the methods of EPR and magnetic susceptibility. The existence of ferromagnetic interactions between Fe(III) complexes in this compound has been revealed, in contrast to unhydrated [Fe(acen)pic₂]BPh₄. The reduction in the integrated intensity of the magnetic resonance signal as the temperature decreases below 80 K has been explained by the transition of high-spin ions to the low-spin state. It has been shown that the phase transition temperature in the presence of intermolecular (ferromagnetic) interactions is lower than that in the case of noninteracting centers.     

White,green, and yellow photoluminescence in the (CaO · Al<Subscript>2</Subscript>O<Subscript>3</Subscript> · SiO<Subscript>2</Subscript>): Eu system

It is shown that nitrogen-laser excited (2CaO · m(Al₂O₃) · SiO₂): Eu photoluminescent phosphors obtained by direct solid-state synthesis at 1350°C emit white, green, and yellow lights when Al₂O₃ content m in the system decreases from 0.40 to 0.05. The coordinates of these colors correspond to the coordinates of light warning systems according to International Commission on Illumination (CIE) and are close to the coordinates of primary colors in the EBU and NTSC TV standards.     

Size effect in spin-crossover systems investigated by FORC measurements,for surfacted [Fe(NH<Subscript>2</Subscript>-trz)<Subscript>3</Subscript>](Br)<Subscript>2</Subscript>·3H<Subscript>2</Subscript>O nanoparticles: reversible contributions and critical size

We investigated the thermal transition of coated nano-particles of the title compound, on a set of samples of average diameter ⟨d⟩ ~ 30, 50, 70, 110 nm, with rather broad size distributions. As expected, the width of the major hysteresis loop was an increasing function of ⟨d⟩. We recorded first-order reversal curves (FORC), the initial parts of which displayed a finite slope, revealing the presence of reversible contributions expected from particles smaller than the critical size d _C associated with the collapse of the hysteresis loop. Kinetic effects were also evidenced thanks to isothermal stages. Reversibility of the FORC curves at the vicinity of the reversal temperature was controlled. Thanks to the reversibility property we could determine the reversible contributions to the total response of all samples and derive the corresponding d _C values. Consistent results were obtained by accounting for an anhysteretic contribution from the large particles, leading to an accurate determination d _C  ~ 45−50 nm, much better than the width of the size distributions.     

Growth of polar Al(IO<Subscript>3</Subscript>)<Subscript>3</Subscript> · 8H<Subscript>2</Subscript>O crystals from aqueous solutions

The growth conditions of perfect acentric aluminum iodate octahydrate (Al(IO₃)₃ · 8H₂O) crystals from aqueous solutions was experimentally studied. The properties of the crystals grown are reported.