Li8Cu12+xAl6−x (x = 1.16): a new structure type related to Laves phases

The new ternary lithium copper aluminide Li₈Cu_12+xAl_6−x (x = 1.16) crystallizes in the P6₃/mmc space group with six independent atom positions of site symmetries m. (Al/Cu mixture), m2 (Li atoms), 3m. (Al/Cu mixture and Li atoms) and .m. (Cu atoms). The compound is a derivative of the K₇Cs₆ binary structure type and is related to the binary MgZn₂ Laves phase and the LiCuAl₂, MgCu_1.07Al_0.93 and Mg(Cu_1−xAl_x)₂ (x = 0.465) ternary Laves phases. The coordination polyhedra of the atoms in this structure are icosahedra (Cu atoms), slightly distorted icosahedra and bicapped hexagonal antiprisms (Al/Cu statistical mixture), and Frank–Kasper and distorted Frank–Kasper polyhedra (Li atoms). All interatomic distances indicate metallic type bonding.     

Li12Cu12.60Al14.37: a new ternary derivative of the binary Laves phases

New ternary dodecalithium dodecacopper tetradecaaluminium, Li₁₂Cu_12.60Al_14.37 (trigonal, Rm, hR39), crystallizes as a new structure type and belongs to the structural family that derives from binary Laves phases. The Li atoms are enclosed in 15‐ and 16‐vertex and the Al3 atom in 14‐vertex pseudo‐Frank–Kasper polyhedra. The polyhedra around the statistical mixtures of (Cu,Al)1 and (Al,Cu)2 are distorted icosahedra. The electronic structure was calculated by the TB–LMTO–ASA (tight‐binding linear muffin‐tin orbital atomic spheres approximation) method. The electron localization function, which indicates bond formation, is mostly located at the Al atoms. Thus, Al—Al bonding is much stronger than Li—Al or Cu—Al bonding. This indicates that, besides metallic bonding which is dominant in this compound, weak covalent Al—Al interactions also exist.     

Crystal and electronic structures of La2LiGe6−x (x = 0.21) and La2LiGe4Si2

The synthesis and characterization of a new ternary dilanthanum lithium hexagermanide, La₂LiGe_6−x (x = 0.21), belonging to the Pr₂LiGe₆ structure type, and a quaternary dilanthanum lithium tetragermanium disilicide, La₂LiGe₄Si₂, which crystallizes as an ordered variant of this type, are reported. In both structures, Li is on a site of mmm symmetry. All other atoms are on sites of m2m symmetry. These structures are new representatives of a homologous linear structure series based on structural fragments of the AlB₂, CaF₂ and ZrSi₂ structure types. The observed 17‐vertex polyhedra are typical for La atoms and the environment of the Li atom is cubic. Two Ge atoms are enclosed in a tetragonal prism with one added atom (nine‐vertex polyhedron). The trigonal prismatic coordination is typical for Ge or Si atoms. The metallic nature of the bonding is indicated by the interatomic distances and electronic structure calculations.     

Cu Doping-Induced Transformation from [Ag62S12(SBut)32]2+ to [Ag62−xCuxS12(SBut)32]4+ Nanocluster

The change in the valence state of nanocluster can induce remarkable changes in the properties and structure. However, achieving the valence state changes in nanoclusters is still a challenge. In this work, we use Cu²⁺ as dopant to “oxidize” [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ (4 free electrons) to obtain the new nanocluster: [Ag_62−xCu_xS₁₂(SBu^t)₃₂]⁴⁺ with 2 free electrons. As revealed by its structure, the [Ag_62−xCu_xS₁₂(SBu^t)₃₂]⁴⁺ (x=10∼21) has a similar structure to that of [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ precursor and all the Cu atoms occupy the surface site of nanocluster. It′s worth noting that with the Cu atoms doping, the [Ag_62−xCu_xS₁₂(SBu^t)₃₂]⁴⁺ nanocluster is more stable than [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ at higher temperature and in electrochemical cycle. This result has laid a foundation for the subsequent application and exploration. Overall, this work reveals crystals structure of a new Ag−Cu nanocluster and offers a new insight into the electron reduction/oxidation of nanocluster.     

Ba3Li2V2O7Cl4, a new vanadate with a channel structure

The tribarium dilithium divanadate tetrachloride Ba₃Li₂V₂O₇Cl₄ is a new vanadate with a channel structure and the first known vanadate containing both Ba and Li atoms. The structure contains four non‐equivalent Ba²⁺ sites (two with m and two with 2/m site symmetry), two Li⁺ sites, two nonmagnetic V⁵⁺ sites, five O²⁻ sites (three with m site symmetry) and four Cl⁻ sites (m site symmetry). One type of Li atom lies in LiO₄ tetrahedra (m site symmetry) and shares corners with VO₄ tetrahedra to form eight‐tetrahedron Li₃V₅O₂₄ rings and six‐tetrahedron Li₂V₄O₁₈ rings; these rings are linked within porous layers parallel to the ab plane and contain Ba²⁺ and Cl⁻ ions. The other Li atoms are located on inversion centres and form isolated chains of face‐sharing LiCl₆ octahedra.     

Monoclinic La1−xBaxMnO3 (x = 0.185) at 160 K

Single‐crystal X‐ray diffraction has shown that lanthanum barium manganese trioxide, La_0.815Ba_0.185MnO₃, is monoclinic (I2/c) below a first‐order phase transition at 187.1 (3) K. This result differs from the Pbnm symmetry usually assigned to colossal magnetoresistance oxides, A_1−xA′_xMnO₃ with x≃ 0.2, which adopt a distorted perovskite‐type crystal structure. The Mn atom lies on an inversion center, the disordered Li/Ba site is on a twofold axis and one of the two independent O atoms also lies on a twofold axis.     

Li9Al4Sn5 as a new ordered superstructure of the Li13Sn5 type

Alloys from the ternary Li–Al–Sn system have been investigated with respect to possible applications as negative electrode materials in Li‐ion batteries. This led to the discovery of a new ternary compound, a superstructure of the Li₁₃Sn₅ binary compound. The ternary stannide, Li₉Al₄Sn₅ (nonalithium tetraaluminium pentastannide; trigonal, P m 1, hP18 ), crystallizes as a new structure type, which is an ordered variant of the binary Li₁₃Sn₅ structure type. One Li and one Sn site have m . symmetry, and all other atoms occupy sites of 3m . symmetry. The polyhedra around all types of atoms are rhombic dodecahedra. The electronic structure was calculated by the tight‐binding linear muffin‐tin orbital atomic spheres approximation method. The electron concentration is higher around the Sn and Al atoms, which form an [Al₄Sn₅]^m− polyanion.     

A new phase in the system lithium-aluminum: Characterization of orthorhombic Li2Al

Investigation of the Li rich part of the binary Li-Al system revealed the existence of a new phase, orthorhombic Li₂Al, which is isostructural to Li₂Ga and Li₂In. The crystal structure was determined from single crystal X-ray diffraction data (Cmcm, a=4.658(2) Å, b=9.767(4) Å, c=4.490(2) Å, Z=4). Refinement of atomic position site occupancies yielded a composition Li_1.92Al_1.08 (64 at% Li) indicating a small homogeneity range, Li_2−xAl_1+x. Li₂Al is the peritectic decomposition product of the stoichiometric compound Li₉Al₄, which is stable below 270±2 °C. Li₂Al itself decomposes peritectically to Li₃Al₂ and Li rich melt at 335±2 °C. The discovery of Li₂Al (Li_2−xAl_1+x) settles a long standing inconsistency in the Li-Al phase diagram which was based on the assumption that Li₉Al₄ possesses a high temperature modification.     

Lithium barium silicate,Li2BaSiO4, from synchrotron powder data

The structure of lithium barium silicate, Li₂BaSiO₄, has been determined from synchrotron radiation powder data. The title compound was synthesized by high‐temperature solid‐state reaction and crystallizes in the hexagonal space group P6₃cm. It contains two Li atoms, one Ba atom (both site symmetry ..m on special position 6c), two Si atoms [on special positions 4b (site symmetry 3..) and 2a (site symmetry 3.m)] and four O atoms (one on general position 12d, and three on special positions 6c, 4b and 2a). The basic units of the structure are (Li₆SiO₁₃)⁵⁻ units, each comprising seven tetrahedra sharing edges and vertices. These basic units are connected by sharing corners parallel to [001] and through sharing (SiO₄)⁴⁻ tetrahedra in (001). The relationship between the structures and luminescence properties of Li₂SrSiO₄, Li₂CaSiO₄ and the title compound is discussed.     

Li15Al3Si6 (Li14.6Al3.4Si6), a compound displaying a heterographite‐like anionic framework

The title compound, lithium aluminium silicide (15/3/6), crystallizes in the hexagonal centrosymmetric space group P6₃/m. The three‐dimensional structure of this ternary compound may be depicted as two interpenetrating lattices, namely a graphite‐like Li₃Al₃Si₆ layer and a distorted diamond‐like lithium lattice. As is commonly found for LiAl alloys, the Li and Al atoms are found to share some crystallographic sites. The diamond‐like lattice is built up of Li cations, and the graphite‐like anionic layer is composed of Si, Al and Li atoms in which Si and Al are covalently bonded [Si—Al = 2.4672 (4) Å].     

Barium‐deficient celsian,Ba1−xAl2−2xSi2+2xO8 (x = 0.20 or 0.06)

Barium‐deficient forms of celsian (barium aluminium silicate) with the formula Ba_1−xAl_2−2xSi_2+2xO₈ (x = 0.20 and 0.06) have been identified. In contrast with the celsian–orthoclase solid solutions which have been reported previously, these forms, refined in the space group C2/m, with Ba and one O atom in the 4i sites with m site symmetry, and a further O atom in a 4g site with twofold axial symmetry, suggest a slight solid solution with silica. The serendipitous preparation of the compounds represents a possible hazard associated with solid‐state synthesis.     

Li3Al(MoO4)3, a lyonsite molybdate

Trilithium aluminium trimolybdate(VI), Li₃Al(MoO₄)₃, has been grown as single crystals from α‐Al₂O₃ and MoO₃ in an Li₂MoO₄ flux at 998 K. This compound is an example of the well known lyonsite structure type, the general formula of which can be written as A₁₆B₁₂O₄₈. Because this structure can accomodate cationic mixing as well as cationic vacancies, a wide range of chemical compositions can adopt this structure type. This has led to instances in the literature where membership in the lyonsite family has been overlooked when assigning the structure type to novel compounds. In the title compound, there are two octahedral sites with substitutional disorder between Li⁺ and Al³⁺, as well as a trigonal prismatic site fully occupied by Li⁺. The (Li,Al)O₆ octahedra and LiO₆ trigonal prisms are linked to form hexagonal tunnels along the [100] axis. These polyhedra are connected by isolated MoO₄ tetrahedra. Infinite chains of face‐sharing (Li,Al)O₆ octahedra extend through the centers of the tunnels. A mixed Li/Al site, an Li, an Mo, and two O atoms are located on mirror planes.     

Rhombohedral boron subnitride,B13N2, by X‐ray powder diffraction

The structure of the title compound consists of distorted B₁₂ icosahedra linked by N—B—N chains. The compound crystallizes in the rhombohedral space group Rm (No. 166). The unit cell contains four symmetry‐independent atom sites, three of which are occupied by boron [in the 18h, 18h (site symmetry m) and 3b (site symmetry m) Wyckoff positions] and one by nitrogen (in the 6c Wyckoff position, site symmetry 3m). Two of the B atoms form the icosahedra, while N atoms link the icosahedra together. The main feature of the structure is that the 3b position is occupied by the B atom, which makes the structure different from those of B₆O, for which these atom sites are vacant, and B_4+xC_1−x, for which this position is randomly occupied by both B and C atoms.     

New quaternary carbide Mg1.52Li0.24Al0.24C0.86 as a disorder derivative of the family of hexagonal close‐packed (hcp) structures and the effect of structure modification on the electrochemical behaviour of the electrode

Magnesium alloys are the basis for the creation of light and ultra‐light alloys. They have attracted attention as potential materials for the accumulation and storage of hydrogen, as well as electrode materials in metal‐hydride and magnesium‐ion batteries. The search for new metal hydrides has involved magnesium alloys with rare‐earth transition metals and doped by p‐ or s‐elements. The synthesis and characterization of a new quaternary carbide, namely dimagnesium lithium aluminium carbide, Mg_1.52Li_0.24Al_0.24C_0.86, belonging to the family of hexagonal close‐packed (hcp) structures, are reported. The title compound crystallizes with hexagonal symmetry (space group Pm2), where two sites with m2 symmetry and one site with 3m. symmetry are occupied by an Mg/Li statistical mixture (in Wyckoff position 1a), an Mg/Al statistical mixture (in position 1d) and C atoms (2i). The cuboctahedral coordination is typical for Mg/Li and Mg/Al, and the C atom is enclosed in an octahedron. Electronic structure calculations were used for elucidation of the ability of lithium or aluminium to substitute magnesium, and evaluation of the nature of the bonding between atoms. The presence of carbon in the carbide phase improves the corrosion resistance of the Mg_1.52Li_0.24Al_0.24C_0.86 alloy compared to the ternary Mg_1.52Li_0.24Al_0.24 alloy and Mg.     

The series RE5Li2Sn7 (RE = Ce,Pr, Nd,Sm) revisited: crystal structure of RE5Li2−xSn7+x [0 ≤x≤ 0.03 (1)]

The series of RE₅Li₂Sn₇ (RE = Ce–Sm) compounds were synthesized by high‐temperature reactions and structurally characterized by single‐crystal X‐ray diffraction. The compounds are pentacerium dilithium heptastannide, Ce₅Li_1.97Sn_7.03, pentapreseodymium dilithium heptastannide, Pr₅Li_1.98Sn_7.02, pentaneodymium dilithium heptastannide, Nd₅Li_1.99Sn_7.01, and pentasamarium dilithium heptastannide, Sm₅Li₂Sn₇. All five compounds crystallize in the chiral orthorhombic space group P2₁2₁2₁ (No. 19), which is relatively uncommon among intermetallic phases. The structure belongs to the Ce₅Li₂Sn₇ structure type (Pearson symbol oP56), with 14 unique atoms in the asymmetric unit. Minor compositional variations exist, due to the mixed occupancy of Li and Sn atoms at one of the Li sites. The small occupational disorder is most evident for RE₅Li_2−xSn_7+x (RE = Ce, Pr; x≃ 0.03), while the structure of Nd₅Li₂Sn₇ and Sm₅Li₂Sn₇ show no apparent disorder.     

A new tetragonal structure type for Li2B2C

The ternary dilithium diboron carbide, Li₂B₂C (tetragonal, space group Pm2, tP10), crystallizes as a new structure type and consists of structural fragments which are typical for structures of elemental lithium and boron or binary borocarbide B₁₃C₂. The symmetries of the occupied sites are .m. and 2mm. for the B and C atoms, and m2 and 2mm. for the Li atoms. The coordination polyhedra around the Li atoms are cuboctahedra and 15‐vertex distorted pseudo‐Frank–Kasper polyhedra. The environment of the B atom is a ten‐vertex polyhedron. The nearest neighbours of the C atom are two B atoms, and this group is surrounded by a deformed cuboctahedron with one centred lateral facet. Electronic structure calculations using the TB–LMTO–ASA method reveal strong B...C and B...B interactions.     

The novel arsenate Na4Co7−xAl2/3x(AsO4)6 (x = 1.37): crystal structure,charge‐distribution and bond‐valence‐sum investigations

The title compound, tetrasodium cobalt aluminium hexaarsenate, Na₄Co_7−xAl_2/3x(AsO₄)₆ (x = 1.37), is isostructural with K₄Ni₇(AsO₄)₆; however, in its crystal structure, some of the Co²⁺ ions are substituted by Al³⁺ in a fully occupied octahedral site (site symmetry 2/m) and a partially occupied tetrahedral site (site symmetry 2). A third octahedral site is fully occupied by Co²⁺ ions only. One of the two independent tetrahedral As atoms and two of its attached O atoms reside on a mirror plane, as do two of the three independent Na⁺ cations, all of which are present at half‐occupancy. The proposed structural model based on a careful investigation of the crystal data is supported by charge‐distribution (CHARDI) analysis and bond‐valence‐sum (BVS) calculations. The correlation between the X‐ray refinement and the validation results is discussed.     

Tm2.22Co6Sn20 and TmLi2Co6Sn20 stannides as disordered derivatives of the Cr23C6 structure type

A new ternary dithulium hexacobalt icosastannide, Tm_2.22Co₆Sn₂₀, and a new quaternary thulium dilithium hexacobalt icosastannide, TmLi₂Co₆Sn₂₀, crystallize as disordered variants of the binary cubic Cr₂₃C₆ structure type (cF116). 48 Sn atoms occupy sites of m.m2 symmetry, 32 Sn atoms sites of .3m symmetry, 24 Co atoms sites of 4m.m symmetry, eight Li (or Tm in the case of the ternary phase) atoms sites of symmetry and four Tm atoms sites of symmetry. The environment of one Tm atom is an 18‐vertex polyhedron and that of the second Tm (or Li) atom is a 16‐vertex polyhedron. Tetragonal antiprismatic coordination is observed for the Co atoms. Two Sn atoms are enclosed in a heavily deformed bicapped hexagonal prism and a monocapped hexagonal prism, respectively, and the environment of the third Sn atom is a 12‐vertex polyhedron. The electronic structures of both title compounds were calculated using the tight‐binding linear muffin‐tin orbital method in the atomic spheres approximation (TB–LMTO–ASA). Metallic bonding is dominant in these compounds, but the presence of Sn—Sn covalent dumbbells is also observed.     

Study on the effect of Li doping in spinel Li4+xTi5−xO12 (0 ⩽ x ⩽ 0.2) materials for lithium-ion batteries

The effect of Li doping in spinel Li_4+xTi_5−xO₁₂ (0 ⩽ x ⩽ 0.2) materials on the structural and electrochemical properties were investigated. The ratio of the capacity in the voltage plateau (1.5 V) to the overall discharge capacity for Li_4.1Ti_4.9O₁₂ (x = 0.1) and Li_4.2Ti_4.8O₁₂ (x = 0.2) were higher than that of Li₄Ti₅O₁₂ especially at high current rates due to their enhanced lithium-ion and electronic conductivity by the substitution of Ti atoms by Li atoms. With the increasing of Li doping amount, lithium-ion and electronic conductivity of Li_4+xTi_5−xO₁₂ increased, however its cycling stability was depressed when the Li doping was of x = 0.2. The Li doping of x = 0.1, the appropriate Li doping amount, showed improved rate capability and better high rate performance comparing to undoped Li_4+xTi_5−xO₁₂ (x = 0).     

A Shuttle-Free Solid-State Cu−Li Battery Based on a Sandwich-Structured Electrolyte

Cu−Li batteries leveraging the two-electron redox property of Cu can offer high energy density and low cost. However, Cu−Li batteries are plagued by limited solubility and a shuttle effect of Cu ions in traditional electrolytes, which leads to low energy density and poor cycling stability. In this work, we rationally design a solid-state sandwich electrolyte for solid-state Cu−Li batteries, in which a deep-eutectic-solvent gel with high Cu-ion solubility is devised as a Cu-ion reservoir while a ceramic Li_1.4Al_0.4Ti_1.6(PO₄)₃ interlayer is used to block Cu-ion crossover. Because of the high ionic conductivity (0.55 mS cm⁻¹ at 25 °C), wide electrochemical window (>4.5 V vs. Li⁺/Li), and high Cu ion solubility of solid-state sandwich electrolyte, a solid-state Cu−Li battery demonstrates a high energy density of 1 485 Wh kg_Cu⁻¹and long-term cyclability with 97 % capacity retention over 120 cycles. The present study lays the groundwork for future research into low-cost solid-state Cu−Li batteries.