New real ternary and pseudoternary phases in the Li-Au-In system

Two real ternary lithium gold indides LiAu₂In and Li₂₈₀Au₂₂In₁₃₀ (Li_0.65Au_0.05In_0.30) were found in the Li-Au-In system. They are isostructural to the respective Ag-alloys. LiAu₂In crystallizes in the MnCu₂Al-type structure (Fm-3m, Heusler phase, a=6.4982(8) Å, based on single crystal XRD-data) and Li₂₈₀Au₂₂In₁₃₀ in the Li₂₇₈Ag₄₀In₁₁₄-type structure (F-43m, a=19.9970(2) Å, based on powder XRD-data). The analogy of the two ternary systems Li-Au-In and Li-Ag-In is additionally reaffirmed by the wide homogeneity range of the pseudoternary solid solution with NaTl-type structure (Zintl phase),which expands not only in the direction of the quasibinary cut Li(Au_xIn_1−x) with 0≤x≤0.5, but also into the directions of both higher and lower Li-concentrations.     

The crystal structure of the LiAg2In compound

The newly established intermetallic compound LiAg₂In crystallizes in the MnCu₂Al-type structure (Fm-3m, Heusler phase) with . The homogeneity range of this phase in the ternary Li-Ag-In phase diagram along the adjacent quasibinary cut Li_0.25(Ag_1−xIn_x)_0.75 was determined by X-ray powder diffraction and extends from x∼0.33, Li_0.25Ag_0.50In_0.25, up to x∼0.44, Li_0.25Ag_0.42In_0.33. The homogeneity ranges of Heusler- and Zintl-type phases in the Li-Ag-In system are separated from each other by a broad heterogeneous region.     

An experimental investigation of ionic transport properties in CuI-Ag2WO4 and CuI-Ag2CrO4 mixed systems

The phenomenon of ionic transport in the case of two different mixed systems (CuI)_(1−x)-(Ag₂WO₄)_x(0.15?x?0.6) and (CuI)_(1−y)-(Ag₂CrO₄)_y(0.15?y?0.5) has been investigated. Powder X-ray diffraction (XRD) analysis coupled with differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), FT-Raman and electrical transport studies involving ionic transport number and temperature-dependent electrical conductivity measurements have been carried out in order to identify the various phases responsible for the conduction process. The occurrence of typical ionic conductivity values of 4.5×10⁻³ Scm⁻¹ for the composition (CuI)_0.45-(Ag₂WO₄)_0.55 and 1.1×10⁻⁴ Scm⁻¹ in the case of (CuI)_0.55-(Ag₂CrO₄)_0.45 at room temperature has been discussed in terms of the observed characteristics.     

Phase formation in the system involving silver, magnesium, and indium molybdates

The subsolidus region of the Ag₂MoO₄-MgMoO₄-In₂(MoO₄)₃ ternary salt system has been studied by X-ray powder diffraction. The formation of new compounds Ag_{1 ? x} Mg_{1 ? x} In_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.6) and AgMg₃In(MoO₄)₅ has been established. The unit cell parameters of solid-solution samples have been determined. The Ag_{1 ? x} Mg_{1 ? x} In_{1 + x} (MoO₄)₃ phase of variable composition has a NASICON-type structure (space group R $ \bar 3 $ c) AgMg₃In(MoO₄)₅ is isostructural to sodium magnesium indium molybdate of the same formula unit and crystallizes in triclinic system (space group P $ \bar 1 $ , Z = 2) with the following unit cell parameters: a = 7.0374(5) Å, b = 17.932(1) Å, c = 6.9822(4) Å, α = 87.309(6)°, β = 100.832(6)°, γ = 92.358(6)°. The compounds Ag_{1 ? x} Mg_{1 ? x} In_{1 + x} (MoO₄)₃ and AgMg3In(MoO₄)₅ are thermally stable up to 960 and 1030°C, respectively.     

The Crystal Chemistry of Lithium in the Alluaudite Structure: A Study of the (Na1−xLix)CdIn2(PO4)3 Solid Solution (x=0 to 1)

Several compounds of the (Na_1−xLi_x)CdIn₂(PO₄)₃ solid solution were synthesized by a solid-state reaction in air, and pure alluaudite-like compounds were obtained for x=0.00, 0.25, and 0.50. X-ray Rietveld refinements indicate the occurrence of Cd²⁺ in the M(1) site, and of In³⁺ in the M(2) site of the alluaudite structure. This non-disordered cationic distribution is confirmed by the sharpness of the infrared absorption bands. The distribution of Na⁺ and Li⁺ on the A(1) and A(2)′ crystallographic sites cannot be accurately assessed by the Rietvled method, probably because the electronic densities involved in the Na⁺→Li⁺ substitution are very small. A comparison with the synthetic alluaudite-like compounds, (Na_1−xLi_x)MnFe₂(PO₄)₃, indicates the influence of the cations occupying the M(1) and M(2) sites on the coordination polyhedra morphologies of the A(1) and A(2)′ crystallographic sites.     

Mn environment in layered Li[Mg0.5−xNixMn0.5]O2 oxides monitored by EPR spectroscopy

X-band and high-frequency EPR spectroscopy were used for studying the manganese environment in layered Li[Mg_xNi_0.5−xMn_0.5]O₂, 0?x?0.5. Both layered LiMg_0.5Mn_0.5O₂ and monoclinic Li[Li_1/3Mn_2/3]O₂ oxides (containing Mn⁴⁺ ions only) were used as EPR standards. The EPR study was extended to the Ni-substituted analogues, where both Ni²⁺ and Mn⁴⁺ are paramagnetic. For LiMg_0.5−xNi_xMn_0.5O₂ and Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂, an EPR response from Mn⁴⁺ ions only was detected, while the Ni²⁺ ions remained EPR silent in the frequency range of 9.23-285 GHz. For the diamagnetically diluted oxides, LiMg_0.25Ni_0.25Mn_0.5O₂ and Li[Li_0.10Ni_0.35Mn_0.55]O₂, two types of Mn⁴⁺ ions located in a mixed (Mn-Ni-Li)-environment and in a Ni-Mn environment, respectively, were registered by high-field experiments. In the X-band, comparative analysis of the EPR line width of Mn⁴⁺ ions permits to extract the composition of the first coordination sphere of Mn in layered LiMg_0.5−xNi_xMn_0.5O₂ (0?x?0.5) and Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ (x>0.2). It was shown that a fraction of Mn⁴⁺ are in an environment resembling the ordered “α,β”-type arrangement in Li_1−δ1Ni_δ1[Li_{(1−2x)/3+δ1}Ni_2x/3−δ1)_α(Mn_(2−x)/3Ni_x/3)_β]O₂ (where and δ₁=0.06 were calculated), while the rest of Mn⁴⁺ are in the Ni,Mn-environment corresponding to the Li_1−δ2Ni_δ2[Ni_1−yMn_y]O₂ () composition with a statistical Ni,Mn distribution. For Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ with x?0.2, IR spectroscopy indicated that the ordered α,β-type arrangement is retained upon Ni introduction into monoclinic Li[Li_1/3Mn_2/3]O₂.     

Structural and vibrational studies of Li[Kx(NH4)1−x]SO4 and Li2KNH4(SO4)2 mixed crystals

Mixed crystals of Li[K_x(NH₄)_1−x]SO₄ have been obtained by evaporation from aqueous solution at 313 K using different molar ratios of mixtures of LiKSO₄ and LiNH₄SO₄. The crystals were characterized by Raman scattering and single-crystal and powder X-ray diffraction. Two types of compound were obtained: Li[K_x(NH₄)_1−x]SO₄ with x?0.94 and Li₂KNH₄(SO₄)₂. Different phases of Li[K_x(NH₄)_1−x]SO₄ were yielded according to the molar ratio used in the preparation. The first phase is isostructural to the room-temperature phase of LiKSO₄. The second phase is the enantiomorph of the first, which is not observed in pure LiKSO₄, and the last is a disordered phase, which was also observed in LiKSO₄, and can be assumed as a mixture of domains of two preceding phases. In the second type of compound with formula Li₂KNH₄(SO₄)₂, the room-temperature phase is hexagonal, symmetry space group P6₃ with cell-volume nine times that of LiKSO₄. In this phase, some cavities are occupied by K⁺ ions only, and others are occupied by either K⁺ or NH₄⁺ at random. Thermal analyses of both types of compounds were performed by DSC, ATD, TG and powder X-ray diffraction. The phase transition temperatures for Li[K_x(NH₄)_1−x]SO₄x?0.94 were affected by the random presence of the ammonium ion in this disordered system. The high-temperature phase of Li₂KNH₄(SO₄)₂ is also hexagonal, space group P6₃/mmc with the cell a-parameter double that of LiKSO₄. The phase transition is at 471.9 K.     

Synthesis and structural study of a new NASICON-type solid solution: Li1−xLax/3Zr2(PO4)3

A new complete solid solution of NASICON-type compounds between LiZr₂(PO₄)₃ and La_1/3Zr₂(PO₄)₃ was evidenced with the general formula Li_1−xLa_x/3Zr₂(PO₄)₃ (0?x?1). These phases were synthesized by a complex polymerizable method and structurally characterized from Rietveld treatment of their X-ray and neutron powder diffraction data. This solid solution results from the substitution mechanism Li⁺→1/3La³⁺+2/3□ leading to an increase of the vacancies number correlated to an increase of the La content. According to this substitution mechanism, the general formula can then be written Li_1−xLa_x/3□_2x/3Zr₂(PO₄)₃ (0?x?1) in order to underline the correlation between the La content and the vacancies rate. For all the compounds, the structure is clearly related to that of the NASICON family with three crystallographic domains evidenced. For 0?x?0.5, all the members adopt at high temperature the typical NASICON-type structure (s.g. R3¯c), while at lower temperature, their structure distorts to a triclinic form (s.g. C 1¯), as observed for LiZr₂(PO₄)₃ prepared above 1100 °C. Moreover, in this domain, the reversible transition is clearly soft and the transition temperature strongly depends of the x value. For 0.6?x?0.9, the compounds crystallize in a rhombohedral cell (s.g. R3¯), while for x=1, the phase La_1/3Zr₂(PO₄)₃ is obtained (s.g. P3¯, Z=6, a=8.7378(2) Å, c=23.2156(7) Å).This paper is devoted to the structure analysis of the series Li_1−xLa_x/3Zr₂(PO₄)₃ (0?x?1), from X-ray and neutron powder thermo diffraction and transmission electron microscopy (TEM) studies.     

Phase relationships of the lithium halide spinels Li2MCl4-Li2MBr4 with M = Mn,Fe, Cd

The sections Li₂MCl_4?4xBr_4x of the quaternary systems LiCl-LiBr-MCl₂-MBr₂ with M = Mn, Cd, and Fe were studied by high-temperature X-ray diffraction patterns and DTA and DSC measurements. In the quasibinary lithium manganese halide system complete series of solid solutions exist between the inverse spinels Li₂MnCl₄ and Li₂MnBr₄. Li₂MnBr₄ and solid solutions with x > 0.54 undergo phase transitions to tetragonal spinels at lower temperatures. In the nonquasibinary system with M = Cd, only at temperatures near 400°C a complete series of mixed crystals is formed. At lower temperatures the system is mainly two-phase with rock salt-type Li_1?yCd_0.5yCl_1?xBr_x and cadmium chloride-type Cd_1?yLi_2yCl_2?2xBr_2x solid solutions in equilibrium. The lithium iron halide system is similar to that of cadmium, but spinel-type Li₂FeBr₄ does not exist at any temperature. The manganese and cadmium halide spinels and spinel solid solutions undergo phase transitions to NaCl defect structures at elevated temperatures.     

Effect of the high pressure on the structure and intercalation properties of lithium-nickel-manganese oxides

Lithium-nickel-manganese oxides (Li_1+x(Ni_1/2Mn_1/2)_1−xO₂, x=0 and 0.2), having different cationic distributions and an oxidation state of Ni varying from 2+ to 3+, were formed under a high-pressure (3 GPa). The structure and cationic distribution in these oxides were examined by powder X-ray diffraction, infrared (IR) and electron paramagnetic resonance (EPR) in X-band (9.23 GHz) and at higher frequencies (95 and 285 GHz). Under a high pressure, a solid-state reaction between NiMnO₃ and Li₂O yields LiNi_0.5Mn_0.5O₂ with a disordered rock-salt type structure. The paramagnetic ions stabilized in this oxide are mainly Ni²⁺ and Mn⁴⁺ together with Mn³⁺ (about 10%). The replacement of Li₂O by Li₂O₂ permits increasing the oxidation state of Ni ions in lithium-nickel-manganese oxides. The higher oxidation state of Ni ions favours the stabilization of the layered modification, where the Ni-to-Mn ratio is preserved: Li(Li_0.2Ni_0.4Mn_0.4)O₂. The paramagnetic ions stabilized in the layered oxide are mainly Ni³⁺ and Mn⁴⁺ ions. The disordered and ordered phases display different intercalation properties in respect of lithium. The changes in local Ni,Mn-environment during the electrochemical reaction are discussed on the basis of EPR and IR spectroscopy.     

Calcium aluminates hydration in presence of amorphous SiO2 at temperatures below 90 °C

The hydration behaviour of Ca₃Al₂O₆, Ca₁₂Al₁₄O₃₃ and CaAl₂O₄ with added amorphous silica at 40, 65 and 90 °C has been studied for periods ranging from 1 to 31 days. In hydrated samples crystalline phases like katoite (Ca₃Al₂(SiO₄)_3−x(OH)_4x) and gibbsite, Al(OH)₃, were identified, likewise amorphous phases like Al(OH)_x, calcium silicate hydrates, C-S-H, and calcium aluminosilicate hydrates, C-S-A-H, were identified. The stoichiometry of Ca₃Al₂(SiO₄)_3−x(OH)_4x (0?3−x?0.334), which was the main crystalline product, was established by Rietveld refinement of X-ray and neutron diffraction data and by transmission electron microscopy.     

Composition dependence of the photophysical and photocatalytic properties of (AgNbO3)1−x(NaNbO3)x solid solutions

A series of orthorhombic photocatalysts (AgNbO₃)_1−x(NaNbO₃)_x solid solutions have been synthesized by a solid-state reaction method. The composition dependence of the photophysical and photocatalytic properties of synthesized solid solutions has been investigated systematically. With an increase in the content of NaNbO₃, we found that (1) the lattice parameters decreased; (2) the Nb-O bond length in NbO₆ octahedron reduced; (3) the band gap increased; and (4) the mean particle size decreased while the Brunauer-Emmett-Teller (BET) surface area increased. Photocatalytic activities of the (AgNbO₃)_1−x(NaNbO₃)_x (0?x?0.5) samples were evaluated from gaseous 2-propanol (IPA) decomposition into acetone and CO₂ under visible-light irradiation emitted from blue-light-emitting diodes (BLEDs; light intensity: 0.01 mW cm⁻²). Among all the samples, the (AgNbO₃)_0.6(NaNbO₃)_0.4 sample showed the highest photocatalytic activity.     

Crystal structure, phase relations and electrochemical properties of monoclinic Li2MnSiO4

Phase relations in the MnO-SiO₂-Li₄SiO₄ subsystem have been investigated by X-ray diffraction after solid-state reactions in hydrogen at 950-1150 °C. Both cation-deficient and cation-excess solid solutions Li_2+2xMn_1−xSiO₄ (−0.2?x?0.2) based on Li₂MnSiO₄ have been found. According to Rietveld analysis, Li₂MnSiO₄ (monoclinic, P2₁/n, a=6.3368(1), b=10.9146(2), c=5.0730(1) Å, β=90.987(1)°) is isostructural with γ_II-Li₂ZnSiO₄ and low-temperature Li₂MgSiO₄. All components are in tetrahedral environment, (MnSiO₄)²⁻ framework is built of four-, six- and eight-member rings of tetrahedra. Testing Li₂MnSiO₄ in an electrochemical cell showed that only 4% Li could be extracted between 3.5 and 5 V against Li metal. These results are discussed in comparison with those for recently reported orthorhombic layered Li₂MnSiO₄ and other tetrahedral Li₂MXO₄ phases.     

The new binary intermetallic YbGe2.83

The new compound YbGe_2.83 was obtained from the reaction of Yb and Ge in liquid indium. The crystal structure of YbGe_2.83 adopts the trigonal, P3?m1 space group with a=b=8.3657(12) Å and c=7.0469(14) Å. The structure of YbGe_2.83 is a variant of the CaAl₂Si₂ structure type with ordered vacancies. Germanium atoms form double layers of puckered hexagons creating slabs that sandwich the Yb atoms. YbGe_2.83 can be classified as a Zintl compound with the formula Yb^(2+x)+(Ge_2.83)^(2+x)−. The deficiencies at the Ge sites cause a mixed/intermediate valent state of ytterbium (Yb^2.35+). Valence bond sum calculations suggest an average valence of Yb ions in YbGe_2.83 of 2.51 consistent with an intermediate valence compound.     

Long- and short-range order in stuffed titanate pyrochlores

We report a structural study of the stuffed pyrochlore series Ln₂(Ti_2−xLn_x)O_7−x/2 (Ln=Ho, Yb; 0?x?0.67). Electron microscopy and Rietveld refinements of neutron powder diffraction data for the x=0.67 end members, Ho₂TiO₅ and Yb₂TiO₅, reveal that small domains (∼50 Å or less) exist where the Ln and Ti/Ln sublattices are pyrochlore like, while the average structure is fluorite like. Both the Ho and Yb stuffed pyrochlore series for 0.1?x?0.5 are shown to be a composite of long- and short-range-ordered pyrochlore phases. The relative fraction of long-range vs. short-range pyrochlore order decreases with increasing Ln doping. An additional complex structural modulation of the pyrochlore structure is observed in electron diffraction and high-resolution electron microscopy images.     

Non-stoichiometric 1:2 ordered perovskites in the Ba(Li1/4Nb3/4)O3-Ba(Li2/5W3/5)O3 system

Although both end members in the (1−x)Ba(Li_1/4Nb_3/4)O₃-xBa(Li_2/5W_3/5)O₃ (BLNW) system adopt a hexagonal perovskite structure, B-site ordered cubic perovskites are formed for the majority of their solid solutions (0.238?x?0.833). Within this range, single-phase 1:2 order (, , ) is stabilized for 0.238?x?0.385. In contrast to all known A(B_1/3^IB_2/3^II)O₃ perovskites, the 1:2 ordered BLNW solid solutions do not include any composition with a 1:2 cation distribution and the structure exhibits extensive non-stoichiometry. Structure refinements support a model where Li and W occupy different positions and Nb is distributed on both sites, i.e. Ba[(Li_3/4+y/2Nb_1/4−y/2)_1/3(Nb_1−yW_y)_2/3]O₃ (y=0.21-0.35, where y=0.9x). The stabilization of the non-stoichiometric order arises from the large charge/size site differences; the loss of 1:2 order for W-rich compositions is related to local charge imbalances on the A-site sub-lattice. The range of single-phase 1:1 order is confined to x=0.833, (Ba(Li_3/4Nb_1/4)_1/2(W)_1/2)O₃), where the site charge/size difference is maximized and the on-site mismatches are minimized. The microwave dielectric loss properties of the ordered BLNW solid solutions are significantly inferior as compared to their stoichiometric counterparts.     

Substitution mechanism and structural study of Ag-doped LiCu2O2

Plate-like stoichiometric crystals of Ag-doped LiCu₂O₂ have been grown by slowly cooling Li₂CO₃·4(1 – x)CuO·4xAgNO₃ (0 ≤ x ≤ 0.5) melts. X-ray single crystal diffraction has shown that the crystals are isostructural with LiCu₂O₂ and contain around 5 at % Ag (relative to the Cu atoms). The addition of silver to lithium cuprate crystals significantly increases their electrical conductivity but has little effect on the temperature behavior of their magnetic moment. The possible substitution mechanism is determined which supports Ag⁺ ↔ Cu⁺, rather than Ag⁺ ↔ Li⁺ in the Ag-doped LiCu₂O₂ crystals.     

Electron-poor SrAuxIn4−x (0.5?x?1.2) and SrAuxSn4−x (1.3?x?2.2) phases with the BaAl4-type structure

Solid solutions SrAu_xIn_4−x (0.5?x?1.2) and SrAu_xSn_4−x (1.3?x?2.2) have been prepared at 700 °C and their structures characterized by powder and single-crystal X-ray diffraction. They adopt the tetragonal BaAl₄-type structure (space group I4/mmm, Z=2; SrAu_1.1(1)In_2.9(1), a=4.5841(2) Å, c=12.3725(5) Å; SrAu_1.4(1)Sn_2.6(1), a=4.6447(7) Å, c=11.403(2) Å), with Au atoms preferentially substituting into the apical over basal sites within the anionic network. The phase width inherent in these solid solutions implies that the BaAl₄-type structure can be stabilized over a range of valence electron counts (vec), 13.0-11.6 for SrAu_xIn_4−x and 14.1-11.4 for SrAu_xSn_4−x. They represent new examples of electron-poor BaAl₄-type compounds, which generally have a vec of 14. Band structure calculations confirm that substitution of Au, with its smaller size and fewer number of valence electrons, for In or Sn atoms enables the BaAl₄-type structure to be stabilized in the parent binaries SrIn₄ and SrSn₄, which adopt different structure types.     

Caractérisation de la solution solide In1−xLi3xVO4 (0 < x ≤ 0,4) dans le système InVO4Li3VO4 et examen des systèmes CrVO4Li3VO4 et InVO4CrVO4

In the InVO₄Li₃VO₄ system, a continuous solid solution In_1−xLi⁽⁶⁾_a□⁽⁶⁾_bLi⁽⁴⁾_c□⁽⁶⁾_dVO₄ exists between InVO₄ and In_0.6Li_1.2VO₄, with a + b = x, c + d = 1, and a + c = 3x. The solid solution is of two types: in the first, 0 < x ≤ 0.33, a = 0, interstitial Li⁺ ions are in the vacant tetrahedral sites of InVO₄; in the second, 0.33 < x ≤ 0.4, c = 1, Li⁺ ions are also in the octahedral sites vacated by In³⁺. The ionic conductivity measured for some compositions is weak, 10⁻⁷ (Ω cm)⁻¹ at 493 K. Solid solution has not been found between CrVO₄ and Li₃VO₄, although CrVO₄ is isostructural with InVO₄. Mutual solid solution between CrVO₄ and InVO₄ is extremely limited. Yellow and weakly hygroscopic monocrystals have been synthetized for R₂Li₃(VO₄)₃ compositions (R = In,Cr,Fe); their chemical formula can be symbolized by LiVO₃: R³⁺. The R³⁺ percentage was too low to be detected by analysis of electronic densities based on X-ray diffraction intensities.     

Crystal growth and properties of Ln2Ag1−xGa10−y (Ln=La, Ce), a disordered variant of the Ce2NiGa10-structure type

We report the flux growth and characterization of Ln₂Ag_1−xGa_10−y (Ln=La, Ce), a disordered variant of the Ce₂NiGa₁₀ structure type. Single crystals of La₂Ag_1−xGa_10−y (x∼0.3; y∼0.6) and Ce₂Ag_1−xGa_10−y (x∼0.3; y∼0.9) were grown by the self-flux method and characterized using single-crystal X-ray diffraction. Transport measurements of Ce₂Ag_1−xGa_10−y (x∼0.3; y∼0.9) reveal metallic behavior with a transition at 3 K. Magnetic measurements indicate antiferromagnetic ordering at 3 K of localized Ce³⁺ moments for Ce₂Ag_1−xGa_10−y. Magnetoresistance is positive with a maximum value of 16% at 9 T. La₂Ag_1−xGa_10−y exhibits metallic behavior with magnetic susceptibility showing temperature independent paramagnetism. We will compare Ce₂Ag_1−xGa_10−y (x∼0.3; y∼0.9) to Ce₂NiGa₁₀ to examine the effects of transition metal substitution and to the related Ce(Ag,Ga)₄ phase to examine the effects of crystal structure on the physical properties.