Mn2+ and Tl+ luminescence in β-aluminas

The compounds AGa₁₁O₁₇ (A = K, Rb, Cs) and AAl₁₁O₁₇ (A = Na, K, Rb) have the β-alumina structure. The Mn²⁺-activated gallates show efficient luminescence under 254 nm excitation with an emission peaking at 498 nm and a quantum efficiency up to 70%. The Tl⁺-activated aluminates show efficient luminescence under 254 nm excitation with an emission peaking at 380–390 nm and a quantum efficiency up to 70%. In AAl₁₁O₁₇: Tl⁺ energy is transferred from Tl⁺ to Mn²⁺, resulting in an emission peaking at 512 nm with a quantum efficiency up to 55%.     

Magnetic and magneto-lattice dynamics in GdMn<Subscript>2</Subscript>O<Subscript>5</Subscript>

The dynamics of magnetoelectric RMn₂O₅ crystals (R=Eu and Gd) was studied in the frequency and temperature ranges 20–300 GHz and 5–50 K, respectively. The crystals possessed magnetic and ferroelectric long-range order and had close transition temperatures, T_{N, C}?36 and 30 K for R=Eu and Gd, respectively. Mixed magneto-lattice excitations were observed in GdMn₂O₅; the excitations were most intense near the transition temperature T?30 K at frequencies close to the antiferromagnetic resonance frequencies of the Mn subsystem. Along with the antiferromagnetic resonance of the Mn subsystem, the ferromagnetic resonance of the Gd subsystem was observed in GdMn₂O₅ in an external magnetic field. No such dynamics was characteristic of EuMn₂O₅.     

Superconductivity in the metallic–oxidized sodium interface

Superconductivity at 20–34 K in the interface formed by metallic and oxidized sodium has been observed by ac magnetic susceptibility measurements. By means of X-ray diffraction measurements, it has been found that the oxidized sodium layer consists of a mixture of Na₂O, Na₂O₂, NaO₂ and NaO₃ compounds.     

Ionic conduction in Sr hexa-aluminate with β-alumina structure

A new type of strontium β-alumina was developed by a single solid state reaction. Polycrystals of Sr β-alumina with the chemical formula of SrMgAl₁₀O₁₇ were prepared and examined by a conductivity. The values of ionic conductivity in the Sr β-alumina were 5 to 3 orders of magnitude lower than those of polycrystalline Na β-alumina between 773 and 1273 K. The ion exchange of Sr β-alumina for sodium was also examined, and the values of conductivity for the partially ion-exchanged samples increased with the increase of the excess amount of Na⁺ up to 0.5–0.6 in comparison with that of the ideal Na β-alumina.     

Phase transitions in Pb8O5(XO4)2 (X = As and V) compounds

Raman spectroscopy, polarized microscopy and thermal measurements were used to investigate the sequence of phase transition in the lead oxide salts Pb₈O₅(XO₄)₂ (where X = As and V). For Pb₈O₅(AsO₄)₂, a second‐order phase transition is observed at 500 K. For Pb₈O₅(VO₄)₂, a second‐order and a first‐order structural phase transitions are observed at 425 and 525 K, respectively. The ferroelastic character of Pb₈O₅(VO₄)₂ is also discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Dielectric response of PVC polymer loaded with Ba0.3Na0.7Ti0.3Nb0.7O3 ceramic powder

Dielectric response of poly(vinyl chloride), (PVC), loaded with different amount of Ba_0.3Na_0.7Ti_0.3Nb_0.7O₃ (BNTN) ceramic powders was investigated in frequency range 100 Hz–1 MHz and temperature range 100–450 K. Ceramic solid solution of barium titanate and sodium niobate with composition Ba_0.3Na_0.7Ti_0.3Nb_0.7O₃ was obtained from BaCO₃, TiO₂, Na₂CO₃ and Nb₂O₅ by conventional method. Powders were prepared by grinding of ceramics. The obtained ceramics, used to produce BNTN–PVC composites, are characterized by the relaxor behaviour with a broad peak of dielectric permittivity ε′ at T _m ≈ 230 K. The microstructure of the powders was observed and the grain size was estimated using scanning electron microscope Hitachi S-4700. The EDS analysis confirms the qualitative and quantitative chemical composition of powders and ceramics. The BNTN–PVC composite samples of 0-3 connectivity were prepared from ceramic and polymer powders by hot-pressing method. The dielectric response of the composites displays features originated from the PVC polymer modified by those of BNTN ceramics. The relaxation time of the α-process of PVC obeys the Vogel–Fulcher law and decreases with increasing volume fraction of the ceramics.     

High-temperature heat capacity of CdO–V2O5 oxides

Vanadates Cd₂V₂O₇ and CdV₂O₆ have been prepared from CdO и V₂O₅ by three-phase synthesis with subsequent burning at 823–1073 K and 823–853 K, respectively. The molar heat capacity of these oxide compounds has been measured by differential scanning calorimetry. The enthalpy change, the entropy change, and the reduced Gibbs energy are calculated using the experimental dependences C _p = f(T). It is shown that there is a correlation between the specific heat capacity and the composition of CdO–V₂O₅ oxide system.

     

Size effect on the structure and magnetic properties of SmMn2O5 nanorods

Three sizes of SmMn₂O₅ nanorods that are labeled with (<L_C>) × axial lengths of 58(17) nm × 25(6) nm, 92(21) nm × 32(8) nm, and 126(25) nm × 52(13) nm were fabricated by the hydrothermal method. All the samples exhibited an antiferroicmagnetic (AFM) peak at approximately 6 K, which was associated with Sm magnetic ordering and no size independence. Another AFM magnetic ordering that belongs to the Mn ion was found with <L_C> = 58 nm, 92 nm, and 126 nm at 26 K, 28 K, and 30 K, respectively. The spin-orbit interaction increases with size in the magnetic susceptibility experiment. All the samples displayed a hysteresis loop at 2 K. The coercivity decreases as the size increases. The effects of the size on the crystal structure were elucidated from the Raman spectra of the <L_C> = 92 and 126 nm samples at various temperatures. The 126 nm sample displayed a red-shift for the Ag mode with warming, revealing that the Mn–O bonds are more sensitive to temperature in larger SmMn₂O₅ nanorods. These results demonstrate that the size effect importantly affects the structure and magnetic properties in SmMn₂O₅ multiferroic nanorods.     

Particle size effect of a.c. superconducting properties in compound

Using a new starting material of Ba₂Cu₃O₅ and a three step heat treatment, single phase Tl₂Ca₁Ba₂Cu₂O₈ high- superconducting samples have been prepared, possessing the onset- and critical temperatures K and K. The morphology dependent value of is 17 Oe, 8 Oe and 5 Oe at 77 K in the case of bulk, crushed and powdered materials, respectively. The a.c. susceptibility, r.f. susceptibility and microwave absorption properties show a significant dependence on the particle size with a sharp change in the interval between 750 μm and 1200 μm. These experiments provide characteristic parameters for intergrain material (treated as 3D Josephson network) as mm, Oe and A/cm² at 77 K. The data are controlled by modulated microwave absorption measurements. The results obtained can be explained well both by the finite size junction model and cavity mode absorption model. The Josephson network is determined unambiguously by metallic S-N-S weak links. Received 10 October 1998     

Two magnetic phase transitions in quasi-one-dimensional system SrCo2V2O8

Magnetic properties of SrCo₂V ₂O₈ single crystal are investigated by means of ac magnetic susceptibility, dc magnetization and heat capacity measurements. The results show that SrCo₂V ₂O₈ possesses two canted antiferromagnetic transitions at ∼5 and ∼3 K, which is different from isostructural BaCo₂V ₂O₈ with only one antiferromagnetic transition at ∼5 K. We suggest that such different magnetic properties are mainly due to their different structural symmetry.     

Sputtering and backscattering of keV light ions bombarding random targets

The fission fragment fluence required to render CaUO₄, Na₂U₂O₄, MgUO₄, Sr₂U₃O₁₁ and u₃O₈ x-ray amorphous was deduced as ～5 × 10¹⁵ events cm³. Significant annealing of the structural damage occurred in the 300–-500°C range.     

Electron energy-loss spectroscopy at incommensurately modulated crystalline and glassy Ba2TiGe2O8

Based on cluster molecular orbital calculations, high-energy resolution (ΔE?～ 0.4?eV) Ti–L_2,3 electron energy loss near-edge structures of single-crystalline and glassy Ba₂TiGe₂O₈ are interpreted. The finding that the Ti–L_2,3 near-edge structure of the Ba₂TiGe₂O₈ single crystal possesses less pronounced peaks than the glass under identical experimental conditions can be attributed to distinct distortions of the titanium environment caused by the very strong one-dimensional structural modulation hosted by the Ba₂TiGe₂O₈ crystal lattice. As lattice periodicity is absent in the glass, the titanium environment is more regular in the vitreous surroundings. Moreover, the modulation in crystalline Ba₂TiGe₂O₈ is responsible for the virtually indiscernible O–K near-edge structures of the glassy and crystalline samples.     

Phase stability and structure of alkali doped-beta-gallia rutile intergrowths

The incorporation of alkali cations into the tunneled structure of Ga₄TiO₈ was investigated and compared to predictions based on atomistic computer simulations. Samples were prepared as A_xGa_4−xTi_1−xO₈, A=Li, Na, and K, x ≤ 0.7, and as Na_xGa_4+xTi_2−xO₁₀ (x = 0.7, 0.85, and 1.0) using solid-state reactions at 1050–1350 °C. The sodium-containing tunneled structure, Na_xGa_4−xTi_1−xO₈, formed via solid-state reaction, but the potassium and lithium analogs did not. Instead, these systems formed mixed-phase assemblages, which are discussed in reference to compatibility triangles in the Li₂O–Ga₂O₃–TiO₂ and K₂O–Ga₂O₃–TiO₂ systems. Experimental results were compared to the results of energy minimization calculations using the General Utility Lattice Program (GULP). For the lithium-containing system, the computer simulations correctly predicted the formation of a mixed-phase assemblage containing LiGa₅O₈, Ga₂O₃, and TiO₂. For the sodium- and potassium-containing system, the computer simulations suggested that mixtures of the single-cation oxide components should be the stable phase assemblages, in contradiction with experimentally observed results. Energy minimization calculations conducted on structurally different Na_xGa_4+xTi_2−xO₁₀ and Na_xGa_4+xTi_3−xO₁₂ phases indicated that those based on the n = 6 and n = 7 β-gallia rutile intergrowth structures have lower lattice energies than the experimentally observed sodium titanogallate structures reported previously in literature.     

High-temperature specific heat of Bi2GeO5 and SmBiGeO5 compounds

The SmBiGeO₅ compound is synthesized from Sm₂O₃, Bi₂O₃, and GeO₂ by solid-state synthesis with subsequent annealing at 1003, 1073, 1123, 1143, 1173, and 1223 K. The metastable Bi₂GeO₅ compound is prepared from melt. Temperature dependences of specific heat of Bi₂GeO₅ (350–1000 K) and SmBiGeO₅ (370–1000 K) are measured by differential scanning calorimetry. Basing on the experimental dependences C _P = f(T), the thermodynamic functions of the oxide compounds are calculated.

     

Effects of Y incorporation in TaON gate dielectric on electrical performance of GaAs metal–oxide–semiconductor capacitor

In this study, GaAs metal–oxide–semiconductor (MOS) capacitors using Y‐incorporated TaON as gate dielectric have been investigated. Experimental results show that the sample with a Y/(Y + Ta) atomic ratio of 27.6% exhibits the best device characteristics: high k value (22.9), low interfacestate density (9.0 × 10¹¹ cm^–2 eV^–1), small flatband voltage (1.05 V), small frequency dispersion and low gate leakage current (1.3 × 10^–5A/cm² at V_fb + 1 V). These merits should be attributed to the complementary properties of Y₂O₃ and Ta₂O₅:Y can effectively passivate the large amount of oxygen vacancies in Ta₂O₅, while the positively‐charged oxygen vacancies in Ta₂O₅ are capable of neutralizing the effects of the negative oxide charges in Y₂O₃. This work demonstrates that an appropriate doping of Y content in TaON gate dielectric can effectively improve the electrical performance for GaAs MOS devices.

Capacitance–voltage characteristic of the GaAs MOS capacitor with TaYON gate dielectric (Y content = 27.6%) proposed in this work with the cross sectional structure and dielectric surface morphology as insets.     

Experimental Study and Modelling of Formation and Decay of Active Species in an Oxygen Discharge

A microwave (2.45 GHz) oxygen discharge (3 hPa, 150 W, 50 mL.min^–1) is studied by optical emission spectroscopy of O(⁵P) (line 777.4 nm) and of the atmospheric system of O₂(head‐line 759.4 nm). Calibration of the spectral response of the optical setup is used to determine the concentrations of O(⁵P) and O₂(b). The concentration of the O(⁵P) atoms is in the range 108–109 cm^–3 and the concentration of the O₂(b) molecules is in the range 10¹⁴ – 2 × 10¹⁴ cm^–3 along the discharge tube. An attempt is made to simulate the experimental results by using coupling the Boltzmann equation, homogeneous energy transfer V‐V and V‐T, heterogeneous reactions on the walls (energy transfer and recombination of atoms) and a kinetic scheme (electronic transfer and chemical reactions). The Boltzmann equation includes momentum transfer, inelastic and superelastic processes and e‐e collisions. V‐V and V‐T transfer equations are obtained from the SSH theory and the kinetic scheme includes 65 reactions with 17 species [electrons e, ions O^– and O₂^–, fundamental electronic neutral species O(³P), O₂, O₂(X,v), O₃ and excited neutral species O₂(a), O₂(b), O₂(A), O(¹D), O(¹S), O(⁵P), O(4d ⁵D^o), O(5s ⁵S^o), O(3d ⁵D^o) and O(4s ⁵S^o)]. A fair agreement between experimental results and modelling is obtained with the following set of fitting values: – heterogeneous deactivation coefficient for O₂(b) γ = 2.6 × 10^–2; – rate constant of reaction [O(¹D) + O(³P) → 2 O(³P)] k₃₄ = 1.4 × 10^–11 cm³.s^–1; – electron concentration in the range 10¹⁰ – 10¹¹ cm^–3. Modelling shows that the recombination coefficient for oxygen atoms on the silica wall (range 1.4 × 10^–3 – 0.2 × 10^–3) is of the same order as the values obtained in a previous paper and that the ratio ([O] / 2 [O₂]initial) is about 33–50%. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High temperature superconductivity in bismuth-alkaline earth-copper-oxygen system

Electrical resistivity measurements of a series of compounds in the bismuth-alkaline earth-copper-oxygen system have been carried out. Several compositions (BiSrCaCu₂O _x , BiSrCaCu₃O _x , Bi₂Sr₂CaCu₄O _x and Bi₄Sr₃Ca₃Cu₈O _x ) showed superconducting onset temperatures in the range 90–130 K, though none of them showedT _cf(R=0) above 77 K. ExtrapolatedT _cf of three compounds are in the range 72–75 K. All compounds are multiphasic.     

Hydration behavior of Ba2Sc2O5 with an oxygen-deficient perovskite structure

The hydration behavior of the barium scandates with oxygen-deficient perovskite-related structures of tetragonal Ba₂Sc₂O₅ and cubic BaScO_3−δ (δ ∼ 0.5) was studied. Both the tetragonal Ba₂Sc₂O₅ and cubic BaScO_3−δ absorbed water and formed Ba₂Sc₂O₅·0.60H₂O and BaScO_3−δ·0.37H₂O, respectively, during cooling in a humidified atmosphere. The hydration and the dehydration temperatures for the barium scandates were ∼ 533 K and ∼ 553 K, respectively; these temperatures were 30–70 K lower than that for Ba₂In₂O₅. A distinct difference in the hydration behavior of the structurally different tetragonal Ba₂Sc₂O₅ and cubic BaScO_3−δ was not observed. The Ba₂Sc₂O₅ shows protonic conduction below 673K and p-type conduction above 773K in a humidified atmosphere.     

Experimental study of carbon particle charging at shock-wave pyrolysis of C3O2

The temporal variation in electron and ion concentrations have been measured in shock-heated mixtures of Ar + (0-2)% C₃O₂ in the 2000-3600 K temperature and 15-30 bar pressure range. Experiments in pure argon proved that the observed free electrons and ions originate from inherent impurities of sodium. The equilibrium concentrations of free charges in argon were established during (1-3) × 10⁻⁵ s and varied from 4 × 10¹¹ cm⁻³ at T₅ = 2500 K to 5 × 10¹² cm⁻³ at 3500 K. In the reactive mixtures, containing C₃O₂, the time profiles of electron and ion concentrations showed a more complicate behavior—a fast rise to a maximum followed by a gradual decay. The maximum ion concentrations were much higher and electron concentrations were much lower than in similar conditions in argon. The extent of the subsequent decay of electron concentration increased proportionally to the square of the C₃O₂ concentration. In the mixture with 2% C₃O₂ the final electron concentration was about 100 times less than in pure argon. The characteristic decay time of free charges varied from 400 to 40 μs and decreased proportionally to the square root of the charge concentration. The data analysis is based on the assumption that the observed redistribution of electron and ion concentrations is caused by charging of the carbon particles formed during pyrolysis of C₃O₂. The kinetics of particle charging and the final distribution of charges were evaluated by the analysis of electron and ion fluxes to the particles in accordance with the electric potentials of charged particles and corresponding sodium ionization. A predominance of negatively charged particles, caused by the high electron mobility, resulted in their much higher concentration than the concentration of free electrons.     

Effect of ultrasound on the synthesis of low-modulus zeolites from a metakaolin

It was studied the effect of ultrasonic processing (22 kHz) of the aqueous suspension of metakaolin, sodium hydroxide and alumina with a molar ratio 2Al₂Si₂O₇:12NaOH:2Al₂O₃ on the low-modulus zeolite synthesis processes. To investigate the XRD, SEM, IR, EDS had been used. It was shown that after ultrasonic processing, sodium aluminates are formed, what leads to a change in process of further synthesis. It was found that without ultrasonic processing on the stage of thermal treatment at 650 °C, SOD zeolite (|Na₆|[Al₆Si₆O₂₄]) and sodium aluminosilicate (Na₆Al₄Si₄O₁₇) are synthesized. In the sample after ultrasound during thermal treatment, only sodium aluminosilicates of cubic syngony (Na₆Al₄Si₄O₁₇ and Na₈Al₄Si₄O₁₈) are formed. It was demonstrated that sodium aluminosilicates are precursors for the formation of LTA zeolite (|Na₁₂|[Al₁₂Si₁₂O₄₈]). As a result zeolitization of sodium aluminosilicates after the hydrothermal crystallization in alkaline solution, the sonicated sample contained 97 wt% LTA. Without ultrasonic processing, the product of synthesis contained 50 wt% SOD and 40 wt% LTA.