A1Σu+-X1Σg+ and B1Πu-X1Σg+ fluorescence of 6Li2 and 6Li7Li excited by a krypton ion laser

The A¹Σ_u⁺-X¹Σ_g⁺ and B¹Π_u-X¹Σ_g⁺ fluorescence of the ⁶Li₂ and ⁶Li⁷Li molecules has been studied for all krypton ion laser lines (468.0–799.3 nm) which might be expected to excite such fluorescence. Only two A-X fluorescence series of ⁶Li₂ were found (one excited by 647.1 nm, and one by 752.5 nm). No A-X fluorescence series of ⁶Li⁷Li was found. Five B-X fluorescence series of ⁶Li₂ were found (one each excited by 468.0, 476.2, and 530.9 nm, and two by 568.2 nm). Four B-X fluorescence series of ⁶Li⁷Li were found (one each excited by 468.0 and 482.5 nm and two by 520.8 nm). Calculated Einstein A coefficients and lifetimes for these transitions are also given.     

NMR study of pure and doped β-LiAl

The NMR spin-lattice relaxation time, T_I, has been measured as a function of temperature for both ⁷Li and ²⁷Al in pure and doped β-LiAl alloys. Compositions with ⁷Li concentration in the range 48.3–54.5% and doping in the form Li₅₀Al_50?xM_x, where M = Ag or In, were studied. The relaxation rates T₁^?1 for the ²⁷Li and the ²⁷Al resonances were found to be peaked functions of temperature with the maxima for ⁷Li appearing at composition dependent temperatures. The ²⁷Al maxima always appeared at a lower temperature, independent of composition, and the ²⁷Al maximum relaxation rate was a strong function of composition in contrast with ⁷Li where the maximum rate was only weakly dependent on composition. The principle relaxation mechanisms are identified as dipole-dipole coupling in the ⁷Li and coupling of the ²⁷Al quadrupole moment to electric field gradients. The temperature dependence of these rates is attributed to the thermally activated diffusion of vacancies of a non-thermal origin in the Li sub-lattice. These vacancies are also responsible for the fluctuating electric field gradients. The results have been analyzed to give the Li diffusion coefficients with associated activation energies and estimates of the vacancy concentration as functions of alloy composition.     

Ionic conductivity and NMR relaxation study on Li3N single crystal

Both ionic conductivity and ⁷Li NMR relaxation time T₂ were studied on Li₃N single crystal samples containing an oxygen impurity. Owing to the O impurity, the samples showed a high ionic conductivity (σ⊥ = 0.83 S m^?1 and σ_∥= 0.013 S m^?1 at 300 K) and a low activation energy (E_a,⊥ = 0.19 eV and E_a,∥ = 0.24 eV). The intrinsic conduction accompanying vacancy generation within the Li₂N layer was observed in the high temperature region. In the extrinsic region only a motion of the Li ion located in the Li₂N layer is responsible for both σ_⊥ and σ_∥. The site exchange motion of two kinds of Li ion has little importance to the ionic conduction.     

7Li NMR study on Li+ ionic diffusion and phase transition in LixCoO2

The temperature dependence of the spin-lattice relaxation time, T₁ and the line width of the ⁷Li nucleus were measured in delithiated Li_xCoO₂ (x = 0.6, 0.8, 1.0). Two different relaxation behaviors were observed in the temperature dependence of T₁^− 1 in a x = 0.8 sample. These would have arisen from inequivalent Li sites in two coexisting phases; an original hexagonal (HEX-I) and a modified hexagonal (HEX-II) phase in the x = 0.8 sample. We analyzed using a phenomenological non Debye-type relaxation model. Motional narrowing in the line width was observed in each sample, the result revealing that Li⁺ ions begin to move at low temperature in samples with less Li content. It was found that the activation energy associating with Li⁺ ion hopping in the HEX-II phase is smaller than that in the HEX-I phase. These results show that the HEX-II phase produced in the Li deintercalation process would be suitable for Li⁺ ionic diffusion in multi-phase Li_xCoO₂, and it is expected that this would enable fast ionic diffusion. Li⁺ ionic diffusion related to phase transition is discussed from ⁷Li NMR results.     

Hyperfine interaction of13O and23Mg implanted in Pt

The spin relaxation timeT ₁ for short-lived beta emitters¹³O and²³Mg implanted in Pt have been measured for the first time;T ₁T¹³O) = 2.90 ±0.65 Ks andT ₁ T(²³Mg) = 1665 ±140 Ks. The Knight shift for¹³O in Pt was measured at 300 K to beK(¹³O) = +(4.23 ±0.14) × 10^–3. In the case of¹³O, the Knight shift is unusually large and the relaxation time is unusually fast compared with other interstitial impurities in Pt. A KKR band-structure calculation reproduces the present large Knight shift fairly well.     

A nuclear magnetic resonance study of the structural properties and molecular motions of Li2KH(SO4)2 and LiKSO4 single crystals

The structural properties and relaxation mechanisms of Li₂KH(SO₄)₂ crystals were determined using the temperature dependences of NMR spectra and the spin-lattice relaxation times (T₁) of their ¹H, ⁷Li, and ³⁹K nuclei. The results obtained were compared with the previously reported physical properties of LiKSO₄ crystals. The substitution of the potassium ions with protons in the LiKSO₄ crystals were variations in the phase transition temperatures, and the non-appearance of ferroelastic properties. The ⁷Li T₁ for the Li₂KH(SO₄)₂ crystals was much shorter than the ⁷Li T₁ for the LiKSO₄ crystals, and these findings indicate that the presence of the protons in Li₂KH(SO₄)₂ causes the Li ions to move with greater freedom.     

NMR and magnetic susceptibility study of rapidly quenched Ni100-XPX metallic glasses

In order to investigate the electronic structure of the rapidly quenched Ni_100-XP_X metallic glass system (18 ≦ x ≦ 22), NMR and magnetic susceptibility measurements have been carried out for temperatures 4.2 °K ≦ T ≦ 295 °K and magnetic fields H ≦ 20 kOe. The ³¹P Knight shift and relaxation rate behavior demonstrate a metalloid concentration dependence which is consistent with earlier work on the ternary NiPdP and NiPtP metallic glass systems. A consideration of the trends in the magnetic susceptibility indicates that, relative to the Fermi energy, the d-states associated with Ni are higher (the number of d-holes are greater) than those for Pd or Pt.     

NMR studies of metal-nonmetal transition in lithium-methylamine solutions

The Knight shift and the spin-lattice relaxation time of ⁷Li and ¹H have been measured in Li-methylamine solutions, in which a transition from the metallic to the nonmetallic states occurs.     

Microwave spectrum of γ-valerolactone

An Ar⁺ laser at 4579 Å is used to excite the B¹Π_u-X¹Σ_g⁺ fluorescence of the ⁶Li⁷Li molecule in a crossed heat pipe oven. The spectrum in the region 4400–6300 Å is recorded photoelectrically with an emphasis on the observation of higher vibrational levels in the ground state close to the dissociation limit. P and R doublets corresponding to v″ ≤ 26 originating from the (v′ = 13, J′ = 19) level are observed and identified using mass-reduced quantum numbers. Two additional ⁶Li⁷Li series, known from earlier work of Velasco, Ottinger, and Zare, are also analyzed. These data are used to construct effective Rydberg-Klein-Rees (RKR) potentials for specific J″ (=9, 19) quantum numbers of the ground state and from them the true (rotationless) potential energy curve (for X¹Σ_g⁺) is derived. This extends the previously known curve of Li₂ from 4.28 to 5.18 Å (outer turning point); this turning point corresponds to an energy which is approximately 88% of the dissociation energy, which is estimated here to be 8516 ± 18 cm^?1.     

Critical nuclear relaxation in cobalt metal

Nuclear magnetic resonance of cobalt metal was investigated in the paramagnetic and ferromagnetic states and in the critical region below T_c. The Knight shift and spin lattice relaxation times were measured in the paramagnetic phase in the solid and liquid states from 1578 K to 1825 K. The resonant frequency, spin-lattice and spin-spin relaxation times were measured in the ferromagnetic phase from room temperature to 1385 K. The main part of (T₁T)^-1 results from fluctuating orbital moments in both phases except near T_c where this process forms the background for critical spin relaxation. The critical exponents for T^-1₁ and for the magnetization in the ferromagnetic state were found to be n' = 0.96 ± 0.07 and β = 0.308 ± 0.012, respectively.     

X-ray and pulsed NMR studies of lithium nitride chlorides in anti-fluorite type structures

Lithium nitride chloride, Li_2-2xN_0.5-xCl_0.5+x′ have been found to possess anti-fluorite type structures in the range 0.05 <x< 0.1, with Fm3m, and with the lattice parameter in the range 5.354 ≈ 5.375 Å. The ⁷Li relaxation was studied in the temperature range 178–625 K, and the activation energy for Li⁺ hopping motion, E_a = 0.19 eV was obtained for x = 1. Small variation of E_a with composition or with occupancy of the Li⁺ site was confirmed.     

Anomalous properties of crystals with ferroelectric phase transition induced by off-center ions

It is given the theoretical study of some properties of strongly polarizable dielectric crystals in which off-center impurity ions induce ferroelectric phase transition. The spontaneous polarization, transition temperature, soft mode frequency, dielectric susceptibility, ultrasonic attenuation, nuclear spin-lattice relaxation are analyzed. The theory explains observed in K_1?xLi_xTaO₃ saturation of remanent polarization with off-center Li⁺ concentration increasing, close to $\text{x}$ dependence of phase transition temperature, the anisotropy of ultrasonic attenuation, the absence of anomalies of Li nuclear spin-lattice relaxation rate near T_c.     

The C1Πu-X1Σg+ fluorescence of Li2 excited by ultraviolet lines of an argon ion laser

The fluorescence spectra of ⁷Li₂ and ⁶Li₂ excited by an argon ion (3511 Å) laser are analyzed. No fluorescence was observed for 3514- or 3638-Å excitation or for ⁶Li⁷Li. For the C¹Π_u-X¹Σ_g⁺ electronic transition, the spectrum of ⁷Li₂ shows R and P doublets for 0 ≤ v″ ≤ 6 and that of ⁶Li₂ consists of Q lines for 0 ≤ v″ ≤ 11. Through the assignments of these lines (a) Hsu's (Ph.D. thesis, Fordham University, 1974, unpublished) molecular constants for C state have been verified, (b) the reliability of C- and X-state constants for ⁶Li₂ derived from those of ⁷Li₂ through mass-reduced scaling has been verified, and (c) the transition moment for the C-X transition of Li₂ has been shown by comparison of the observed and calculated intensities to be roughly independent of internuclear distance in the region near R_e for the C state.     

7Li NMR study of the mobility of lithium ions in one-dimensional channels of Nb3Se4

The temperature dependence of the spin-lattice relaxation time T ₁ and the ⁷Li NMR spectra of the Li_0.7Nb₃Se₄ intercalation compound with one-dimensional channel structure have been studied. It is found that the temperature dependence of T ₁ exhibits two relaxation minima, and the quadrupole splitting in the Li NMR spectra shows an anomalous temperature behavior. The inference is drawn that the observed effects are associated with the high-rate diffusive motion of lithium ions along one-dimensional channels and the interchannel transitions.     

Temperature dependence of Knight shifts for 12 B in Pt

The Knight shift of a short lived β-emitting nucleus ¹²B (I = 1, T _1/2 = 20 ms) implanted into Pt has been measured as a function of temperature (140?600 K) by means of the β-NMR method. The relation between the Knight shift and the susceptibility for Pt was deduced, which shows the similar tendency to that for the case of ¹²B in Pd.     

Electrochemical behavior of Li intercalation processes into a Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 cathode

Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ (X=0.17, 0.25, 0.33, 0.5) compounds are prepared by a simple combustion method. The Rietvelt analysis shows that these compounds could be classified as having the α-NaFeO₂ structure. The initial charge-discharge and irreversible capacity increases with the decrease of x in Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂. Indeed, Li[Ni_0.50Mn_0.50]O₂ compound shows relatively low initial discharge capacity of 200 mAh/g and large capacity loss during cycling, with Li[Ni_0.17Li_0.22Mn_0.61]O₂ and Li[Ni_0.25Li_0.17Mn₀.₅₈]O₂ compounds exhibit high initial discharge capacity over 245 mAh/g and stable cycle performance in the voltage range of 4.8 -2.0 V. On the other hand, XANES analysis shows that the oxidation state of Ni ion reversibly changes between Ni²⁺ and about Ni³⁺, while the oxidation state of Mn ion sustains Mn⁴⁺ during charge-discharge process. This result does not agree with the previously reported ‘electrochemistry model’ of Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂, in which Ni ion changes between Ni²⁺ and NI⁴⁺. Based on these results, we modified oxidation-state change of Mn and Ni ion during charge-discharge process.     

Ionic lithium conductivity in sulphur base glasses. 7Li NMR study of xLi2S−(1−x)GeS2 system

The lithium mobility in glasses of composition xLi₂S?(1?x)GeS₂ has been followed by c.w. (for x = 0.3; 0.4 and 0.5) and pulsed NMR (for x = 0.3 and 0.5) between ? 150 and + 280°C.The second moment of the resonance line of ⁷Li(0.89–1.51 G²) is proportional to the molar fraction of Li₂S, which may be correlated to an homogeneous Li nuclei distribution.The resonance line profiles and their thermal evolution seem to show that some Li⁺ ions do not participate in the conduction.Thermal variation of the spin-lattice relaxation time T₁, shows a strongly asymmetrical shape, if one considers In $\text{T}{}^{\mathrm{?1}}{}_1\text{= ?(T}{}^{\mathrm{?1}}\text{)}$ on both sides of the observed maxima. This behaviour may be explained by a distribution of the Li correlation times τ corresponding to different jump distances between various possible sites. The Cole-Davidson model allows the best agreement between experimental and theoretical values of the correlation times.The activation energies deduced from this model are close to those obtained from conductivity measurements (0.43 eV by NMR, 0.56 eV by conductivity determinations for x = 0.50), they may be correlated to the longer Li⁺ jumps in the vitreous matrix.     

Transport processes in heavy metal fluoride glasses

Na self-diffusion, Li self-diffusion, Na⁺–Li⁺ ion exchange, electrical conductivity, and mechanical relaxation have been studied below T_g on glasses of the system ZrF₄–BaF₂–LaF₃–AF (A=Na, Li), with A=10, 20, 30 mol%. Compared to the transport mechanism in alkali-containing silicate glasses, the mechanisms in these non-oxide glasses are anomalous. Thus the self-diffusion coefficient of Na decreases with increasing NaF content, whereas that of Li increases with increasing LiF content. Both the electrical conductivity and the Na⁺–Li⁺ ion exchange reach a minimum at ≈ 20 mol% LiF, and the mechanical relaxation shows one peak for the 20 and 30 mol% LiF-glasses and two peaks for the glass with 10 mol% LiF, evidencing both a contribution of F⁻ and Li⁺ ions to the transport. Moreover, the presence of the three partially interacting mobile species F⁻, Na⁺, Li⁺ obviously leads to an anionic–cationic mixed ion effect. Applying the Nernst–Einstein equation to the Li⁺ transport in LiF-containing glasses shows that its mechanism is dissimilar to that in oxide glasses. Calculated short jump distances possibly can be interpreted as an Li⁺ movement via energetically suitable sites near F⁻ ions. Likewise the Nernst–Planck model, successfully applied to the ionic transport in mixed alkali silicate glasses, obviously does also not hold for the present heavy metal fluoride glasses.     

β NMR on8Li in the superiqnic conductor Li3N

Polarized⁸Li nuclei were produced in a Li₃N single crystal by irradiation with polarized neutrons, Β-ray detected NMR signals and spin-lattice relaxation of⁸Li were observed between B and 300 K. In Li₃N there are two non-equivalent Li sites. The corresponding two quadrupole split NMR spectra could be resolved. From the measured relaxation rates activation enthalpies for two diffusion processes were deduced.     

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：