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Different modifications of LixMoO2 (1) without metallic Mo–Mo bonds (R-3m, a = 2.858(2) A, c = 15.701(13) A), (2) with endless Mo chains with metallic bonds (C2/m, a = 10.614(3) A, b = 2.878(1) A, c = 4.955(2) A, β = 99.37(3)°), and (3) with Mo4O16 clusters (C2/m, a = 9.905(6) A, b = 5.739(3) A, c = 5.472(4) A, β = 107.43(7)°) were synthesized by high-temperature solid-state reaction. Increasing lithium content supports the formation of the rhombohedral form. In situ structural investigations during electrochemical Li extraction and insertion between 2.4–3.5 V on Li1.0MoO2 material containing rhombohedral and monoclinic modifications with endless molybdenum chains revealed the instability of the monoclinic Li0.9MoO2 form with decreasing Li content against transformation into two rhombohedral phases LixMoO2 and Lix≈0MoO2. In contrast, the rhombohedral Li1.0(Mo0.9Li0.1)O2 form showed a topotactical single-phase behavior during Li extraction and insertion. Further oxidation of LixMoO2 at voltages above 4.5 V...

Electrochemical performance and structural properties of the high-voltage cathode material Li2CoPO4F have been investigated. The cyclic voltammetry and coulometry under potential step mode in the voltage range 3.0–5.1 V vs. Li revealed a structural transformation at potentials above 4.8 V. This transformation occurring upon Li-extraction appears to be irreversible: the subsequent Li-insertion does not result in restoration of the initial structure, but takes place within a new “modified” framework. According to the structure refinement this modification involves the mutual rotations of (CoO4F2) octahedra and (PO4) tetrahedra accompanied by the considerable unit cell expansion which is expected to enhance the Li-transport upon subsequent cycling. The new framework demonstrates a reversible Li-insertion/extraction in a solid-solution regime with stabilized discharge capacity at around 60 mAh g−1.

Li(4)V(3)O(8) materials have been prepared by chemical lithiation by Li(2)S of spherical Li(1.1)V(3)O(8) precursor materials obtained by a spray-drying technique. The over-lithiated vanadates were characterised physically by using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and electrochemically using galvanostatic charge-discharge and cyclic voltammetry measurements in both the half-cell (vs. Li metal) and full-cell (vs. graphite) systems. The Li(4)V(3)O(8) materials are stable in air for up to 5 h, with almost no capacity drop for the samples stored under air. However, prolonged exposure to air will severely change the composition of the Li(4)V(3)O(8) materials, resulting in both Li(1.1)V(3)O(8) and Li(2)CO(3). The electrochemical performance of these over-lithiated vanadates was found to be very sensitive to the conductive additive (carbon black) content in the cathode. When sufficient carbon black is added, the Li(4)V(3)O(8) cathode exhibits good cycling behaviour and excellent rate capabilities, matching those of the Li(1.1)V(3)O(8) precursor material, that is, retaining an average charge capacity of 205 mAh g(-1) at 2800 mA g(-1) (8C rate; 1C rate means full charge or discharge of a battery in one hour), when cycled in the potential range of 2.0-4.0 V versus Li metal. When applied in a non-optimised full cell system (vs. graphite), the Li(4)V(3)O(8) cathode showed promising cycling behaviour, retaining a charge capacity (Li(+) extraction) above 130 mAh g(-1) beyond 50 cycles, when cycled in the voltage range of 1.6-4.0 V, at a specific current of 117 mA g(-1) (C/3 rate).

In situ synchrotron diffraction revealed a stepwise appearance of two new phases upon electrochemical lithium extraction from LiCoPO4. These phases were demonstrated to have the same olivine-like structure as the pristine compound. The lithium-deficient phases were proposed to be Li0.7CoPO4 and CoPO4. The completely delithiated phase appears to be unstable in air and undergoes amorphization. The phase transitions are reversible, but a slow kinetics of the initial delithiation was identified by in situ synchrotron diffraction and the potentiostatic intermittent titration technique. We demonstrated that the electrochemical extraction of lithium is accompanied by significant electrolyte decomposition, contributing to the capacity loss upon cycling. The galvanostatic intermittent titration technique combined with impedance spectroscopy revealed self-discharge of the cell in the charged state. This study argues different mechanisms of lithium extraction from LiCoPO4 in comparison with LiFePO4 and LiMnPO4.

Five different crystalline phases are established in the quaternary system Na–Fe–Mo–O with isolated MoO 4 tetrahedra: NaFe(MoO 4 ) 2 , Na 3 Fe 2 (MoO 4 ) 3 , α - and β -NaFe 2 (MoO 4 ) 3 and NaFe 4 (MoO 4 ) 5 . The optimized conditions for sample preparation are described together with structural analyses by X-ray and neutron powder diffraction. The observed crystal structures are compared with known structure types. The high-temperature behaviour, thermal expansion, decomposition or congruent melting, is reported together with some preliminary characterisation of oxygen release as requested for catalytic activity in partial oxidation of hydrocarbons. Magnetic properties and antiferromagnetic ordering have been studied by magnetisation measurements and neutron diffraction.

The electrochemical performance of LiCoPO4-based electrodes was studied in dependence on synthetic conditions. The role of particle size distribution is illustrated. Structural changes occurring at lithium extraction–insertion were explored by ex situ and in situ synchrotron XRD measurements. For the samples annealed at temperature lower than 600 °C the amorphisation of the cathode material was identified. For a high-temperature sample the two-phase character of electrochemical reaction was confirmed. The character of structural changes observed at charge and discharge is different: the two-phase reaction LiCoPO4–“CoPO4” occurs during charging, while discharge induces a strong increase of the cell volume for the Li-poor phase.

The influence of the annealing temperature on the degree of cation-disordering in the layered structures was examined for three different compositions of LiNiyCo1-yO2 (y = 0.2, 0.66 and 0.75, respectively). A minimum in cation-disorder is found for annealing temperatures between 700 and 800 °C for y = 0.75, between 750 and 810 °C for y = 0.66 and a less pronounced minimum between 795 and 870 °C for y = 0.2. One optimum annealed sample with y = 0.75 was used for an in situ characterisation using synchrotron radiation. The obtained structural data correlate well with the electrochemical data. The known phase transition occurring during the first cycle was closely observed by ADXRD (angular dispersive X-ray diffraction). The two states of the material during the first cycle could be distinguished and the obtained data were processed by Rietveld refinement.

A new sodium molybdate, Na6Mo11O36, has been synthesized, and its crystal structure was determined by single crystal X-ray diffraction (space group P-1; a = 7.2722(6)A, b = 22.376(1)A, c = 9.6686(8)A, α = 89.98(1)°, β = 112.12(1)°, γ = 90.29(1)°; Z = 2). The compound can be considered as a new structure type related to the anatase structure. Na2MoO4 exists in four different modifications between room temperature and the melting point. The α-phase is isostructural with spinel-type Na2WO4, the γ-phase with thenardite, Na2SO4 (V), and the δ-phase with Na2SO4 (I). The diffraction patterns of β-Na2MoO4 are similar to those of the γ-phase, but could not be indexed. Untersuchung des Na2O—MoO3-Systems Na6Mo11O36, ein neues Oxid mit anatasverwandter Struktur und die Kristallstrukturen von Na2MoO4 Die Kristallstruktur des neuen Natrium-Molybdan-Oxids Na6Mo11O36 wurde mit Hilfe der Einkristallrontgenstrukturanalyse aufgeklart (Raumgruppe P-1; a = 7.2722(6)A, b = 22.376(1)A, c = 9.6686(8)A, α = 89.98(1)°, β = 112.12(1)°, γ = 90.29(1)°; Z = 2). Sie weist eine enge Verwandtschaft zur Anatas-Struktur auf. Na2MoO4 liegt zwischen Zimmertemperatur und Schmelzpunkt in 4 verschiedenen Modifikationen vor: Die α-Phase ist isostrukturell zu Na2WO4 (Spinell-Typ), die γ-Phase zu Thenardit, Na2SO4 (V), und die δ-Phase zu Na2SO4 (I). Die Diffraktogramme von β-Na2MoO4 weisen eine grose Ahnlichkeit zu denen der γ-Phase auf, konnten aber nicht indiziert werden.

The double-perovskite series Ba 2 (Fe,Re 1− x W x ) 2 O 6 , where x =0, 0.2, 0.4 and 0.5, have been prepared as pure powders by a conventional solid-state reaction and studied by X-ray powder diffraction and magnetization measurements. X-ray powder diffraction has been carried out at different temperatures (between 90 and 300 K) to study structural and magnetic properties of Ba 2 (Fe,Re) 2 O 6 . Rietveld analysis of X-ray diffraction patterns show a partial disorder of Re/W and Fe on the B sites of the double-perovskite, which plays a dominant role in the structural and magnetic properties of these compounds. The symmetry is cubic ( Fm 3 m ) for all samples, and no phase transition was detected for Ba 2 (Fe,Re) 2 O 6 between 95 K and room temperature. The magnetic properties of these series are remarkable: T C goes to a maximum reaching 338 K for x =0.2, with a spontaneous moment lower than the theoretical value.

Ceramics of Ba 2 (Fe,B') 2 O 6 double-perovskites have been prepared and studied for B' = Mo, W and Re. Rietveld analysis confirms that all samples crystallize in a cubic double-perovskite structure with Fm 3 m space group.Magnetization measurements performed in the temperature range from 5 K to 350 K show a ferromagnetic behaviour for both materials Ba 2 (Fe,Mo) 2 O 6 and Ba 2 (Fe,Re) 2 O 6 , with T C = 335 K, 318 K respectively, and antiferromagnetic behaviour for Ba 2 (Fe,W) 2 O 6 with T N = 20 K.

The crystal structure of yttrium rhenium oxide, Y7ReO14−δ, is a 2×2×2 superstructure of the CaF2 structure, space group Fm 3 m , a=10.4770(14) A. The 32 cations within the unit cell are distributed with yttrium on the (4a)- and (24d)-sites and with rhenium on the (4b)-site. The 64 oxygen atoms occupy two (32f) sites (x,x,x), O(1) with x1=0.1351(9) and O(2) with x2=0.6054(11), in the undistorted fluorite structure x=0.125 and 0.625. The site occupation factor for the O(2) site is only 77(8)% in agreement with the maximum of 75% for δ=0 in the proposed stoichiometry. The electrical DC conductivity, measured on a single crystal, reveals semiconducting behavior between 165 and 265 K with a band gap of 157.4 meV.

Ternary oxides with general formula MMoO4 (where M is a 3d-transitional metal) were characterized as cathode materials for lithium rechargeable batteries by galvanostatic charge–discharge technique and cyclic voltammetry. The significant capacity fading after the first cycle of lithium insertion/removal takes place for different copper molybdates (α-CuMoO4 and high-pressure modification CuMoO4-III) corresponding to the irreversible copper reduction and formation of Li2MoO4 during the first discharge. X-ray powder diffraction data reveal the decomposition of pristine ZnMoO4 by electrochemical reaction, lithium zinc oxide with the NaCl-type structure and Li2MoO3 seem to be formed. Lithium intercalation into nickel and iron molybdates is shown to proceed without phase transitions, but at unsatisfactory low operating voltages.

Synchrotron diffraction and Mossbauer spectroscopy on Ba2(Fe,W)2O6 confirmed an Fe excess in this double-perovskite, better described as Ba2Fe(FexW1−x)O6−δ with x=0.2. The crystal structure is cubic ( Fm 3 m ) down to 10 K, and a recently reported tetragonal structure of Ba2FeWO6 is critically reviewed. Magnetic properties of Ba2(Fe,W1−xMox)2O6 compounds were studied by SQUID measurements and revealed weak ferromagnetism at low temperatures, and TC increases with more substitution of Mo for W.

The complex oxide Na3Fe2Mo5O16 has been synthesized, and its crystal structure was determined by single-crystal X-ray diffraction (space group (SG) P-3m1; a=5.7366(6) A, c=22.038(3) A; Z=2). The compound can be considered as a new structure type containing Mo3O13 cluster units, which can be derived from the Na2In2Mo5O16 structure model by doubling of the cell along the c-axis. Na3Fe2Mo5O16 crystallizes in centrosymmetric SG (P-3m1) and the positions of the sodium atoms are fully occupied in contrast to the proposed Na2In2Mo5O16 model SG (P3m1). Magnetic properties of Na3Fe2Mo5O16 were studied by superconducting quantum interference device measurements, revealing antiferromagnetic ordering below Tχmax=10(1) K. Thermal stability in air was investigated by in situ high-temperature X-ray powder diffraction. Structural relationships to Na2In2Mo5O16 and NaFe(MoO4)2 are discussed.

The magnetic structure of Fe 2 Mo 3 O 12 was determined by neutron powder diffraction and magnetization studies. The magnetic unit cell is identical with the monoclinic chemical one ( Z =8), and the magnetic space group is P2 1 /a. The magnetic moments are ferromagnetically aligned along the b -axis for each sublattice corresponding to each Fe-site. There are four different Fe-sites, and the magnetic moments are parallel within two of them, but antiparallel to those of the other two sublattices, so that a ferrimagnetic structure results. The dominant antiferromagnetic supersuperexchange couplings are those along Fe–O–O–Fe paths with the two bridging oxygens belonging to one [MoO 4 ]-tetrahedron and forming large Fe–O–O and O–O–Fe angles.

The complex oxide Sr 7 Re 4 O 19 has been synthesized and its crystal structure was determined by X-ray diffraction powder data analysis (space group C 2/ m ; a =13.6379(3) A, b =5.6035(2) A, c =10.3700(3) A; β =98.348(2)°, Z =2, R I =0.018, R P =0.050). The compound crystallizes in a new structure type, which can be derived from the Ba 7 Ir 6 O 19 structure by removing the Ir atoms from the middle octahedron of three face-sharing IrO 6 octahedra units. This change results in the infinite cis -bridged chains of the ReO 6 octahedra linked together by common corners. Each chain is connected with another one by the corner-sharing of each second ReO 6 octahedron. The 10- and 12-coordinated Sr atoms are situated between these infinite structure fragments. Magnetic properties of the Sr 7 Re 4 O 19 compound were studied by SQUID measurements.

A new monohydrate of lithium perrhenate LiReO 4 ·H 2 O was prepared by dehydration of LiReO 4 ·1.5H 2 O at room temperature. The single crystals of LiReO 4 ·H 2 O were obtained by crystallisation from the isoamyl acetate solution of LiReO 4 ·1.5H 2 O. The structure of monohydrate ( a =5.6674(4), b =10.771(1), c =7.4738(7) A, β =102.422(7)°, R 1 =0.0414, space group P 2 1 / a , Z =4) is built up from LiO 3 (H 2 O) 2 trigonal bipyramids and ReO 4 tetrahedra sharing common edges and corners inside the layers. The layers are connected together by hydrogen bonds. The relationships between the structures of sesquihydrate, monohydrate and anhydrous LiReO 4 are discussed.

The new complex oxide (V0.5Re0.5)O2 has been synthesized under high pressure of 60 kbar at 1000°C, and its crystal structure determined by single crystal X-ray diffraction data analysis (S.G.: P42/mnm, a = 4.6357(4) Å, c = 2.8292(3) Å, V = 60.80(1) Å3). This compound adopts a rutile-type structure with random cat ion distribution on one crystallographic site. The substitution of 50 vanadium by rhenium stabilizes the high temperature form of VO2 at room temperature. The cation ratio of 1 : 1 was confirmed by EDX analysis performed by electron microscopy on the same crystals used for X-ray diffraction.

Li1.0MoO2 (I), Li0.91MoO2 (II), and Li0.75MoO2 (III) are synthesized by solid state reactions of stoichiometric mixtures of Li2MoO4, Mo, and MoO3 (alumina crucibles, 1223 K, 20 h) and characterized by single crystal XRD, powder XRD, XPS, and electrochemical measurements.

Ln4Re6O19 (Ln=Ce, Pr) and Nd4Re5.5O19 compounds have been synthesized for the first time in sealed evacuated silica tubes and characterized by X-ray powder diffraction, electron diffraction and EDX analysis. The crystal structure of Nd4Re5.5O19 (S.G. I23, Z=2, a=8.9396(4) A) has been refined from X-ray powder data. The influence of the Ln size on the stability of the Ln4Re6O19 structure is discussed.

A new monohydrate of lithium perrhenate LiReO 4 ·H 2 O was prepared by dehydration of LiReO 4 ·1.5H 2 O at room temperature. The single crystals of LiReO 4 ·H 2 O were obtained by crystallisation from the isoamyl acetate solution of LiReO 4 ·1.5H 2 O. The structure of monohydrate ( a =5.6674(4), b =10.771(1), c =7.4738(7) A, β =102.422(7)°, R 1 =0.0414, space group P 2 1 / a , Z =4) is built up from LiO 3 (H 2 O) 2 trigonal bipyramids and ReO 4 tetrahedra sharing common edges and corners inside the layers. The layers are connected together by hydrogen bonds. The relationships between the structures of sesquihydrate, monohydrate and anhydrous LiReO 4 are discussed.

We have investigated spin and orbital magnetic moments of the Re 5d ion in the double perovskites A2FeReO6 (A = Ba, Sr, Ca) by X-ray magnetic circular dichroism (XMCD) at the Re L(2,3) edges. In these ferrimagnetic compounds an unusually large negative spin and positive orbital magnetic moment at the Re atoms was detected. The presence of a finite spin magnetic moment in a 'non-magnetic' double perovskite as observed in the double perovskite Sr2ScReO6 proves that Re has also a small, but finite intrinsic magnetic moment. We further show for the examples of Ba and Ca that the usually neglected alkaline earth ions undoubtedly also contribute to the magnetism in the ferrimagnetic double perovskites.

In situ synchrotron diffraction revealed a stepwise appearance of two new phases upon electrochemical lithium extraction from LiCoPO4. These phases were demonstrated to have the same olivine-like structure as the pristine compound. The lithium-deficient phases were proposed to be Li0.7CoPO4 and CoPO4. The completely delithiated phase appears to be unstable in air and undergoes amorphization. The phase transitions are reversible, but a slow kinetics of the initial delithiation was identified by in situ synchrotron diffraction and the potentiostatic intermittent titration technique. We demonstrated that the electrochemical extraction of lithium is accompanied by significant electrolyte decomposition, contributing to the capacity loss upon cycling. The galvanostatic intermittent titration technique combined with impedance spectroscopy revealed self-discharge of the cell in the charged state. This study argues different mechanisms of lithium extraction from LiCoPO4 in comparison with LiFePO4 and LiMnPO4.

The ternary oxide MnReO4, manganese rhenium oxide, has been synthesized under a high pressure of 5.5 GPa at 1473 K and its crystal structure has been determined by single-crystal X-ray diffraction. MnReO4 crystallizes in a wolframite-type structure with average bond lengths of 〈Re—O〉 = 1.935 and 〈Mn—O〉 = 2.160 Å that are in good agreement with the ionic radii of Re6+ and Mn2+. The magnetic properties of MnReO4 have been studied by SQUID measurements, revealing magnetic ordering below 275 (10) K and a weak ferromagnetic component of the ordered magnetic structure.

LiCoPO4 samples were synthesized by two different techniques (high-temperature solid-state reaction and lower-temperature synthesis using NH4CoPO4·H2O as precursor) and tested as cathode materials for 5-V lithium batteries. An irreversible lithium deinsertion was observed for the high-temperature sample. In contrast, the application of lower-temperature synthesis led to a significant improvement of the lithium storage reversibility. Different delithiation mechanisms in LiCoPO4 were found for the samples obtained by different synthetic techniques. The nature of capacity fading during cycling of the cells is discussed.

The complex oxides M2MgReO6 (M=Ca, Sr, Ba) have been synthesized, and their crystal structures were determined by X-ray diffraction powder data analysis. These compounds belong to the A2BB′O6 (M2MgReO6) perovskites with a “rock-salt” type distribution of Re and Mg atoms over the B-cation sublattice, since a big M cation is located in A positions. The magnetic properties of the M2MgReO6 compounds (M=Ca, Sr, Ba) were investigated and an unexpected behavior observed: significant hysteresis effects were detected for all M2MgReO6 oxides at temperatures up to 300 K. These results point at a ferromagnetic component in all of the M2MgReO6 magnetic structures, even at room temperature.

Four new crystalline structures within the Na–Fe–Mo–O system are reported: sodium tetrairon pentamolydate (1), NaFe4(MoO4)5, α-sodium diiron trimolybdate (2), α-NaFe2(MoO4)3, β-sodium diiron trimolybdate (3), β-NaFe2(MoO4)3, trisodium diiron trimolybdate (4), Na3Fe2(MoO4)3. All these structures belong to orthomolybdate class of compound and are described as networks of [FeO6] octahedra and [MoO4] tetrahedra. They are compared with each other and with other related structures.

Ternary oxides with general formula MMoO4 (where M is a 3d-transitional metal) were characterized as cathode materials for lithium rechargeable batteries by galvanostatic charge-discharge technique and cyclic voltammetry. The significant capacity fading after the first cycle of lithium insertion/removal takes place for different copper molybdates (standard a-CuMoO4and high-pressure modification CuMoO4 –III) corresponding to the irreversible copper reduction and formation of Li2MoO4 during the first discharge. X-ray powder diffraction data reveal the decomposition of pristine ZnMoO4 by electrochemical reaction, lithium zink oxide with the NaCl-type structure and Li2MoO3 seem to be formed.

Three lithium vanadate materials with the nominal composition Li 1.1 V 3 O 8 have been prepared by a spray-drying technique with subsequent heat-treatment (A) at 320°C, (B) at 585°C, and (C) at 585°C with carbon. They have been analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electronic conductivity, Brunauer-Emmett-Teller surface-area characterization, and electrochemical charge-discharge tests in lithium cells. The best material had a spherical aggregate morphology and exhibited, at 25°C in a narrow potential range of 2.0-3.3 V vs Li/Li + , at 116 mA/g (C/3) a high discharge capacity of 260 mAh/g in the 2nd cycle and 220 mAh/g in the 60th cycle, respectively, which is to the best of our knowledge the best electrochemical performance reported so far for Li 1.1 V 3 O 8 . The rate capability of these positive-electrode materials was found to be limited mainly by the lithium diffusion length in the primary particles.

Electrochemical lithium extraction from LiMn0.6Fe0.4PO4 was revealed to proceed through two two-phase regions in contrast to the mechanism earlier reported. All phases appearing during charging of the cell have the same olivine-like structure with different cell parameters.