Effect of cation substitution in Cs<Subscript>1–2<Emphasis Type="Italic">x</Emphasis></Subscript>Ba<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript> on structural properties and proton conductivity

We synthesized compounds with partial substitution of Cs⁺ cations in CsH₂PO₄ by Ba²⁺ cations. The structural, electron transport and thermodynamic properties of Cs_1–2x Ba _x H₂PO₄ (x = 0–0.15) were studied for the first time with the help of a set of physicochemical methods: infrared and impedance spectroscopy, X-ray diffraction and synchronous thermal analysis. The proton conductivity of Cs_1–2x Ba _x H₂PO₄ at 50–230°C was investigated in detail by impedance measurements. The formation of solid substitution solutions isostructural with CsH₂PO₄ (P2₁/m) is observed in the range of substitution degrees of x = 0–0.1, with a slight decrease in the unit cell parameters and some salt amorphization. The conductivity of disordered Cs_1–2x Ba _x H₂PO₄ in the low-temperature region increases by two orders of magnitude at x = 0.02 and increases with an increasing fraction of barium cations by three or four orders of magnitude at x = 0.05–0.1; the superionic phase transition practically disappears. At x = 0.15, heterophase systems based on salts are formed, showing high conductivity and a further decrease in the activation energy of conductivity to 0.63 eV. The conductivity of the high-temperature phase of Cs_1–2x Ba _x H₂PO₄ does not change with increasing fraction of the substituent.     

Influence of Matrix Nature on the Structural Characteristics of In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CeO<Subscript>2</Subscript> and SnO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> Composites Fabricated by the Impregnation Method

The structural characteristics, valence states, and distribution of cerium ions between the components in In₂O₃–CeO₂ and SnO₂–CeO₂ nanocomposites fabricated using the impregnation method were studied. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) were used to show that, during impregnation, cerium ions are not included into In₂O₃ crystals and are disposed only on their surface in the form of nano-sized crystallites or amorphous clusters. On the other side, under the contact of CeO₂ clusters with a surface of SnO₂ matrix crystals, cerium ions penetrate into the surface layer of these crystals. In contrast to an In₂O₃–CeO₂ system, where the addition of CeO₂ does not affect the conduction activation energy, where cerium oxide is added to SnO₂, the observed increase in the resistance of a SnO₂–CeO₂ composite is accompanied by a sufficient increase in activation energy. These data and the XPS spectra confirm the modification of the surface layers of conductive SnO₂ crystals as, a result of the penetration of cerium ions into these layers.     

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.     

A comparative study of singlet-oxygen generation by С<Subscript>60</Subscript> and С<Subscript>70</Subscript> fullerenes

The results of comparative investigations of singlet-oxygen generation by С₆₀ and С₇₀ fullerenes in tetrachloromethane solutions, aqueous suspensions, and solid-phase powders of fullerenes optically excited by cw diode arrays with different wavelengths and by pulsed xenon lamps with a band filter are presented. The measurements were performed by recording singlet-oxygen phosphorescence at the O²(¹Δ_g)–O₂(³Σ_g) transition (λ = 1270 nm).     

Emission spectra and stimulated emission characteristics of [N<Subscript>2</Subscript>]<Subscript>2</Subscript>−N<Subscript>2</Subscript> molecular dimer

It has been proved byab initio calculation and theoretical analysis that there exist [N₂]₂−N₂ molecular dimers with D_2h symmetry group, and there also exists an electric dipole excimer-like transition a¹B_2g→a¹B_3u. The theoretical spectra accord with the experimental results for transition a¹B_2g→a¹B_3u. The stimulated emission characteristic of N₂ molecular dimer was researched through the microwave excited highly pure nitrogen and the method of amplified spontaneous emission. The experimental results show that N₂ molecular dimer has stimulated emission characteristics when the microwave power is more than 100 W and the N₂ pressure is in the range from 260 Pa to 2200 Pa.     

Intermediate phases in [111]- and [001]-oriented PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>–29PbTiO<Subscript>3</Subscript> single crystals

Phase transformations in [111]- and [001]-oriented PbMg_1/3Nb_2/3O₃–29PbTiO₃ single crystals have been studied using dielectric and optical measurements before and after applying an electric field. It is shown that the subsequence of phase transitions rhombohedral (R)—tetragonal (T)—cubic (C) phases is observed in nonpolarized samples of both orientations as temperature increases. In the [111]-oriented crystal, an additional intermediate monoclinic phase (it is possible, M _a ) is induced after preliminary polarization at room temperature and the R–M _a –T–C phase transitions are observed on heating. In the [001]-oriented crystal, after its polarization, the monoclinic phase forms instead of the rhombohedral phase even at room temperature and the M _a –T–C transitions occur on heating. The results are discussed from the point of view of the existence polar nanoregions with different local symmetries in a glasslike matrix.     

Investigation of quasicrystalline Al<Subscript>62.5</Subscript>Cu<Subscript>25</Subscript>Fe<Subscript>12.5</Subscript> and crystalline β-Al<Subscript>50</Subscript>Cu<Subscript>33</Subscript>Fe<Subscript>17</Subscript> alloys by X-ray photoelectron spectroscopy

The electronic spectra of the valence band and core levels of the surface of polygrain alloys with the icosahedral structure and the β-(CsCl)-type solid solution of Al₅₀Cu₃₃Fe₁₇ were investigated by X-ray photoelectron spectroscopy (XPS). The obtained XPS spectra of the Al_62.5Cu₂₅Fe_12.5 alloy, in comparison with those of the crystalline Al₅₀Cu₃₃Fe₁₇ alloy demonstrate narrowing and a decrease in asymmetry of the Fe2p core level and a decrease in the electron state density N(E _F ) near the Fermi level, features expected for the poorly conducting icosahedral phase. The XPS data are compared with the estimates of N(E _F ) based on the low-temperature specific heat measurements.     

Crystal Structure,Luminescence and Triboluminescence of the Complex [Eu(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>3hmpa] NO<Subscript>3</Subscript>·HQuin

The atomic structure of crystals of the complex [Eu(NO₃)₂3hmpa] NO₃·HQuin , (hmpa – hexamethylphosphortriamide, HQuin – quinaldic acid) characterized by intensive luminescence and triboluminescence has been determined by the X-ray method. The noncentro-symmetric crystals of the compound are rhombic : a = 16.8193(3), b = 12.2877(2), c = 27.6516(5) Å, пр. гр. Pca2(1), Z = 4, ρ _{calc. .} = 1.427 g/сm³. The crystals have a structure of the insular type which is presented by the isolated complex molecules, outer-sphere NO₃ ^? – groups, and neutral molecules of quinaldic acid. Some structural aspects of formation of the luminescent and triboluminescent properties of the compound were discussed: the role of break planes in the crystal destruction was revealed.     

Temperature dependence of the quenching of N<Subscript>2</Subscript> (C <Superscript>3</Superscript>Π<Subscript>u</Subscript>) by N<Subscript>2</Subscript> (X) and O<Subscript>2</Subscript> (X)

The temperature dependences of the quenching rate constants of the states N₂ (${\rm C} \ {^{3}{ \rm \Pi }_{u}}${\rm C} \ {^{3}{ \rm \Pi }_{u}} v^′=0,1) by N₂ (X) and of the state N₂ (${\rm C} \ {^{3}{ \rm \Pi }_{u}} \ v^{\prime}=0${\rm C} \ {^{3}{ \rm \Pi }_{u}} \ v^{\prime}=0) by O₂ (X) are studied. Time-resolved light emission from the gas was analyzed in the temperature range from 300 K to 210 K keeping the gas at constant density. In case of quenching by N₂ (X), the quenching rate constant for the vibrational level v^′= 0 increases by (13 ±3)% with gas cooling whereas the quenching rate constant for v^′= 1 decreases by (5.0 ±2.5)% in this temperature range. For quenching by O₂ (X), the quenching rate constant decreases by (3 ±2)% with gas cooling. The temperature variation of the N₂ (C ³Π_u v^′=0) emission intensity for pure nitrogen and dry air are calculated using the obtained quenching rate constants and is compared with the experimental data available in the literature.     

Effect of a structural disorder on the magnetic properties of the sodium–cobalt tellurate Na<Subscript>3.70</Subscript>Co<Subscript>1.15</Subscript>TeO<Subscript>6</Subscript>

A new layered oxide, sodium–cobalt tellurate Na_3.70Co_1.15TeO₆, is synthesized and structurally characterized, and its static and dynamic magnetic properties are studied. This compound has a new monoclinic structure type with quasi-one-dimensional cation ordering in magnetically active layers. This compound is antiferromagnetically ordered at a Néel temperature T _N ~ 3.3 K, and the temperature and field dependences of magnetization suggest competing antiferromagnetic and ferromagnetic interactions. EPR spectroscopy reveals complex spin dynamics when temperature changes and the presence of two different paramagnetic centers, which is attributed to the existence of two structurally nonequivalent (regular and antisite) positions for magnetic Co²⁺ ions.     

A structural,magnetostrictive and Mössbauer study of Tb<Subscript>0.3</Subscript>Dy<Subscript>0.7</Subscript>(Fe<Subscript>0.9</Subscript><Emphasis Type="Italic">T</Emphasis><Subscript>0.1</Subscript>)<Subscript>1.95</Subscript> alloys

The effect of IIIA metal and transition metalT substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 (T=Mn, Fe, Co, B, Al, Ga) alloys at room temperature were investigated systematically. It was found that the primary phase of the Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 alloys is the MgCu₂-type cubic Laves phase structure for different substitution. The magnetostrictionλ _s decrases greatly for the substitution of IIIA metal, B, Al and Ga, but is saturated more easily for Al and Ga substitution, showing that the Al and Ga substitution is beneficial to a decrease in the magnetocrystalline anisotropy of Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 alloys. However, the substitution of transition metal Mn and Co decreases slightly the magnetostrictionλ _s . It was also found that the effect of different substitutions on the spontaneous magnetostrictionλ ₁₁₁ is distinct. The analysis of the Mössbauer spectra indicates that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry for Al and Ga substitution, namely spin reorientation, but it does not change evidently for B, Mn and Co substitution.     

First-order phase transition characteristic of the high temperature metal–semiconductor transition in [Ca<Subscript>2</Subscript>CoO<Subscript>3</Subscript>]<Subscript>0.62</Subscript>[CoO<Subscript>2</Subscript>]

Transportation and thermodynamic properties of misfit-layered polycrystalline [Ca₂CoO₃]_0.62[CoO₂] were measured in order to clarify the nature of metal– semiconductor transition (MST) at T _MS≈400 K, above which the simultaneous decrease of resistivity and increase of thermopower with temperature give rise to a great enhancement of thermoelectric power factor up to 1000 K. A first-order phase transition characteristic around T _MS was revealed by anomalies of resistivity, differential scanning calorimetry, and thermal expansion. The first-order characteristic of the MST can be rationalized from the Virial theorem at an itinerant to localized electron transition in the narrow e ^T band within the [CoO₂] plane. Above T _MS, the reduction of the retained delocalized states within the matrix of localized states and the enhancement of charge carrier effective mass with increasing temperature might account for the considerable enhancement of the thermopower.     

Effect of process parameters and post-deposition annealing on the microwave dielectric and optical properties of pulsed laser deposited Bi<Subscript>1.5</Subscript>Zn<Subscript>1.0</Subscript>Nb<Subscript>1.5</Subscript>O<Subscript>7</Subscript> thin films

Bismuth Zinc niobate (Bi_1.5Zn_1.0Nb_1.5O₇) thin films were deposited by pulsed laser deposition (PLD) method on fused silica substrates at different oxygen pressures. The structural, microwave dielectric and optical properties of these thin films were systematically studied for both the as-deposited and the annealed films at 600°C. The as-deposited films were all amorphous in nature but crystallized on annealing at 600°C in air. The surface morphology as studied by atomic force microscopy (AFM) reveals ultra-fine grains in the case of as-deposited thin films and cluster grain morphology on annealing. The as-deposited films exhibit refractive index in the range of 2.36–2.53 (at a wavelength of 750 nm) with an optical absorption edge value of 3.30–3.52 eV and a maximum dielectric constant of 11 at 12.15 GHz. On annealing the films at 600°C they crystallize to the cubic pyrochlore structure accompanied by an increase in band gap, refractive index and microwave dielectric constant.     

Colossal Magnetoresistance of Layered Manganite La<Subscript>1.2</Subscript>Sr<Subscript>1.8</Subscript>Mn<Subscript>2</Subscript>O<Subscript>7</Subscript> and Its Description by a “Spin–Polaron” Conduction Mechanism

The resistance of a La_1.2Sr_1.8Mn_2(1–z)O₇ single crystal has been studied in magnetic fields from 0 to 90 kOe. The magnetoresistance at temperature T = 75 K, near which a colossal magnetoresistance maximum is observed, has been successfully described in terms of the “spin–polaron” electric conduction mechanism. This value of the colossal magnetoresistance is due to a three-fold increase in the polaron size. The method of separating contributions of various conduction mechanisms to the magnetoresistance developed for materials with activation type of conduction is generalized to compounds in which a metal–insulator transition is observed. It is found that, at a temperature of 75 K, the contribution of the “orientation” mechanism is maximum (≈20%) in a magnetic field of 5 kOe and almost disappears in fields higher than 50 kOe.     

Mass and kinetic energy distribution of the species generated by laser ablation of La<Subscript>0.6</Subscript>Ca<Subscript>0.4</Subscript>MnO<Subscript>3</Subscript>

The mass distributions of the species generated by laser ablation from a La_0.6Ca_0.4MnO₃ target using laser irradiation wavelengths of 193 nm, 266 nm and 308 nm have been investigated with and without a synchronized gas pulse of N₂O. The kinetic energies of the species are measured using an electrostatic deflection energy analyzer, while the mass distributions of the species were analyzed with a quadrupole mass filter. In vacuum (pressure 10⁻⁷ mbar), the ablation plume consists of metal atoms and ions such as La, Ca, Mn, O, LaO, as well as multiatomic species, e.g. LaMnO⁺. The LaO⁺ diatomic species are by far the most intense diatomic species in the plume, while CaO and MnO are only detected in small amounts. The interaction of a reactive N₂O gas pulse with the ablation plume leads to an increase in plume reactivity, which is desired when thin manganite films are grown, in order to incorporate the necessary amount of oxygen into the film. The N₂O gas pulse appears to have a significant influence on the oxidation of the Mn species in the plume, and on the creation of negative ions, such as LaO⁻,O⁻ and O₂⁻.     

KF-doped BaTi<Subscript>2</Subscript>O<Subscript>5</Subscript> ferroelectric ceramics by solid-state reaction of KF and sol–gel-derived BaTi<Subscript>2</Subscript>O<Subscript>5</Subscript> powders

We report KF-doping work on the recently found ferroelectric material BaTi₂O₅. The ceramic samples, Ba_1-xK_xTi₂O_5-xF_x, were synthesized by solid-state reaction of mixed KF and sol–gel-derived BaTi₂O₅ powders at 1150 °C. An almost pure phase was obtained for nominal composition x≤0.097, while electron probe microanalysis indicated that the real incorporated K and F contents were less than half of the nominal values. It was observed that KF-doping is beneficial in enhancing the ceramic density to some extent, which is a key issue in sol–gel-derived BaTi₂O₅ ceramics, due to a possible liquid-phase sintering mechanism through the presence of melted KF at the sintering temperature. Scanning electron microscopy images showed that these porous ceramic samples are composed of sub-micron-sized powder aggregates which, with increasing KF-doping, undergo further agglomeration. Dielectric measurement from room temperature to ∼ 560 °C showed a broad ferroelectric phase transition, with T_C ∼ 430 °C for the undoped sample. As KF-doping increases, T_C decreases, and the magnitude of the dielectric constant maximum also displays a decreasing trend. The strongly reduced dielectric response can be partly understood by regarding the porous ceramic sample as a composite material composed of bulk BaTi₂O₅ and air, where the porosity has a significant influence on the effective dielectric constant. PACS 77.84.-s; 77.84.Dy; 81.20.Fw     

Superconducting Phase Diagram of the Yttrium,Barium, and YBa-core in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7–δ</Subscript> by an Ising Model

We investigate the temperature dependent of magnetizations, hysteresis properties and present the superconducting phase diagrams of the YBa₂Cu₃O_7–δ (YBCO) by an Ising model within the effective-field theory. We obtain the magnetizations of the YBCO and its components (Cu1, Cu2, O1, O2, O3, O4, Ba, Y, CuO-shell, YBa-core, and total YBCO) versus the reduced temperature and external magnetic field. We find that the copper atoms have two different magnetizations (Cu1 and Cu2) and oxygen atoms have four different magnetizations (O1, O2, O3, O4) but yttrium and barium has one magnetization. The differences in the magnetizations of the copper and oxygen atoms result from the lattice location of them on the YBCO lattice. The magnetization of the Cu1 atoms is the lowest and the yttrium is highest than those of the others; hence magnetizations of the YBCO increase from the corner to inner of the orthorhombic YBCO lattice. We also find that the YBa-core, yttrium and barium atoms of the YBCO exhibit superconductivity behaviors. Therefore, Y–Ba core, yttrium and barium atoms have the superconducting phase diagram and it has Meissner, vortex, and normal states. It is also found that the upper critical coercive field (H_c2) and the critical vortex temperature (T_v) of the Ba are high than those of the Y and YBa-core.     

Broadening and shift of lines of the ν<Subscript>2</Subscript> + ν<Subscript>3</Subscript> band of water vapor induced by helium pressure

The broadening and shift coefficients of more than 100 absorption lines of the ν₂ + ν₃ band of water vapor that are induced by the pressure of helium are measured and calculated. The broadening and shift coefficients are obtained from analysis of the room-temperature absorption spectra of an H₂O-He mixture measured with a resolution of 0.007 cm^?1 on a Fourier spectrometer in a large range of helium pressures. The specific features in the rotational dependence of the line center shifts are determined, which, in contrast to the broadening induced by other gases, are mainly positive. The calculated coefficients of the line broadening and shift of line centers are determined by a semiclassical method. An unusual dependence of the shift coefficients is explained by the rotational dependence of the intermolecular isotropic interaction potential.     

Investigation of the IR spectra of weakly hydrogen-bonded complex Cl<Subscript>3</Subscript>CH…O(CD<Subscript>3</Subscript>)<Subscript>2</Subscript> in a cryosolution in liquid krypton

The IR absorption spectra of cryosolutions of chloroform, dimethyl ether, and their mixtures in liquefied krypton have been measured. It has been shown that, in solutions of mixtures, Cl₃CH…O(CD₃)₂ complexes with a weak hydrogen bond are formed. The spectral characteristics of individual absorption bands that refer to proton donors and to proton acceptors have been determined. From temperature measurements of the integrated intensities of the bands of monomers and of the complex (T ~ 120–160 K), the enthalpy of the complex formation has been estimated. The measurement data have been analyzed in comparison with the results of ab initio calculations in terms of the МР2/6-311++G(2df, 2pd) approximation. The analysis has been done taking into account peculiarities of the dipole moment function of chloroform and possible effects of the anharmonic interaction between the С–Н stretching vibration and the overtone of the Cl–C–H bending vibration.