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International audience; The spin chain oxide Ba 4 CoPt 2 O 9+Δ gathers several features that make it close to a 1D Ising S = 1/2 system: (i) it contains only one type of spins, which are associated to a Kramers doublet with a substantial gap from the first excited state; (ii) these spins exhibit a pronounced uniaxial anisotropy; (iii) their easy-axis is perfectly oriented along the spin chain direction; (iv) the spin chains remain uncoupled down to at least 2 K. It is reported that the magnetic susceptibility, the isothermal magnetization and the specific heat in fields up to 9 T can be well accounted for by the theoretical predictions for 1D Ising S = 1/2 systems, yielding consistent set of values for the Landé factors and the intrachain coupling. The presence of missing spins associated to the oxygen overstoichiometry is taken into account, as well as the polycrystalline nature of the samples which requires to consider angular averages of the anisotropic physical properties.

We report cooperative magnetic orderings in a $6H$-perovskite multiferroic system, ${\mathrm{Ba}}_{3}\mathrm{Ho}{\mathrm{Ru}}_{2}{\mathrm{O}}_{9}$, via comprehensive neutron powder diffraction measurements. This system undergoes long-range antiferromagnetic ordering at ${T}_{N1}\ensuremath{\sim}50\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ with a propagation wave vector of ${K}_{1}=(0.5\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}0)$, a transition temperature much higher than the previously reported one at \ensuremath{\sim}10 K (${T}_{N2}$). Both Ru and Ho moments order simultaneously below ${T}_{N1}$, followed by spin reorientations at lower temperatures, demonstrating strong $\mathrm{Ru}(4d)\ensuremath{-}\mathrm{Ho}(4f)$ magnetic correlation. Below ${T}_{N1}$ another magnetic phase with a propagation wave vector ${K}_{2}=(0.25\phantom{\rule{0.16em}{0ex}}0.25\phantom{\rule{0.16em}{0ex}}0)$ emerges and coexists with the one associated with ${K}_{1}$, which is rarely observed and suggests complex magnetism due to phase competition in the magnetic ground state. We argue that the exchange striction arising from the up-up-down-down spin structure associated with a ${K}_{2}$-wave vector below ${T}_{N2}$ may be responsible for the small ferroelectric polarization reported previously in this compound.

Quintuple perovskites Sm2Ba3Fe5-xCoxO15-δ (x ​= ​0.5, 1.0 and 1.5) have been prepared by glycerin-nitrate technique in air. The phase purity was confirmed by XRD. Partial substitution of Co for Fe decreases the oxygen content and thus the mean oxidation state of 3d-metals. It also slightly decreases the thermal expansion coefficient of oxides. Positive value of the Seebeck coefficient confirmed p-type conductivity, though the thermopower decreases as the Co content increases. The temperature dependence of electrical conductivity reveals a maximum at 550–750°С. © 2021 Elsevier Inc. Russian Foundation for Basic Research, РФФИ: 18-33-00822; Ministry of Education and Science of the Russian Federation, Minobrnauka: 075-15-2019-1924 The work was financially supported in parts from the Ministry of Science and Higher Education of Russian Federation [Agreement No. 075-15-2019-1924 ] and Russian Foundation for Basic Research [project No 18-33-00822 ].

Synchrotron irradiation of the oxide YBaFe4O7.0 below 190 K converts the low temperature monoclinic structure to a higher symmetry tetragonal form analogous to the room temperature structure. This photo-induced metastable tetragonal form is stable even in the absence of irradiation over the range 4–60 K, however, above 60 K the photo-transition is reversible. These structural phenomena are correlated to the magnetic behaviour of this system, suggesting possible spin-lattice coupling. A scenario explaining the low temperature photo-induced transition is proposed, based on the different distributions of the valence electrons in the iron sub-lattice of the monoclinic and tetragonal phases.

The possibility to lift the geometric frustration in the “114” stoichiomeric tetragonal oxide YBaFe4O7.0 by decreasing the temperature has been investigated using neutron and synchrotron powder diffraction techniques. Besides the structural transition from tetragonal to monoclinic symmetry that appears at TS=180 K, a magnetic transition is observed below TN=95 K. The latter corresponds to a lifting of the 3D geometric frustration toward an antiferromagnetic long range ordering, never observed to date in a cubic based “114’” oxide. The magnetic structure, characterized by the propagation vector k1=(0,0,½), shows that one iron Fe2 exhibits a larger magnetic moment than the three others, suggesting a possible charge ordering according to the formula YBaFe 3 + Fe 3 2 + O 7.0 . The magnetic M(T) and χ′(T) curves, in agreement with neutron data, confirm the structural and magnetic transitions and evidence the coexistence of residual magnetic frustration. Moreover, the transport measurements show a resistive transition from a thermally activated conduction mechanism to a variable range hopping mechanism at TS=180 K, with a significant increase of the dependence of the resistivity vs. temperature. Mossbauer spectroscopy clearly evidences a change in the electronic configuration of the iron framework at the structural transition as well as coexistence of several oxidation states. The role of barium underbonding in these transitions is discussed.

Members of the YFe1−xMnxO3 (0≤x≤0.45) family crystallize in the GdFeO3 type orthorhombic perovskite structure (space group Pnma) where the Fe and Mn ions are disordered at the 4b crystallographic site. Upon substitution of Mn at the Fe-site in the canted antiferromagnetic YFeO3 (TN=640 K), a first-order spin-reorientation transition occurs at a temperature, TSR, where the magnetic structure changes from the canted to a collinear state. With increasing Mn-concentration, TSR increases whereas TN decreases. Neutron diffraction studies on the x=0.4 sample reveal that the spin structure changes from Γ4 to Γ1 below TSR. Intriguingly, when x=0.4 and 0.45, a temperature-induced magnetization reversal is observed below a compensation temperature T⁎ (T⁎

The authors demonstrate a compositionally induced superconductor-to-semiconductor transition in the system (Pb{sub 0.75}Cu{sub 0.25})Sr{sub 2}(Ca{sub 1{minus}x}Y{sub x})Cu{sub 2}O{sub 7-{delta}}. Superconducting behavior is observed over the composition range 0.1 {le} x {le} 0.6. Samples with 0.1 {le} x {le} 0.3 are multiphasic, but the superconducting transition temperature is a maximum (55 K) over this range of compositions. The sample having x = 0.5 gives rise to an acceptable phase purity, a superconducting transition temperature of 45 K, and the maximum superconducting (Meissner) volume fraction (20.2%). A superconductor-to-semiconductor transition occurs at x = 0.7.

We report the synthesis, superconducting properties, X-ray diffraction, and microstructure of the Tl2Ba2Ca2Cu3O10−δ phase having Tc of 119 K (an as-synthesized sample) and 127 K (a vacuum-annealed sample). The electron diffraction and [010] bright field image of the 119-K phase indicate a nearly perfect periodicity along the c-axis of Tl2Ba2Ca2Cu3O10−δ. In contrast, the 127-K phase exhibits a significant change in microstructure, where intergrowth defects of Tl2Ba2Cu3Cu4O12−δ and Tl2Ba2Ca2Cu3O9−δ are observed for this vacuum-annealed sample. These kinds of intergrowth defects arising from the unavoidable loss of thallium during the high-temperature (750°C), extended vacuum annealing (10 days) and the resulting oxygen nonstoichiometry appear to play an important role in the enhancement of Tc from 119 to 127 K.

International audience; The investigation of the CaBaCo4-xFex07 oxide shows that a huge decrease of ferrimagnetism is produced for very low Fe contents (x andlt; 0.05) at the benefit of magnetic phase separation and magnetic frustration. This gigantic effect of iron doping at the Co3+ sites in CaBaCo4O7 is compared to that produced by diamagnetic Ga3+ and Al3+ dopants, showing that the antiferromagnetic interactions between the dopant Fe3+ and the Co2+ ferromagnetic chains has a crucial role in the destabilization of the ferrimagnetic structure, whereas the triangular geometry of the cobalt sublattice imposes the appearance of magnetic frustration. © 2015 Elsevier B.V. All rights reserved.

Molybdenophosphates Na 2Y 1-xEu x(MoO 4)(PO 4) and Na 2Y 1-xTb x(MoO 4)(PO 4), were shown to exhibit photoluminescence (PL) properties for a broad substitution range. Under near-UV excitation, Na 2Y(MoO 4)(PO 4):Eu 3+ and Na 2Y(MoO 4)(PO 4):Tb 3+ phosphors show emission lines corresponding to 5D 0? 7F J (J = 0-4, red) and 5D 4? 7F J (J = 4-6, green), respectively. The critical concentrations of Eu 3+ and Tb 3+ are 0.5 and 0.7, respectively beyond which concentration quenching occurs. This behavior is explained on the basis of Eu 3+-Eu 3+ and Tb 3+-Tb 3+ distances. For x = 1, Na 2Tb(MoO 4)(PO 4), emission from the 5D 4 level of Tb 3+ that appears yellow in color is observed. � 2012 The Electrochemical Society.

(Bi0.5Sr0.5)(Fe0.5Mn0.5)O3 crystallizes in a rhombohedral structure, with space group Rc, where the cations Bi3+/Sr2+ and Fe3+/Mn4+ occupy 6a and 6b sites respectively. Neutron diffraction, Mossbauer and magnetization measurements confirm long range antiferromagnetic ordering of the Fe3+ and Mn4+ moments at TN (226 K). Below TN, this oxide exhibits a cluster glass behavior and at low temperatures (∼30 K) a spin glass state is observed. The complex magnetic behavior is attributed to cation disorder in the system. Magnetic properties of this oxide are compared with those of the isostructural Bi0.5La0.5Fe0.5Mn0.5O3 where both Fe and Mn ions exist in trivalent state.

The photoluminescence (PL) studies on NaIn 1-xRE xW 2O 8, with RE=Eu 3, Tb 3, Dy 3 and Tm 3 phases have shown that the relative contribution of the host lattice and of the intra-ff emission of the activators to the PL varies with the nature of the rare earth cation. In the case of Dy 3 and Tm 3 activators, with yellow and blue emission, respectively, the energy transfer from host to the activator plays a major role. In contrast for Eu 3, with intense red emission, the host absorption is less pronounced and the intra-ff transitions of the Eu 3 ions play a major role, whereas for Tb 3 intra-ff transitions are only observed, giving rise to green emission. � 2011 Elsevier Inc. All rights reserved.

Synthesis, crystal structure and optical properties of AgY 0.95Eu 0.05(WO 4) 2-x(MoO 4) x and AgY 1-xEu x(MoO 4) 2 phases with scheelite related structures are described. The 5D 0- 7F 2 electric dipole transition at 615 nm is predominant in the photoluminescence (PL) emission spectra, under 465 nm excitation. The critical concentration of Eu 3+ is x 0.5 in AgY 1-x(MoO 4) 2, beyond which concentration quenching is observed. In AgY 0.95Eu 0.05(WO 4) 2-x(MoO 4) x phases, the 5D 0- 7F 2 emission intensity of Eu 3+ is increased with the increase of Mo content. � 2011 The Electrochemical Society.

The role of sensitization by co-doping Ce 3+ /Eu 2+ in the Sr 2 SiO 4 :Dy 3+ phosphor system is studied with a view of improving the emission properties and chromaticity coordinates. The concentration dependence of the emission intensity of Dy 3+ in Sr 2−2 x Dy x Li x SiO 4 : ( x =0.01–0.05 in steps of 0.01) is studied, and the critical concentration is found to be 3 mol% Dy 3+ per formula unit. Partial energy transfer from Ce 3+ to Dy 3+ is observed, and the luminescence intensity of Dy 3+ is enhanced. It is also found that Eu 2+ , Ce 3+ containing compositions show better white emission than the corresponding Sr 2 SiO 4 :Dy 3+ . LEDs fabricated by coating the ultraviolet (UV) emitting chips with the synthesized phosphor compositions show bright white emission with reasonable chromaticity coordinates.

The ordered oxygen deficient ‘112’ perovskites, LnBaCo2O5·50+δ (Ln = lanthanide or Y), exhibit a very flexible structure which can either uptake (δ > 0) or release oxygen (δ 0 (Co3+/Co4+). The competition between ferromagnetism and antiferromagnetism in these phases and the various transitions are discussed taking into consideration the spin state of cobalt, the issue of phase separation and the effect of cobalt coordination and disproportionation.

A new phase, Li4VO(PO4)2 was synthesized by a lithium ion exchange reaction from protonic phase, VO(H2PO4)2. The structure was determined from neutron and synchrotron powder diffraction data. The exchange of lithium causes a stress, leading to a change in the dimensionality of the structure from 3D to 2D by the displacement of oxygen atoms. Thus, Li4VO(PO4)2 crystallizes in P4/n space group with lattice parameters a=8.8204(1) A and c=8.7614(2) A. It consists of double layers [V2P4O18]∞ formed by successive chains of VO6 octahedra and VO5 pyramids with isolated PO4 tetrahedra. The lithium ions located in between the layers promote mobility. Furthermore, the ionic conductivity of 10−4 S/cm at 550 °C for Li4VO(PO4)2 confirms the mobility of lithium ions in the layers. On the other hand, VO(H2PO4)2 exhibits a conductivity of 10−4 S/cm at room temperature due to the presence of protons in tunnels.

The electrochemical reactivity of the layered titanium hydrogeno phosphate Ti(HPO4)2�H2O versus lithium has been studied. Lithium intercalation occurs at ?2.5 V with low polarization, leading to a new lithiated Ti(III) phase, LiTi(HPO4)2�H2O. Ti(HPO4)2�H2O exhibits a reversible capacity of 80 mAh g-1 in the voltage window 1.8-3.5 V at C/10 rate. The stable reversible capacity reveals that the presence of H2O lattice is not affecting the electrochemical reaction. The reversibility of the reaction is demonstrated by extracting lithium from LiTi(HPO4)2�H2O and the host structure is intact. The electrochemical behaviour of dehydrated phases Ti(HPO4)2 and TiP2O7 has also been investigated. � 2007 Elsevier B.V. All rights reserved.

The cation ordering in the fluorite-like transparent conductors In{sub 4+} {sub x} Sn{sub 3-2} {sub x} Sb {sub x} O{sub 12} and In{sub 6}TeO{sub 12}, was investigated by Time of Flight Neutron Powder Diffraction and X-ray Powder Diffraction (tellurate). The structural results including atomic positions, cation distributions, metal-oxygen distances and metal-oxygen-metal angles point to a progressive cation ordering on both sites of the Tb{sub 7}O{sub 12}-type structure with a strong preference of the smaller 4d {sup 10} cations (Sn{sup 4+}, Sb{sup 5+}, Te{sup 6+}) for the octahedral sites. The corresponding increase of the overall structure-bonding anisotropy is analyzed in terms of the crystal chemical properties of the OM {sub 4} tetrahedral network of the antistructure. The relationships between the M {sub 7}O{sub 12} and the M {sub 2}O{sub 3} bixbyite-type structures are explored. Within the whole series of compositions In{sub 4+} {sub x}M {sub 3-} {sub x} O{sub 12} (M=Sn, Sb, Te) there exists an increase of the symmetry gap between the more symmetrical bixbyite structure and the M {sub 7}O{sub 12} type. This is tentatively correlated with the progressive weakening of thermal stability of these compositions from Sn to Te via Sb. - Graphical abstract: Hexagonal cell of themore » fluorite-like oxygen-deficient M {sub 7}O{sub 12} structure: symmetrical octahedra and distorted sevenfold-coordinated polyhedra are shown.« less

Numerous Structures of Oxides can be built up from the ReO3-Type Framework

The exchange of lithium for proton in VO(H2PO4)2 has been studied. Beside the continuous exchange from VO(H2PO4)2 to Li2H2VO(PO4)2, a new cathode material Li4VO(PO4)2 has been synthesized, whose structure is closely related to that of VO(H2PO4)2. The electrochemical evaluation of Li4VO(PO4)2 vs. Li shows that it undergoes reversible lithium deintercalation/intercalation at high voltage, ∼4.0 V with a reversible capacity of ∼70 mAh/g. Keywords: Li4VO(PO4)2, Ion exchange, Cathode material, Li-ion battery

Nanocrystalline rutile TiO2 is prepared at RT from acidic solution by sol–gel method using titanium tetraisopropoxide as precursor. Samples of varying crystallite sizes are prepared by post annealing the as synthesized rutile TiO2 at different temperatures. The absorption spectra of synthesized samples reveal a large blue shift (311 nm) vis a vis bulk rutile TiO2 (394 nm) indicating the nanocrystalline nature of the material. Electrochemical studies performed at RT show that one Li per formula unit is inserted into the nanocrystalline rutile TiO2. Variation in the voltage profiles is observed with respect to small changes in the crystallite sizes within the nanometric regime. Keywords: Nanocrystalline rutile TiO2, Sol–gel synthesis, Room temperature Li insertion

Combining low-temperature electron (ED) and synchrotron powder diffraction (SPD) techniques, we have precisely determined the phase-separated crystal structure of Pr{sub 0.5}Ca{sub 0.5}Mn{sub 0.97}Ga{sub 0.03}O{sub 3}. We demonstrate that the phase separation is associated with the onset of charge/orbital ordering at {approx}230K and that two ordered phases coexist at low temperature. In order to account for the significant anisotropic linewidth broadening observed in the SPD patterns, we had to include a specific strain model in the refinements. One of the phases, the most severely strained, is suggested to result from an imperfect charge ordering.

A new transparent conductor, containing pentavalent antimony, In{sub 4+x}Sn{sub 3-2x}Sb{sub x}O{sub 12}, has been synthesized for 0=

The first member of the Ruddlesden–Popper family, Ca2MnO4, has been revisited. Coexistence of two structures has been shown from electron microscopy at room temperature and neutron diffraction data have evidenced two antiferromagnetic structures at low temperature. Two forms, with an orthorhombic Aba2 ( a≈b≈a p 2 and c≈12 A) and a tetragonal I41/cad ( a≈a p 2 and c≈24 A) symmetries, were found to coexist coherently within the same matrix.

A new sodium hydroxygallophosphate, Na 3 Ga 4 O(OH)(H 2 O)(PO 4 ) 4 ·H 2 O, has been prepared by hydrothermal synthesis. Its structure has been determined from a single-crystal X-ray diffraction study. It crystallizes in the P 2 1 / c space group with the cell parameters a =9.445(2) A, b =9.028(1) A, c =19.209(3) A, β =102.08(2), V =1603.4(4) A 3 . Its three-dimensional framework can be described from PO 4 monophosphate groups sharing their apices with original Ga 4 O 16 (OH)(H 2 O) tetrameric building units, which result from the assembly of one GaO 4 tetrahedron, one GaO 5 trigonal bipyramid and two octahedra: GaO 5 (OH) and GaO 4 (OH)(H 2 O). The sodium cations and one water molecule are located in tunnels running along b .

A new sodium gallophosphate, NaGa 2 (OH)(PO 4 ) 2 , has been obtained by hydrothermal synthesis under autogeneous pressure at 473 K. It crystallizes in the P 2 1 / n space group with the cell parameters a =8.9675(8) A, b =8.9732(5) A, c =9.2855(7) A, β =114.812(6)°, V =678.2 A 3 ( Z =4). In its original three-dimensional framework, monophosphate groups share their apices with [Ga 4 O 16 (OH) 2 ] tetrameric units, which are built from two GaO 5 (OH) octahedra and two GaO 4 (OH) trigonal bipyramids. The sodium cations are located in tunnels running along a , whereas the tunnels running along b are empty.

A molybdenum (IV) phosphate containing lead, Pb 2 Mo 2 (PO 4 )2P 2 O 7 , has been synthesized for the first time. It crystallizes in the space group C 2/ c with a =14.098(1) A, b =14.187(2) A, c =6.5592(4) A and β =102.08(1)°. Its original tunnel structure, built up of Mo 2 O 11 bioctahedra, P 2 O 7 and PO 4 phosphate groups can be described from the assemblage of [Mo 4 P 4 O 24 ] ∞ ribbons interconnected through monophosphate groups. The stereoactivity of the 6 s 2 lone pair of Pb 2+ , which is surrounded by nine oxygen atoms, is discussed.

The investigation of the n =1 member of the Ruddlesden Popper family, Pr 1− x Ca 1+ x MnO 4 , using electron microscopy, transport and magnetic measurements shows that these 2D manganites exhibit long-range charge–orbital ordering over a wide composition range (0.50⩽ x ⩽0.80). These oxides show a remarkably high T CO temperature depending on the x value, up to 330 K, the highest that has been observed to date in 2D manganites. They are characterized by the appearance of a smooth structural transition from P- to C-type inside the charge-ordered state. The high-resolution electron microscopy images of Pr 0.5 Ca 1.5 MnO 4 registered at room temperature evidence a system of double stripes similar to those observed for Bi 0.5 Sr 0.5 MnO 3 , suggesting that double stripes of one sort of manganese alternate with double or quadruple stripes of a second sort of manganese.

Sodium insertion in the tetrahedral layer structure of the ferrites Ba 2− x Sr x Fe 4 O 8 was performed by solid state reaction at 1220 K in air. Superstoichiometric oxides with the actual formula (Ba 2− x Sr x ) 1−y/4 Na y Fe 4 O 8 — y ⩽0.56; 0.60⩽Ba/Sr⩽1.67—were characterized by X-ray and neutron powder diffraction. The hexagonal unit-cell volume shows an increasing dependence on the sodium insertion when the Ba/Sr ratio reaches the largest values. The marked expansion of the c parameter is the likely signature of the location of the inserted sodium cations within the interlayer space. One-half of the sodium cations partly sits on the Sr(Ba) sites in octahedral coordination and the other half occupies extra octahedral and tetrahedral sites. ac conductivity measurements point to a cationic conductivity whose thermally activated regime— E a ♯ 0.7 eV—evidenced from 570 K, is unsensitive to the sodium content. The bottleneck of the 2D sodium mobility regards the crossing of the oxygen triangular faces shared by the different polyhedra within the interlayer space.

The possibility to synthesize layered oxycarbonates, with nominal composition Sr 4 Fe 2− x Mn x O 6 CO 3 involving trivalent manganese, with 0≤ x ≤1.5, is reported for the first time. The structural study of Sr 4 FeMnO 6 CO 3 using NPD, HREM, Mossbauer and XANES, shows that this phase is closely related to n =3 member of the Ruddlesden–Popper family. It derives from the latter by replacing the middle layer of transition metal octahedra by triangular CO 3 groups, with two different “flag” and “coat hanger” configurations. The magnetic order is antiferromagnetic and fundamentally different from the magnetic behavior of Sr 4 Fe 2 O 6 CO 3 .

The exploration of the Hg–Sr/Ca–Co–O system using EDS and electron microscopy has shown the possibility to incorporate mercury and excess cobalt in the middle rock salt layer of the misfit cobaltite structure, leading to the new series [Hg1−xCoxSr2−yCayO3]RS[CoO2]b1/b2 with 0.6⩽x⩽0.90, 0⩽y⩽2, and b1/b2 ranging from 1.63 to 1.79. These new composite oxides, built up from [CoO2]∞ layers of the CdI2-type stacked with triple [Hg1−xCoxSr2−yCayO3]. rock salt layers are remarkable by their large thermopower S values similarly to the thallium and lead misfit cobaltites. More importantly, the S value is sensitive to the composition of the triple rock salt layer, increasing as the calcium content increases, so that an enhancement of the figure of merit of the pure calcium compound is expected.

A new manganese oxide Ba7Ca2Mn5O20, with an original structure derived from the 21 L hexagonal perovskite, has been synthesized and studied by XRPD and HREM. This rhombohedral phase (R 3 m), with a=5.8207(2) A and c=51.359(1) A, consists of [BaO3] (h and c) layers and [BaO2] (c′) layers with a (hhccc′cc)3 stacking sequence. This structure is closely related to that of Ba8Ca1.8Mn6.2O23−δ, containing identical blocks “Ba5Ca2Mn3O14” built up of layers of corner-sharing CaO6 octahedra, MnO6 octahedra and MnO4 tetrahedra. Both oxides can be described as the members n=2 and 3 of the new structural family Ba5+nCa2Mn3+nO3n+14 , which differs from the hexagonal perovskite family by its bidimensional character, due to the disconnection of the MnO4 tetrahedra layers. The charge distribution of manganese, Mn3+/Mn4+ in octahedra and Mn5+ in tetrahedra is a particular feature of this structure.

A series of non-hydrated triphosphates containing cesium, Cs 2 M P 3 O 10 ( M =Ga, Al, Cr), has been synthesized for the first time. Their original structure crystallizes in the space group P 2 1 / c , with a ≈12.3 A, b ≈9.0 A, c ≈9.5 A and β ≈95°. The [ M P 3 O 10 ] ∞ layers built up of corner-sharing M O 6 octahedra and tritetrahedral P 3 O 10 groups can be described from M P 3 O 13 units in which one M O 6 octahedra shares the three corners of one face with one P 3 O 10 group. The open character of the layers makes that Cs + cations are not only interleaved between the layers, but also located in the pseudo-tunnels they present.

The Ho0.5Sr0.5MnO3 perovskite, synthesized in air, has been studied by combining neutron powder and electron diffraction techniques. The Pnma-type structure exhibits a strong tilting of the MnO6 octahedra. This octahedra tilting and microtwinning involve a complex strained structure. No structural transition is observed down to 1.4 K, but short-range A-type antiferromagnetism running over only a few perovskite subcells is evidenced below ≈90 K. The different behavior of this perovskite compared to other Ln0.5Sr0.5MnO3 perovskites is discussed in terms of A-site cationic mismatch.

An experimental study of the low T magnetic field dependence of the magnetization, specific heat and resistivity for an orbital and charge-ordered perovskite manganite doped in the Mn-site is presented. Well-defined steps are found in all these three physical properties. The abruptness of these jumps for T

A copper uranyl monophosphate, Cu2UO2(PO4)2, has been synthesized for the first time. It crystallizes in the space group C2/m with a=14.040(1) A, b=5.7595(4) A, c=5.0278(5) A and β=107.24(1)°. Its original structure consists of [CuO2]∞ puckered chains of edge-sharing CuO4 groups running along b, interconnected with [UP2O10]∞ ribbons. The coordination of uranium is characteristic of the [UO2]2+ uranyl ion, forming flattened UO6 octahedra, whereas the planar CuO4 groups exhibit a rectangular configuration. This compound shows original antiferromagnetic interactions at low temperature, due to the presence of [CuO2]∞ chains, but the latter are more complex than those of 1-D spin 1 2 chains.

A new vanadium (V) hydroxymonophosphate hydrate, K 3 (VO 2 ) 2 PO 4 PO 3 OH·H 2 O, with a “tape-like” structure has been synthesized. This compound crystallizes in the space group P 2 1 / c with a =5.099(1) A, b =29.168(3) A, c =8.115(1) A, β =91.65(1)°. Its structure consists of [V 2 P 2 O 11 OH] ∞ ribbons built up of corner-sharing VO 5 pyramids, PO 4 , and PO 3 OH tetrahedra, interleaved with K + ions and H 2 O molecules. In spite of its unidimensional character, this structure forms pentagonal tunnels. Relationships with frameworks involving tetragonal tunnels are studied.

Air-synthesised La 0.5 Ca 0.5 MnO 3 and Ar/H 2 annealed La 0.5 Ca 0.5 MnO 2.85 are studied by electron diffraction versus temperature and by high-resolution electron microscopy at low temperatures. The results are correlated to magnetisation measurements, in order to elucidate the influence of oxygen content on the charge ordering process. The way a reduction of the oxygen content favours La 0.5 Ca 0.5 MnO 3− δ ferromagnetically and suppresses charge ordering at low temperatures is studied. The difference between La 0.5 Ca 0.5 MnO 3− x , other Ln-elements of the Ln 0.5 Ca 0.5 MnO 3−δ series and doped materials is discussed. Lattice images obtained for both samples at low temperature reveal the nanostructural aspects of a change in oxygen stoichiometry.

A molybdenum(V) monophosphate containing lead has been synthesized for the first time. This new phase Pb3(MoO)3(PO4)5 crystallizes in the Pnma space group with a=14.280(1) A, b=15.679(1) A, and c=8.129(1) A. The crystal structure was refined up to R=0.0406 and Rw=0.0446. The original three-dimensionnal framework of this compound, [Mo3P5O23]∞, can be described by the assemblage of [Mo3P5O28]∞ ribbons running along b→ and forming elliptic tunnels where the Pb2+ cations are located. The topological analogy of this structure with aeschynite is emphasized. The stereoactivity of the 6s2 lone pair of Pb2+ is discussed.

International audience; Sodium insertion into the vanadate NaVO3 shows the formation of an amorphous phase with the composition Na1.5 + yVO3. The latter phase exhibits reversible electrochemical sodium intercalation/de-intercalation properties through a solid solution-like process, for 0 \textless y \textless 0.7, with redox cycling at 1.8 V vs. Na+/Na and a capacity of 150 mAh/g. This result opens the route to the investigation of amorphous matrices involving transition metal oxides for sodium ion battery applications. (C) 2013 Elsevier B.V. All rights reserved.

A novel lead vanadophosphate, PbVOP2O7, has been synthesized. This phase crystallizes in the Pnma space group with a=8.899(1) A, b=7.534(1) A, and c=9.142(1) A. The [VP2O8]∞ framework consists of ReO3-type [VO3]∞ chains running along b>→, interconnected through P2O7 groups forming large intersecting tunnels running along b→, a→, and c→, respectively, where the Pb2+ cations are located. This is the second lead vanadophosphate, beside Pb(VO)3(P2O7)2, that consists of [VO3]∞ chains interconnected by P2O7 groups.

The new phosphovanadate Co(NH3)6(V1.5P0.5)O6OH has been synthesized by a hydrothermal method at 220°C. It crystallizes in the P21/c space group with a=9.5206(8), b=6.9631(6), c=17.108(1), β=93.028(7), and Z=4. The structural resolution using single-crystal X-ray diffraction leads to R(Fo)=3.63% and Rw(F2o)=10.67%. This structure consists of [Co(NH3)6]3+ cations and [V1.5P0.5O6OH]3− anions assembled in a distorted rock salt arrangement. The presence of the Co(III) hexammine complex [Co(NH3)6]3+ is particularly original in this structure since no complexes have been isolated up to now in phosphovanadates. The V1.5P0.5O6OH diphosphovanadate group, with one vanadium tetrahedral site and one tetrahedral site statistically occupied by 0.5 vanadium and 0.5 phosphorus atom, corresponds to the random distribution of V2O6OH and VPO6OH groups as confirmed by the IR spectroscopy study. Magnetic measurements show that the Co(III) cation adopts a low spin configuration.

We have investigated the role of the stress-induced by the presence of the substrate in thin films of colossal magnetoresistive manganites on structural, resistive and magnetic properties. Because of the strong coupling between the small structural distortions related to the charge-ordering (CO) and the resistive properties, the presence of the substrate prevents the full developpement of the charge ordering in Pr$_{0.5}$Ca$_{0.5}$MnO$_{3}$, especially in the very thin films. For thicker films, the CO state exists, but is not fully developped. Correlatively, the magnetic field which is necessary to suppress the CO is decreased drastically from 25 Tesla to about 5 Tesla on SrTiO$_{3}$ substrates. We have also investigated the influence of the doping level by studying the case of Pr$_{0.6}$Ca$_{0.4}$MnO$_{3}$.

Thin films of the charge-ordered (CO) compound ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}$ have been deposited onto (100)-oriented ${\mathrm{SrTiO}}_{3}$ substrates using pulsed laser deposition. Magnetization and transport properties are measured when the thickness of the film is varied. While the thinner films do not exhibit any temperature-induced insulator-metal transition under an applied magnetic field up to 9 T, for thickness larger than 1100 \AA{} a 5 T magnetic field is sufficient to melt the CO state. We have established the temperature-field phase diagram and compared it to the bulk material. It indicates that the robustness of the CO state in thin films depends strongly on the strains and the thickness. We proposed an explanation based on the distortion of the cell of the film.

A new mixed valent chromium-layered oxide, Sr 4.5 Cr 2.5 O 9 , with a structure closely related to the “0201–1201” structure of the superconducting cuprate TlBa 2− x La 2+ x Cu 2 O 9 , has been synthesized at normal pressure. This orthorhombic phase ( a =10.7959(2) A, b =5.4012(1) A, and c =30.0755(6) A) consists of the regular intergrowth of [Sr 2 CrO 4 ] 0201 blocks and [(Sr 0.5 Cr 0.5 )Sr 2 CrO 5 ] 1201 blocks. It differs from the thallium cuprate by the 1:1 ordering of Sr and Cr species within the intermediate layer of the “1201” block, so that at this level CrO 4 tetrahedra, containing Cr 6+ species, are obtained. Moreover, at the boundary between the “1201” and “0201” blocks, CrO 6 octahedra alternate with CrO 5 pyramids, both occupied by Cr 3+ species. The magnetic measurements show an original metamagnetic transition from an antiferromagnetic to a weak ferromagnetic state. These properties are interpreted in terms of strong intralayer and weak interlayer magnetic couplings between Cr 3+ species through a superexchange mechanism.

We have observed a superstructure derived from the compound Tl0.75Sr1.8Ba0.2CuO(y). This compound arises from the 'collapse' of the parent oxynitrate compound TlSr2Ba2Cu2O7 (NO3) under controlled thermal decomposition. A combined X-ray and neutron powder diffraction study of the title compound indicates that the superstructure possesses the Pmmm space group, with unit cell parameters (derived from neutron diffraction data) of a = 3.7362(3) Å, b = 11.5449(9) Å, and c = 9.1494(8) Å. This superstructure takes the form of a three-fold repeat along the crystal b-axis produced through local distortions of the thallium and barium/strontium positions. This compound is nonsuperconducting due to the presence of a large number of vacancies in the electronically active copper-oxygen planes. (C) 2000 academic Press.

The electron microscopy study of the Ru-doped manganites Sm 0.2 Ca 0.8 Mn 1− x Ru x O 3 (0≤ x ≤0.10) shows that the magnetic properties of these materials are strongly correlated to their microstructure. Charge ordering induced by Mn-site doping is shown for the first time, in contrast to what is generally observed. It is shown that Ru-doping paradoxically favors the simultaneous development of ferromagnetic orthorhombic domains and charge-ordered antiferromagnetic domains at low temperature, starting from a monophasic orthorhombic paramagnetic sample at room temperature. This structural phase separation phenomenon at low temperature is explained in terms of two antagonist effects introduced by Ru 5+ substitution: ferromagnetic superexchange interactions and Mn valency.

A new form of WPO 5 has been synthesized which is to our knowledge the second pentavalent tungsten phosphate actually known. This phase is isotypic to CsP 8 W 8 O 40 and consequently can be described as a tungsten diphosphate, W 2 O 3 ·P 2 O 7 , with large empty eight-sided tunnels. Although it fundamentally differs from the first form, which is a monophosphate, WOPO 4 , the two structures are closely related by the existence of ReO 3 -type chains and slices, interconnected by P 2 O 7 or PO 4 groups, respectively. The stabilization of such an opened structure by adducts such as PbF 2 or KBr is discussed.

Charge ordering (CO) between Fe3+ and Fe5+ species and magnetotransport transition have been shown for the first time in the perovskite Sm1/3Sr2/3FeO3−δ by electron diffraction microscopy, by 57Fe Mossbauer spectroscopy, and by measurements of transport and magnetic properties. This compound is charge ordered at TCO=110 K, which is significantly lower than the temperature TN=150 K of the magnetotransport transition. A charge disproportionation 2Fe4+↔Fe3++Fe5+ is evidenced by Mossbauer spectroscopy. The electron diffraction study shows the coexistence of orthorhombic and rhombohedral-type domains. A comparison with the other lanthanides (La, Pr, Nd) is also made. This suggests that the size of the Ln3+ ion is not the only parameter which governs the charge ordering in these perovskites, but the oxygen stoichiometry, which influences the Fe5+ formation, may also play a role in the CO phenomenon.