Ionic conductivity of Li4GeO4, Li2GeO3 and Li2Ge7O15

The ionic conductivity of polycrystalline samples of three lithium germanates: Li₄GeO₄, Li₂GeO₃, and Li₂Ge₇O₁₅, has been determined using a c techniques and complex plane analysis. Conductivities at 400°C are 8.7 × 10^?5, 1.5 × 10^?5, and $\text{1.4 × 10}{}^{\mathrm{?7}}\text{(Ω·}\text{cm}\text{)}{}^{\mathrm{?1}}$ respectively. The conductivity of Li₄GeO₄ rises appreciably in the range 700–750°C.     

Ionic conductivity of substituted Li2SO4 phases

Lithium ion conductivity of Li₂SO₄-Y₂(SO₄)₃, Li₂SO₄-La₂(SO₄)₃ and Li₂SO₄-Li₃PO₄ systems has been measured as a function of composition and temperature using AC complex impedance methods. Substitution of the trivalent cations results in a small enhancement of the ionic conductivity within the limit of solid solution formation. Considerable increase of the conductivity results by substitution of PO₄^3? for SO₄^2?. The maximum conductivity observed is $\text{1.1×10}{}^{\mathrm{?3}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 300°C for the composition Li_2.2S_0.8P_0.2O₄ with E_a = 0.8 eV. These results are discussed in terms of the structural properties.     

Ionic conductivity of solid lithium ion conductors with the spinel structure: Li2MCl4 (M = Mg,Mn, Fe,Cd)

The ionic conductivity of the polycrystalline samples of the lithium chloride spinel, Li₂MCl₄ (M = Mg, Mn, Fe, Cd) is measured by the help of ac techniques in the temperature range of 25–500°C. The highest conductivity of 0.3 Scm^?1 at 400°C is obtained in Li₂CdCl₄. In addition, the solid solution, Li_2?2δM_1+δCl₄, has been examined. It is found that Li_1.9Cd_1.05Cl₄ has higher conductivity than that of Li₂CdCl₄. The phase transitions of these compounds are also discussed.     

New Li+ ion conductors in the system,Li4GeO4-Li3VO4

New Li⁺ ion conducting solid electrolytes have been found in the system Li₄GeO₄-Li₃VO₄. Of the compositions studied, Li_3.6Ge_0.6V_0.4O₄ has the highest conductivity with σ ～ 4 × 10^?5 ohm^?1cm^?1 at 18°C rising to ～ 10^?2 ohm^?1 cm^?1 at 190°C. The activation energy is ～0.44 eV. These conductivity values are among the highest yet found for Li⁺ ion conductors; the room temperature value is much higher than in LISICON, Li_3.5Zn_0.25GeO₄, or in Li_3.4Si_0.4P_0.6O₄ and is comparable to that in $\text{LiI/A}\text{l}{}_2\text{O}{}_3$ mixtures. These solid electrolytes are easy to synthesize, thermodynamically stable and insensitive to atmospheric attack. Structurally, they are solid solutions based on γ_II Li₃VO₄, a γ tetrahedral structure; high conductivity is due to the interstitial Li⁺ ions which are created during solid solution formation.     

Domaine vitreux,structure et conductivite electrique des verres du systeme LiCl /1b Li2O /1b P2O5

The glass forming region in the LiCl /1b Li₂O /1b P₂O₅ system was determined. Glass transition temperature was obtained from differential thermal analysis studies. The determination of the electrical conductivity as a function of the temperature and the composition in Li₂O and LiCl was carried out. The conductivity reaches a maximum value of the order of 5·10^?7 (ohm^?1·cm^?1) at 25° C. Raman spectra are examined in order to show the influence of the composition on the vitreous structure.     

The solid electrolyte system,Li3PO4Li4SiO4

The phase diagram of the system Li₄SiO₄Li₃PO₄ has been studied. At subsolidus temperatures, ? 1000°C, Li₄SiO₄ forms a short range of equilibrium solid solutions between 0 and ～ 12 mole % Li₃PO₄; γ-Li₃PO₄ forms a range of equilibrium solid solutions between ～ 58 and 100% Li₃PO₄. In addition to these equilibrium solid solutions, Li₄SiO₄ forms an extensive range of metastable solid solutions containing up to ～ 60% Li₃PO₄, on quenching melts from ? 1050°C. Hence compositions around 60% Li₃PO₄, 40% Li₄SiO₄ may be prepared in two structural forms, i.e. as solid solutions of either Li₄SiO₄ or γ Li₃PO₄. Conductivity measurements show that, at these compositions, the two solid solution structures have similar, high conductivity of Li⁺ ions.     

Lithium ion conduction in Li5A104, Li5GaO4 and Li6ZnO4

Polycrystalline samples of Li₅Al0₄, Li₅Ga0₄, and Li₆Zn0₄ have been synthesized, and their ionic conductivity measured over a range of temperature. These materials, which have the antifluorite structure with large concentrations of intrinsic cation vacancies, have Arrhenius-like conductivities at low temperatures, with a steep rise in the range 385–450°C, reaching very high values, with a very small temperature dependence, thereafter. Materials of this type, which exhibit the highest values of lithium ion conductivity yet found, may have important practical applications in devices such as elevated temperature batteries.     

New fast lithium ionic conductor in the Li3NLiILiOH system

The electrical properties of Li₃NLiILiOH (1:2:x molar ratio) compounds are investigated. These quasi-ternary compounds have a cubic crystal structure similar to Li₅NI₂. The Li₃NLiILiOH (1:2:0.77) compound has a conductivity of 0.95 × 10_?1 (S/m at 25°C with an activation enthalpy of 24.6 (kJ/mol). All the compounds investigated are predominantly ionic conductors. The electronic transference number is smaller than 10^?5 and the decomposition voltage of these compounds is about 1.6V at 25°C.     

Dielectric and photoconducting properties of Ga2Te3 and In2Te3 crystals

Single crystals of defect III–VI semiconductors Ga₂Te₃ and In₂Te₃ have been grown by the Bridgman method. Capacitance vs frequency measurements have been carried out from which the low frequency dielectric constants ?₅ have been determined to be 10.95 ± 0.26 and 12.3 ± 0.13 respectively. These values are compared with the high-frequency dielectric constants ?₆₀ calculated from the Phillips' model. Dark conductivity and photoconductivity have been studied as a function of annealing upto 210°C, maxinum photosensitivity being obtained for both crystals for T_anneal = 80°C. This behaviour has been related to lattice ordering through x-ray diffraction studies. Measurements of photo conductive gain indicate carrier life-times of 2 × 10^?4s and 5 × 10^?4s respectively at room-temperature.     

Phase equilibria in the system Li2O-TiO2

The system Li₂O-TiO₂ contains four stable phases: Li₄TiO₄, Li₂TiO₃, Li₄Ti₅O₁₂ and Li₂Ti₃O₇, and one metastable phase, H. Li₂TiO₃ undergoes an order-disorder phase transition at 1215°C. High Li₂TiO₃ forms an extensive range of solid solution between ～44 and 66 mole % TiO₂ and low Li₂TiO₃ forms a more limited range of solid solution between ～47 and 51% TiO₂. The temperature of the order-disorder transition decreases to either side of the Li₂TiO₃ composition. The spinel phase Li₄Ti₅O₁₂, has an upper limit of stability at 1015 ± 5°C, above which it decomposes to high Li₂TiO₃ ss and Li₂Ti₃O₇. Li₂Ti₃O₇ has a lower limit of stability at 957 ± 20°C, below which it decomposes to Li₄Ti₅O₁₂ and rutile. During this decomposition of Li₂Ti₃O₇, phase H, a metastable phase of unknown composition, forms as an intermediate. Li₂Ti₃O₇ forms a short range of solid solutions between ～74 and 76% TiO₂. A phase diagram for the system Li₂O-TiO₂ has been constructed using a combination of results determined here and those reported by GICQUEL, MAYER and BOUAZIZ. X-ray powder diffraction data are given for Li₂Ti₃O₇, Li₄Ti₅O₁₂ and phase H.     

Lithium insertion into Li2Ti3O7

Li₂Ti₃O₇ with the ramsdellite-type structure undergoes lithium insertion reactions with n-BuLi. Li_2+xTi₃O₇ phases form with x = 0.5 and 1.0 at room temperature and at 50°C, respectively. The ESR spectrum of Li₃Ti₃O₇ confirms the partial reduction of Ti⁴⁺ ions to Ti³⁺. The electrical conductivity of the fully lithiated phase is several orders of magnitude higher than that of the host compound, suggesting charge hopping in the mixed valent lithiated compound.     

Phase diagram of the LISICON,solid electrolyte system,Li4GeO4Zn2GeO4

The phase diagram of the system Li₄GeO₄Zn₂GeO₄ is fairly similar to the corresponding silicate system and contains a wide range of solid solutions that extend to either side of the composition Li₂ZnGeO₄. These solid solutions are polymorphic. The high temperature ^γII solid solutions have a crystal structure derived from that of ^γII Li₃PO₄ and a formula, Li_{2 + 2x}Zn_1?xGeO₄ : ?0.36 < x < +0.87. LISICON, x = 0.75, is one member of the ^γII solid solution series. The compositional extent of the ^γII solid solutions is temperature dependent and eg. the LISICON composition is stable as a single phase γII structure only ? 630°C. On annealing LISICON and other lithiumrich, ^γII solid solutions in the range ～100 to 600°C, various reactions occur, including 1) precipitation of Li₄GeO₄, 2) phase transition(s) to metastable low temperature, γ-derivative structure(s) and 3) atmospheric attack to give Li₂GeO₃, Li₂CO₃ and other phases. The low temperature ^βII, ^βII′ solid solutions occur over a much smaller range of compositions to either side of Li₂ZnGeO₄ and have a crystal structure derived from that of ^βII Li₃PO₄. Li₄GeO₄ forms a short range of solid solutions.     

Conductivite ionique des oxydes Li8MO6 (M = Ce,Hf)

The electrical conductivity of the oxides Li₈CeO₆ and Li₈HfO₆, which are thermodynamically stable against Li (1), has been studied under oxygen atmosphere in the temperature range between room temperature and 200°C. As for Li₈ZrO₆ and Li₈SnO₆ (2), the materials can be considered as solid electrolytes with medium conductivity. The interpretation of the results, considering the Ca²⁺ ions as impurities, are in agreement with those based on the diffusion mechanisms of the Li⁺ ions recently established by ⁷Li NMR in isostructural oxides by Simpson et al. (3).     

Determination structurale et proprietes de conduction d'un nouveau compose de type hollandite: K1,8(Li2,45Sb5,55)O16; mise en evidence d'une surstructure d'ordre 3

The crystal structure of a synthetic hollandite phase K_1,8(Li_2,45Sb_5,55)O₁₆ has been refined by the full matrix least-squares method using 940 three-dimensional reflexions to a final R value of 0.046. The K atoms are randomly distributed on the special positions 2b (0 0 $\text{1}\text{2}$) and 4e (0 0 ±z) with z = 0.340(4).A long-exposure rotation photograph along the c axis shows diffuse X-ray scattering between the layer line. After a thermal treatment the X-ray diffraction pattern shows weak but sharp reflexions that could be indexed by tripling the short axis. The structural studies indicate an ordering of the large K atoms within the channels.The ionic conductivity of this phase has been investigated on a single crystal by hyperfrequences method. The potassium ion conductivity is the ordre of magnitude of 10^?3 (ohm cm^?1) at 30°C along the c axis.     

Electrical conductivity in Ta2O5

The defect structure of undoped polycrystalline Ta₂O₅ was investigated by determining the temperature [850–1050°C] and oxygen partial pressure [10⁰–10^?19 atm.] dependence of the electrical conductivity. The data were found to be proportional to the $\text{～?}\text{1}\text{4}\text{th}$ power of the oxygen partial pressure for the oxygen pressure range <10^?8 atm. and independent of the oxygen partial pressure for P_O2 > 10^?6 atm. The enthalpy of formation of doubly ionized oxygen vacancies plus two electrons is estimated to be 118.31 Kcal/mole [5.13 eV]. The observed conductivity data are explained on the basis of the presence of unknown acceptor impurities in the undoped samples.     

Contribution a l'etude du systeme Na3PO4-Na2SO4 et proprietes de conduction ionique des materiaux de type γ-Na3PO4: Na3−xP1−xSxO4 (0<x≤0,58)

The study of the Na₃PO₄Na₂SO₄ system at 1050°C has proved the existence of the solid solution Na_3?xP_1?xS_xO₄ (0<x≤0.58) for which the cubic symmetry (Li₃Bi-type structure) of the “high temperature” form γ-Na₃PO₄ is maintained. The room temperature variation of the parameter of the unit cell as a function of doping level and the homogeneity range are discussed. The replacement of PO^3?₄ ions by SO^2?₄ ions in Na_3?xP_1?xS_xO₄ leads to better ionic conductivity. The results are explained on the bases of structural and size considerations. A conduction mechanism is proposed.     

Conductivity of Zr-doped Na3PO4: A new Na+ ion conductor

Na₃PO₄ forms an extensive range of solid solutions with the replacement mechanism, 4Na⁺ ? Zr⁴⁺ and formula Na_3–4xZr_xPO₄:0 < x < 0.20. With increasing x, the conductivity increases markedly and passes through a maximum at $\text{x ? 0.13}$ with a value of 2.5 × 10^?2 ohm^?1cm^?1 at 300°C. The solid solutions are thermodynamically stable, easily prepared and sinter into dense ceramics at ～1000°C.     

Structure and ionic conductivity of Lix(MeO)4Me30O90 (Me = NbV, WVI)

The compound Li_x(MeO)₄Me₃₀O₉₀ (Me = Nb^V, W^VI) has been prepared and investigated by X-ray powder and electron diffraction techniques as well as by measurements of complex impedance. The structure is of the tripled tetragonal tungsten bronze type with one third of the pentagonal tunnels filled with equal numbers of Me and 0 atoms. The conductivity at 300°C is 0.20 and 0.25 ohm^?1m^?1 for sintered samples with x equal to 2 and 4, respectively. The location and probable routes of transport of the lithium ions are discussed.     

The incommensurate solid solution phase Na5−4x Zr1+x(PO4)3:0.04 <x <0.15

The orthophosphate solid solution phase, Na_5?4x Zr_1+x(PO₄)₃:0.04 ? x ? 0.15 has trigonal symmetry with an apparent one dimensional incommensurate superstructure parallel to c_HEX. Using selected area electron diffraction patterns as a guide, an indexing scheme for the powder X-ray data has been devised. The parameter $\text{k = c}{}_{\mathrm{<mtext>supercell</mtext>}}\text{c}{}_{\mathrm{<mtext>subcell</mtext>}}$ varies smoothly with composition from ～ 10.4 at x = 0.04 to ～4.4 at x = 0.11 and is believed to originate in ordering of the extra interstitial Zr⁴⁺ ions. The Na⁺ ion conductivity increases gradually with x and for x = 0.108 varies from ～5×10^?8 ohm^?1 cm^?1 at 25°C to ～1×10^?3 ohm^?1 cm^?1 at 300°C.     

Nombre de transport et conductivite cationique dans le dioxyde de thorium: ThO2

The cationic transport number for thorium dioxide has been determined using thermal expansion measurements coupled with coulometric titration (“dilato-coulometry”). Polycrystalline ThO₂ was studied in the temperature range 1000–1500° C, under oxygen partial pressures ranging from 1 to 10^?12 atm. In air, t_Th ～ 5 × 10_?7 at 1200° C. Values for total conductivity are compared with data obtained by the Nernst-Einstein relation from the self-diffusion coefficient of Th in ThO₂.