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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.

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.

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.

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.