Spin dynamics in LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript> and NaCu<Subscript>2</Subscript>O<Subscript>2</Subscript> low-dimensional helical magnets

Comprehensive NMR investigation of low-frequency spin dynamics of LiCu₂O₂ (LCO) and NaCu₂O₂ (NCO) low-dimensional helical magnets in the paramagnetic state has been carried out for the first time. Temperature dependences of the spin–lattice relaxation rate and anisotropy on various LCO/NCO nuclei have been determined at various orientations of single crystals in an external magnetic field. The spatial asymmetry of spin fluctuations in LCO multiferroic has been discovered. The quantitative analysis of the anisotropy of spin–lattice relaxation in LCO/NCO has allowed estimating the contributions of individual neighboring Cu²⁺ ions to the transferred hyperfine field on Li⁺(Na⁺) ions.     

Conductivity and spectroscopic studies of Li<Subscript>2</Subscript>O-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

Lithium vanadium-borate glasses with the composition of 0.3Li₂O–(0.7-x)B₂O₃–xV₂O₅ (x?=?0.3, 0.325, 0.35, 0.375, 0.4, 0.425, 0.45, and 0.475) were prepared by melt-quenching method. According to differential scanning calorimetry data, vanadium oxide acts as both glass former and glass modifier, since the thermal stability of glasses decreases with an increase in V₂O₅ concentration. Fourier transform infrared spectroscopy data show that the vibrations of [VO₄] structural units occur at V₂O₅ concentration of 45 mol%. It is established that the concentration of V⁴⁺ ions increases exponentially with the growth of vanadium oxide concentration. Direct and alternative current measurements are carried out to estimate the contribution both electronic and ionic conductivities to the value of total conductivity. It is shown that the electronic conductivity is predominant in the total one. The glass having the composition of 0.3Li₂O-0.275B₂O₃-0.475V₂O₅ shows the highest electrical conductivity that has the value of 7.4?×?10^?5 S cm^?1 at room temperature.     

Incommensurate helical magnetic order in LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript> and NaCu<Subscript>2</Subscript>O<Subscript>2</Subscript> quasi-one-dimensional compounds

The results of the measurements of the ^{6, 7}Li and ²³Na nuclear magnetic resonance (NMR) and ^{63, 65}Cu nuclear quadrupole resonance in LiCu₂O₂ and NaCu₂O₂ quasi-one-dimensional compounds with a spin chains in the paramagnetic and magnetically ordered states are presented. The shape of the NMR line below T _c = 24 and 13 K for LiCu₂O₂ and NaCu₂O₂, respectively, is characteristic of the incommensurate static modulation of the local magnetic field matching with the incommensurate spiral modulation of the magnetic moments. The differences in the shape of the NMR spectra of ²³Na and ⁷Li are discussed in terms of the features of the crystal structure of LiCu₂O₂ and NaCu₂O₂.     

High-temperature heat capacity of stannates Pr<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript> and Nd<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript>

Oxide compounds Pr₂Sn₂O₇ and Nd₂Sn₂O₇ have been obtained by solid-phase synthesis. The effect of temperature on the heat capacity of Pr₂Sn₂O₇ (360–1045 K) and Nd₂Sn₂O₇ (360–1030 K) has been studied using differential scanning calorimetry. The thermodynamic properties of the compounds (changes in enthalpy, entropy, and the reduced Gibbs energy) have been calculated by the experimental data of C_p = f(T).     

NMR study of the paramagnetic state of low-dimensional magnets LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript> and NaCu<Subscript>2</Subscript>O<Subscript>2</Subscript>

A comprehensive NMR study of the magnetic properties of single crystal LiCu₂O₂ (LCO) and NaCu₂O₂ (NCO) is carried out in the paramagnetic region of the compounds for various orientations of single crystals in an external magnetic field. The values of the electric-field gradient (EFG) tensor, as well as the dipole and transferred hyperfine magnetic fields for ^63,65Cu, ⁷Li, and ²³Na nuclei are determined. The results are compared with the data obtained in previous NMR studies of the magnetically ordered state of LCO/NCO cuprates.     

Gas sensor based on nanosize In<Subscript>2</Subscript>O<Subscript>3</Subscript>:Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> film

Nanosize films of In₂O₃:Ga₂O₃ (96:4 weight %) have been deposited on a glassceramic substrate by the method of rf magnetron sputtering. The surfaces of fabricated films were studied with use of a scanning electron microscope; sizes of grains were determined and the thicknesses of films were measured. In order to prepare a gas-sensitive structure, a thin catalytic palladium layer and ohmic comb contacts were deposited on the In₂O₃:Ga₂O₃ film surface by the method of ion-plasma sputtering. The sensitivity of sensors based on the glassceramic/In₂O₃:Ga₂O₃ (96:4 weight %)/Pd structure to different concentrations of propane and butane gas mixture, as well as to methane was investigated at temperatures of working substance from 250 to 300°C.     

Spin-wave resonances in Eu<Subscript>0.8</Subscript>Ce<Subscript>0.2</Subscript>Mn<Subscript>2</Subscript>O<Subscript>5</Subscript> and EuMn<Subscript>2</Subscript>O<Subscript>5</Subscript> multiferroics

Spin-wave resonances have been observed in superlattices arising due to the phase separation and self-organization of charge carriers in Eu_0.8Ce_0.2Mn₂O₅ single crystals. The resonances are found within the 5–80 K temperature range at frequencies close to 30 GHz. Similar resonances with intensities about an order of magnitude lower are also observed in EuMn₂O₅. The latter suggests the existence of charge transfer processes between the manganese ions of different valences in EuMn₂O₅.     

Polarization processes in BaBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> and SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics in infralow-frequency fields

The dielectric nonlinearity in BaBi₂Nb₂O₉ and SrBi₂Ta₂O₉ layered ceramics was studied by measuring their polarization loops and reverse dependences of permittivity. It was shown that the features of the dielectric response of BaBi₂Nb₂O₉ and SrBi₂Ta₂O₉ in strong fields can be explained by glass-like properties and the contribution of the domain structure of the ferroelectric material to repolarization processes, respectively.     

New magnetic states in copper metaborate CuB<Subscript>2</Subscript>O<Subscript>4</Subscript>

The static and resonance properties of copper metaborate CuB₂O₄ were experimentally studied in a magnetic field applied in the crystal tetragonal plane. The field-induced second-order phase transition to a weakly ferromagnetic state was observed in the temperature range 10–20 K. The low-field state is characterized by the absence of spontaneous moment, and it represents, presumably, a long-period helicoid. At temperatures below 2 K, two sequential first-order phase transitions were observed. They were accompanied by jumps in resonance absorption with a hysteresis upon changing field-scan direction. These transitions can be caused by the transformation of the incommensurate spin structure into the helicoidal states with periods commensurate with the lattice translation period.     

Methane sensor based on SnO<Subscript>2</Subscript>/In<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanostructure

Two sets of samples of SnO₂/In₂O₃/TiO₂ system have been fabricated with different concentrations of component materials. In the first set TiO₂ with rutile structure was used, while in the second set it has the structure of anatase. Thin films (up to 50 nm) of obtained mixtures were deposited. Their sensitivity and selectivity with respect to methane (CH4) were studied. Nanostructure on the basis of 70%SnO₂ — 10%In₂O₃ — 20%TiO₂(anatase) exhibits sufficient sensitivity to methane.     

O<Subscript>2</Subscript> photodesorption from a Ag<Subscript>8</Subscript>O<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack> cluster

The decay path of an Ag₈(O₂)^- cluster photoexcited by a 3.1 eV photon is elucidated using time-resolved photoelectron spectroscopy. Photoabsorption results in the formation of an excited state giving rise to a peak in the photoelectron spectra with well-resolved vibrational finestructure. With a lifetime of about 100 fs this bound state decays into an anti-bonding state which dissociates into O₂ and Ag₈^- on a timescale of 10 ps. In the photoelectron spectra, this corresponds to a broad maximum shifting gradually towards higher binding energy while the O₂ and Ag₈^- separate. Finally, the spectrum of bare Ag₈^- appears. This process is unique to small clusters, because on metal surfaces excited state lifetimes are too short to allow for direct dissociation.     

Synthesis of ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> complex substrates and growth of GaN films

With the solid phase reaction between pulsed-laser-deposited (PLD) ZnO film and α-Al₂O₃ substrate, ZnAl₂O₄/α-Al₂O₃ complex substrates were synthesized. X-ray diffraction (XRD) spectra show that as the reaction proceeds, ZnAl₂O₄ changes from the initial (111)-oriented single crystal to poly-crystal, and then to inadequate (111) orientation. Corresponding scanning electron microscope (SEM) images indicate that the surface morphology of ZnAl₂O₄ transforms from uniform islands to stick structures, and then to bulgy-line structures. In addition, XRD spectra present that ZnAl₂O₄ prepared at low temperature is unstable at the environment of higher temperature. On the as-obtained ZnAl₂O₄/α-Al₂O₃ substrates, GaN films were grown without any nitride buffer using light-radiation heating low-pressure MOCVD (LRH-LP-MOCVD). XRD spectra indicate that GaN film on this kind of complex substrate changes fromc-axis single crystal to poly-crystal as ZnAl₂O₄ layer is thickened. For the single crystal GaN, its full width at half maximum (FWHM) of X-ray rocking curve is 0.4°. Results indicate that islands on thin ZnAl₂O₄ layer can promote nucleation at initial stage of GaN growth, which leads to the (0001)-oriented GaN film.     

Fluorimetry Studies of Oscillating Chemilumnescence in the Luminol= H<Subscript>2</Subscript>O<Subscript>2</Subscript>= KSCN= CuSO<Subscript>4</Subscript>= TMAOH System

Oscillating chemical reactions are complex systems, involving a large number of chemical species. In oscillating chemical reaction, some species, usually a reaction intermediate, exhibit fluctuation in its concentration. In this report, visible oscillating chemiluminescence produced by the addition of luminol (3-aminophthalhydrazide) to the oscillating system of H₂O₂=KSCN=CuSO₄=TMAOH was investigated using spectrofluorimetry method. The effects of ingredient concentration of the oscillating system and complexing agents like citric acid and cysteine on the behavior of the oscillating system were investigated. Moreover, the influence of nonaqueous solvents such as ethanol and ethylene glycol has been studied.     

Interaction of carbon monoxide with In<Subscript>2</Subscript>O<Subscript>3</Subscript> and In<Subscript>2</Subscript>O<Subscript>3</Subscript>-Au nanocomposite

This is an IR spectroscopic study of the interaction of CO with In₂O₃ and the nanocomposite In₂O₃-Au. A mechanism for low-temperature detection of CO on nanocomposite In₂O₃-Au can be determined from these data. This process includes catalytic oxidation of CO through formation of intermediate complexes involving hydroxyl groups of In₂O₃.     

Evaluation of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>-LiNi<Subscript>0.80</Subscript>Co<Subscript>0.15</Subscript>Al<Subscript>0.05</Subscript>O<Subscript>2</Subscript> hybrid material as cathode in soft-packed lithium ion battery

The major electrochemical performances of LiMn₂O₄ (LMO)-LiNi_0.80Co_0.15Al_0.05O₂ (NCA) blending cathodes with full-range ratios are evaluated in industrial perspective. The results indicate that the reversible lithium ions can be fully utilized when NCA percentage reaches up to 50 %. The median voltages of blends are higher than the value calculated from a linear relationship of the two pristine cathodes, which is beneficial to energy density. But a synergy effect on room-temperature cycle performance is not observed for the hybrid cathode. However, the high-temperature (45 °C) capacity retention with 70 % NCA is 97.9 % after 100 cycles, higher than both pristine cathodes. It is not until NCA content increases to more than 50 % that the high-rate performance is much deteriorated. Additionally, the swelling of fully charged pouch-type battery after 4 h storage at 85 °C disappears when NCA percentage is less than 50 %. Hence, it is practically manifested that critical flaws of NCA and LMO can be compromised by blending with each other in a critical ratio. In this way, NCA can be practically used in soft-packed battery.     

Electrical instability of LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript> crystals

The temperature behavior of I-U curves and the field and temperature dependences of the electrical resistivity and dielectric permittivity of crystals of the LiCu₂O₂ phase have been studied. It was established that the crystals belong to p-type semiconductors and that their static resistivity in the range 80–260 K follows the Mott law ρ=Aexp(T₀/T)^1/4 describing variable-range hopping over localized states. At comparatively low electric fields, the crystals exhibit threshold switching and characteristic S-shaped I-U curves containing a region of negative differential resistivity. In the critical voltage region, jumps in the conductivity and dielectric permittivity are observed. Possible mechanisms of the disorder and electrical instability in these crystals are discussed.     

Spectral-luminescent investigations of glasses and glass-ceramic materials in Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-GeO<Subscript>2</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Glasses of 2Bi₂O₃-3GeO₂-xFe₂O₃ composition, where x = 0–1.5, are obtained under oxidizing and reducing conditions. Glass-ceramic materials are produced by the thermal treatment of the glasses, the properties of which, as well as those of the original glasses, are studied by the methods of X-ray phase analysis and optical and luminescent spectroscopy. It is found that the Fe³⁺/Fe²⁺ ion ratio in the samples changes depending on the synthesis conditions of the original glasses and crystallization process.     

Long-range magnetic order in quasi-one-dimensional NaCrSi<Subscript>2</Subscript>O<Subscript>6</Subscript> and NaCrGe<Subscript>2</Subscript>O<Subscript>6</Subscript> metal oxides

Formation of a long-range magnetic order is observed at low temperatures in NaCrSi₂O₆ and NaCrGe₂O₆ quasi-one-dimensional metal oxide compounds with a pyroxene structure. The first of these compounds, NaCrSi₂O₆, is an antiferromagnet with the Néel temperature T _N =3 K, while the second, NaCrGe₂O₆, is a ferromagnet with the Curie temperature T _C =6 K. From the measurements of magnetization and specific heat of these compounds, the main parameters of their magnetic subsystems are determined. In NaCrSi₂O₆, a spin-flip transition is observed. A change in the type of magnetic order that accompanies the replacement of Si by Ge can be attributed to a change in the parameters of the competing direct antiferromagnetic Cr-Cr and indirect ferromagnetic Cr-O-Cr interactions in isolated chains of CrO₆ octahedra.     

Elevated electrochemical property of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> originated from nano-sized Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>

By employment of nano-sized pre-prepared Mn₃O₄ as precursor, LiMn₂O₄ particles have been successfully prepared by facile solid state method and sol-gel route, respectively. And the reaction mechanism of the used precursors of Mn₃O₄ is studied. The structure, morphology, and element distribution of the as-synthesized LiMn₂O₄ samples are characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Compared with LiMn₂O₄ synthesized by facile solid state method (SS-LMO), LiMn₂O₄ synthesized by modified sol-gel route (SG-LMO) possesses higher crystallinity, smaller average particle size (~175 nm), higher lithium chemical diffusion coefficient (1.17 × 10^?11 cm² s^?1), as well as superior electrochemical performance. For example, the cell based on SG-LMO can deliver a capacity of 85.5 mAh g^?1 at a high rate of 5 °C, and manifests 88.3% capacity retention after 100 cycles at 0.5 °C when cycling at 45 °C. The good electrochemical performance of the cell based on SG-LMO is ascribed mainly to its small particle size, high degree of dispersion, and uniform element distribution in bulk material. In addition, the lower polarization potential accelerates Li⁺ ion migration, and the lower atom location confused degree maintains integrity of crystal structure, both of which can effectively improve the rate capability and cyclability of SG-LMO.     

Solid state synthesis of nonstoichiometric Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>/Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> composites as visible-light photocatalyst

Nonstoichiometric Bi₂WO₆ photocatalyst with the composition of Bi_2?+?x WO_6?+?1.5x (?0.25 ≤ x ≤ 1) wa synthesized by a facile solid state reaction method. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis absorption spectrum. The Bi_2.5WO_6.75 photocatalyst showed excellent visible-light-driven photocatalytic performance; nearly 100 % of RhB (10 ppm, pH?=?3?~?4) was decomposed within 25 min, which demonstrated that nonstoichiometric semiconductors could be an efficient visible-light-driven photocatalyst.