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.     

晶态-非晶态复合锂离子导体的电学性质

本文研究了晶态LiCl-非晶态Li₂O·3B₂O₃复合锂离子导体的电学性质。实验发现这种晶态-非晶态新型复合离子导体的电学性质变化具有新的现象,即在宏观电导率σ_m-组成曲线上出现了电导率增加的“双峰”效应。相应地,在表观活化能E_m-组成曲线和介电常数ε_m-组成曲线上出现了“双谷”。本文还详细讨论了这些实验现象,得到了与理论相符合的结果。 关键词：     

NMR study on an Li+-ion diffusion in the solid solution Li4−x(PO4)x(SiO4)1−x with the Li4SiO4-type structure

Diffusive motion of an Li⁺ion in the solid solution Li_4?x(PO₄)_x(SiO₄)_1?x (0 ≦ x ≦ 0.35) was studied by ⁷Li pulsed nmr between ? 70 and 440°C. Activation energies for an Li⁺ ion diffusion decreased monotonically with increasing x in the composition. These values are smaller than those reported from the measurement of ionic conductivity. Discrepency seems to result from the local nature of an Li⁺ diffusion observed by nmr contrary to the long-range one in the ionic conduction.     

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 3&#x0303; × 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.     

Ionic conductivity and point defects in pure and doped MnF2 and MgF2 single crystals

Conductivity, σ, of MnF₂ and MgF₂ single crystals, pure and doped (with Li⁺, Na⁺, Y³⁺, Gd³⁺), has been measured, from room temperature to 500°C. Further, some crystals were contaminated with O^2? as an additional impurity. These tetragonal (rutile structure) crystals both behave like typical ionic conductors. Of particular interest is the existence of a large anisotropy, σ being largest when measured parallel to the c-axis. Study of the conductivity isotherms and anisotropy as functions of impurity concentration allows identification of the conduction mechanism in terms of the migration of two mobile defects: the fiuorine-ion vacancy, V_F, and interstitial, F_i. A value of 1.44 eV was obtained for the enthalpy of formation of the intrinsic anion Frenkel defect, 0.80 eV for the migration enthalpy of a V_F and 0.88 eV for an F₁ in MnF₂ parallel to the c-axis. Similar values were obtained for MgF₂. This work shows that more information about point defects can be obtained from conductivity measurements in non-cubic cyrstals than in cubic ionic crystals, because of the additional information from conductivity anisotropy.     

The temperature dependence of optical gap and photoconductivity threshold in undoped hydrogenated amorphous silicon films

We report on the temperature dependences of the optical gap E_o and the photoconductivity threshold (?ω)_o for undoped hydrogenated amorphous silicon films. When increasing the temperature, both E_o and (?ω)_o are seen to linearly decrease at respective rates β= 3.5 10^?4 eV K^?1 (temperature range 290 K–460 K) and γ= 5.2 10^?4 eV K^?1 (temperature range 220 K – 360 K). At higher temperatures E_o decreases at the rate β = 14.3 10^?4 ev K^?1. Our results are discussed in terms of conduction in extended states. We show there is no physical reason in relating the temperature dependence of the activation energy and that of the gap as generally assumed. From optical absorption we deduce a minimum metallic conductivity σ_min the value of which agrees with Mott's predictions. On the contrary, σ_min measured from dark conductivity is nearly two orders of magnitude lower. A discussion is proposed infering band bending at the film substrate interface.     

Ionic conductivity of lithium nitride doped with hydrogen

Lithium ionic conductivity of Li₃N single crystals is reported for temperatures from 120 K to 350 K. The intrinsic ionic conductivity is rather small (< 10^?6 Ω^?1 cm^?1 at 300 K) and shows no strong anisotropy. The activation energy is near 0,6 eV. It is shown that hydrogen is the critical impurity in the crystals grown and studied at this laboratory. The relative impurity concentration is determined from infrared transmission measurements near 3130 cm^?1. An estimate for absolute values is obtained from dielectric studies. Increases in ionic conductivity with hydrogen doping by a factor 5000 are reported for E⊥c but no significant effects are found for E6c. The proposed defect is an impurity-vacancy complex consisting of an NH^?? and a lithium vacancy.     

插层化合物Li1+xV3O8的合成及其物理性能的初步研究

本文成功地合成了插层化合物Li_1+xV₃O₈,并用X射线粉末衍射和等离子体发射光谱元素定量分析进行了鉴定。同时进行了NMR研究。在298—400K之间观察到了锂离子的运动致窄效应,并以此求得它的离子运动激活能为0.18eV。还测得该材料的室温电导率为10^-3Ω^-1·cm^-1数量级。 关键词：     

Magnetic susceptibility and electrical conductivity of transition-metal platinum oxides: Evidence for one-dimensional electronic interactions

Bulk magnetic susceptibility measurements have been made on the orthorhombic compounds CoPt₃O₆, MnPt₃O₆, and NiPt₃O₆, and the structurally related cubic phase Co_0.37Na_0.14Pt₃O₄, in the temperature range 300-4 K. These compounds, which are rather unusual in that they contain first-row transition metals in eight coordination, are all paramagnetic above 25 K and show Curie-Weiss behavior with effective magnetic moments μ_eff(Co) = 4.8 ± 0.2μ_B,μ_eff(Mn) = 5.8 ± 0.1 μ_B, μ_eff(Ni) = 3.9 ± 0.2 μ_B, and μ_eff(Co) = 4.2 ± 0.5 μ_B, respectively. The inverse susceptibilities of CoPt₃O₆ and MnPt₃O₆ exhibit deviations from Curie-Weiss behavior below 25 K, and a minimum is observed for CoPt₃O₆ at about 8K. Single-crystal electrical conductivity measurements along the c-axis (σ_∥) in CoPt₃O₆ and MnPt₃O₆ show these materials to be semiconducting, but with relatively high conductivities and low activation energies σ_∥ (294 K) = 40 Ω^?1-cm^?1 and E_a = 0.07 eV for CoPt₃O₆ and σ_∥ (303 K) = 111Ω^?1cm^?1 and E_a = 0.02 eV for CoPt₃O₆. The results for CoPt₃O₆. MnPt₃O₆, and NiPt₃O₆are discussed in terms of their anisotropic structures, which favor magnetic coupling in one-dimension along linear arrays of eight-coordinated paramagnetic ions and one-dimensional electrical conduction along columnar stacks of planar PtO₄ groups containing partially oxidized linear chains of platinum. One-dimensional electronic interactions in MPt₃O₆ compounds are suggested by metal-metal distances along the c-axis of 3&#x0303;.1 A for both the platinum and the 3d transition metal ions, compared to a distance of 6.1 A between the chains in the perpendicular plane. These materials and their electronic properties are compared with systems with well characterized examples of one-dimensional magnetic coupling and electrical conductivity.     

Ionic transport in the lithium nitride bromides,Li6NBr3 and Li1 3N4Br

The ionic and electronic conductivities of the lithium nitride bromides Li₆NBr₃ and Li_{1 3}N₄Br have been studied in the temperature range from 50 to 220°C and 120 to 450°C, respectively. Both compounds are practically pure lithium ion conductors with negligible electronic contribution. Li₆NBr₃ has an ionic conductivity Ω of 2 × 10^-6Ω^-1cm^-1 at 100°C and an activation enthalpy for σT of 0.46 eV. Li_{1 3}N₄Br shows a phase transition at about 230°C. The activation enthalpy for σT is 0.73 eV below and 0.47 eV above this temperature. The conductivities at 150 and 300°C were found to be 3.5 × 10^-6 Ω^-1cm^-1 and 1.4 × 10^-3Ω^-1cm^-1, respectively. The crystal structure is hexagonal at room temperature with $\text{a = 7.415 (1)}\text{A}\text{?}$ and $\text{c = 3.865 (1)}\text{A}\text{?}$.     

Absolute cross sections of electron attachment to molecular clusters: Part I. Formation of (CO2) N −

A procedure of determining absolute cross section σ^? of electron attachment to (CO₂)_N clusters at pair collisions in crossed beams is suggested. The cross section is measured as a function of energy (E = 0.1–50 eV) and of cluster mean size N in a beam $(\bar N = 2 - 4000 molecules)$ . It is found that, even at $\bar N > 200$ and E ≤ 3 eV, σ^? is equal to, or larger than, 7 × 10^?13 cm², i.e., by more than one order of magnitude exceeds the maximal cross section of CO₂ ionization by electron impact. The dependences σ^? $(\bar N,E)$ have two wide continua at E ≤ 5.2 eV and E ≥ 6.9 eV, which correlate well with known functions of CO₂ electron-impact-induced excitation. These continua are attributed largely to formation of (CO₂) _N ^? ions during electron thermalization and solvation in the clusters. At E → 0, the polarization capture of an incident electron by the cluster leads to a sharp increase in cross section σ^?(E). From the dependences σ^? $(\bar N,E)$ measured, the thermalization and sovation probabilities for electrons with E ≤ 0.8 eV and the rate of electron energy loss in the cluster are found.     

Lithium ion conduction in A-site deficient perovskites R1/4Li1/4TaO3 (R=La,Nd, Sm and Y)

New lithium ion conductors of perovskite-type compounds R_1/4Li_1/4TaO₃ (R=La, Nd, Sm and Y) were synthesized, and their crystal structure and lithium ion conductivity were characterized. Symmetry of the perovskite lattice changed from cubic for La_1/4Li_1/4TaO₃ to tetragonal for Nd_1/4Li_1/4TaO₃ and Sm_1/4Li_1/4TaO₃, and to orthorhombic for Y_1/4Li_1/4TaO₃. The alternate ordering of R and Li ions and vacancies at the A-sites was observed for Nd_1/4Li_1/4TaO₃, Sm_1/4Li_1/4TaO₃ and Y_1/4Li_1/4TaO₃. The cube root (V^1/3) of the subcell volume decreased with decreasing the ionic radius of R cations which act as spacers for the perovskite lattice. With decrease in V^1/3 from La_1/4Li_1/4TaO₃ to Y_1/4Li_1/4TaO₃, the bulk conductivity at 400 K decreased from 1.4×10⁻¹ S m⁻¹ to 5.0×10⁻⁷ S m⁻¹ and its activation energy increased from 0.35 eV to 0.85 eV. The subcell volume and the ordering at the A-sites are major factors in influencing lithium ion conduction in these perovskite-type conductors.     

NMR study of Li+-ion diffusion in the solid solution Li3+x(P1−x,Six)O4> with the γII-Li3PO4 structure

Diffusive motion of a Li⁺ ion in the solid solution of Li₃+x(P₁?x, Si_x)O₄ (0?x?0.4) with the γ_II-Li₃PO₄ structure was studied by the measurement of the ⁷Li spin-lattice relaxation time. The observed motion was a local motion instead of a long-range one. In comparison with the previous study on the solid solution of Li₄?x(P_x, Si₁?x)O₄ with the Li₄SiO₄ structure, it is noticeable that the activation energy is low and almost independent of the composition and that the attempt frequency is smaller in this phase. These characteristics were attributed to the availability of a large interstitial void in the γ_II-Li₃PO₄ structure. The low values of activation energy for the Li⁺ ionic conduction may be explained on the same basis.     

Electrical transport properties of gadolinium scandium gallium garnet

Electrical conductivity and thermoelectric power are measured on a single crystal of Gd_3.0Sc_1.8Ga_3.2O₁₂ (GSGG) between 1273 and 1673 K. The measurements are made both in air and in controlled atmospheres, and P_O2 varies from 10^?1.68 to 10^?5.6 MPa. The data indicate GSGG may well be a mixed conductor in this temperature and P_O2 range, with n-type electronic conductivity and ionic transport on the oxygen sublattice. Changes in temperature induce long-lived disequilibrium in electrical conductivity of GSGG (over 30 h at T < 1373 K) that can be explained by temperature dependent cation redistribution. The effective activation energy for equilibrium electrical conductivity is E_a = 2.40 ± 0.05 eV, as opposed to values of E_a between 1.8 and 2.2 eV during actual temperature changes. An additional contribution in the equilibrium E_a, due to thermally activated cation redistribution, can account for the higher value seen.     

Super-protonic phase transition and fast ionic conductivity of Li+ in [Li0.2(NH4)0.8]2TeCl6

The differential scanning calorimetry diagram of [Li_0.2(NH₄)_0.8]₂TeCl₆ showed one anomaly at 526 K accompanied with a shoulder at 505 K.The conductivity plot exhibits two anomalies at 496 and 526 K, which characterize the beginning and the end of the crossing to superionic conductor state. The low temperature conduction is ensured essentially by Li⁺. A sudden jump confirms the presence of a superionic protonic transition related to the fast motion of Li⁺ and H⁺ ions. Above 526 K, the high temperature phase is characterized by high electrical conductivity (10^− 3 Ω^− 1 m^− 1) and low activation energy (E_a < 0.3 eV).The dielectric constant evolution as a function of frequency and temperature revealed the same anomaly.Transport properties in this material appear to be due to Li⁺ and H⁺ ions' hopping mechanism.     

Li ion conduction in Li2ZrO3, Li4ZrO4, and LiScO2

The results of ac and dc conductivity measurements on Li₂ZrO₃, Li₄ZrO₄, and LiScO₂ show that these phases are Li ion conductors. Even though the Li ion conductivity in these phases is quite low, 3.3×10^?5, 3.0×10^?4, and 4.2×10^?7 S m^?1 at 573 K, respectively, they are of special interest since they are among the small group of ternary oxides which may be thermodynamically stable against Li. Mechanisms are proposed for the decomposition of these phases at the anode due to Li loss during dc polarization. In addition the electrical conductivity of ternary oxide phases which are, or may be, thermodynamically stable against Li are summarized.     

LISICON(锗酸锌锂)单晶的Li+离子电导

本文研究了Lisicon(锗酸锌锂)单晶的Li⁺离子电导率。发现各结晶学方向电导率之间的关系为σ_b≤σ_a≤σ_c≤σ_[110],但各向异性不强。晶体中Li含量对电导率有明显的影响,当Li/Zn比率由6.7变到9.2时,300℃a方向电导率由4.3×10^-2Ω^-1·cm^-1增加到1.25×10^-1Ω^-1·cm^-1,logσT对1/T的曲线显示出三个转变点,分别在～80℃,～140℃和～300℃。电导的激活能分别为0.50—0.58eV(25—80℃),0.92eV(～80—140℃),0.64eV(～140—300℃)和0.36eV(>300℃),极化实验表明单晶的电子电导可以忽略。 关键词：     

Lithium conductivity and lithium diffusion in NASICON-type Li<Subscript>1+x</Subscript>Ti<Subscript>2–x</Subscript>Al<Subscript>x</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> (x= 0; 0.3) prepared by mechanical activation

LiTi₂(PO₄)₃ (LTP) and Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) (S. g. R-3c) have been prepared using conventional ceramic and mechanical activation (MA) methods. It has been shown that preliminary mechanical activation of initial mixtures leads to different nature and amount of dielectric admixtures in the final product after heat treatment at 800–1000 °C as compared with ceramic method. Transport properties of as prepared materials have been studied by lithium ionic conductivity at d.c. and a.c. (complex impedance method), and ⁷Li NMR spin-lattice relaxation rate T₁ ^–1 measurements. Lithium ionic conductivity of mechanochemically prepared LTP and LATP was characterized by significant reduction of grain boundary resistance, especially for LTP, while the bulk conductivity and Li ion diffusion does not noticeably change. The activation energy of bulk conductivity and Li ion diffusion, i.e. short-range motion, appeared to be almost the same for all samples and was equal to ~0.20 eV. On contrary, the activation energy of d.c.-conductivity, i.e. long-range Li ion motion decreases from ~0.6 eV for ceramic samples to ~0.4 eV for samples prepared via mechanochemical route. It was proposed that MA leads to formation of nano-particulate high-conductive grain boundaries both in LTP and LATP. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Li2Mo2-xWxO6多晶材料的结构、电学性能与导电机理的研究

本文采用还原气氛制备导电性能优良的多晶多相陶瓷材料Li₂Mo_2-xW_xO₆(x=0,0.1,0.3),采用粉末X射线衍射分析、特征X射线能谱分析、红外光谱分析和电子自旋共振波谱分析等现代测试手段,得到样品的物相结构为Li₂Mo_1-xW_xO₄和MoO₂两相组成。W的掺入主要取代Mo进入Li₂ 关键词：     

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.