Three isostructural iron monophosphates KNiFe(PO4)2 (KNi), KMgFe(PO4)2 (KMg-LT, where LT means “low-temperature stable phase”), and KCoFe(PO4)2 (KCo-LT) are synthesized and structurally characterized from X-ray diffraction data. They crystallize in the monoclinic system with the space group P21/c. Their structures have in common a three-dimensional framework, built up by infinite zigzag chains of edge-sharing MO6 (M = Ni, Mg or Co) octahedra, linked by FeO5 and PO4 polyhedra via vertices and edges to form a rigid skeleton. The K+ ions are located in formed tunnels. DTA showed that KNi has a congruent melting at 941°C, whereas KMg-LT and KCo-LT undergo irreversible phase transitions from P21/c to different high-temperature structures with the C 2/c symmetry. IR absorption bands are assigned to different vibrations of the PO4 tetrahedron.

Iron vanadates and phosphates have been widely explored [1-2] as possible electrode material for Li-ion batteries. In the goal of finding new materials, our approach was to consider existing materials and to investigate the flexibility of their network for possible substitutions. Among the different materials containing iron and vanadium, Cu3Fe4(XO4)6 (X = P, V) are isostructural to Fe7(PO4)6. Lafontaine et al. [3] discussed the structural relationships between β-Cu3Fe4(VO4)6 and several other vanadates, phosphates and molybdates of general formula AxBy(VO4)6. The interesting network flexibility was then demonstrated with the existence of four different crystallographic sites, which can be partially occupied depending on the x+y value : x+y = 7 for β-Cu3Fe4(VO4)6) and x+y = 8 for NaCuFe2(VO4)3. The LixFey(VO4)6 phase was then prepared considering the substitution of Li+ and Fe3+ for Cu2+ ions in β-Cu3Fe4(VO4)6 and the existence of an extra site to accommodate the charge compensation (7 ≤ x+y ≤ 8). As expected, a new lithium iron vanadate, isotructural to mineral Howardevansite was then obtained. Single crystal diffraction data were collected at room temperature on Enraf-Nonius CAD-4 diffractometer. Structure was refined with JANA-2006 program package. Mössbauer and magnetic measurements were also used to check the oxidation state of iron ions, to support the obtained crystal structure and to consider any possible structural/magnetic transitions. All the results will be presented and discussed in this presentation.

The relevance of (bulk) transition-metal oxides for thermoelectric generation is discussed. A large power factor (i.e., a large electronic conductivity coexisting with a large Seebeck coefficient) seems more easily achievable in either hopping-type semiconductors or in highly correlated metallic systems such as layered cobaltites.

A lithium bismuth phosphate, Li2Bi14.67(PO4)6O14, has been synthesized for the first time by the solid-state method. The crystal structure was determined by single crystal X-ray diffraction at 150K. Li2Bi14.67(PO4)6O14 crystallizes in the monoclinic system C2/c (No. 15), with a=30.8189(4)Å, b=5.2691(3)Å, c=24.5302(3)Å, β=122.84(2)°, V=3346.81(1)Å3 and Z=2. The structure along the b axis consists of layers of [Bi2O2] units as the basic building block. These are separated by isolated PO4 and LiO4 tetrahedra. The oxygen co-ordination around two of the phosphorus atoms is disordered. Solid-state 7Li NMR studies confirm the presence of lithium in the structure. The material shows ionic conductivity of the order of 10−5Scm−1 at 600°C.

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This paper is devoted to a comparative study of the AxCoO2 (A = Li, Na and K) systems. For x ~ 0.6, all the investigated alkali cobaltites exhibit a metallic-like behavior. Potassium cobaltites exhibit a T2 dependence of the resistivity - suggesting a Fermi liquid character - and an enhanced Pauli type paramagnetism ascribed to electronic correlations. On the other hand lithium and sodium compounds show linear temperature dependence for the resistivity down to 4 K, a large thermopower above room temperature and a Curie-Weiss paramagnetism denoting larger electronic correlations. Physical properties of these cobaltites are discussed in details especially in the case of K-ordered and disordered K0.6CoO2 phases.

Selected recent results on AxCoO2 (A=Li, Na, K) layered cobaltites are reviewed. Potassium ordering was clearly evidenced in K4Co7O14 using usual X-ray diffraction. Magnetic and transport properties reveal very different behaviors depending on the nature of the alkali element. These results are discussed taking into account an interplay between electronic correlations, spin entropy effects, alkali atom ordering, 2D character of the structure and the possible existence of oxygen vacancies that strongly influences the actual average oxidation state of cobalt.

The new compound RbMnPO4 has been synthesized using a solid state route. Its structure has been determined at room temperature by Rietveld refinement of X-ray powder diffraction data. The space group is P21 with the cell parameters a=8.9476(3), b=5.4511(2), c=9.1655(3)Å and β=90.2912(8)°. The framework of RbMnPO4 has the same topology as that of zeolite ABW-type structures. The phosphorus atoms and half of the manganese atoms are located in tetrahedral site and half of the manganese atoms are penta-coordinated, the rubidium atoms are located in the channels.

The high-temperature polymorphs of two photocatalytic materials, BiNbO4 and BiTaO4 were synthesized by the ceramic method. The crystal structures of these materials were determined by single-crystal X-ray diffraction. BiNbO4 and BiTaO4 crystallize into the triclinic system P1¯ (No. 2), with a=5.5376(4) Å, b=7.6184(3) Å, c=7.9324(36) Å, α=102.565(3)°, β=90.143(2)°, γ=92.788 (4)°, V=326.21 (5) Å3, Z=4 and a=5.931 (1) Å, b=7.672 (2) Å, c=7.786 (2) Å, α=102.94 (3)°, β=90.04 (3)° γ=93.53 (3)°, V=344.59 (1) Å3 and Z=4, respectively. The structures along the c-axis, consist of layers of [Bi2O2] units separated by puckered sheets of (Nb/Ta)O6 octahedra. Photocatalytic studies on the degradation of dyes indicate selectivity of BiNbO4 towards aromatics containing quinonic and azo functional groups.

The crystal structures of the title compounds were solved using the single-crystal X-ray diffraction technique. At room temperature CsKSO4Te(OH)(6) was found to crystallize in the monoclinic system with Pn space group and lattice parameters: a = 12.5463(6) angstrom; b = 6.5765(2) angstrom; c = 12.6916(7) angstrom; beta = 106.53(2)degrees; V = 1003.914(4) angstrom(3); Z = 4 and D-calc = 3.29 g/cm(3). The structural refinement has led to a reliability factor of R-1 = 0.0284 (wR(2) = 0.064) for 7577 independent reflections. Rb1.25K0.75SO4Te(OH)(6) material possesses a monoclinic structure with space group P2(1)/a and cell parameters: a = 11.3411(6) angstrom; b = 6.5819(2) angstrom; c = 13.5730(8) angstrom; beta = 106.860(10)degrees; V = 969.62(10) angstrom(3); Z = 4 and D = 3.16(3) g/cm(3). The residuals are R-1 = 0.0297 and wR(2) = 0.0776 for 3336 independent reflections. The main interest of these structures is the presence of two different and independent anionic groups (TeO66- and SO42-) in the same crystal.Complex impedance measurements (Z* = Z'-iZ") have been undertaken in the frequency and temperature ranges 20-10(6) Hz and 400-600 K, respectively. The dielectric relaxation is studied in the complex modulus formalism M*. (C) 2006 Elsevier Inc. All rights reserved.

A solid solution of the type Ba5x/2Bi(1-x)5/3Nb5O15 has been identified in the BaO-Bi2O3-Nb2O5 system for the first time. The limits of the solid solution are within the range 0.52 <= x <= 0.80. The compositions x = 0.52, 0.60, 0.72, 0.77, 0.78, and 0.80 were synthesized by the solid-state technique from the starting materials in stoichiometric quantities. The powder X-ray patterns of all the phases in the domain indicate a structural similarity to tetragonal tungsten bronzes (TTBs). The compositions below x = 0.52 and those above x = 0.80 exhibit barium niobate and bismuth niobate impurities, respectively. Single crystals of the composition x = 0.77 were obtained by the melt cooling technique. The crystal structure of Ba3.85/2Bi1.15/3Nb5O15 (x = 0.77) was solved in the tetragonal space group P4bm (No. 100) with a = 12.4938 (14) angstrom, c = 3.9519 (2) A, V = 616.87 (10) angstrom(3), and Z = 2 and was refined to an R index of 0.034. Dielectric measurements on all the phases indicate a typical relaxor behavior with a broad phase transition at T-m approximate to 300 K.

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The crystal structures of the title compounds were solved using the single-crystal X-ray diffraction technique. At room temperature CsKSO{sub 4}Te(OH){sub 6} was found to crystallize in the monoclinic system with Pn space group and lattice parameters: a=12.5463(6)A; b=6.5765(2)A; c=12.6916(7)A; {beta}=106.53(2){sup o}; V=1003.914(4)A{sup 3}; Z=4 and D{sub calc.}=3.29g/cm{sup 3}. The structural refinement has led to a reliability factor of R{sub 1}=0.0284 (wR{sub 2}=0.064) for 7577 independent reflections. Rb{sub 1.25}K{sub 0.75}SO{sub 4}Te(OH){sub 6} material possesses a monoclinic structure with space group P2{sub 1}/a and cell parameters: a=11.3411(6)A; b=6.5819(2)A; c=13.5730(8)A; {beta}=106.860(10){sup o}; V=969.62(10)A{sup 3}; Z=4 and D=3.16(3)g/cm{sup 3}. The residuals are R{sub 1}=0.0297 and wR{sub 2}=0.0776 for 3336 independent reflections. The main interest of these structures is the presence of two different and independent anionic groups (TeO{sub 6}{sup 6-} and SO{sub 4}{sup 2-}) in the same crystal. Complex impedance measurements (Z*=Z{sup \u0027}-iZ{sup \u0027}\u0027) have been undertaken in the frequency and temperature ranges 20-10{sup 6}Hz and 400-600K, respectively. The dielectric relaxation is studied in the complex modulus formalism M*.

The layered P2-K4Co7O14 oxide has been prepared and characterized by means of X-ray diffraction, electrical conductivity, thermopower, and magnetic measurements. The crystal structure of K4Co7O14 (P6(3)/m space group, Z=2, a=7.5171(1) A, and c=12.371(1) A) consists of a stacking of slabs of edge-shared CoO6 octahedra with K+ ions occupying ordered positions in the interslab space, leading to a a0 radical7xa0 radical7 supercell. Potential energy calculations at 0 K are in good agreement with the ordered distribution of potassium ions in the (ab) plane. This oxide is metallic, and the magnetic susceptibility is of Pauli-type, which contrasts with the Curie-Weiss behavior of the homologous NaxCoO2 (x approximately 0.6) oxide with close alkali content. The thermopower at room temperature is about one-third that of polycrystalline Na0.6CoO2.

The two hitherto unknown compounds Bi14P4O31 and Bi50V4O85 were prepared by the direct solid-state reaction of Bi2O3 and (NH4)H2PO4 or V2O5, respectively. Bi14P4O31 crystallizes in a C-centred monoclinic symmetry (C2/c space group) with the unit-cell parameters: a=19.2745(2)Å, b=11.3698(1)Å, c=52.4082(2)Å and β=93.63(1)° (Z=16). The symmetry of Bi50V4O85 is also monoclinic (I2/m space group) with lattice parameters of a=11.8123(3)Å, b=11.7425(2)Å, c=16.5396(2)Å and β=90.14(1)° (Z=2). Both structures correspond to a fluorite-type superstructure where the Bi and P or V atoms are ordered in the framework. An idealized structural model is proposed where the structures result of the stacking of mixed atomic layers of composition [Bi14M4O31] and [Bi18O27] respectively. This new family can be formulated Bi18−4mM4mO27+4m with M=P, V and where the parameter m (0⩽m⩽1) represents the ratio of the number of [Bi14M4O31] layers to the total number of layers in the sequence. Bi14P4O31 corresponds to m=1 when Bi50V8O85 corresponds to m=1/3. In this last case, the structural sequence is simply one [Bi14V4O31] layer to two [Bi18O27] layers. As predicted by the proposed structural building principle, Bi14P4O31 is not a good ionic conductor. The conductivity at 650 °C is 4 orders of magnitude lower from those found in Bi46M8O89 (M=P, V) (m=2/3) and Bi50V4O85 (m=1/3).

A solid solution (1 - x)LiCdVO4 - xLi(1/3)Cd(1/3)square 1/3CdVO4 has been observed for 0 <= x <= 1. From the cell parameters evolution, two domains of the solid solution have been distinguished with a discontinuity at x approximate to 0.6. The first one for 0 <= x <= 0.6 corresponds to the LiCdVO4 substructure of the Na2CrO4-type. For 0.75 <= x <= 1 satellite peaks are observed which correspond to a modulated structure. The first end-member LiCdVO4 (x = 0) crystallizes in Cmcm space group with a = 5.911, b = 8.975, and c 6.513 A. The structure consists of infinite edge-sharing chains of [CdO6] octahedra linked together by [VO4] tetrahedra and [LiO4] tetrahedra. According to the general formula Li1-2x/3Cdx/3 square x/3CdVO4 of the solid solution, when x increases cadmium replaces lithium in the [LiO4] tetrahedra leading to [(Li/Cd/square)O-4] disordered tetrahedra. All the phases in the domain 0.7 <= x <= 1 are one-dimensionally modulated with wavevector q = gamma c* and gamma values of 0.75, 0.733, and 0.722 for x = 3/4, 6/7 and 9/10, respectively. The superspace group is Xmcm(00 gamma) where X stands for (1/2, 1/2, 0, 1/2) centering. The main structural result is a strong occupation modulation of lithium and cadmium in the tetrahedral site.

The crystal structures of the two oxides Bi46M8O89 (M=P, V) have been solved from single crystals X-ray data at room temperature. Bi46P8O89 crystallizes in the monoclinic symmetry (space group C2/m) with the cell parameters a=19.6073(4)Å, b=11.4181(4)Å, c=21.1119(4)Å and β=112.14(3)°. The symmetry of Bi46V8O89 is also monoclinic but the space group is P21/c with the unit-cell parameters: a=20.0100(4)Å, b=11.6445(4)Å, c=20.4136(4)Å and β=107.27(3)°. Both structures derive from an oxygen deficient fluorite-type structure where the Bi and M cations (M=P, V) are ordered in the framework. The structures are characterised by isolated MO4 tetrahedra (M=P, V) which contradicts the previous results. The difference between the two structures is only due to a different order of the M atoms (M=P, V) in the fluorite-type superstructure. It will be shown that some oxygen sites are partially occupied in both structures which can explain the ion conduction properties of these phases. A structural building principle will be proposed that can explain the large domain of solid solution related to the fluorite-type observed in both systems.

A single crystal of a new sodium calcium iron (III) phosphate, Na4CaFe4(PO4)6, has been synthesized by a flux method and characterized by X-ray diffraction, Mössbauer spectroscopy and magnetic susceptibility measurements. The compound crystallizes in the monoclinic space group C2/c(a=12.099(5)Å, b=12.480(5)Å, c=6.404(2)Å, β=113.77(3)°, Z=2, R1=0.022, Rw2=0.066). The crystal structure belongs to the alluaudite type, characterized by the X(2)X(1)M(1)M(2)2(PO4)3 general formula. The open framework results from Fe2O10 units of edge-sharing FeO6 octahedra, which alternate with M(1)O6 octahedra (M(1)=12Na+12Ca) that form infinite chains. These chains are linked together through the common corners of PO4 tetrahedra yielding two distinct tunnels of sodium cation occupation. This compound is antiferromagnetic with a Néel temperature of 35K. Mössbauer parameters are consistent with the structural results.

The new oxide and oxyhydrate NaRuO2 and NaxRuO2.yH2O (x = 0.22, y = 0.45) have been characterized. NaRuO2 is isostructural with alpha-NaFeO2. The symmetry is rhombohedral (R3m space group) with lattice parameters of a = 3.018(2) A and c = 16.493(3) A. The structure has been refined by the Rietveld method. The oxyhydrate NaxRuO2.yH2O has been prepared by stirring a sample of NaRuO2 in water at ambient temperature. NaxRuO2.yH2O crystallizes in the space group R3m with lattice parameters of a = 2.930(2) A and c = 21.913(5) A. The structure is related to the CuFeO2 3R polytype structure with the AABBCC sequence of the oxygen close packed layers along the c-axis. Analogies with the related cobalt phases are discussed. The susceptibilities of NaRuO2 and NaxRuO2.yH2O are small and constant in a large temperature range.

A new potassium iron phosphate K11Fe15(PO4)18O has been synthesized by the flux method and characterized by single-crystal X-ray diffraction. The compound crystallizes in the cubic system with the space group P213 and the cell parameter a=9.917(2) Å. The unit cell contains one formula unit K7.33Fe10(PO4)12O0.66. The structure is closely related to that of the Langbeinite-like compounds, the main difference being the existence of a four-coordinated iron atom in the structure of the oxyphosphate. K11Fe15(PO4)18O adopts a complex three-dimensional network involving corner- and edge-linkage between iron polyhedra, and corner-sharing between phosphorus tetrahedra and iron polyhedra. The Mössbauer spectral parameters are consistent with the structure and reveal the presence of octahedral and tetrahedral sites for the iron(III) in the expected 4:1 ratio. The thermal variation of the magnetic susceptibility shows that the title compound is antiferromagnetic with a Néel temperature TN=6 K. At high temperature, the susceptibility follows a Curie–Weiss law with C=58.82 emuKmol−1 and θp=−88.39 K. The relationship between the structure of K11Fe15(PO4)18O and the previous reported trivalent vanadium phosphate K11V15(PO4)18O will be discussed.