Alluaudite-type Structure Research Articles

Two novel phosphates Na2Mg2Fe(PO4)3 and Ag2Mg2Fe(PO4)3 with alluaudite structure: Synthesis, crystal structure and electrical properties

Single crystals and powders of the orthophosphates A2Mg2Fe(PO4)3 with A ​= ​Na+ or Ag+ have been synthesized by solid-state reaction. The X-ray diffraction diagrams of Na2Mg2Fe(PO4)3 and Ag2Mg2Fe(PO4)3 were refined by pattern matching method. The two compounds crystallize in C2/c space group adopting the alluaudite type structure. Refinement of the crystal structure of the silver-containing compound leads to the non-stoichiometric chemical formula Ag1·67Mg2·33Fe0·89(PO4)3 while that of the sodium-containing compound leads to the stoichiometric chemical formula Na2Mg2Fe(PO4)3. The complex impedance plots are obtained in frequency range from 0.1 ​Hz to 1 ​MHz, between 573 ​K and 823 ​K Na2Mg2Fe(PO4)3 presents a conductivity of 0.25 ​× ​10−5 ​S ​cm−1 at 773 ​K, with Ea ​= ​0.81 ​eV. For Ag2Mg2Fe(PO4)3, a better ionic conductivity of 1.8 ​× ​10−3 ​S ​cm−1 ​has been observed at the same temperature with Ea ​= ​0.47 ​eV. The two alluaudite compounds present an intrinsic cationic conductivity type resulting from Na+ or Ag+ ions movement.

Topological Features of the Alluaudite-Type Framework and Its Derivatives: Synthesis and Crystal Structure of NaMnNi2(H2/3PO4)3

A new sodium manganese-nickel phosphate of alluaudite supergroup with the general formula NaMnNi2(H2/3PO4)3 was synthesized by a hydrothermal method. The synthesis was carried out in the temperature range from 540 to 660 K and at the general pressure of 80 atm from the oxides mixture in the molar ratio MnCl2: 2NiCl2: 2Na3PO4: H3BO3: 10H2O. The crystal structure was studied by a single-crystal X-ray diffraction analysis: space group C2/c (No. 15), a = 16.8913(4), b = 5.6406(1), c = 8.3591(3) Å, β = 93.919(3), V = 794.57(4) Å3. The compound belongs to the alluaudite structure type based upon a mixed hetero-polyhedral framework formed by MX6-octahedra and TX4-tetrahedra. The characteristic feature of the title compound is the absence of cations or H2O molecules in channel II, while the negative charge of the framework is balanced by the partial protonation of PO4 tetrahedra. The presence of the transition metals at the A-type sites results in the changes of stoichiometry and the local topological features. Topological analysis of the hetero-polyhedral alluaudite-type frameworks and its derivatives (johillerite-, KCd4(VO4)3-, and keyite-type) and quantitative characterization of their differences was performed by means of natural tilings.

Synthesis, crystal structure and charge-distribution validation of a new alluaudite-type phosphate, Na2.22Mn0.87In1.68(PO4)3.

Na2.22Mn0.87In1.68(PO4)3, sodium manganese indium tris-(phosphate) (2.22/0.87/1.68), was obtained in the form of single crystals by a flux method and was structurally characterized by single-crystal X-ray diffraction. The compound belongs to the alluaudite structure type (space group C2/c) with general formula X(2)X(1)M(1)M(2)2(PO4)3. The X(2) and X(1) sites are partially occupied by sodium [occupancy 0.7676 (17) and 1/2] while the M(1) and M(2) sites are fully occupied within a mixed distribution of sodium/manganese(II) and manganese(II)/indium, respectively. The three-dimensional anionic framework is built up on the basis of M(2)2O10 dimers that share opposite edges with M(1)O6 octa-hedra, thus forming infinite chains extending parallel to [10]. The linkage between these chains is ensured by PO4 tetra-hedra through common vertices. The three-dimensional network thus constructed delimits two types of hexa-gonal channels, resulting from the catenation of M(2)2O10 dimers, M(1)O6 octa-hedra and PO4 tetra-hedra through edge- and corner-sharing. The channels are occupied by Na+ cations with coordination numbers of seven and eight.

CИНТЕЗ, ДОСЛІДЖЕННЯ ТА ПРОВІДНІ ВЛАСТИВОСТІ ФАЗ АЛЮОДИТОВОГО ТИПУ

Complex oxide phosphates Na1.5Co1.5Fe1.5(PO4)3, Na1.75Co1.75Fe1.25(PO4)3, Na2Co2Fe(PO4)3 and Li0.25Na1.75Co2Fe(PO4)3, belonging to the alluaudite structural type (monoclinic system, space group C2/c) were synthesized by the melting method with further annealing of the homogenous glasses at a temperature 600°C. According to powder X-ray diffraction data the partial substitution of sodium cations by lithium cations in the initial phosphate matrix Na2Co2Fe(PO4)3 led to decreasing of lattice parameters for Li0.25Na1.75Co2Fe(PO4)3 (a = 11.7572(3) Å, b = 12.4528(4) Å, c = 6.4416(2) Å and β = 113.911(1)°). The FTIR-spectroscopy results confirmed the presence of PO4-tetrahedra in the composition of prepared phases. Modes in the regions of 400–600 cm-1 and 900–1000 cm–1 were assigned to symmetric and asymmetric stretching vibrations of phosphate tetrahedron in the alluaudite-type structure, respectively. The effect of partial substitution of sodium cations by lithium cations in the phosphate matrix Na2Co2Fe(PO4)3 as well as the decrease of sodium cations amounts in the alluauditerelated structure for the phases of Na1.5Co1.5Fe1.5(PO4)3 and Na1.75Co1.75Fe1.25(PO4)3 on the conductive properties of compounds were analyzed. It was found that increasing of sodium cations amount in the channels of the alluaudite-related structure leads to an increase of the specific conductivity from 0.011 Om-1m-1 for Na1.75Co1.75Fe1.25(PO4)3 to 0.15 Om–1m–1 for Na2Co2Fe(PO4)3 at a temperature of 550 °C. It was also found that partial substitution of sodium cations by lithium cations in the initial phosphate matrix Na2Co2Fe(PO4)3 no significant influence on conductivity of phase Li0.25Na1.75Co2Fe(PO4)3 (σ = 0.095 Оm–1m–1 at a temperature of 550 °C). In the case of phosphates Na1.75Co1.75Fe1.25(PO4)3 and Li0.25Na1.75Co2Fe(PO4)3 decreasing of conductive properties in the temperature ranges 190–250 °С and 550–590 °С, respectively are caused by contribution of different components in general conductivity. The synthesized phases can be used in the development of materials with conductive properties.

The importance of ionic radii in determining the structure obtained for sodium transition metal sulfates: Tuning structure through transition metal and selenate doping

Materials with the alluaudite structure have been attracting increasing interest due to recent reports of promising performance of Na2+2xFe2-x(SO4)3 as a sodium-ion battery cathode material. In previous work, we highlighted how selenate doping could be utilised to expand the range of alluaudite phases that can be synthesised, and proposed an ionic size relationship to determine whether an alluaudite (Na2+2xM2-x(SO4)3-y(SeO4)y) or 2-1-2 (Na2M(SO4)2-y(SeO4)y) (M ​= ​Co, Mn, Ni) phase would form from dehydration of the initial Na2M(SO4)2-y (SeO4)y.2H2O precursor. In this paper, we extend this work to investigate mixed transition metal (Fe–Ni, Mn–Co and Mn–Ni) systems to confirm the applicability of our proposed ion size-structure relationship. In agreement with these prior studies, the smaller transition metal ions (Co and Ni) naturally adopt the Na2M(SO4)2 (2-1-2) structure, while the larger transition metal ions (Fe and Mn) adopt the alluaudite-type structure. By exploiting the ion size design relationship, an Fe-containing 2-1-2 composition has been successfully synthesised with the aid of Ni-doping. Furthermore, for the Co, Ni systems, it has been shown that by co-doping with Mn, the synthesis of Co, Ni containing alluaudite phases can be achieved with lower selenate doping levels than required previously. Thus, this work further illustrates the ability to exploit cation sizes to direct the structure obtained for these sulfate/selenate systems, which allows the design of novel compositions for potential future cathode material applications. We also report the characterisation of the related Na2Cu(SO4)2-y(SeO4)y phases, which adopt a different structure, most likely attributed to the Jahn-Teller nature of the Cu2+.

Camanchacaite, chinchorroite, espadaite, magnesiofluckite, picaite and ríosecoite: six new hydrogen-arsenate minerals from the Torrecillas mine, Iquique Province, Chile

AbstractThe new minerals camanchacaite, NaCaMg2[AsO4]2[AsO3(OH)2], chinchorroite, Na2Mg5(As2O7)2(AsO3OH)2(H2O)10, espadaite, Na4Ca3Mg2[AsO3(OH)]2[AsO2(OH)2]10(H2O)6·H2O, magnesiofluckite, CaMg(AsO3OH)2(H2O)2, picaite, NaCa[AsO3OH][AsO2(OH)2] and ríosecoite, Ca2Mg(AsO3OH)3(H2O)2, were discovered on two closely related specimens collected from the Torrecillas mine, Iquique Province, Chile. These minerals occur as secondary phases on massive quartz–hematite also in association with anhydrite, gypsum, halite and talmessite. Camanchacaite is monoclinic,C2/c,a= 12.470(9),b= 12.554(9),c= 6.848(9) Å, β = 113.75(2)°,V= 981.3(16) Å3andZ= 4. It has a protonated alluaudite-type structure. Chinchorroite is triclinic,P$\bar{1}$,a= 8.7777(2),b= 8.8570(3),c= 9.7981(7) Å, α = 91.097(6), β = 110.544(8), γ = 103.167(7)°,V= 690.43(7) Å3andZ= 1. The structure contains abbreviated chains of five edge-sharing Mg octahedra that are linked by pyroarsenate and hydrogen-arsenate groups. Espadaite is orthorhombic,Ccca,a= 12.3649(10),b= 22.181(2),c= 18.3292(13) Å,V= 5027.1(7) Å3andZ= 4. The structure is based on heteropolyhedral sheets of formula {Ca3Mg2[AsO3(OH)]2[AsO2(OH)2]10}4−that contain large voids; NaO6polyhedra occupy the interlayer region. Magnesiofluckite is triclinic,P$\bar{1}$,a= 8.4143(6),b= 7.5321(5),c= 6.8917(4) Å, α = 82.477(6), β = 97.682(6), γ = 95.379(6)°,V= 427.84(5) Å3andZ= 2. It is isostructural with fluckite. Picaite is monoclinic,P21/c,a= 7.2474(4),b= 14.6547(7),c= 7.2624(5) Å, β = 99.520(7)°,V= 760.70(8) Å3andZ= 4. The structure contains chains of edge-sharing Na− and Ca octahedra with bridging AsO3(OH) and AsO2(OH)2tetrahedra. Ríosecoite is triclinic,P$\bar{1}$,a= 6.8110(9),b= 7.3156(12),c= 11.7773(17) Å, α = 83.466(6), β = 84.394(6), γ = 79.779(6)°,V= 571.95(15) Å3andZ= 2. The structure contains tetramers of edge-sharing CaO7and CaO8polyhedra linked by MgO6octahedra and bridging AsO3(OH) groups to form chains.

Highly efficient K0.4Na3.6Co(MoO4)3 new alluaudite type structure for photocatalytic degradation of methylene blue and green diamine B dyes

A novel alluaudite framework K0.4Na3.6Co(MoO4)3 photocatalyst has been synthesized by a solid-state reaction for degradation of both methylene blue (MB) and green diamine B (GDB) organic pollutants under sunlight. The sample was characterized using X-ray diffraction (XRD), transmission electron microscope, infrared spectroscopy and Raman spectroscopy, as well as by means of photoluminescence probing, impedance spectroscopy and UV–vis–NIR spectrophotometry. The XRD analysis reveals that such alluaudite type structure crystallizes in the monoclinic system with space group C2/c. Emissions of this material have been observed in a visible region at 290 nm excitation with a broad long-wave luminescence band from oxygen vacancies. UV–vis absorption spectrum measurements showed an efficient optical absorption in UV–vis region with a direct band gap of 3.37 eV. The complex impedance spectra suggested that the ac conductivity is a power law (Aωs) derived by the correlated barrier hopping conduction mechanism. The efficiency of the dyes removal in the presence of K0.4Na3.6Co(MoO4)3 particles reaches 83% for MB and 53% for GDB under sunlight irradiation. The current studies establish interesting possibilities for investigating catalytic cycles of these solar light activated photocatalysts.

An alluaudite-type sodium-ion battery cathode candidate Na2Mn2V(PO4)3: Crystal growth, preparation, structure and electrochemical properties

Recently, alluaudite-type cathode materials with two types of large Na tunnels attract considerable attention. Hereby, a compound Na2Mn2V(PO4)3 was synthesized and its high quality single crystals were grown in the NaCl molten-salt media. The single-crystal diffraction data analysis shows that Na2Mn2V(PO4)3 belongs to the typical alluaudite-type structure with unit parameters of a = 12.0533(15) Å. b = 12.5844(16) Å, c = 6.4987(8) Å, β = 114.51(2)˚. The density functional theory calculations based on the nudged elastic band method were used to obtain the migration energy barrier of Na ions in Na2Mn2V(PO4)3 and Na2Fe2V(PO4)3. The results of calculations show that Na2Mn2V(PO4)3 has a better Na+ conductivity than Na2Fe2V(PO4)3. The electrochemical tests also demonstrate that Na2Mn2V(PO4)3 exhibits electrochemical activity operating at an average voltage of 3.5 V (vs. Na/Na+) delivering a capacity of 97 mAh g−1 at 10 mA g−1 rate.

Synthesis, Crystal Structure and Properties of a New Phosphate, Na2Co2Cr(PO4)3

In this work, a novel phosphate Na2Co2Cr(PO4)3 was synthesized by sol–gel method, and its crystal structure was determined from powder X-ray diffraction data using Rietveld method. This new phosphate was further characterized by scanning electron microscopy, IR and Raman spectroscopy. This phosphate crystallizes in the well-known alluaudite-type structure with monoclinc symmetry (S.G. C 2/c). The structure of this phosphate consists of [CoO6] octahedra, [(Co,Cr)2O10] dimer-octahedra and PO4 tetrahedra leading to an open three-dimensional framework containing two types of tunnels running along [001] direction, where Na+ cations are located. The magnetic measurements confirmed that the predominant interactions in this phosphate are antiferromagnetic with a Curie–Weiss constant of θ = − 4.57 K. The electrochemical properties of Na2Co2Cr(PO4)3 as anode material for sodium-ion batteries were assessed using a galvanostatic mode and cyclic voltammetry in the potential window of 0.02–3 V. The electrochemical behavior was investigated by ex situ X-ray diffraction. The results showed that this material undergoes a conversion-type reaction.

Li0.75Mn1.50Fe1.75(PO4)3: First alluaudite-type iron phosphate containing only Li+ as alkaline ions

A new iron phosphate Li0.75Mn1.50Fe1.75(PO4)3 has been prepared by the flux method and its structure was characterized from single crystal X-ray diffraction data. It crystallizes as an alluaudite type structure, characterized by the A(2)A(2)’A(1)A(1)’A(1)”M(1)M(2)2(PO4)3 general formula with a = 12.002(9) Å, b = 12.509(9) Å, c = 6.404(7) Å, β = 115.07(7)° in the monoclinic C2/c space group. The 3D framework consists of infinite chains of edge-sharing M(2)2O10 dimers and M(1)O6 octahedra connected by phosphate tetrahedra leading to two sets of hexagonal tunnels. The Li+ and Mn2+ ions partially occupy one of them, the other tunnel being empty. The Mössbauer spectroscopy confirmed the occurrence of only Fe3+ ions in octahedral environment. Electrochemical cycling tests in Li cells were performed using Li0.75MnII1.50FeIII1.75(PO4)3 powder as electrode material. Only a small amount of Li+ ions can be reversibility deintercalated/intercalated corresponding to a capacity as low as 30 mAh/g with a 3.2 V average voltage. Moreover, a strong polarization due to low electronic and ionic conductivities is observed. The presence of Mn2+ ions in the same tunnel as Li+ probably hinders a good Li+ ionic diffusion.

Synthesis and crystal structure of two new phosphates with Alluaudite type structure: (M, Mn)3Fe(PO4)3 (M= Ca, Cd)

Two new phosphates with alluaudite type structure (M, Mn)3Fe(PO4)3 (M= Ca, Cd), namely Ca1.54Mn1.46Fe(PO4)3 and Cd0.66Mn2.34Fe(PO4)3, has been synthesized by a solid state reaction and characterized by single-crystal X-ray diffraction. The two compounds crystallize in the monoclinic system with C2/c space group. Their open framework results from (Fe1/Mn1)2O10 units of edge-sharing (Fe/Mn)O6 octahedra, which alternate with M(1)O6 octahedra (M(1)=Ca1/Mn2 or Cd1/Mn2) that form infinite chains running along [10-1] direction. These chains are linked together through the common corners of PO4 tetrahedra giving rise to two types of tunnels occupied by bivalent cations Ca2+ or Cd2+ and Mn2+.

Synthesis and crystal structure of two new phosphates with Alluaudite type structure: (M, Mn)3Fe(PO4)3 (M= Ca, Cd)

Synthesis and crystal structure of two new phosphates with Alluaudite type structure: (M, Mn)₃Fe(PO₄)₃ (M= Ca, Cd)

Magnesiocanutite, NaMnMg2[AsO4]2[AsO2(OH)2], a new protonated alluaudite-group mineral from the Torrecillas mine, Iquique Province, Chile

AbstractThe new mineral magnesiocanutite (IMA2016-057), NaMnMg2[AsO4]2[AsO2(OH)2], was found at the Torrecillas mine, Iquique Province, Chile, where it occurs as a secondary phase in association with anhydrite, canutite, halite, lavendulan and magnesiokoritnigite. Magnesiocanutite occurs as pale brownish-pink to rose-pink, lozenge-shaped tablets that are often grouped in tightly intergrown aggregates. The crystal forms are {110} and {102}. Crystals are transparent, with vitreous lustre and white to very pale pink streak. The Mohs hardness is 2½, tenacity is brittle, and the fracture is splintery. Crystals exhibit two perfect cleavages: {010} and {101}. The calculated density is 3.957 g/cm3. Optically, magnesiocanutite is biaxial (+), with α = 1.689(2), β = 1.700(2), γ = 1.730(2) (measured in white light); 2Vmeas. = 64.3(4)°; slight dispersion, r <v; orientation Z = b; X ∧ a = 15° in obtuse angle β. The mineral is slowly soluble in dilute HCl at room temperature. Electron-microprobe analyses, provided Na2O 5.44, CaO 0.26, MgO 8.84, MnO 18.45, CoO 1.47, CuO 2.13, As2O5 59.51, H2O(calc) 2.86, total 98.96 wt.%. Magnesiocanutite is monoclinic, C2/c, a = 12.2514(8), b = 12.4980(9), c = 6.8345(5) Å, β = 113.167(8)°, V = 962.10(13) Å3 and Z = 4. The eight strongest powder X-ray diffraction lines are [dobs Å(I )(hkl)]: 6.25(42)(020), 3.566(43)(310,1̄31), 3.262(96)(1̄12), 3.120(59)(002,131,040,221), 2.787(93)(400,022,041,330), 2.718(100) (4̄21,240,112,402), 2.641(42)(1̄32) and 1.5026(43)(multiple). Magnesiocanutite has a protonated alluaudite-type structure (R1 = 2.59% for 789 Fo > 4σF reflections) and is the Mg analogue of canutite. Using the results of both the microprobe analyses and structure refinement, the structurally based empirical formula is Na(Mn0.78Mg0.22)Σ1.00(Mg1.04Mn0.70Cu0.15Co0.11)Σ2.00[AsO4]2[AsO2(OH)2].

Synthesis, Crystal Structure, and Electrochemical Properties of the New Alluaudite-Type Compounds Ag2-Y Na Y M3(XO4)3 (M= Mn, Fe; X= V, P)

In recent years, sodium batteries have raised interest as cheap rechargeable batteries for large format rechargeable battery applications such as the grid storage. A number of promising cathode materials has already been tested. Among the materials crystallising with the alluaudite-type structure, only phosphates such as Na2 M 2Fe(PO4)3 (M = Mn, Fe, Co, and Ni) [1-3] or sulfates such as Na2+x M 2-y (SO4)3 (M = Mn and Fe) [4,5] were studied. To our knowledge no alluaudite vanadates were reported so far as electrodes for Li- or Na-ion batteries. Herein, we report on for the first time the synthesis, the crystal structure, and the electrochemical properties of the Ag2-y Na y M 3(XO4)3 (M= Mn, Fe; X= V, P; 0 ≤ y ≤ 2) compounds. The new compounds Ag2-y Na y M 3(XO4)3 (M= Mn, Fe; X= V, P) were synthesized by solid state reaction route, and their crystal structures were determined from single-crystal X-ray diffraction data [6,7]. The physical properties were characterized by Mӧssbauer and electrochemical impedance spectroscopies, galvanostatic cycling and cyclic voltammetry. These materials crystallize with a monoclinic symmetry, space group C2/c and the structure can be considered as a new member of the AA’MM’ 2(XO4) 3 alluaudite family. The A, A’, M, and X sites are fully occupied by Ag+/Na+, Mn2+, and P5+/V5+, respectively; whereas a Mn2+/Fe3+ mixture is observed in the M’ site. The Mӧssbauer spectra confirm that iron is trivalent. The impedance measurements indicate that the silver vanadate phase is better conductor than the sodium one. Furthermore, these vanadate phases exhibit ionic conductivities two order of magnitude higher than the homologous phosphates. The electrochemical tests prove that the new Na2 M 3(XO4)3 (M= Mn, Fe; X= V, P) materials, which are reported for the first time, are active in sodium-ion batteries.The electrochemical performances will be detailed during the presentation. References 1) Essehli, R.; Belharouak, I.; Ben Yahia, H.; Maher, K.; Abouimrane, A.; Orayech B.; Calder, S.; Zhou, XL.; Zhou, Z.; Sun, YK. Dalton Trans. 2015, 44, 7881-7886. 2) Essehli, R.; Belharouak, I.; Ben Yahia, H.; Chamoun, R.; Orayech, B.; El Bali, B.; Bouziane, K.; Zhou, XL.; Zhou, Z. Dalton Trans. 2015, 44, 4526-4532. 3) Trad, K.; Carlier, D.; Croguennec, L.; Wattiaux, A.; Ben Amara, M.; Delmas, C. Inorg. Chem. 2010, 49, 10378-10389. 4) Barpanda, P.; Oyama, G.; Nishimura, S.-I.; Chung, S.-C.; Yamada, A. Nat. Comm. 2014, 5, doi:10.1038/ncomms5358. 5) Dwibedi, D.; Araujo, R.B.; Chakraborty, S.; Shanbogh, P.P.; Sundaram, N.G.; Ahuja, R.; Barpanda P.; J. Mater. Chem. A 2015, 3 (36), 18564-18571. 6) Ben Yahia, H.; Shikano, M.; Essehli, R.; Belharouak I. Z. Kristallogr. 2016 DOI: 10.1515/zkri-2016-45678. 7) Ben Yahia, H.; Shikano, M.; Tabuchi, M.; Belharouak I. Inorg. Chem. 2016 in press.

Synthesis, crystal structure and charge-distribution validation of β-Na4Cu(MoO4)3 adopting the alluadite structure-type.

Single crystals of a new variety of tetra-sodium copper(II) tris-[molybdate(VI)], Na4Cu(MoO4)3, have been synthesized by solid-state reactions and characterized by single-crystal X-ray diffraction. This alluaudite structure-type is characterized by the presence of infinite layers of composition (Cu/Na)2Mo3O14 parallel to the (100) plane, which are linked by MoO4 tetra-hedra, forming a three-dimensional framework containing two types of hexa-gonal channels in which Na(+) cations reside. The Cu(2+) and Na(2+) cations are located at the same general site with occupancies of 0.5. All atoms are on general positions except for one Mo, two Na (site symmetry 2) and another Na (site symmetry -1) atom. One O atom is split into two separate positions with occupancies of 0.5. The title compound is isotypic with Na5Sc(MoO4)4 and Na3In2As3O12. The structure model is supported by bond-valence-sum (BVS) and charge-distribution CHARDI methods. β-Na4Cu(MoO4)3 is compared and discussed with the K4Cu(MoO4)3 and α-Na4Cu(MoO4)3 structures.

The alluaudite-type crystal structures of Na2(Fe/Co)2Co(VO4)3 and Ag2(Fe/Co)2Co(VO4)3.

Single crystals of the title compounds, disodium di(cobalt/iron) cobalt tris-(orthovanadate), Na2(Fe/Co)2Co(VO4)3, and disilver di(cobalt/iron) cobalt tris-(orthovanadate), Ag2(Fe/Co)2Co(VO4)3, were grown from a melt consisting of stoichiometric mixtures of three metallic cation precursors and vanadium pentoxide. The difficulty to distinguish between cobalt and iron by using X-ray diffraction alone forced us to explore several models, assuming an oxidation state of +II for Co and +III for Fe and a partial cationic disorder in the Wyckoff site 8f containing a mixture of Co and Fe with a statistical distribution for the Na compound and an occupancy ratio of 0.4875:0.5125 (Co:Fe) for the Ag compound. The alluaudite-type structure is made up from [10-1] chains of [(Co,Fe)2O10] double octa-hedra linked by highly distorted [CoO6] octa-hedra via a common edge. The chains are linked through VO4 tetra-hedra, forming polyhedral sheets perpendicular to [010]. The stacking of the sheets defines two types of channels parallel to [001] where the Na(+) cations (both with full occupancy) or Ag(+) cations (one with occupancy 0.97) are located.

Investigation of Na Removal/Insertion Mechanism in Na1.86Fe3(PO4) 3 Cathode Material

In recent years, sodium batteries have raised interest as cheap rechargeable batteries for large format rechargeable battery applications such as the grid storage. A number of promising cathode materials has already been tested, however their electrochemical performances remain below their lithium counterpart cathodes. Complete structural and electrochemical investigations are needed to improve the characteristics of existing sodium electrode materials, design and synthesis of new ones with improved battery performance. Phosphate based materials are considered as promising cathode materials for sodium batteries due to their low cost and the variety of structural arrangements. In addition, it is predicted that phosphate cathode materials are thermally and electrochemically stable due to the presence of strong P-O bonds. The alluaudite-type structure, with the general formula AA’BB’2(PO4)3 (A and A’ = Li, Na; B is a large six coordinated cation; B’ is a small six coordinated cation), has been intensively studied as electrode materials for LIBs and/or NIBs. In the present work, we report on the synthesis, characterization and electrochemical performance of a new Na1.86Fe3(PO4)3 alluaudite-type structure compound. The material delivers ~ 109 mAhg-1 as a reversible capacity at ~ 3 V with a small capacity fade during cycling. The refinement of the structure by the Rietveld method and results of Mössbauer experiments indicate the presence of sodium deficiency and a Fe2+/Fe3+ ratio below 2/1 in the pristine material. Detailed study on the mechanism of sodium removal/insertion will be presented using X-ray, galvanometric cycling, cyclic voltammetry and Mössbauer techniques.

All-Solid State Na-Ion Batteries Na2-2dFe2-D(SO4)3|Na3-XMxP1-XS4 (M=Ge4+,Ti4+, Sn4+) (x=0,0.1) | Na2Ti3O7

Sodium ion batteries attracted large research community because of earth-abundance and low cost of sodium. Though significant advances have been made in the development of Na-ion cathodes and anodes, a major impediment to the commercial viability of rechargeable Na-ion batteries is the lack of an effective electrolyte. Current Na-ion electrolytes are mostly based on the same fundamental chemistry as Li-ion electrolytes – a mixture of cyclic and linear organic carbonates with a Na-salt. Such organic solvent-based liquid electrolytes are flammable and have limited electrochemical windows. A promising alternative architecture is all-solid-state Na-ion rechargeable batteries utilizing non-flammable ceramic Na superionic conductor electrolytes. Na solid electrolytes such as -alumina and NAtrium Superionic CONductors (NASICON) are well-studied, but they typically exhibit reasonable ionic conductivities only at higher temperatures. Here we report the synthesis, characterization of materials that from our parallel computational studies appeared to be promising components of all-solid state rechargeable Na-ion batteries with high rate capabilities. Recently it is reported that the cubic phase of Na3PS4 (c-Na3PS4, space group: I4-3m) is a promising solid electrolyte with a room temperature Na+ ion conductivity of 0.2mS/cm. In order to increase the ionic conductivity further we prepared Na3-xMxP1-xS4 (M=Ge4+,Ti4+, Sn4+) (x=0,0.1) using mechanical milling followed by annealing at 250°C. Maximum room temperature ionic conductivity of 0.25mS/cm was observed for Sn doped NaP3S4. In situ high temperature XRD showed that all the compounds are stable up to 400°C.When it comes to identifying cathode materials for such a NIB , a considerable fraction of research activity still focuses materials analogous to those that work well in Li-ion batteries containing costly transition metals such as Co, which appears problematic for various reasons: differences in reaction mechanisms of the Na analogues to the Li transition metal oxides, different structural requirements for Na+ mobility, the fact that a cost advantage of Na over Li will only translate into low cost batteries. Hence, research on transition metal electrode materials for Na-ion batteries will have to concentrate on abundant transition metals (essentially Fe, Ti, Mn, and possibly Cr, V). On the other hand, O3- NaFeO2, and P2-type Nax[Fe0.5Mn0.5]O2 utilizing the Fe4+/Fe3+ redox couple are known to suffer from limited reversible capacity and low operating potential. Here we report the preparation of Na2+2dFe2-d(SO4)3 by mechanical milling of Na2SO4 and FeSO4 followed by annealing at 400ºC in an argon environment. The Na2-2dFe2-d(SO4)3 formed an alluaudite-type structure in space group C2/c with lattice constants a=12.654(1)Å, b=12.761(9)Å, c=6.503(5)Å, β=115.52(1)º close those previously reported for d =0.12.For anode transition metal oxides the number of low potential lithium insertion compounds is rather limited owing to the competition of insertion vs conversion reactions, the former being only favored for early 3d metal (Ti, V) oxides. Along that line, NaxVO2 was recently found to reversibly react with Na at ca. 1.5 V but sensibly lower operation voltages would be needed for enhanced energy density. Titanium-based systems are considered as best alternatives. Hence, Na2Ti3O7 was prepared from anatase TiO2 and anhydrous Na2CO3 mixtures with 10% excess of the latter with respect to stoichiometric amounts. These mixtures were milled and treated at 800ºC for 20 h with intermediate regrinding. X-ray diffraction pattern indicated the formation of pure crystalline phase as shown in the figure with space group P121/m.Based on the synthesized and characterized materials we assembled all-solid state sodium-ion batteries combining the alluaudite-type cathode with Na3PS4 as the solid electrolyte and Na2Ti3O7 as the anode. Favourable rate performance of the all solid state sodium-ion battery was demonstrated at room temperature. Figure 1

Unveiling the sodium intercalation properties in Na1.86□0.14Fe3(PO4)3

The new compound Na1.86□0.14Fe3(PO4)3 was successfully synthesized via hydrothermal synthesis and its crystal structure was determined using powder X-ray diffraction data. Na1.86Fe3(PO4)3 was also characterized by operando XRD and Mössbauer spectroscopy, cyclic voltammetry, and galvanostatic cycling. Na1.86Fe3(PO4)3 crystallizes with the alluaudite-type structure with the eight coordinated Na1 and Na2 sodium atoms located within the channels. The combination of the Rietveld- and Mössbauer-analyses confirms that the sodium vacancies in the Na1 site are linked to a partial oxidation of Fe2+ during synthesis. The electrochemical tests indicated that Na1.86Fe3(PO4)3 is a 3 V sodium intercalating cathode. At the current densities of 5, 10, and 20 mA g−1, the material delivers the specific capacities of 109, 97, and 80 mA h g−1, respectively. After 100 charge and discharge cycles, Na1.86Fe3(PO4)3 exhibited good sodium removal and uptake behavior although no optimizations of particle size, morphology, and carbon coating were performed.

Elaboration, étude structurale et analyse CHARDI et BVS d'une nouvelle variété β-Na9Cr(MoO4)6 de type alluaudite.

The title compound, nonasodium chromium(III) hexakis[molybdate(VI)], β-Na9CrMo6O24, was prepared by solid-state reactions. This alluaudite-type structure is constituted of infinite layers formed by links between M 2O10 (M = C/Na) dimers and MoO4 tetra-hedra. The Na(+) and Cr(3+) cations are located in the same site with, respectively, 0.25 and 0.75 occupancies. The layers are connected to each other through MoO4 sharing corners, resulting an in open three-dimensional framework with hexa-gonal-form cavities occupied by Na(+) cations. The proposed structural model is supported by charge-distribution (CHARDI) and bond-valence-sum (BVS) analysis. All atoms are on general positions except for one Mo, two Na (site symmetry 2) and another Na site (site symmetry -1). A comparison is made with the similar structures Na4Co(MoO4)3, Na2Ni(MoO4)2, Cu1.35Fe3(PO4)3 and NaAgFeMn2(PO4)3.