A neutron diffraction study of the d and d lithium garnets Li3Nd3W2O12 and Li5La3Sb2O12

The garnets Li₃Nd₃W₂O₁₂ and Li₅La₃Sb₂O₁₂ have been prepared by heating the component oxides and hydroxides in air at temperatures up to 950 °C. Neutron powder diffraction has been used to examine the lithium distribution in these phases. Both compounds crystallise in the space group with lattice parameters a=12.46869(9) Å (Li₃Nd₃W₂O₁₂) and a=12.8518(3) Å (Li₅La₃Sb₂O₁₂). Li₃Nd₃W₂O₁₂ contains lithium on a filled, tetrahedrally coordinated 24d site that is occupied in the conventional garnet structure. Li₅La₃Sb₂O₁₂ contains partial occupation of lithium over two crystallographic sites. The conventional tetrahedrally coordinated 24d site is 79.3(8)% occupied. The remaining lithium is found in oxide octahedra which are linked via a shared face to the tetrahedron. This lithium shows positional disorder and is split over two positions within the octahedron and occupies 43.6(4)% of the octahedra. Comparison of these compounds with related d⁰ and d¹⁰ phases shows that replacement of a d⁰ cation with d¹⁰ cation of the same charge leads to an increase in the lattice parameter due to polarisation effects.     

Neutron and X-ray powder diffraction study of LixRuO2 and LixIrO2: The crystal structure of Li0.9RuO2

Compounds formed by the insertion of lithium into the rutile structure hosts RuO₂ and IrO₂ were studied by X-ray and neutron powder diffraction techniques. Compositions in the range Li_xMO₂, M = Ru or Ir, 0 < x < 1 are two-phase materials consisting of unreacted host, x = 0, and limiting compositions x = 0.9 in both cases. Preparation of compounds with x > 1 was unsuccessful. Li_0.9RuO₂ and Li_0.9IrO₂ have orthorhombic cells with a = 5.062(3), b = 4.967(4), c = 2.771(4) and a = 4.962(4), b = 4.758(4), c = 3.108(6), respectively. Compared to the host rutile (tetragonal) cells those of the insertion compounds are greatly expanded along [100] and [010], ～0.5 Å for both, and contracted along [001], by ～0.3 Å for Li_0.9RuO₂ and 0.05 Å for Li_0.9IrO₂. The space group for both insertion phases appears to be Pnnm, a subgroup of the rutile space group $\text{P4}{}_2\text{mnm}$. The structure of Li_0.9RuO₂ was solved from neutron diffraction data. Lithium exists as Li⁺ in octahedral sites. The LiO coordination is highly regular with two bonds at 2.05(1) Å and four at 2.08(2) Å. The overall structure is essentially an ordered NiAs-type very similar to but more regular than the previously reported LiMoO₂. Attempts to solve the structure of Li_0.9IrO₂ from both X-ray and neutron powder data were unsuccessful due, presumably, to severe preferred orientation.     

La(Li1/3Ti2/3)O3: a new 1:2 ordered perovskite

A new 1:2 ordered perovskite La(Li_1/3Ti_2/3)O₃ has been synthesized via solid-state techniques. At temperature >1185°C, Li and Ti are randomly distributed on the B-sites and the X-ray powder patterns can be indexed in a tilted (b⁻b⁻c⁺) Pbnm orthorhombic cell (a=a_c√2=5.545 Å, b=a_c√2=5.561 Å, c=2a_c=7.835 Å). However, for T?1175°C, a 1:2 layered ordering of Li and Ti along 〈111〉_c yields a structure with a P2₁/c monoclinic cell with a=a_c√6=9.604 Å, b=a_c√2=5.552 Å, c=a_c3√2=16.661 Å, β=125.12°. While this type of order is well known in the A²⁺(B²⁺_1/3B⁵⁺_2/3)O₃ family of niobates and tantalates, La(Li_1/3Ti_2/3)O₃ is the first example of a titanate perovskite with a 1:2 ordering of cations on the B-sites.     

Effect of sintering on the ionic conductivity of garnet-related structure Li5La3Nb2O12 and In- and K-doped Li5La3Nb2O12

Garnet-structure related metal oxides with the nominal chemical composition of Li₅La₃Nb₂O₁₂, In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ and K-substituted Li_5.5La_2.75K_0.25Nb₂O₁₂ were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li₅La₃Nb₂O₁₂. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In³⁺(r_CN6: 0.79 Å) for smaller Nb⁵⁺ (r_CN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K⁺ for La³⁺ and In³⁺ for Nb⁵⁺ in Li₅La₃Nb₂O₁₂ exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25-300 °C. Among the compounds investigated, the In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ exhibits the highest bulk lithium ion conductivity of 1.8×10⁻⁴ S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10⁻¹⁰-10⁻⁷ cm²/s over the temperature regime 50-200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li₅La₃Nb₂O₁₂ was found to be unsuccessful under the investigated conditions.     

Order-disorder transition in the complex lithium spinel Li2CoTi3O8

Li₂CoTi₃O₈ has an ordered Li₂BB′₃O₈ spinel structure, space group P4₃32, at room temperature with 3:1 ordering of Ti and Li on the octahedral sites, and Li, Co disordered over the tetrahedral site. Rietveld refinement of variable temperature neutron powder diffraction data has shown an order-disorder phase transition in Li₂CoTi₃O₈ which commences at ∼500 °C with Li and Co mixing on the tetrahedral and 4-fold octahedral sites and is complete at a first order structural discontinuity at ∼915 °C. The fraction of Ti on the 12-fold octahedral site exhibits a small decrease with increasing temperature, which may suggest that the disordering involves all three cations. Above 930 °C, the structure, space group Fd3¯m, has Li, Co and Ti sharing a single-octahedral site and Li, Co sharing a tetrahedral site, although Co still exhibits a preference for tetrahedral coordination. A labelling scheme for ordered and partially ordered 3:1 spinels is devised which focuses on the occupancy of the Li,B cations.     

A comparison of the transport properties of lithium-stuffed garnets and the conventional phases Li3Ln3Te2O12

The structures of new phases Li₆CaLa₂Sb₂O₁₂ and Li_6.4Ca_1.4La₂Sb₂O₁₂ have been characterised using neutron powder diffraction. Rietveld analyses show that both compounds crystallise in the space group la3?d and contain the lithium cations in a complex arrangement with occupational disorder across oxide tetrahedra and distorted oxide octahedra, with considerable positional disorder in the latter. Variable temperature neutron diffraction experiments on Li_6.4Ca_1.4La₂Sb₂O₁₂ show the structure is largely invariant with only a small variation in the lithium distribution as a function of temperature. Impedance spectroscopy measurements show that the total conductivity of Li₆CaLa₂Sb₂O₁₂ is several orders of magnitude smaller than related lithium-stuffed garnets with σ=10⁻⁷ S cm⁻¹ at 95 °C and an activation energy of 0.82(3) eV. The transport properties of the conventional garnets Li₃Gd₃Te₂O₁₂, Li₃Tb₃Te₂O₁₂, Li₃Er₃Te₂O₁₂ and Li₃Lu₃Te₂O₁₂ have been evaluated and consistently show much lower values of conductivity, σ≤4.4×10⁻⁶ S cm⁻¹ at 285 °C and activation energies in the range 0.77(4)≤E_a/eV≤1.21(3).     

High-pressure synthesis of solid solutions between trigonal LiNiO2 and monoclinic Li[Li1/3Ni2/3]O2

High-pressure synthesis in an oxygen-rich atmosphere yields solid solutions between LiNiO₂ and Li₂NiO₃ over the whole concentration range. Structural characterization of the high-pressure oxides was performed using powder XRD, SEM analysis, IR spectroscopy, EPR spectroscopy at 9.23 and 115 GHz and magnetic susceptibility measurements. The crystal structure of Li[Li_xNi_1−x]O₂ ,, changes from trigonal R-3m to monoclinic C2/m at Li-to-Ni ratio of 2 (or ). The incorporation of Li into NiO₂-layers causes a decrease in the mean Li-O and Ni_1-xLi_x-O bond distance. Li and Ni ions in the mixed Ni_1-xLi_xO₂-layers display a tendency to order at a short length scale in such a way that mimics the Li_1/3Ni_2/3-arrangment of the end Li[Li_1/3Ni_2/3]O₂ composition. The charge distribution in these oxides proceeds via Ni³⁺ and Ni⁴⁺ ions.     

Synthesis, structure and properties of Li2Rh3B2

Li₂Rh₃B₂ has been synthesized at 1000 °C from a stoichiometric mix of rhodium and boron and an excess of lithium. Li₂Rh₃B₂ crystallizes in the orthorhombic space group Pbam (no. 55, Z=2) with room temperature lattice constants a=5.7712(1) Å, b=9.4377(2) Å, c=2.8301(1) Å and cell volume 154.149(6) Å³. The structure was solved from single crystal X-ray diffraction yielding the final R indices (all data) R1=2.8% and wR2=4.7%. The structure is a distortion of the CeCo₃B₂ structure type, containing a network of Rh₆B trigonal prisms and short Li-Li contacts of 2.28(2) Å. Li₂Rh₃B₂ is a diamagnetic metal with a room temperature resistivity of 19 μΩ cm, as determined by magnetic susceptibility and single crystal transport measurements. The measured diamagnetism and electronic structure calculations show that Li₂Rh₃B₂ contains rhodium in a d¹⁰ configuration.     

Synthesis and structure of Li4Sr3Ge2N6: a new quaternary nitride containing Ge2N6 anions

A new Li-containing quaternary nitride, Li₄Sr₃Ge₂N₆, was obtained as single crystals from constituent elements in molten Na. It crystallizes in space group C2/m (No. 12) with a=6.1398(7) Å, b=10.021(1) Å, c=6.3130(7) Å, β=91.279(2)°, and Z=2. It contains the first example of isolated nitridogermanate anions of Ge₂N₆¹⁰⁻, which is also the first example of edge-sharing tetrahedral [GeN₄].     

Neutron powder diffraction study of tetragonal Li7La3Hf2O12 with the garnet-related type structure

We have successfully synthesized a polycrystalline sample of tetragonal garnet-related Li-ion conductor Li₇La₃Hf₂O₁₂ by solid state reaction. The crystal structure is analyzed by the Rietveld method using neutron powder diffraction data. The structure analysis identifies that tetragonal Li₇La₃Hf₂O₁₂ has the garnet-related type structure with a space group of I4₁/acd (no. 142). The lattice constants are a=13.106(2) Å and c=12.630(2) Å with a cell ratio of c/a=0.9637. The crystal structure of tetragonal Li₇La₃Hf₂O₁₂ has the garnet-type framework structure composed of dodecahedral La(1)O₈, La(2)O₈ and octahedral HfO₆. Li atoms occupy three types of crystallographic site in the interstices of this framework structure, where Li(1) atom is located at the tetrahedral 8a site, and Li(2) and Li(3) atoms are located at the distorted octahedral 16f and 32g sites, respectively. These Li sites are filled with the Li atom. The present tetragonal Li₇La₃Hf₂O₁₂ sample exhibits bulk Li-ion conductivity of σ_b=9.85×10⁻⁷ S cm⁻¹ and grain-boundary Li-ion conductivity of σ_gb=4.45×10⁻⁷ S cm⁻¹ at 300 K. The activation energy is estimated to be E_a=0.53 eV in the temperature range of 300-580 K.     

固体电解质Li9-nxMn+xN2Cl3(M=Na、Mg、Al)的合成及表征

高温固相反应合成了固体电解质Ｌｉ９－ｎｘＭ＾ｎ＋ｘＮ２Ｃｌ３（Ｍ＝Ｎａ、Ｍｇ、Ａｌ）。利用粉末Ｘ射线衍射测定样品结构,测定了离子电导率,分解电压和电子电导。得出掺杂可以提高快离子快离子导体材料Ｌｉ９Ｎ２Ｃｌ３中的Ｌｉ＾＋离子可以很大程度的提高其电导率。     

Synthesis, structural characterization and Li ion conductivity of a new vanado-molybdate phase, LiMg3VMo2O12

A new vanado-molybdate LiMg₃VMo₂O₁₂ has been synthesized, the crystal structure determined an ionic conductivity measured. The solid solution Li_2−zMg_2+zV_zMo_3−zO₁₂ was investigated and the structures of the z=0.5 and 1.0 compositions were refined by Rietveld analysis of powder X-ray (XRD) and powder neutron diffraction (ND) data. The structures were refined in the orthorhombic space group Pnma with a∼5.10, b∼10.4 and c∼17.6 Å, and are isostructural with the previously reported double molybdates Li₂M₂(MoO₄)₃ (M=M²⁺, z=0). The structures comprise of two unique (Li/Mg)O₆ octahedra, (Li/Mg)O₆ trigonal prisms and two unique (Mo/V)O₄ tetrahedra. A well-defined 1:3 ratio of Li⁺:Mg²⁺ is observed in octahedral chains for LiMg₃VMo₂O₁₂. Li⁺ preferentially occupies trigonal prisms and Mg²⁺ favours octahedral sheets. Excess V⁵⁺ adjacent to the octahedral sheets may indicate short-range order. Ionic conductivity measured by impedance spectroscopy (IS) and differential scanning calorimetry (DSC) measurements show the presence of a phase transition, at 500-600 °C, depending on x. A decrease in activation energy for Li⁺ ion conductivity occurs at the phase transition and the high temperature structure is a good Li⁺ ion conductor, with σ=1×10⁻³-4×10⁻² S cm⁻¹ and E_a=0.6 to 0.8 eV.     

Phase stability and non-stoichiometry in M-phase solid solutions in the system LiO0.5-NbO2.5-TiO2

Phase relations at 1050°C have been determined for M-phase solid solutions in the LiO_0.5-NbO_2.5-TiO₂ ternary phase system by the quench method. Rietveld analysis has been used to help determine phase boundaries and to study structure composition relations. The M-phases have trigonal structures based on intergrowth of corundum-like layers, [Ti₂O₃]²⁺, with slabs of (N−1) layers of LiNbO₃-type parallel to (0001). Ideal compositions are defined along the pseudobinary join LiNbO₃-Li₄Ti₅O₁₂ by the homologous series formula Li_NNb_N−4Ti₅O_3N, N?4. Homologues with N?10 lie to the low-lithia side of the LiNbO₃-Li₄Ti₅O₁₂ join and show extended single-phase solid solution ranges separated by two-phase regions. The composition variations along the solid solutions are controlled by a major substitution mechanism, Li⁺+3Nb⁵⁺↔4Ti⁴⁺, coupled with a minor substitution 4Li⁺↔Ti⁴⁺+3□, where □=vacancy. The latter substitution results in increasing deviations from the stoichiometric compositions A_2N+1O_3N with increasing Ti substitution. The non-stoichiometry can be reduced by re-equilibration at lower temperatures. Expressions have been developed to describe the compositional changes along the solid solutions.     

Li+ ion conductivity in the system Li4SiO4Li3VO4

Two ranges of solid solutions were prepared in the system Li₄SiO₄Li₃VO₄: Li_4?xSi_1?xV_xO₄, 0 < x ? 0.37 with the Li₄SiO₄ structure and Li_3+yV_1?ySi_yO₄, 0.18 ? y ? 0.53 with a γ structure. The conductivity of both solid solutions is much higher than that of the end members and passes through a maximum at ～40Li₄SiO₄ · 60Li₃VO₄ with values of ～1 × 10^?5 ohm^?1 cm^?1 at 20°C, rising to ～4 × 10^?2 ohm^?1 cm^?1 at 300°C. These conductivities are several times higher than in the corresponding Li₄SiO₄Li₃(P,As)O₄ systems, especially at room temperature. The solid solutions are easy to prepare, are stable in air, and maintain their conductivity with time. The mechanism of conduction is discussed in terms of the random-walk equation for conductivity and the significance of the term c(1 ? c) in the preexponential factor is assessed. Data for the three systems Li₄SiO₄Li₃YO₄ (Y = P, As. V) are compared.     

Icosahedral Li clusters in the structures of Li33.3Ba13.1Ca3 and Li18.9Na8.3Ba15.3

The intermetallic phases Li_33.3Ba_13.1Ca₃ and Li_18.9Na_8.3Ba_15.3 have been prepared and their crystal structures have been determined. According to single-crystal X-ray diffraction data, both compounds crystallize in new structure types with trigonal unit cells (Li_33.3Ba_13.1Ca₃: R3¯c, a=19.9127(4) Å, c=90.213(3) Å, Z=18, V=30,978(1) Å³ and Li_18.9Na_8.3Ba_15.3: P3¯, a=20.420(3) Å, c=92.914(19), Z=18, V=33,550(10) Å³). The first compound can be described as a complicated variant of the arsenic structure. The second has similar packing of the Ba atoms but differs from the Ca-containing phase in the packing of the light elements. Both compounds contain icosahedron-based polytetrahedral clusters, typical for Li-rich phases, e.g. Ba₁₉Li₄₄.     

Ion-beam irradiation of lanthanum compounds in the systems La2O3-Al2O3 and La2O3-TiO2

Thin crystals of La₂O₃, LaAlO₃, La_2/3TiO₃, La₂TiO₅, and La₂Ti₂O₇ have been irradiated in situ using 1 MeV Kr²⁺ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La₂O₃ remained crystalline to a fluence greater than 3.1×10¹⁶ ions cm⁻² at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (T_c) of 647 K for LaAlO₃, 840 K for La₂Ti₂O₇, 865 K for La_2/3TiO₃, and 1027 K for La₂TiO₅. The T_c values observed in this study, together with previous data for Al₂O₃ and TiO₂, are discussed with reference to the melting points for the La₂O₃-Al₂O₃ and La₂O₃-TiO₂ systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between T_c and melting temperature (T_m) in the two systems. More complex relationships exist between T_c and crystal structure, with the stoichiometric perovskite LaAlO₃ being the most resistant to amorphisation.     

Li2MTiO4 (M=Mn, Fe, Co, Ni): New cation-disordered rocksalt oxides exhibiting oxidative deintercalation of lithium. Synthesis of an ordered Li2NiTiO4

We describe the synthesis and characterization of a new series of oxides, Li₂MTiO₄ (M=Mn, Fe, Co, Ni) that crystallize in the rocksalt structure. For M=Ni, we have also obtained a low-temperature modification that adopts a Li₂SnO₃-type structure. All the phases, excepting M=Ni, undergo oxidative deinsertion of lithium in air/O₂ at elevated temperatures (>150°C), yielding LiMTiO₄ (M=Mn, Fe) spinels and a spinel-like Li_1+xCoTiO₄ as final products.     

Synthesis crystal structure and ionic conductivity of Ca0.5Bi3V2O10 and Sr0.5Bi3V2O10

Two new compounds Ca_0.5Bi₃V₂O₁₀ and Sr_0.5Bi₃V₂O₁₀ have been synthesized in the ternary system: MO-Bi₂O₃-V₂O₅ system (M=M²⁺). The crystal structure of Sr_0.5Bi₃V₂O₁₀ has been determined from single crystal X-ray diffraction data, space group and Z=2, with cell parameters a=7.1453(3) Å, b=7.8921(3) Å, c=9.3297(3) Å, α=106.444(2)°, β=94.088(2)°, γ=112.445(2)°, V=456.72(4) Å³. Ca_0.5Bi₃V₂O₁₀ is isostructural with Sr_0.5Bi₃V₂O₁₀, with, a=7.0810(2) Å, b=7.8447(2) Å, c=9.3607(2) Å, α=106.202(1)°, β=94.572(1)°, γ=112.659(1)°, V=450.38(2) Å³ and its structure has been refined by Rietveld method using powder X-ray data. The crystal structure consists of infinite chains of (Bi₂O₂) along c-axis formed by linkage of BiO₈ and BiO₆ polyhedra interconnected by MO₈ polyhedra forming 2D layers in ac plane. The vanadate tetrahedra are sandwiched between these layers. Conductivity measurements give a maximum conductivity value of 4.54×10⁻⁵ and 3.63×10⁻⁵ S cm⁻¹ for Ca_0.5Bi₃V₂O₁₀ and Sr_0.5Bi₃V₂O₁₀, respectively at 725 °C.     

Structural Stability of LiCoO2 at 400°C

The relative stability of the lithiated-spinel structure, Li₂[Co₂]O₄, at 400°C to the layered LiCoO₂ structure has been investigated. “Low-temperature” LT-LiCoO₂ samples were synthesized at 400°C by the solid-state reaction of Li₂CO₃ with CoCO₃ (or Co₃O₄) for various times between 10 min and 232 days. Least-squares refinements of X-ray powder diffraction patterns were used to determine the fractions of lithiated-spinel Li₂[Co₂]O₄ and layered LiCoO₂ in the samples. X-ray powder diffraction and transmission electron microscope data show that Li₂[Co₂]O₄ nucleates from an intermediate Li_xCo_1−x[Co₂]O₄ spinel product before transforming very slowly to layered LiCoO₂. The experimental data confirm the theoretical prediction that layered LiCoO₂ is thermodynamically more stable than the lithiated-spinel structure at 400°C and support the arguments that a non-ideal cation distribution in Li₂[Co₂]O₄, non-stoichiometry and kinetic factors restrict the transformation of the lithiated-spinel structure to layered LiCoO₂ at this temperature.     

High-resolution X-ray diffraction, DIFFaX, NMR and first principles study of disorder in the Li2MnO3-Li[Ni1/2Mn1/2]O2 solid solution

X-ray diffraction patterns of Li[Li_(1−2x)/3Ni_xMn_2/3−x/3]O₂ show reflections between 20° and 35°, 2θ (CuKα) due to Li₂MnO₃-like ordering of the transition metal (Ni, Mn and Li) layers. The ordering is rarely perfect, resulting in characteristic broadening and changes in the intensities of these reflections. ⁶Li MAS NMR studies of Li₂MnO₃ show that the [Li_1/3Mn_2/3] layers are well ordered, the disorder arising from the stacking of the layers in the c-direction. DIFFaX was used to model the Li₂MnO₃ XRD data and extract the stacking fault frequency. The results show that even well-ordered cation layers may show only weak or no superstructure reflections, if there is no or little ordering in the c-direction.