Proton and Li-7 NMR study on the effect of the OH− anion upon the Li+-ion conduction in the solid solution Li5NI2LiOH

From ¹H and ⁷LiNMR relaxation times T₁, T₂ and T_1ρ in Li₅NI₂ and the solid solution Li₅NI₂?0.77LiOH, the diffusive motion of the Li⁺ ion was studied to make clear the role of the OH^? ion in improving the Li⁺ ionic conduction. At temperatures as low as 140 K, each Li⁺ ion jumps among four available positions. Its activation energies are 9.26 and 11.8 kJ mol^?1 for Li₅NI₂ and Li₅NI₂?0.77LiOH, respectively. Diffusive motion was observed in T₂ and T_1ρ above 240 K. The mode of the cation distribution and the diffusion mechanism are not affected by the presence of the OH^? anion. The most noticeable fact is that the OH^? ion is substituted selectively for the N^3? ion that is the nearest neighbour of the Li⁺ ion. This selective substitution increases the concentration of the Li⁺ vacancy most effectively up to 4.2% of the total Li positions. At the same time it diminishes the strong attractive force of the N^3? anion binding the Li⁺ ion to the position, and thus the activation energy. For the diffusion, an anomalously low attempt frequency of 3̃ × 10⁹Hz was obtained from T_1ρ, while the normal value of 4.8 × 10¹²Hz was obtained from the ionic conductivity. The large discrepancy was attributed to the collective nature of the Li⁺ diffusive motion.     

Shock-tube study of HCN self-broadening and broadening by argon for the P(10) line of the ν1 band at 3 μm

A tunable infrared diode laser was used to measure the fully resolved absorption line shape of the P(10) line in the ν₁ band (10°0–00°0) of HCN for shock-heated mixtures of HCN-Ar at temperatures of 1000, 1500 and 2000 K. The temperature dependence of the collision-broadening coefficients 2γ (cm^-1 atm^-1, FWHM) were inferred for both self-broadening and broadening by argon. For the assumed form 2γ = 2γ₀(T₀/T)ⁿ the exponent n was determined to be 0.63 ± 0.06 with 2γ₀ = 0.11 cm^-1atm^-1 and T₀ = 300 K for argon-broadening in the range 300 < T < 2000 K, and 1.2 ± 0.6 with 2γ₀ = 0.68 cm^-1atm^-1 and T₀ = 1000 K for self-broadening in the range 1000 < T < 2000 K.     

Study of lithium adsorption on the TiO2 surface by electron-stimulated desorption

This paper reports on a study of electron-stimulated desorption (ESD) of O⁺ and Li⁺ ions from titanium dioxide as a function of the preheating temperature T and of the concentration of lithium adsorbed at 300 K, which was carried out with a static magnetic mass spectrometer combined with a retarding-field energy analyzer. For T>1500 K, the TiO₂ surface undergoes irreversible rearrangement. At temperatures from 300 to 900 K and at lithium coverages Θ<1, the ESD cross sections of the O⁺ and Li⁺ ions vary in a reversible manner with temperature, while for lithium coverages Θ>1, the changes in the Li⁺ and O⁺ ESD cross sections become irreversible. For θ<1, the appearance threshold of the Li⁺ and O⁺ ions is 25 eV, whereas for θ>1, the ESD threshold of Li⁺ ions shifts to 37 eV.     

Mössbauer study of Na0.82Co0.99Fe0.01O2

We studied by Mössbauer spectroscopy the Na_0.82CoO₂ compound using 1% ⁵⁷Fe as a local probe which substitutes for the Co ions. Mössbauer spectra at T=300 K revealed two sites which correspond to Fe³⁺ and Fe⁴⁺. The existence of two distinct values of the quadrupole splitting instead of a continuous distribution should be related with the charge ordering of Co⁺³, Co⁺⁴ ions and ion ordering of Na(1) and Na(2). Below T=10 K part of the spectrum area, corresponding to Fe⁴⁺ and all of Fe³⁺, displays broad magnetically split spectra arising either from short-range magnetic correlations or from slow electronic spin relaxation.     

Electrical and optical properties of single crystal In2Te3 and Ga2Te3

Electrical conductivity and thermopower measurements are reported for the defect semiconductors p-In₂Te₃ and n-Ga₂Te₃. The hole mobility μ_p in the former varied as Tⁿwheren=+5.98 forT<350 K and n=-4.13 forT>350 K showing a maximum of 210 cm²V^-1 sec^-1 at 350 K. Electron mobility in n-Ga₂Te₃ also went through a maximum at 320 K. The optical band-gaps for both were found to be direct, with values of 1.01 and 1.08 eV for In₂Te₃ and Ga₂Te₃ respectively at 300 K. Pronounced effects of annealing on TEP and optical absorption gave evidence of defect ordering at low temperatures followed by defect creation at T>350 K.     

Li3VO4-Li4TO4(T=Ge,Si)固溶体离子导体7Li的NMR研究

在150—573K温度范围内,研究了固溶体Li₃VO₄-Li₄TO₄(T=Ge,Si)系统不同成分的⁷Li的NMR谱。发现γ_II相固溶体室温⁷Li的NMR线宽和自旋晶格弛豫时间T₁的值都比Li₄GeO₄,Li₄SiO₄和Li₃VO₄小约一个数量级。这表明在γ_II相固溶体离子导体中,Li⁺离子运动有可能比固溶前有数量级增长。同时还发现⁷Li的电四极分裂伴线数随成分和温度而异,以及伴线强度百分比依赖于温度。这反映γ_II相的不同成分中,间隙Li⁺离子占有的不等价位置个数不同,而Li⁺离子在每个不等价位置上的占有率又随温度而变化。 关键词：     

Low temperature electrical conductivity and magnetoconductivity of Fe39Ni39Mo4Si6B12 and Co58Ni10Fe5Si11B16 metallic glass alloys

A detailed study on the weak localization phenomenon vis-a-vis electron-electron interaction effects in magnetic metallic glasses has been carried out. We measured the electrical conductivity and magnetoconductivity within the temperature range 1.8≤T≤300K. A maximum on the conductivity versus temperature curve exists atT=T _m. The conductivity was observed to follow aT ^1/2 law forT<T _m andT ² law forT>T _m. Magnetoconductivity data of these alloys indicate the prominence of electron-electron interaction at low temperatures. The authors have determined the inelastic scattering field and spin-orbit scattering field from the magnetoconductivity data. The inelastic scattering field obeys aT ^p law (p=2) at low temperatures.     

Magnetic susceptibility studies of (CH2)3(NH3)2FeCl2Br2 and (CH2)6(NH3)2FeCl2Br2

The magnetic susceptibility of the layered compounds (CH₂)₃(NH₃)₂FeCl₂Br₂ and (CH₂)₆(NH₃)₂FeCl₂Br₂ has been measured in the range 80 < T < 300 K. The results follow a Curie-Weiss behavior in the range 120 < T < 300 K but are field dependent for T < 120 K. The results are interpreted in terms of a two-dimensional antiferromagnetic interaction which is canted. A comparison with the corresponding pure chloride compounds is given.     

Ab initio chemical kinetics for the reactions of HNCN with O(P) and O2

The kinetics and mechanisms of the reactions of cyanomidyl radical (HNCN) with oxygen atoms and molecules have been investigated by ab initio calculations with rate constant prediction. The doublet and quartet state potential energy surfaces (PESs) of the two reactions have been calculated by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on geometries optimized at the CCSD/6-311++G(d, p) level. The rate constants for various product channels of the two reactions in the temperature range of 300-3000 K are predicted by variational transition state and RRKM theories. The predicted total rate constants of the O(³P) + HNCN reaction at 760 Torr Ar pressure can be represented by the expressions k_total (O + HNCN) = 3.12 × 10⁻¹⁰ × T^−0.05 exp (−37/T) cm³ molecule⁻¹ s⁻¹ at T = 300-3000 K. The branching ratios of primary channels of the O(³P) + HNCN are predicted: k₁ for producing the NO + CNH accounts for 0.72-0.64, k₂ + k₉ for producing the ³NH + NCO accounts for 0.27-0.32, and k₆ for producing the CN + HNO accounts for 0.01-0.07 in the temperature range studied. Meanwhile, the predicted total rate constants of the O₂ + HNCN reaction at 760 Torr Ar pressure can be represented by the expression, k_total(O₂ + HNCN) = 2.10 × 10⁻¹⁶ × T^1.28exp (−12200/T) cm³ molecule⁻¹ s⁻¹ at T = 300-3000 K. The predicted branching ratio for k₁₁ + k₁₃ producing HO₂ + ³NCN as the primary products accounts for 0.98-1.00 in the temperature range studied.     

Thermomagnetic transitions and coercivity mechanism in bulk composite Nd60Fe30Al10 alloys

The thermomagnetic behaviour (within the temperature range 553-300 K) for the bulk composite Nd₆₀Fe₃₀Al₁₀ alloy is described in terms of a transition from paramagnetic to superferromagnetic state at T=553 K, followed by a ferromagnetic ordering for T<473 K. For the superferromagnetic regime, the alloy thermomagnetic response was associated to a homogeneous distribution of magnetic clusters with mean magnetic moment and size of 1072 μ_B and 2.5 nm, respectively. For T<473 K, a pinning model of domain walls described properly the alloy coercivity dependence with temperature, from which the domain wall width and the magnetic anisotropy constant were estimated as being of ≈8 nm and ≈10⁵ J/m³, typical values of hard magnetic phases. Results are supported by microstructural and magnetic domain observations.     

The effects of elements doping on transport and thermoelectric properties of Sr3Ti2O7

The Ruddlesden–Popper (RP) phase compounds (Sr_0.95R_0.05)₃Ti₂O₇ (R=Er, Y, Dy, Gd, Eu, Sm, Nd and La) were prepared, and their transport and thermoelectric properties were investigated. The results indicate that high-T electrical resistivity ρ (300 K<T<1000 K) increases monotonically with temperature and basically has a relation ρ∝T^M, with M varying from 0.91 to 1.92 at temperatures T>~650 K, suggesting acoustic phonon scattering is dominant. At low temperatures (5 K<T<300 K), ρ for (Sr_0.95R_0.05)₃Ti₂O₇ (R=Nd and La) decreases monotonously with decreasing temperature, whereas ρ for (Sr_0.95R_0.05)₃Ti₂O₇ (R=Er, Y, Dy, Gd, Eu and Sm) decreases first, and then increases instead as T decreases to a critical temperature T_c. Moreover, electrical conductivity σ∝T^1/2 holds at lower temperatures, indicating that the electron–electron interaction caused by the presence of disorder dominates the transport process at the low temperatures. Besides, experiments show that at T<~400 K the lattice thermal conductivity of the doped compounds basically decreases with increase of the atomic mass of dopants. Generally, the figure of merit (ZT) at 1000 K increases first, and then decreases with the increase of the dopants' ionic radius, and the largest ZT is achieved in (Sr_0.95Gd_0.05)₃Ti₂O₇ mainly owing to its lower lattice thermal conductivity.     

Temperature dependence of the lattice parameters in the S1G and S2G phases of HxBPA

The temperature dependence of the monoclinic lattice constants in the two smectic phases, S¹_G and S²_G, of HxBPA, has been obtained from X-ray diffraction data, in the temperature range 300 K < T < 240 K. The variation of b (unique axis) is consistent with the chain ordering in the S²_G phase indicated by Raman and NMR measurements.     

Theoretical study on the kinetics for OH reactions with CH3OH and C2H5OH

Kinetics and mechanisms for reactions of OH with methanol and ethanol have been investigated at the CCSD(T)/6-311 + G(3df, 2p)//MP2/6-311 + G(3df, 2p) level of theory. The total and individual rate constants, and product branching ratios for the reactions have been computed in the temperature range 200-3000 K with variational transition state theory by including the effects of multiple reflections above the wells of their pre-reaction complexes, quantum-mechanical tunneling and hindered internal rotations. The predicted results can be represented by the expressions k₁ = 4.65 × 10⁻²⁰ × T^2.68 exp(414/T) and k₂ = 9.11 × 10⁻²⁰ × T^2.58 exp(748/T) cm³ molecule⁻¹ s⁻¹ for the CH₃OH and C₂H₅OH reactions, respectively. These results are in reasonable agreements with available experimental data except that of OH + C₂H₅OH in the high temperature range. The former reaction produces 96-89% of the H₂O + CH₂OH products, whereas the latter process produces 98-70% of H₂O + CH₃CHOH and 2-21% of the H₂O + CH₂CH₂OH products in the temperature range computed (200-3000 K).     

Infrared studies of lithium intercalation in the FePS3 and NiPS3 layer-type compounds

Infrared spectra (700-30 cm^-1) of several lithium intercalates (chemically prepared) Li_xMPS₃, with M=Fe, Ni and 0<x<1.5, have been recorded and compared with those known for the corresponding host lattices. These lithium intercalates are mainly characterized by new absorption bands at 336 cm^-1 and 310 cm^-1 for the iron and nickel compounds, respectively. These bands assigned to lithium vibrations increase progressively with lithium content : it is concluded that Li⁺ ions are more likely to occupy the 2d and 4h “octahedral” sites in the gaps. In addition, the spectra of the nickel derivatives reveal some geometric distortion within the layers and a progressive strengthening of the Ni-S interactions. These results are correlated to the best energy yields obtained in NiPS₃/lithium batteries.     

Enhanced luminescence from spontaneously ordered Gd2O3:Eu based nanostructures

Nanostructured Gd₂O₃:Eu³⁺ and Li⁺ doped Gd₂O₃:Eu³⁺ thin films were prepared by pulsed laser ablation technique. The effects of annealing and Li⁺ doping on the structural, morphological, optical and luminescent properties are discussed. X-ray diffraction and Micro-Raman investigations indicate a phase transformation from amorphous to nanocrystalline phase and an early crystallization was observed in Li⁺ doped Gd₂O₃:Eu³⁺ thin films on annealing. AFM images of Li⁺ doped Gd₂O₃:Eu³⁺ films annealed at different temperatures especially at 973 K show a spontaneous ordering of the nanocrystals distributed uniformly all over the surface, with a hillocks (or tips) like self-assembly of nanoparticles driven by thermodynamic and kinetic considerations. Enhanced photoemission from locations corresponding to the tips suggest their use in high resolution display devices. An investigation on the photoluminescence of Gd_2−xEu_xO₃ (x=0.10) and Gd_2−x−yEu_xLi_yO₃ (x=0.10, y=0.08) thin films annealed at 973 K reveals that the enhancement in luminescence intensity of about 3.04 times on Li⁺ doping is solely due to the increase in oxygen vacancies and the flux effect of Li⁺ ions. The observed decrease in the values of asymmetric ratio from the luminescence spectra of Li⁺ doped Gd₂O₃:Eu³⁺ films at high temperature region is discussed in terms of increased EuO bond length as a result of Li⁺ doping.     

Low field magnetoresistance and conduction noise in layered manganite La1.4Ca1.6Mn2O7

Temperature dependence of conduction noise and low field magnetoresistance of layered manganite La_1.4Ca_1.6Mn₂O₇ (DLCMO) are reported and compared with the infinite layered manganite La_0.7Ca_0.3MnO₃ (LCMO). The double layered manganite was prepared using standard solid state reaction method and had a metal-insulator transition temperature (T_M-I) of 155 K. The temperature dependence of susceptibility showed evolution of ferromagnetic ordering at 168 K. The observed voltage noise spectral density (S_V) shows 1/f^α type of behaviour at all temperatures from 77 K to 300 K. In the ferromagnetic region (T<168 K), S_V/V² shows two peaks at 164 K and 114 K. The observed two peaks in normalised conduction noise of DLCMO is attributed to the excess noise generated due to setting up of short range 2D-ferromagnetic ordering and long range 3D-ferromagnetic ordering at two different temperatures T_C2 and T_C1. In temperature range between T_C1 and T_C2, the magnetoresistance (MR) showed a gradual increase with the magnetic field. The observed MR has been explained in the framework of the two phase model [ferromagnetic (FM) domains and paramagnetic (PM) regions].     

Non-stoichiometric molybdenum oxides as cathodes for lithium cells. part v. thermodynamic,kinetic and structural aspects of the behaviour of Mo8O23 and Mo18O52

A deeper insight in the electrochemical behaviour of Li cells based on two non-stoichiometric Mo oxides, Mo₈O₂₃ and Mo₁₈O₅₂, was obtained by determining the OCV's, the diffusion coefficients and the variations of lattice parameters as a function of depth of discharge. The first material is a monoclinic framework-structured compound endowed with large channels which provide easy paths for Li⁺. Occupation of sites in the cavities of this structure produces at first a shrinkage of the unit cell, followed by a moderate re-expansion. Mo₁₈O₅₂ is a triclinic step-layered material which markedly expands upon Li⁺ intercalation. Li⁺ diffuses in it relatively slowly for x<1, i.e. before increasing the interlayer distance, and for x>0.4 due to coulombic repulsion between Li⁺ ions.     

Magnetic properties and structural chemistry of ternary silicides (RE,Th, U)Ru2Si2 (RE = RARE EARTH)

Ternary silicides (RE, Th, U)Ru₂Si₂ have been synthesized from the elements. All the compounds (RE = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were found to be isotypic and to crystallize with the structure type of ThCr₂Si₂ (ordered derivative of the BaAl₄-type). The magnetic behavior of these alloys was studied in the temperature range 1.5 K < T < 1100 K. Magnetic susceptibilities at temperatures T > 300 K closely follow a typical Van Vleck paramagnetism of free RE³⁺-ions. In the case of CeRu₂Si₂ susceptibilities are well described for 20 K < T < 1100 K by a Van Vleck paramagnetism of widely spaced multiplets; the observed effective paramagnetic moment μ_eff = 2.12 BM indicates a high percentage (85%) of Ce³⁺. SmRu₂Si₂ yields an effective moment μ_eff = 0.54 BM, which compares reasonably well with the Hund's rule J = 5/2 ground level for free Sm⁺ and a low-lying excited level with J = 7/2. For temperatures T > 15 K the magnetic susceptibility as a function of temperature follows the “Van Vleck behavior” for free Sm³⁺. At low temperatures ferromagnetic ordering was encountered for (Pr, Nd, Ho, Er, Tm)Ru₂Si₂, whereas antiferromagnetic ordering was observed for (Sm, Gd, Tb, Dy)Ru₂Si₂. The ordering temperatures are generally below 55 K. No superconductivity was found for temperatures as low as 1.8 K.     

New Li+ ion conductors in the system Li4SiO4−Li3AsO4

In the system Li₄SiO₄-Li₃AsO₄, Li₄SiO₄ forms a short range of solid solutions containing up to 14 to 20% Li₃AsO ₄, depending on temperature, and γ-Li₃AsO₄ forms a more extensive range of solid solutions containing up to ≈55% Li₄SiO₄. The Li₄SiO₄-Li₃AsO₄ phase diagram has been determined and is of binary eutectic character. The ac conductivity of polycrystalline samples was measured over the range 0 to at least 300°C for nine different compositions. The two solid solution series have much higher conductivity than the pure end-members; maximum conductivity was observed in the γ-Li₃AsO₄ solid solutions containing ≈40 to 55% Li₄SiO₄, with values of $\text{≈2×10}{}^{\mathrm{?6}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 20°C rising to ≈0.02 Ω^?1 cm^?1 at 300°C. These values are comparable to those found in the system Li₄SiO₄-Li₃PO₄. The variation with composition of the Arrhenius prefactor and activation energy has been interpreted in terms of the mechanisms of conduction. Li₃AsO₄ is a poor conductor essentially because the number of mobile Li⁺ ions is very small. This number, and hence the conductivity, increases dramatically on forming solid solutions with Li₄SiO₄, by the creation of interstitial Li⁺ ions. At ≈40 to 55% Li₄SiO₄, the number of mobile Li⁺ ions appears to be optimised. An explanation for the change in activation energy of conduction at ≈290°C in Li₄SiO₄ and at higher temperatures in Li₄SiO₄ solid solutions is given in terms of order-disorder of the Li⁺ ions.     

非晶锂离子导体B2O3-0.7Li2O-0.7LiCl-xAl2O3晶化初期的核磁共振研究

通过真空密封热处理、避免了样品晶化后吸水引起的误差,采用脉冲法在293K和77K测量了晶化过程初期三种非晶锂离子导体B₂O₃-0.7Li₂O-0.7LiCl-xAl₂O₃(x=0.15,0.10和0.05)的⁷Li核磁共振谱。发现在低温(77K)只有固相锂离子对应的自旋-自旋弛豫时间T₂=87μs,严格按高斯函数衰减。在室温下固相锂离子对应的T_2s=127μs,仍是高斯型;但液相锂离子对应的T₂却按洛仑兹函数衰减。这反映出锂离子导体的固-液二相性。三种非晶B₂O₃-0.7Li₂O-0.7LiCl-xAl₂O₃(x=0.15,0.10和0.05)分别在热处理温度401,388和381℃附近,其液相锂离子对应的T_2l都剧增,其吸收谱线宽都变窄。由此再次验证了非晶母体与微晶之间的两相界面效应的物理图象。 关键词：