First principles calculations of the electronic, dynamical, and thermodynamic properties of the rocksalt ScX (X = N, P, As, Sb)

We have investigated the electronic, dynamical, and thermodynamic properties of the rocksalt ScX (X = N, P, As, Sb) using a plane-wave pseudopotential method within the generalized gradient approximation in the frame of density functional perturbation theory. The calculated lattice constants are found to differ by less than 0.56% from the available experimental values. These materials have the indirect Γ–X band gaps and a wide and direct band gap at the X-point in band structure, which are closer to experimental results than the previous calculations. A linear-response approach is used to calculate the phonon frequencies, the phonon density of states and LO–TO splitting. The obtained phonon frequencies at the zone-center (Γ-point) for the Raman-active and infrared-active modes are analyzed. We also calculate the thermodynamic functions using the phonon density of states, and the calculated values are in nearly perfect agreement with experimental data.     

Synthesis of layered Li1.2+x[Ni0.25Mn0.75]0.8−xO2 materials (0 ≤ x ≤ 4/55) via a new simple microwave heating method and their electrochemical properties

Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55) was prepared by a new simple microwave heating method and the effect of extra Li⁺ content on electrochemistry of Li_1.2Ni_0.2Mn_0.6O₂ (x = 0) was firstly revealed. X-ray diffraction identified that they had layered α-NaFeO₂ structure (space group R-3m). Linear variation of lattice constant as a function of x value supported the formation of solid solution, that is, extra Li⁺ is possibly incorporated in structure of layered Li_1.2Ni_0.2Mn_0.6O₂ (x = 0), accompanying oxidization of Ni²⁺ to Ni³⁺ to form Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55). This was confirmed by X-ray photoelectron spectroscopy that Ni³⁺ appeared and increased in content with increasing x value. Charge–discharge tests showed that Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55) truly displayed different electrochemical properties (different initial charge–discharge plots, capacities and cycleability). Li_1.2Ni_0.2Mn_0.6O₂ (x = 0) in this work delivered the highest discharge capacity of 219 mAh g⁻¹ between 4.8 and 2.0 V. Increasing Li content (x value in Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂) reduced charge–discharge capacities, but significantly enhancing cycleability.     

Mass Spectrometric Observations of Enhanced Rates of Association Reactions: nLiF = Li n F n (n = 2, 3) at LiF Single Crystal Surfaces

A mass spectrometric method was used to study the kinetics of lithium fluoride single-crystal sublimation. In electron impact ionization mass spectra, Li⁺, LiF⁺, Li₂F⁺, and Li₃ F ₂ ⁺ ions originating from monomer (LiF), dimer (Li₂F₂), and trimer (Li₃F₃) molecular precursors were detected in the temperature range 970–1070 K. The dimer-to-monomer and trimer-to-monomer flux ratios were found to increase progressively with increasing temperature and also in comparison with those measured under equilibrium of crystalline LiF with its saturated vapor. The temperature dependence of the ion current ratio I(Li₂F⁺)/I(Li⁺) measured over the interval 916–1087 K was shown to pass reproducibly through a minimum at about 975 K. The enhancement of the rate of association reactions at LiF crystal surfaces is discussed in light of the terrace-ledge-kink model of vaporization and surface charge concept.     

Processing and properties of Al–Li–SiCp composites

Al–Li–SiC_p composites were fabricated by a modified version of the conventional stir casting technique. Composites containing 8, 12 and 18 vol% SiC particles (40 μm) were fabricated. Hardness, tensile and compressive strengths of the unreinforced alloy and composites were determined. Ageing kinetics and effect of ageing on properties were also investigated. Additions of SiC particles increase the hardness, 0.2% proof stress, ultimate tensile strength and elastic modulus of Al–Li–8%SiC and Al–Li–12%SiC composites. In case of the composite reinforced with 18% SiC particles, although the elastic modulus increases the 0.2% proof stress and compressive strength were only marginally higher than the unreinforced alloy and lower than those of Al–Li–8%SiC and Al–Li–12%SiC composites. Clustering of SiC particles appears to be responsible for reduced the strength of Al–Li–18%SiC composite. The fracture surface of unreinforced 8090 Al-Li alloy (8090Al) shows a dimpled structure, indicating ductile mode of failure. Fracture in composites occurs by a mixed mode, giving rise to a bimodal distribution of dimples in the fracture surface. Cleavage of SiC particles was also observed in the fracture surface of composites. Composites show higher peak hardness and lower peak ageing time compared with unreinforced 8090Al alloy. Macro- and microhardness increase significantly after peak ageing. Ageing also results in considerable improvement in strength of the unreinforced 8090Al alloy and its composites. This is attributed to formation of δ^′ (Al₃Li) and S^′ (Al₂CuMg) precipitates during ageing. Per cent elongation, however, decreases due to age hardening. Al–Li–12%SiC, which shows marginally lower UTS and compressive strength than the Al–Li–8%SiC composite in extruded condition, exhibits higher strength than Al–Li–8%SiC in peak-aged condition.     

Mechanochemical Synthesis of Double Hydroxides

It has been demonstrated that the formation of magnesium-aluminium double hydroxides [Mg_{(1 – X)}Al _X (OH)₂] ^X+(A ^n– _X/n ) m H₂O, (A–Cl^–, NO^– ₃, SO^2– ₄) occurs during mechanical activation of the mixture of magnesium hydroxide (brucite) with aluminium chloride, nitrate and sulphate in high-energy planetary-type activators. The effect of activation time on the formation of the double hydroxide has been investigated. Thermal decomposition of the chloride form of the double hydroxide has been studied.     

Electrical transport properties of amorphous Se78−x Te22Bi x films

D.C. Conductivity measurements on the thin films of a-Se_78–x Te₂₂Bi _x system (where x = 0, 0.5, 2 and 4) are reported in the temperature range 213–390 K and the density of states (DOS) near the Fermi level is calculated using dc conductivity data. It is found that the conduction in all the samples takes place in the tails of localized states. The conduction in the high temperature region 296–390 K is due to thermally assisted tunneling of electrons in the localized states at the conduction band edge. In the low temperature region 213–296 K conduction takes place through variable range hopping in the localized states near the Fermi level.     

Electrical Properties of Amorphous S<Subscript>0.60</Subscript>Ge<Subscript>0.40</Subscript>:H<Subscript>x</Subscript> Films

Amorphous Si_0.60Ge_0.40:H_x films containing 1.7, 3.9, 7.1, 12.1, and 17.3 at % H are prepared by magnetron sputtering at different hydrogen partial pressures, and their electrical conductivity is measured from 80 to 350 K. The conductivity of the films exhibits Arrhenius behavior in the range 250–350 K and satisfies the relation log(σT ^1/2) ∼ T^−1/4 between 80 and 250 K. The conductivity data are used to evaluate the electron localization radius, hop distance, and activation energy of hopping conduction at 80 K; the electron mobility at the Fermi level and in the conduction band; and the 300-K activation energy of conduction.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 787–791.Original Russian Text Copyright © 2005 by Najafov, Isakov.     

Thermomechanical processing of Ti–5Al–5Mo–5V–3Cr

The constitutive behaviour and microstructural evolution of the near-β alloy Ti–5Al–5Mo–5V–3Cr in the α + β condition has been characterised during isothermal subtransus forging at a range of temperatures and strain rates. The results indicate that Ti–5Al–5Mo–5V–3Cr has a shallower approach curve, and therefore, offers a more controllable microstructure than the near-β alloy Ti–10V–2Fe–3Al. Flow softening is small in magnitude in both alloys in the α + β condition. The steady state flow stresses obey a Norton–Hoff constitutive law with an activation energy of Q = 183 kJ mol⁻¹, which is similar to the activation energy for self-diffusion in the β phase, suggesting deformation is dominated by dynamic recovery in the β matrix. Good evidence is found for the existence of ω phase after both air cooling and water quenching from above the β transus. In addition, dissolution of the α phase is found to be slow at near-transus temperatures.     

Density function theory investigation on the thermodynamic properties of the Li–N–H system

The electronic structures and formation enthalpies of compounds in the Li–N–H system have been studied by using the density functional theory. In order to evaluate the competition between each reaction in the system, the chemical potential phase diagrams of compounds in the Li–N–H system have been computed and discussed. Our calculations show that for LiNH₂, Li⁺ combines with [NH₂]^- by an ionic bond. For Li₂NH, the N–H bond displays covalent characteristics. The calculated formation enthalpy of compounds in the Li–N–H system is in agreement with previous results, the LiNH₂ is −212.27 kJ mol⁻¹, LiH is −91.66 kJ mol⁻¹, Li₂NH is −243.14 kJ mol⁻¹, Li₄NH is −309.72 kJ mol⁻¹, Li₃N is −189.11 kJ mol⁻¹, and NH₃ is −102.27 kJ mol⁻¹, respectively. Using the chemical potential phase diagrams, six reversible reactions are discussed. It is found that Li₄NH takes part in the three reversible reactions and some NH₃ formed in the system react with other compounds in the Li–N–H system. These reversible reactions are confirmed by the proposed mechanism from experiments.     

Novel highly luminescent europium dinitrosalicylates

A series of lanthanide dinitrosalicylates M₃Ln(3,5-NO₂-Sal)₃ · nH₂O (Ln = Eu, Gd; M = Li, Na, K, Cs) was synthesized. It was found that the luminescence efficiency of some M₃Eu(3,5-NO₂-Sal)₃ · nH₂O compounds was near to the high efficiency of europium dibenzoylmethanate with 1,10-phenanthroline, Eu(DBM)₃ · Phen. The luminescence excitation spectra, electron-vibrational luminescence spectra, and vibrational IR spectra were investigated. The energy of the lowest excited triplet state of the ligand was obtained from phosphorescence spectra of M₃Gd(3,5-NO₂-Sal)₃ · nH₂O, M(3,5-NO₂-HSal) · nH₂O, and M₂(3,5-NO₂-Sal) · nH₂O. The details of the structure of compounds were discussed. The influence of different M-cations on the Eu³⁺ luminescence efficiency and on the processes of excitation energy transfer to a Eu³⁺ ion was analyzed. The presence of large alkali metal cations in lanthanide dinitrosalicylates and an increase in the temperature weaken the network of hydrogen bonds and, to some extent, the “ligand–metal” bonds. This is a cause of a long-wavelength shift of the intraligand charge transfer (ILCT) band in Eu³⁺ excitation spectra arising at inclusion of Cs⁺ instead of Li⁺ cations in the crystal lattice and at the heating of compounds. A change of the energies of ligand electronic states at substitution of Li⁺ and Na⁺ for Cs⁺ can give a tenfold enhancement of the Eu³⁺ luminescence efficiency at 300 K.     

Variable—Range hopping in Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

The dc conductivity of the glasses in the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system was studied at temperatures between 223 and 393 K. At temperatures from 300 to 223 K, T^–1/4 (T is temperature) dependence of the conductivity was found, however, both Mott variable-range hopping and Greaves intermediate range hopping models are found to be applicable. Mott and Greaves parameters analysis gave the density of states at Fermi level N (E_F) = 3.13 × 10²⁰–21.01 × 10²⁰ and 1.93 × 10²¹–16.39 × 10²¹ cm^–3eV^–1 at 240 K, respectively. The variable-range hopping conduction occurred in the temperature range T = 300–223 K, since W_D was found to be large (W_D = 0.08–0.14 eV for these glasses) and dominated the conduction at T < 300 K.     

Mechanochemical Synthesis of Complex Zirconium Phosphates

Cation- and anion-substituted zirconium phosphates of X _kZr _m (PO₄) _n–y Y composition, where X = Na⁺, La³⁺, NH₄ ⁺, Y = F^–, WO₄ ^2–, 1/3 < k < 2, 2 < m < 4, 3 < n < 6 were synthesized by the procedure, including mechanical activation of the starting salts mixture followed by annealing at 300–900°C. The interaction between components was studied by XRD, EXAFS, FT–IR, [³¹P-MAS] NMR. The possibility of synthesizing nonstoichiometric compounds is demonstrated and prospects for application of the mechanochemical method for synthesis of complex zirconium phosphates are outlined.     

Dielectric properties of low-fitting Pb(Mg1/3Nb2/3)1−xTixO3-Bi2O3/Li2O ceramics

Dielectric properties of low-firing Pb(Mg_1/3Nb_2/3)_1–x Ti _x O₃-Bi₂O₃/Li₂O ceramics are studied in this work. With the addition of Bi₂O₃/Li₂O eutectic composition, the sintering temperature of PMN_1–x PT _x could be lowered to 900° C. Relaxor behaviour of PMN_1–x PT _x is enhanced by the incorporation of Bi₂O₃/Li₂O due to the substitution of Bi⁺³/Li⁺ into the PMN_1–x PT _x framework. Bi₂O₃/Li₂O eutectic composition is used as a fluxing agent, Curie shifter and depressor. Evaporation of Bi₂O₃/Li₂O and PbO during firing is checked and examined via energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) is used to clarify the Curie shifting and depressing effect of Bi₂O₃/Li₂O.     

Franck-Condon Factors to High Vibrational Quantum Numbers III: CN

Franck-Condon factor arrays have been computed numerically to high vibrational quantum numbers for the red (A²II_i–X²Σ⁺) and violet (B²Σ⁺ – X²Σ⁺) band systems of CN.     

Effects of Li+ ions on the enhancement of up-conversion emission in Ho3+-Yb3+ co-doped transparent glass–ceramics containing Ba2LaF7 nanocrystals

The up-conversion (UC) emission of Ho³⁺-Yb³⁺ and Li⁺ co-doped transparent glass ceramics 45SiO₂-15Al₂O₃-12Na₂CO₃-21BaF₂-7LaF₃-0.2HoF₃-1YbF₃-xLi₂CO₃ (x = 0, 0.5, 1, 2, 4 and 6 mol%) containing Ba₂LaF₇ nanocrystals were investigated. These glass ceramics samples were prepared using the conventional quenching techniques. The Ba₂LaF₇ nanocrystals precipitated from the glass matrix was confirmed by X-ray diffraction (XRD). Compared with the glass ceramics sample without Li⁺, the UC emission intensity of glass ceramics samples with Li⁺ were enhanced. It can be proved that the Li⁺ can affect the enhancement up-conversion (UC) emission. Particularly, the green UC emission intensity band centered at 546 nm was strongly increased twice with the concentration of Li⁺ increasing up to 4 mol%. Through the comparison and analysis of the energy graph, it was shown that the ⁵F₄/⁵S₂→⁵I₈ transition of Ho³⁺ ion obtained the green (546 nm) light. There are two weak fluorescences in the red (657 nm) region and near infrared (753 nm) region of spectrum, which is the ⁵F₄/⁵S₂→⁵I₇ and ⁵F₅→⁵I₈ transition of Ho³⁺. Therefore, the emission results showed that the incorporation of Li⁺ ions into the Ba₂LaF₇:Eu³⁺ lattice could induce a remarkable change of the emission intensity in red region (R = I_ED/I_MD) with 393 nm excitation wavelength. It was indicated that the symmetry of the lattice was destroyed by Li⁺ in glass ceramics. The possible mechanism responsible for the enhancement of UC emission in Ho-Yb co-doped was discussed.     

Dielectric, magnetic and spectroscopic properties of Li2O–WO3–P2O5 glass system with Ag2O as additive

Li₂O–WO₃–P₂O₅ glasses containing small concentrations of Ag₂O from 0 to 1 mol% were prepared. A number of studies viz., chemical durability, dielectric studies (constant ′, loss tan δ, a.c. conductivity σ_ac over a range of frequency and temperature), spectroscopic (infrared, optical absorption ESR spectra) and magnetic susceptibility studies of these glasses, have been carried out. The interesting variations observed in all these properties with the concentration of Ag⁺ ions have been analyzed in the light of different oxidation states and environment of tungsten ions in the glass network.     

First principles calculations of structural, electronic and optical properties of BaLiF3

Structural and electronic parameters of the perovskite BaLiF3 are obtained from density functional theory using the full-potential linearized augmented plane wave method (FP-LAPW) within the local density and the generalized gradient approximations. Detailed comparisons are made with the existing measured values and with results obtained in previous theoretical studies and with experimental measurements. The calculated band structure shows a direct band gap (Γ–Γ). The contribution of the different bands was analyzed from total and partial density of states curves. We have presented the assignment of the different optical transitions existing in BaLiF3 from the imaginary part of the dielectric function spectra with respect to their correspondence in the electronic band. Finally we have presented a theoretical study of the high hydrostatic pressure dependence of the electronic properties of perovskite BaLiF3.     

Simulation of the Processes of Formation and Dissociation of Neutral Particles in Air Plasma: Vibrational Kinetics of Ground States of Molecules

The results are given of the calculations of populations of vibrational levels of N₂(X ¹·⁺ ₈ ), ₂(X ³·^- ₈ ), and NO(X²) molecules in an air plasma whose parameters correspond to the positive column of a DC discharge at pressures of 30–300 Pa and currents of 20–110 mA. Different processes are analyzed that form the distribution of molecules over levels, including the electron impact, V–Vand V–T exchange, chemical reactions, and heterogeneous deactivation. The calculation results for N₂(X ¹·⁺ ₈ ) are compared with experiment. It is found that the values of the effective vibrational temperature characterizing the populations of N₂(X ¹·⁺ ₈ ) are close to the values realized in a nitrogen plasma, and the difference of the vibrational temperatures of ₂(X³·^- ₈ ) and NO(X²) from the gas temperatures is not significant, which is due to high frequencies of V–T relaxation of vibrational states of these molecules in collisions with (³ P) atoms.     

On electrical transport in CoWO4 single crystals

CoWO₄ is a p-type semiconductor with conductivity in the range 10^–8 to 10^–3 ohm^–1 cm^–1. The solid exhibits extrinsic behaviour up to 750 K and intrinsic behaviour above 750 K. In this solid conduction by hopping of small polarons seems to be dominating up to 750 K and above 750 K conduction becomes band type. The energy band gap of the solid has been found to be 2.80 eV. The values of mobility and the mean free path are estimated. The variation of dielectric constant with temperature has been attributed to changes in atomic and ionic polarization and space charge polarization of thermally generated charge carriers.     

Electrical Conductivity of M2V12O30 · nH2O (M = K, Rb, Cs)

The ac electrical conductivity of the M₂V₁₂O₃₀ · nH₂O (M = K, Rb, Cs) polyvanadates prepared via hydrolytic precipitation is measured at 1 kHz between 298 and 423 K in air of 12% relative humidity. The 298-K conductivity of the samples is found to decrease with increasing cation size (in going from K to Rb and to Cs). The activation energy for conduction in the polyvanadates is 0.31–0.34 eV as determined during heating in the range 323–373 K and 0.20–0.23 eV above 373 K and during cooling. The activation energy is higher in Rb₂V₁₂O₃₀ · 6H₂O. The 298-K ionic transference numbers inferred from dc conductivity measurements are 0.7, 0.2, and 0.7 for K⁺, Rb⁺, and Cs⁺, respectively.