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International audience; The recent paper by Deng et al. showed that a copper sulphide with Cu7Sn3S10 composition is a promising thermoelectric material reaching a figure of merit ZT of 0.8 at 750 K via Cl doping. However, structural reinvestigations of the Cu7Sn3S10 sample (i.e., Cu2.10Sn0.90S3) prepared in the reported conditions show that the phase of interest is not tetragonal (space group I (4) over bar 2m, a(t) = 5.4164 angstrom, c(t) = 10.832 angstrom), but crystallizes in the cubic symmetry (space group P (4) over bar 3n, a(c) = 10.832 angstrom) with a composition close to Cu22Sn10S32 similar to the results published by Pavan Kumar et al. These observations indicate that the main phase around the composition Cu7Sn3S10 is cubic, and a revision needs to be imposed for the understanding of the relationships between the structure and thermoelectric properties in this family.

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 ].

International audience; Formation of five-layered Ln 2–ε Ba 3+ε Fe 5 O 15–δ phases [exhibiting nanoscale ordering with layer-by-layer location of the cations in the Ln–Ba–(Ln,Ba)–(Ln,Ba)–Ba–Ln perovskite-type structure] has occurred in the Ln–Ba–Fe–O (Ln = Y, Pr, Nd, Sm, Eu, and Gd) systems at 1100°С in air. Partial substitution of iron with cobalt (Ln 2–ε Ba 3+ε Fe 5–y Co y O 15–δ , Ln = Nd, Sm, Eu) has stabilized formation of the ordered structure. The oxygen content in the complex oxides has been determined in air over a wide temperature range by means of high-temperature thermogravimetry and iodometric titration. The change in oxygen content with temperature for the phases with five-layered ordering was significantly smaller than for the disordered phases. © 2016, Pleiades Publishing, Ltd.

$\mathrm{S}{\mathrm{r}}_{2}\mathrm{C}{\mathrm{a}}_{2}\mathrm{CoM}{\mathrm{n}}_{2}{\mathrm{O}}_{9}$ is made of Ising spin chains distributed on a triangular lattice, with antiferromagnetic coupling between them. In spite of a unique interchain distance, this compound exhibits two peculiarities making it deviate from the textbook case of geometrical frustration expected in ideal triangular lattices: first, there are three subclasses of chains shifted from each other along the chain direction; second, these chains fall into two categories which differ by some of the intrachain distances between spins. These features are found to confer a character of centered honeycomb lattice on this system of spin chains. Experimental investigation of the magnetism of $\mathrm{S}{\mathrm{r}}_{2}\mathrm{C}{\mathrm{a}}_{2}\mathrm{CoM}{\mathrm{n}}_{2}{\mathrm{O}}_{9}$ reveals a peculiar pretransitional regime, which is manifested by a frequency-dependent peak of susceptibility. We put this behavior in relation with the formation of short-range one-dimensional ferromagneticlike segments taking place a few degrees above the ${T}_{N}$. This phenomenon is itself regarded as a precursor effect of the long-range ordering, induced by the particular topology of the spin system.

Bornite Cu

Accessed by 09/2014; International audience; Insertion of lithium into the jarosite hydroxysulfate NaFe3(SO4)2(OH)6 leads to an amorphous phase Li2+xNaFe3(SO4)2(OH)6 (with 0 < x

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.

In this study, we show the dramatic effect of the doping of the octahedral sites with M3+ cations (Fe3+, Al3+ and Cr3+) upon the structure and magnetism of the rhombohedral double perovskite CaMn7O12. In the oxides CaMn7−xMxO12, charge ordering between Mn3+ and Mn4+ octahedral sites is destroyed leading to the cubic structure (Im-3), whereas the initial magnetic properties (TN~90 K) have disappeared leading to canted antiferromagnetism (TN≈50–70 K) for small x values (x ~0.2–1). A spin glass like behaviour is also observed for larger values (x~1) in the case of Fe substitution.

Polycrystalline “112” ordered oxygen deficient double perovskites YBaCo2−xMexO5+δ (Me = Fe, Cu, Ni) were synthesized by a glycerol-nitrate route with 0.0 ≤ x ≤ 0.7 for Me = Fe, 0.0 ≤ x ≤ 0.6 for Me = Cu and x = 0.1 for Me = Ni. The combined X-ray diffraction, electron microscopy and thermo-gravimetric studies show that all these oxides exhibit the ap × ap × 2ap tetragonal structure (S.G. P4/mmm); moreover, the oxygen content increases continuously with x in the iron-substituted oxide YBaCo2−xFexO5+δ, whereas the opposite is observed for the copper phase YBaCo2−xCuxO5+δ. This difference, which is due to the more electropositive character of Fe3+ compared to Cu2+, is hindered in the Ni2+ case due to its inability to accommodate the pyramidal coordination. The changes of the conductivity of these compounds versus temperature are closely related to their oxygen loss, in agreement with a defect structure model suggested earlier. Thermal expansion measurements prove the absence of phase transition in all oxides within the temperature range studied. The chemical compatibility of YBaCo1.4Fe0.6O5+δ with the electrolyte Ce0.8Sm0.2O2−δ is also demonstrated.

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.

The investigation of strongly sintered “quasi molten” CuS and CuSe chalcogenides shows that they exhibit a sharp diamagnetic transition and a resistivity drop around 40 K. The reminiscence of such high temperature superconductivity features, never observed to date for these phases, is strongly supported by two chemical characteristics: bidimensionality of the structure and mixed valency of copper. The absence of zero resistance suggests that the internal chemical pressure in the samples has a key role in the existence of superconductivity: the S–S or Se–Se interlayer distances are very sensitive to the pressure, so that the critical distance for the percolation can be reached in the core of the samples, but not at the vicinity of the surface, where relaxation may appear.

Indium oxide ceramics doped with different doping levels of germanium (from 0 to 10 at.%) were prepared with nano-sized powders obtained by citrate gel process. Ge for In substitution in the In 2 O 3 bixbyite structure below the solubility limit (about 0.5–1 atom%) leads to a large decrease in the electrical resistivity and the absolute value of the Seebeck coefficient. X-ray diffraction and scanning electron microscopy show the presence after sintering of well dispersed secondary phases In 2 Ge 2 O 7 when the Ge solubility in the In 2 O 3 matrix is passed. The thermal properties measurements confirm that the decrease in the lattice thermal conductivity observed in these composite materials can be attributed to the presence of insulating In 2 Ge 2 O 7 phases. Furthermore, preliminary microwave sintering experiments have been tested in order to keep the nanoscale after sintering. Particular nano–microstructures were obtained due to minimal grain growth induced by this rapid sintering process.

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 exploration of the systems Fe-H-P-O, Li-Fe-H-P-O, and K-Fe-H-P-O using soft chemistry methods has allowed three new hydrogenophosphates to be synthesized, whose structures have been determined by ab initio calculations. The structures of two of them--FeH(2)P(2)O(7) and LiH(3)Fe(P(2)O(7))(2)--exhibit close relationships: their 3D framework consists of [FeO(4)](infinity) and [LiFe(2)O(12)](infinity) chains of edge-sharing octahedra, respectively, interconnected through diphosphate groups. These two diphosphates exhibit a paramagnetic to antiferromagnetic transition at low temperatures. The former phase exhibits intrachain ferromagnetic interactions (theta(p) > 0) in competition with the antiferromagnetic interchain ordering, whereas for the second one, the ferromagnetic interactions have disappeared due to the presence of Li in the chains. Differently, the third phosphate, K(2)Fe(HP(2)O(7))(H(2)PO(4))(2), exhibits a chain structure, involving isolated FeO(6) octahedra, and consequently is paramagnetic in the whole temperature range (4-300 K). Among these three phosphates, only the latter exhibits ionic conductivity, which may originate from the proton mobility.

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.

The effect of calcium doping upon the magnetic and transport properties of the smaller size lanthanide cobaltites of the type Ln1−xCaxBaCo2O5.50+δ (Ln=Dy and Ho) has been investigated for 0 ≤ x ≤ 0.2 . The substitution of Ln by calcium induces a large deterioration of the long-range magnetic ordering in the system finally leading to a paramagnetic state. Such instability in the magnetic ordering could be related to strong bending of the Co–O–Co bond, the local lattice distortion and the random vacancies in oxygen sublattice. The present results suggest that not only the cobalt valence but also the size of the lanthanide and the local lattice distortion play a crucial role in determining the physical properties of this layered cobaltite.

A new mixed-valence ferrite, YBaFe4O7, has been synthesized. Its unique cubic structure, with a = 8.9595(2) Å, is closely related to that of the hexagonal 114 oxides YBaCo4O7 and CaBaFe4O7. It consists of corner-sharing FeO4 tetrahedra, forming triangular and kagome layers parallel to (111)C. In fact, the YBaFe4O7 and CaBaFe4O7 structures can be described as two different ccc and chch close packings of [BaO3]∞ and [O4]∞ layers, respectively, whose tetrahedral cavities are occupied by Fe2+/Fe3+ cations. The local structure of YBaFe4O7 is characterized by a large amount of stacking faults originating from the presence of hexagonal layers in the ccc cubic close-packed YBaFe4O7 structure. In this way, they belong to the large family of spinels and hexagonal ferrites studied for their magnetic properties. Differently from all the ferrites and especially from CaBaFe4O7, which are ferrimagnetic, YBaFe4O7 is an insulating spin glass with Tg = 50 K.

A new form of CaTe2O5 (ɛ) has been synthesized by hydrothermal method and its crystal structure has been solved and refined from single crystal X-ray diffraction data. ɛ-CaTe2O5 crystallizes in a monoclinic unit cell (P21/c; a = 9.4639(4) A; b = 5.7566(3) A; c = 11.2280(4) A; β = 115.14(1)°) different from those already reported in the literature for four CaTe2O5 polymorphs. Its unique layered structure can be described by the stacking along the a-axis of [Te2O5]∞ layers interleaved with [Ca]∞ layers. Inside the [Te2O5]∞ layers, large tunnels extend along the [010], [011] and [ 01 1 ¯ ] directions, respectively. They result from the association of TeO4E distorted bipyramids where E denotes the Te(IV) electron lone pair. Ab initio density functional (DFT) calculations show that the electron lone pairs sit in the tunnels and in the tunnel walls along the [010], [011] and [ 01 1 ¯ ] directions.

The outermost member of the 112 family LaBaCo2O5.5 has been synthesized using a multistep method to stabilize its structure. Its structural study, combining neutron powder diffraction and electron microscopy, shows that its orthorhombic matrix consists of layers of corner-shared CoO6 octahedra interconnected through CoO5 pyramids like in the other 112 cobaltates but contains small LaBaMn2O5.5-type domains (8%) due to local oxygen displacement. Its magnetic properties and magnetic structure evidence the following features: G-type antiferromagnetic/G-type ferrimagnetic/paramagnetic with TN = 260 K and TC = 326 K. This cobaltate differs from other 112 cobaltates by its antiferromagnetic structure which keeps the same symmetry as its ferrimagnetic phase, probably due to the size effect of La3+ upon crystal field. Trivalent cobalt is shown to keep the intermediate spin state in the whole temperature range from 10 to 326 K.

The effect of calcium doping on the magnetic and transport properties of the intermediate size lanthanide cobaltites of the type Ln 1− x Ca x BaCo 2 O 5.50± δ (Ln=Y, Gd, Eu and Sm) has been investigated for 0⩽ x ⩽0.2. The substitution of Ln by calcium induces a large expansion of the ferromagnetic state in the whole temperature range below T C . The unusual trend of the decrease in T C with the increase in Ln size in the undoped parent oxides becomes opposite in the calcium doped samples. Such an unusual behavior of the ferromagnetic T C in the parent compounds is explained on the basis of thermally activated hole-mediated ferromagnetic coupling between the high-spin cobalt ions. The ferromagnetic state of the Ca-doped samples originates from the Co 3+ –O–Co 4+ superexchange interaction, where Co 4+ emerges from the disproportionation mechanism of the cobalt Co 3+ into Co 2+ and Co 4+ . However, the Ca-doping does not significantly affect the metal–insulator transition, which is associated with the structural change and not related to the spin state transition.

Similar to the A-site and Mn-site substitution in orbital–charge ordered (OO–CO) polycrystalline Pr0.5Ca0.5MnO3, the decrease in x from x = 0.50 in Pr1−xCaxMnO3 can also induce sharp magnetization steps. It has been interpreted by a martensitic-like mechanism based on phase separation. With the decrease in x , the ideal Mn3+/Mn4+=1:1 orbital–charge ordering will be weakened, which is due to the disorder created by the extra Mn3+ cations. Therefore, small ferromagnetic (FM) regions with higher symmetrical structure can be induced in the antiferromagnetic (AFM) OO–CO matrix with a strongly distorted structure. Due to their different symmetry, the strains will be created at the interface between the FM regions and the AFM matrix. In a magnetic field, the FM domains cannot grow continuously because of the existence of the interfacial strains. In order to achieve their further growth, a higher magnetic field must be applied to overcome the interfacial strains. As a result, sharp magnetization steps will appear in magnetization versus magnetic field curves of Pr1−xCaxMnO3. The x is smaller, the stability of the OO–CO phase is weaker, and then the interfacial strains become lower. Consequently, the critical magnetic field corresponding to the step appearance will decrease. Furthermore, the existence of the additional OO–CO state, which was recently reported by Asaka et al. [T. Asaka, S. Yamada, S. Tsutsumi, C. Tsuruta, K. Kimoto, T. Arima, T. Matsui, Phys. Rev. Lett. 88 (2002) 97201], has not been supported by our magnetic results and microscopic studies.

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.

Multiferroics are materials which display simultaneously ferroelectricity and ferromagnetism and possess the multiferroic coupling. However, availability of these materials are rare. Thus, designing the materials with these extraordinary properties is a big challenge. In the present paper, we address the basic question as to how one can design the artificial multiferroics by an alternative technique, namely the superlattice approach. We show such a possibility by taking the examples of our work on the superlattices composed of the ultrathin layers of La 0.7 Ca 0.3 MnO 3 and BaTiO 3 . Films were grown on SrTiO 3 at 720 °C and 100 mTorr O 2 partial pressure by pulsed laser deposition technique. Films are characterized by the various techniques for their structural and physical properties. The origin of the multiferroism in these structures will also be described.

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

Electron magnetic resonance (EMR), neutron powder diffraction (NPD) and ac susceptibility techniques were employed for studying the crystallographic structure and magnetic ordering in CaMn1−xRuxO3 (x ≤ 0.40) manganite system. EMR measurements were done on polycrystalline samples at 120 ≤ T ≤ 500 K. High temperature EMR spectra of pristine antiferromagnetic (AFM) CaMnO3 show a singlet Lorentzian-like line, whose intensity diminishes, zeroing at Neel temperature TN=120 K. Strong broadening of paramagnetic (PM) lines with increase of Ru-content (Δ Hpp ∼ 1 T for x=0.10) was found. Upon cooling low-doped (x ≤ 0.06) samples remain AFM, whereas higher doped ones (0.10 ≤ x ≤ 0.40) clearly show progressive appearance of ferromagnetic (FM) phases. Thus, EMR evidences that Ru-doping modifies both PM and AFM states and creates an inhomogeneous phase separated FM and AFM ground states at x0.06. Complementary measurements of NPD and ac susceptibility corroborate the complex character of magnetic ordering, revealed by EMR. The changes of the magnetic ordering in CaMn1−xRuxO3 supposed to be solely determined by doping of Mn-sites with Ru.

The magnetic properties of the Nd0.5Ca0.5−xBaxMnO3 series have been investigated. Similar to the Pr0.5Ca0.5−xBaxMnO3 series (Raveau et al., J. Phys.: Condens. Matter 15 (2003) 7055), the substitution of Ba for Ca can also induce a ferromagnetic (FM) ground state and sharp magnetization steps at low temperature (2.5 K) in the Nd ones. The FM fraction first quickly increases with x due to the local ‘counter-distortion’ effect introduced by barium cations, reaches a maximum value of 26% for x = 0.03, and then slowly decreases as more Ba is introduced where the A-site size mismatch has increased dramatically. In comparison with the Pr series, the Nd series exhibit a greater ability to induce ferromagnetism. When the magnetic field is increased, for low substitution levels (x

The crystal structure, transport and magnetic properties of Sr2.5La0.5Co1.3Ni0.7O6.4 and Sr2.5La0.5Co1.3Ni0.7Ox(OH)y·zH2O samples are detailed. Contrary to the first compound, the second one is not strictly speaking a second member of the well-known Ruddlesden–Popper (RP) series, but it exhibits very close relationships. Indeed, due to topotactical reactions with air (hydrolysis and hydration), water molecules are included within the rock salt layer of the “perfect” RP oxide, Sr2.5La0.5Co1.3Ni0.7O6.4, to form the hydrated oxyhydroxide phase presented in this paper. Cationic homogeneity of the samples was confirmed by energy dispersive spectroscopy analyses performed with a transmission electron microscope. The crystal structure of samples was determined by combined refinements of powder X-ray and electronic diffraction data. Physical properties of compounds are discussed, for instance the hydrated compound and the “perfect” RP oxide both exhibit typical magnetic frustrated systems and no long range order prevails at low temperature. Transport property measurements reveal a semi-conducting behavior for Sr2.5La0.5Co1.3Ni0.7O6.4. Finally, relationships between structure and physical properties are described herein.

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

The magnetic and transport properties of Pr 0.5 Ca 0.5− x A x MnO 3 (A = Sr, Ba) have been investigated in this paper. The substitution of Ca with bigger cations such as Sr and Ba can favour the field-induced ferromagnetism and induce sharp steps in the magnetization versus field and resistivity versus field curves. These properties strongly depend on the thermal history of the samples. All the results have been interpreted by a martensitic-like mechanism based on phase separation induced by A-site size mismatch. The above model can also explain the result that the less efficient ability of Sr substitution than Ba substitution to induce ferromagnetism and sharp steps. Another interesting feature in the system is the existence of an optimum substitution range to induce magnetization steps and reach high field-induced magnetization values for both Sr ( x = 0.07–0.10) and Ba ( x = 0.01–0.08) substitution. We suggest that the disappearance of the steps beyond the optimum substitution range possibly results from the different nature of phase separation in the optimum substitution range and beyond this range.

Miniaturization of the electronic devices has prompted the search for new materials with multifunctional properties. In this regard, multiferroics have distinct advantages as multifunctional materials because they possess for instance both ferroelectricity and ferromagnetism. Therefore, in addition to the fundamental interest, these “smart” materials, which are able to react to external stimuli or signals, are very attractive for a wide range of potential applications, e.g., in information storage or spintronics. However, very few multiferroics are known to the humankind. In this article, we report the synthesis of artificial multiferroics using the superlattices approach by pulsed laser deposition (PLD) technique. A series of films were grown by combining the magnetic layers, e.g., Pr0.85Ca0.15MnO3 or La0.7Ca0.3MnO3, and ferroelectric (FE) layers like (Ba1−x Sr x )TiO3 with different thicknesses. The magneto-electric and multiferroic (magnetic and dielectric) properties of these materials have been inves...

Two solid solutions In2−xM2x/3Sbx/3O3 (M = Cu, Zn) with the bixbyite structure have been synthesized in air at 1300 °C. The homogeneity range is larger for Zn (x = 0.42) than for Cu (x = 0.20) and the cationic distribution of the Cu/Sb and Zn/Sb couples is weakly ordered. These new oxides appear to be transparent conductors. Even fully deprived of tin, they have good potential properties. These oxides are either semiconductors with a small band gap (Cu/Sb) or semimetals (Zn/Sb) with σ = 3 × 102 (Ω cm)−1 at room temperature. These materials are more efficient than bulk ITO prepared under the same experimental conditions, i.e. without reducing treatment (σ = 50 (Ω cm)−1).

In the present paper, we present one route for increasing the copper content in the misfit cobaltites by studying the [Ca 2-y Ln y Cu 0.7+y Co 1.3-y O 4 ][CoO 2 ] b1/b2 (Ln = Pr,Y) series (Ln = magnetic Pr and nonmagnetic Y). We pay special attention to the modulated character of these compounds. The electron diffraction study shows a double modulation of the structure. The parameters of the two systems (rock salt and CdI 2 types) are a 1 = a 2 = 4.805(9) A, b 1 = 4.482(9) A, b 2 = 2.804(9) A, c 1 = c 2 = 12.75(3) A, and β 1 = β 2 = 93.7(2)°, v = b 1 /b 2 = 1.599(4). The first modulation vector q 1 * = 0.63b 1 * is associated with the misfit character of the compound, and the second one, q 2 * = 0.44a 1 * + 0.43c 1 *, is an intrinsic modulation of the rock salt layers. Accounting for this second modulation, the reconstruction of the reciprocal space leads the super-space group C2/m(1q0,α0γ)mm, with q 1 * = 0.63b 1 * and q 2 * = 0.44a* + 0.43c*. The intrinsic modulation in the double [(Co,Cu)O] 2 rock salt-type layer of a misfit cobaltite is shown for the first time by electron microscopy. Different twinning mechanisms are also characterized. The relationships with the strontium ferrites built up from four rock salt-related layers are discussed. An increase of the thermopower is obtained, as well with a magnetic (Pr) as a nonmagnetic (Y) cation, which shows that the enhancement is due to a valence effect rather than to a magnetic effect.

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

The study of the “112” ordered oxygen-deficient perovskites EuBaCo2O5.43, EuBaCo1.92Zn0.08O5.45, and EuBaCo1.92Cu0.08O5.40 evidences a magnetic transition at 40 K which may be due to the ordering of europium moments. Below 40 K, one observes phase separation that consists of superparamagnetic droplets and ferromagnetic (FM) regions embedded in an antiferromagnetic matrix. The existence of two sorts of crystallographic sites for cobalt, and its trivalent state, suggest that these phenomena correspond to ferromagnetism induced by the presence of intermediate spin Co3+ species. Moreover, the magnetization hysteresis loops of the Zn- and Cu-doped phases exhibit ultrasharp magnetization multisteps, which are interpreted by the pinning effect of Zn2+ and Cu2+ cations at the narrow domain walls of the FM phase.

The iron phosphate, Fe(H 2 PO 4 ) 3 , was synthesized through a precipitation route by means of acidic media. As the compound is highly hygroscopic, the structure was solved ab initio by powder X-ray diffraction under nitrogen flow at room temperature and 200 °C. This phase is antiferromagnetic below 30 K . It converts into Fe(PO 3 ) 3 at 550 °C, after dehydration. Electrochemical characterizations, performed on the last compound, show irreversible decomposition into metallic iron.

The incommensurate modulated structure of Sr4Fe6O13±δ refined in super space formalism, from single crystal X-ray diffraction data. The analysis of this structure shows that the geometry of the iron polyhedra, their respective positions and arrangement are fundamentally different from those previously described for this oxide. Three types of iron environment, namely trigonal bipyramids, tetragonal pyramids and monocaped tetrahedra are observed in the double iron oxygen layers. The peculiar role of a structural unit built up from double trigonal bipyramids is outlined and the notion of disorder is detailed. The structural mechanism of this modulation character of the double iron layer is analyzed, compared to other related phases built of one single perovskite layer inter-grown with a complex slice made of one modulated double layer sandwiched between two [AO]∞ layers.