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Oxides with the CaFe2O4-type structure have been predicted as being suitable hosts for reactions of intercalation of light cations such as Li and Mg because of their favorable cationic diffusion. A...

In a recent theoretical study [Jacobs et al., Adv. Energy Mater., 2018, 8, 1702708], BaFe0.125Co0.125Zr0.75O3−δ was predicted to be a stable phase with outstanding performance as an auspicious cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). It is shown here that the theoretical predictions are valid. The material can be synthesized by the citrate method as a single cubic Pmm phase with a significant amount of oxygen vacancies, randomly distributed in the anionic sublattice facilitating oxygen vacancy conduction. A thermal expansion coefficient of 8.1 × 10−6 K−1 suggests acceptable compatibility with common electrolytes. Electrochemical impedance spectroscopy of symmetrical cells gives an area-specific resistance of 0.33 Ω cm2 at 700 °C and 0.13 Ω cm2 at 800 °C. These values are reduced to 0.13 Ω cm2 at 700 °C and 0.05 Ω cm2 at 800 °C when the material is mixed with 30 wt% Ce0.9Gd0.1O2−δ.

International audience; Metal fluorides with 3D open structures, pyrochlore (pyr) or hexagonal tungsten bronze (HTB), are promising materials as positive electrodes for rechargeable batteries or catalysts. Herein, we have developed a two-step synthesis procedure to obtain new anhydrous mixed-metal-cation fluorides crystallizing in the pyrochlore structure. The first step consists of preparing mixed-metal ammonium fluorides (NH4)M2+Fe3+F6 (M = Mn, Fe, Co Ni) using different synthesis strategies. For M = Mn, three allotropic varieties of (NH4)Mn2+Fe3+F6 are obtained; two phases adopt the expected pyrochlore network with either the cubic Fm3̅m or the orthorhombic Pnma space group, and the third phase exhibits a 3D network with narrow pseudotriangular cavities. 57Fe Mössbauer spectrometry indicates that the crystal structures are governed by the Fe3+/Mn2+ cationic order or disorder. The second step is a topotactic oxidation of pyr-(NH4)M2+Fe3+F6 under a molecular F2 flow. To better understand the reaction mechanism, the topotactic oxidation was followed by thermogravimetry, XRD, FTIR, and Mössbauer spectrometry. The successful synthesis of the first anhydrous pyr-M3+0.5Fe0.5F3 provides a new route to prepare anhydrous mixed-metal fluorides pyrochlore with empty cavities of the open framework.

β-V2O5, obtained by a high-temperature high-pressure method, exhibits a layered structure that favours the insertion of Na+. In this work, we report the electrochemical insertion of sodium in high pressure β-V2O5 and its performance as cathode material for sodium-ion batteries. The material shows a first discharge capacity of 132 mAh g−1 in the 3.6–2.0 V range at a C/20 current density and a maximum capacity of 147 mAh g−1 under equilibrium conditions, corresponding to the insertion of 1 Na+ ion per formula unit. The β-V2O5//Na cell delivers a specific energy as high as 370–410 Wh kg−1. The amount of inserted sodium points to the reduction of 50% of the available V5+ ions. After 20 cycles, the discharge capacity retains 86% of the initial capacity. Concerning the reaction mechanism of high pressure β-V2O5 upon sodium insertion/de-insertion, several phase transitions are inferred from the voltage-composition profile. Ex situ XRD reveals the appearance of several NaxV2O5 phases in the 0 ≤ x ≤ 1 compositional range, which are closely related with the non-sodiated high pressure β-V2O5 structure. An irreversible structural transformation occurs during the very first inserted sodium, at the beginning of the first discharge, and the original high pressure β-V2O5 structure is not recovered upon full Na+ extraction. Electrochemical performances are outstanding though.

Maghemite-like materials containing Fe(3+) and Cr(3+) in comparable amounts have been prepared by solution-combustion synthesis. The conditions of synthesis and the magnetic properties are described. These materials are ferrimagnetic and are much more stable than pure iron maghemite since their maghemite-hematite transformation takes place at about ∼ 700 °C instead of ∼ 300 °C, as usually reported. These materials were studied by synchrotron radiation X-ray diffraction (XRD) and by X-ray absorption fine structure (XAFS) of the K-absorption edge of two elements. High-resolution XRD patterns were processed by means of the Rietveld method. Thus, maghemites were studied by XAFS in both Fe and Cr K-edges to clarify the short-range structure of the investigated systems. Pre-edge decomposition and theoretical modeling of X-ray absorption near edge structure transitions were performed. The extended X-ray absorption fine structure (EXAFS) spectra were fitted considering the facts that the central atom of Fe is able to occupy octahedral and tetrahedral sites, each with a weight adjustment, while Cr occupies only octahedral sites. Interatomic distances were determined for x = 1, by fitting simultaneously both Fe and Cr K-edges average EXAFS spectra. The results showed that the cation vacancies tend to follow a regular pattern within the structure of the iron-chromium maghemite (FeCrO3).

Legislation to replace lead-based ferroelectric ceramics for electromechanical transducers (commonly made of lead titanate-zirconate (PZT)) started in Europe shortly before the year 2000 in the context of elimination of toxic substances from electric and electronic equipment. From that date there has been a large, worldwide research effort to develop new ecological, lead-free compositions that can substitute PZT. Some issues involved in this effort will be reviewed here, from the synthesis procedures to functional properties and trends. New properties on lead-free systems that surpass those of PZT (bismuth sodium titanates for actuators) and enhanced properties of other compositions in which lead-free materials are already at work in devices will be analyzed in this chapter. Present limits of well-known lead-free materials (barium titanate, Aurivillius-type structure compounds, sodium potassium niobate, bismuth sodium titanate, and barium calcium titanate-zirconate) will be summarized, and new and recently studied compositions based on materials with high spontaneous polarization will be considered as future lead-free alternatives.

Hitherto unreported vanadium oxyfluoride VO2F has been synthesized using a solid state reaction at a pressure of 4 GPa and 800 °C. This long awaited vanadium oxyfluoride fills the existing gap of ReO3-type MO2F compounds of Group 5 elements, from which only NbO2F and TaO2F have been known to exist to date. VO2F crystallizes with the VF3-type structure, space group Rc, with a = 5.1226(1) A and c = 13.0686(3) A as determined by powder X-ray diffraction. Highly structured diffuse streaking observed in electron diffraction patterns evidences local O/F ordering. VO2F exhibits two regions upon discharge in a lithium cell, an upper sloped region in the range of 3.9–2.2 V and a lower plateau at 2.15 V. Discharge of VO2F to 1 V provides a gravimetric capacity of 450 mA h g−1. VO2F can reversibly insert up to 1 Li+ per vanadium above 2.15 V without destruction of the host structure, delivering a gravimetric capacity as high as 250 mA h g−1 and pointing to VO2F as a promising intercalation electrode.

Detailed studies of the electronic states for Mo(0.3)Cu(0.7)Sr(2)ErCu(2)Oy samples with different oxygen contents are presented here. The influence of oxygenation on the electronic states for the Mo(0.3)Cu(0.7)Sr(2)ErCu(2)Oy system from the semiconducting to the superconducting state has been investigated by means of X-ray photoelectron spectroscopy (XPS). The XPS studies show that Mo is in a mixed Mo(V) and Mo(VI) oxidation state and Mo(V) is predominant over the Mo(VI) in the as-prepared (AP) sample. Yet annealing under an oxygen atmosphere enhances the Mo(VI) state. At the same time, a reduction in the copper species is observed. In the Cu 2p spectra, a larger energy separation between the satellite and main peaks (E(S)-E(M)) and a lower intensity ratio (I(S)/I(M)) are found to correlate with higher values of the superconducting transition temperature (T(C)). Analysis of these spectra within the Configuration Interaction (CI) model suggests that higher values of TC are related to lower values of the O 2p-Cu 3d charge transfer energy. The change in the Sr 3d and O 1s core level spectra correlates with the oxygen insertion in the (Mo/Cu)O(1+δ) chain site, after oxygenation. The hole concentration (Ph) in the copper plane has been obtained using the room temperature thermoelectric power (TEP) value; this shows an increasing tendency with increasing T(C), after oxygenation. From these experimental results, one observes that T(C)increases with decreasing charge transfer energy. This is, indeed, opposite to the accepted views and occurs in parallel with the shortening of the apical copper-oxygen distance (Cu(2)-O(2)) and the increasing of the CuO(2) plane buckling angle.

H 2 V 3 O 8 nanobelts have been successfully synthesised from commercial V 2 O 5 powder through a fast and environmental friendly microwave-hydrothermal method. X-ray diffraction, field-emission scanning electron microscopy, thermogravimetric analysis, infrared spectroscopy, high-resolution transmission electron microscopy and ICP spectroscopy were used to characterise the morphology and structure–microstructure details. Nanobelts about 100 nm wide and several micrometres long are easily prepared in no more than 2 h. The electrochemical study reveals the reversible insertion of ca. 4 Li per formula unit (400 mAh g −1 ), through several pseudo- plateaus in the 3.75–1.5 V vs Li + /Li voltage range showing the interest of this material produced by a “green” route as an electrode for lithium rechargeable batteries. After the first cycle a significant capacity loss is observed, though a high capacity, ca. 300 mAh g −1 , remains upon cycling. Furthermore, the similarity of discharge and charge curves, pointing to the absence of hydrogen displacement during lithium insertion in H 2 V 3 O 8 , shows that not all protonated systems must be discarded as prospective electrode materials. On the other hand, further reduction down to 1 V is possible to insert up to 5 Li per formula unit (480 mAh g −1 ). Interestingly it corresponds to full reduction of vanadium to V 3+ as it is also confirmed by EELS experiments. However, the full reduction to V 3+ is associated with a fast decay of the extra capacity developed at low voltage with increasing current rate. Then for practical use we may consider only the capacity obtained down to 1.5 V.

A new procedure to prepare oxides materials from oxalates complexes precursors is presented. Detailed description of the method is reported, illustrated with examples of the preparation of oxides. A solid-solid reaction between the oxalic acid and nitrate salt of metal leads to the formation of the corresponding oxalate. These oxalates are used as precursors and are heated to form the corresponding oxides by thermal-decomposition. This article relates the first examples of oxides prepared by this new method: the synthesis of the copper oxide CuO, the hexagonal phase of lanthanum oxide La2O3, and the lanthanum cuprate La2CuO4. All the samples are characterized by SEM and XRD. Thermal analysis TGA and DTA show the expected thermo-decomposition behavior for both copper and lanthanum oxalates. This study reveals also the formation mechanism of the cuprate La2CuO4 from the used precursor.

Electrodes consisting of composites of nanosized-LaPO4/Carbon-Super P yield irreversible capacities as large as 872 mAh/g carbon (down to 0.2 V), which would be equivalent to the reaction of 0.9 lithium ions with LaPO4. Increasing the crystallite size of LaPO4 drastically decreases the specific capacity delivered by the cell, reaching a minimum value of 330 mAh/g carbon for micrometer-LaPO4. A significant capacity is also detected in nanosized LaPO4 /Carbon-KS6 and LaPO4/Ni electrodes. An in situ XRD investigation proves that the bulk of LaPO4 does not react with lithium, evidencing that LaPO4 is useless as electrode material for lithium cells. The reactivity of the electrode is likely due to the electrolyte decomposition on the surface of both the electronic conductor additives (C or Ni) and the LaPO4 nanoparticles.

Double perovskites which exhibit 1:2 B-site ordering are under focus because of their interesting structure−property relationships and high chemical versatility. Perovskites with a big cation, such as Sr2+ or Ca2+, occupying the octahedral B site are very scarce because the calculated Goldschmidt tolerance factor becomes quite small as these types of cations usually occupy the A-site. This work describes the synthesis and structural and microstructural characterization of a new calcium and strontium antimoniate which shows face-centered cubic symmetry and a rock-salt ordered distribution of Sb5+ and Sr2+. The ordered-cation distribution occurs due to the differences in both the ionic sizes and the bonding character of the two B-site cations. As a consequence of the cation stoichiometry of the title phase and assuming a pentavalent state for Sb, a large concentration of oxygen vacancies are created (y ∼ 0.25). Diffraction studies reveal that these vacancies tend to arrange in a short-ordered way and are re...

A series of lanthanum perovskites, LaMO 3 (M = Al, Cr, Mn, Fe, Co), having important technological applications, have been successfully prepared by a very fast, inexpensive, reproducible, environment-friendly method: the microwave irradiation of the corresponding mixtures of nitrates. Worth to note, the microwave source is a domestic microwave oven. In some cases the reaction takes place in a single step, while sometimes further annealings are necessary. For doped materials the method has to be combined with others such as sol–gel. Usually, nanopowders are produced which yield high density pellets after sintering. Rietveld analysis, oxygen stoichiometry, microstructure and magnetic measurements are presented.

A novel Pr2Cu2O5 phase has been prepared under high-pressure and high-temperature conditions (P ∼6 GPa and T ∼1673 K) in a Belt-type apparatus and characterized by X-ray diffraction and electron microscopy. The crystal structure appears to be an orthorhombic “oxygen-deficient perovskite” (M.T. Anderson, J.T. Vaughey, and K.R. Poeppelmeier, Structural similarities among oxygen-deficient perovskites, Chem. Mater. 5 (1993), pp. 151–165) isostructural with La2Cu2O5 (J.F. Bringley, B.A. Scott, S.J. La Placa, R.F. Boheme, T.M. Shaw, M.W. McElfresh, S.S. Trail, and D.E. Cox, Synthesis of the defect perovskite series LaCuO 3−δ with copper valence varying from 2+to 3+, Nature 347 (1990), pp. 263–265) and Nd2Cu2O5 (B.-H. Chen, D. Walker, E. Suard, B.A. Scott, B. Mercey, M. Hervieu, and B. Raveau, High pressure synthesis of NdCuO3−δ perovskites (0≤δ≤0.5). Inorg. Chem. 34 (1995), pp. 2077–2083).

The behavior of Li 3 PO 4 and Li 2 MSiO 4 ( M = Mn, Co) compounds under high pressure/high temperature is investigated. Pmn2 1 -Li 3 PO 4 remains stable up to the higher experimental limit of 80 kbar (900 °C). A sample of Li 2 MnSiO 4 consisting of a mixture of Pn2 1 and Pmnb polymorphs converts upon high pressure/high temperature treatment into the Pmn2 1 polymorph; the latter being stable at 80 kbar and 900 °C. A sample of Li 2 CoSiO 4 - P2 1 /n transforms to the denser Pmn2 1 polymorph at 40 kbar/900 °C, but decomposes at higher pressure (60 kbar/900 °C). No evidence on any novel Li 2 MSiO 4 polymorph is detected in any of the high-pressure products.

Silicates LiMSiO 4 are potential positive electrode materials for lithium ion batteries. In this work we analyse from first principles calculations the relative stability of possible LiFeSiO 4 -polymorphs within four structural types. Olivine-LiFeSiO 4 is predicted to be more stable than the LiFeSiO 4 prepared by delithiation of Li 2 FeSiO 4 ; the latter being the only LiFeSiO 4 compound reported so far. Attempts to prepare olivine-LiFeSiO 4 from a mixture of reactants at ambient pressure (600–1100 °C) resulted in a mixture of quartz-SiO 2 , Li 2 SiO 3 , LiFe 5 O 8 and LiFeSi 2 O 6 phases. Conducting the reaction under HP conditions (40 kbar) leads to the formation of LiFeSi 2 O 6 as a majority phase, regardless the nature of the reactants/precursors. First principles calculations indicate that the preparation of the olivine-LiFeSiO 4 is thermodynamically hindered due to the competition with the more stable LiFeSi 2 O 6 pyroxene, in the range of pressure/temperature investigated.

We describe the synthesis, structural and microstructural characterization of a strontium antimonate, Sr 1.5 Sb 0.5 O 3− y ( y ∼ 0.25), with a cubic, double-perovskite structure and a large concentration of oxygen vacancies with no apparent long-range order. High resolution electron microscopy indicates, however, that short-range ordering phenomena may occur. Electrical conductivity is independent of oxygen partial pressure ( p O 2 ) for p O 2 −1.25 atm, typical of ionic transport ( σ ∼ 10 −4 S cm −1 at 600 °C), whereas the conductivity is dominated by p-type charge carriers at higher p O 2 .

Under high pressure (40 kbar) V2O5 transforms into a layered polymorph, HP-V2O5, consisting of V5+O6 octahedra instead of V5+O5− square pyramids. HP-V2O5 reversibly intercalates up to 2 lithium ions down to 1 V vs. Li. The typical discharge/charge voltage–composition curve shows a step-like profile where six new LixHP-V2O5 phases are detected. The specific capacity retention with cycling of HP-V2O5∥Li cells (250 Ah/Kg at a C/3.5 rate) is comparable to that of the ambient pressure polymorph. To our knowledge, HP-V2O5 is the first example of a high pressure material displaying such a good electrochemical performance. Keywords: V2O5, Electrode material, Lithium batteries, High pressure, Lithium intercalation

We have performed an investigation of the structural, microstructural and magnetic properties of the new compound IrSr{sub 2}GdCu{sub 2}O{sub 8}. The sample was prepared under high temperature ({approx}1393K) and high-pressure conditions ({approx}60Kbars) in a Belt type apparatus. X-ray diffraction (XRD) analysis shows that this irido-cuprate is isostructural with the corresponding Ru-1212 phase. Structurally, this material shows an interesting hierarchy of ordering phenomena, whose observation actually depends on the technique used to analyze the material: from a 'simple' cell a{sub p}xa{sub p}x3a{sub p} which is supported by XRD, through a 'diagonal' one, {approx}2a{sub p}x2a{sub p}x3a{sub p} as seen by SAED, to a microdomain texture of this last one cell supported by HREM. A ferrimagnetic Ir{sup IV}-Gd{sup III} spin ordering is observed below 15K. The iridium oxidation state seems to be +4.

By using a domestic microwave furnace and depending on the nickel precursor used, either tetrahydrated nickel acetate or dihydrated nickel formate, different nanosized materials are obtained: Ni/NiO composites, Ni metal, or NiO. The acetate leads to core−shell composites: Ni on the outside and NiO on the inside, while the formate behaves oppositely, yielding the metal that is progressively oxidized in air, the shell being in this case NiO. All these materials show ferromagnetic behavior.

The present study describes the preparation, characterization, and thermal decomposition of the compound Ni(MnO 4 ) 2 · x H 2 O, which was synthesized by a coprecipitation method at a low temperature. The role of this compound as a precursor in the synthesis of a Ni–Mn spinel was determined via X-ray, TG-DTA, electron diffraction, and EDAX measurements.

We describe the synthesis, crystal structure and lithium deinsertion-insertion electrochemistry of two new lithium-rich layered oxides, Li3MRuO5 (M = Mn, Fe), related to rock salt based Li2MnO3 and LiCoO2. The Li3MnRuO5 oxide adopts a structure related to Li2MnO3 (C2/m) where Li and (Li0.2Mn0.4Ru0.4) layers alternate along the c-axis, while the Li3FeRuO5 oxide adopts a near-perfect LiCoO2 (R3[combining macron]m) structure where Li and (Li0.2Fe0.4Ru0.4) layers are stacked alternately. Magnetic measurements indicate for Li3MnRuO5 the presence of Mn(3+) and low spin configuration for Ru(4+) where the itinerant electrons occupy a π*-band. The onset of a net maximum in the χ vs. T plot at 9.5 K and the negative value of the Weiss constant (θ) of -31.4 K indicate the presence of antiferromagnetic superexchange interactions according to different pathways. Lithium electrochemistry shows a similar behaviour for both oxides and related to the typical behaviour of Li-rich layered oxides where participation of oxide ions in the electrochemical processes is usually found. A long first charge process with capacities of 240 mA h g(-1) (2.3 Li per f.u.) and 144 mA h g(-1) (1.38 Li per f.u.) is observed for Li3MnRuO5 and Li3FeRuO5, respectively. An initial sloping region (OCV to ca. 4.1 V) is followed by a long plateau (ca. 4.3 V). Further discharge-charge cycling points to partial reversibility (ca. 160 mA h g(-1) and 45 mA h g(-1) for Mn and Fe, respectively). Nevertheless, just after a few cycles, cell failure is observed. X-ray photoelectron spectroscopy (XPS) characterisation of both pristine and electrochemically oxidized Li3MRuO5 reveals that in the Li3MnRuO5 oxide, Mn(3+) and Ru(4+) are partially oxidized to Mn(4+) and Ru(5+) in the sloping region at low voltage, while in the long plateau, O(2-) is also oxidized. Oxygen release likely occurs which may be the cause for failure of cells upon cycling. Interestingly, some other Li-rich layered oxides have been reported to cycle acceptably even with the participation of the O(2-) ligand in the reversible redox processes. In the Li3FeRuO5 oxide, the oxidation process appears to affect only Ru (4+ to 5+ in the sloping region) and O(2-) (plateau) while Fe seems to retain its 3+ state.

Different solid/liquid "exchange" reactions involving divalent cations, protons, or ammonium ions have been performed at low/moderate temperatures (between 80 and 500 degrees C) on alpha-NaFeO2 dipped in molten salts (or acid) media. Several ferrites have been obtained which are nonstoichiometric with partially inverse spinel structures. When sodium is replaced by divalent cations (Mg2+, Co2+, Ni2+, and Zn2+), the obtained ferrites are hyperstoichiometric (cation/oxygen ratio higher than 3/4) whereas proton or ammonium reactions result in hypostoichiometric materials (cation/oxygen lower than 3/4). All these ferrites present a platelet-like morphology and show ferrimagnetic, soft magnet behavior.

The stoichiometry range, crystal chemistry, ionic conductivity, and electrochemical window of the La2/3LixTi1-xAlxO3 system with perovskite-related structure have been studied. The range of the existence of the solid solution is (0.06 = x = 0.3). Powder X-ray diffraction and transmission electron microscopy results show that these oxides have a unit cell multiple of the perovskite cell with dimensions a ≈ √2ap, b ≈ √2ap, c ≈ 2ap. The ionic conductivity of the materials and its dependence on composition and temperature have been examined by complex impedance spectroscopy. Lithium ion conductivity increases with increasing lithium content up to a value (7.6 × 10-5 S cm-1 at room temperature) corresponding to x = 0.25. Electrochemical experiments indicate that these materials can be used as solid electrolytes in secondary batteries having Li metal as the anode down to 1.6 V.

The SeCu 1 m x Zn x O 3 solid solution, with a distorted perovskite-type structure, has been synthesized under high pressures and temperatures. X-ray diffraction analysis indicates that the zinc ions occupy the copper sites, a solid solution being formed. It seems that high-pressure stabilises a small cation such as Se 4+ in the A site of the perovskite structure ABO 3 although the material is better described as formed by selenite anions \rm{SeO}_{3}^{-} and Cu 2+ /Zn 2+ cations.

At room pressure, Sm, Eu and Gd seem to be the only RE elements that accept to enter into the structure of RuSr 2 GdCu 2 O 8 . However high pressure and high temperatures allow one to replace gadolinium by other lanthanide cations. We have been successful in replacing Gd by Y, La, Pr, Nd, Tb, Dy, Ho and Er. X-ray diffraction patterns fitted by the Rietveld method show that the average crystal structure of RuSr 2 RECu 2 O 8 is tetragonal with P 4/ mmm space group symmetry. Micro-Raman experiments have been performed on RuSr 2 GdCu 2 O 8 samples synthesized at both high and room pressure; the resulting spectra are consistent with the same structure, since there are no major changes in the low-frequency range.

Low energy electron diffraction (LEED) and photoelectron spectroscopy (PES) have been employed to study the (100) SrTiO3 surface annealed in ultra high vacuum. The annealing was performed up to 830°C. After annealing at 830°C, we have observed from PES spectra the appearance of the conduction band and from LEED patterns the (√5 x √5)R 26.6° superstructure. Both features seem to have the same origin: the ordering of oxygen vacancies.

Sodium insertion in W18O49 proceeds through the formation of a solid solution for the whole range of intercalant NaxW18O49 with 0≤x≤1.8. The different features detected in −∂x/∂E vs E plots have been associated with continuous phase transitions. In order to know more about these transitions, several samples NaxW18O49 with compositions around the minimum in the −∂x/∂E curve have been synthesized and then characterized by both X-ray and electron diffraction techniques. An interesting correlation with the electrochemical results has been established.

Complex admittance measurements have been performed on α-NaFeO 2 and on the product Na 0.9 FeO 2 obtained by sodium extraction, both being polycrystalline powders. The electrical conductivity in both samples is proposed to be due to sodium ions hopping between octahedral positions through the adjacent, empty, tetrahedral ones characteristic of a rock-salt structural framework. The parent material shows an activation energy in the dc conductivity of 0.31 eV between 306 and 498 K. Removal of sodium, in spite of creating octahedral vacancies, results in lower conductivity values, and a higher activation energy of 0.58 eV in a similar temperature range.

Superconducting films of the Bi–Sr–Ca–Cu–O family of oxides were prepared by electrodeposition of the constituent metals followed by an oxidative thermal treatment. The influence of water, stirring of the electrolyte, cleaning of the substrate, and deposition time on the quality of the films were studied. Before the thermal treatment, the electrodeposited films consisted of a mixture of different metals and carbonates of the constituent elements. The oxidation of the metallic phases and the decomposition of the carbonates occurred in the ranges 260–280 °C and 400–470 °C, respectively. The final oxides were obtained after an oxidative thermal treatment at 800 °C. Lower temperatures were not sufficient for the preparation of the superconducting oxide films. The prepared Bi-2201 films consisted of a mixture of two phases with different strontium, bismuth, and oxygen contents. The Bi-2212 films were composed of platelike particles with a preference to orientate along the (001) direction. These films showed critical temperatures up to 92 K and critical current densities up to 15,000 A/cm2 (at 77 K and zero field) when the films were pressed before the thermal treatment.

In this paper, a contribution to the search of new electrode materials for lithium batteries is reported. First, we will present the electrochemical behavior of an Aurivillius-type phase with the composition Bi 4 V 2 O 11 . This oxide may be used as cathode material (390 A h/kg) if the voltage is not so low (average voltage 1.6 V). On the other hand, if Bi 4 V 2 O 11 is reduced down to 0.5 V, it reacts with 28 Li ions per formula unit. Considering only the low voltage region, Li 28 Bi 4 V 2 O 11 could be a candidate to anode material (360 A h/kg at 0.7 V). Our research has also been directed towards the applications of several types of titanium oxides in lithium batteries. Among these compounds, we present the results for K x Ti 8 O 16 and Li 2 Ti 3 O 7 . The best results are those obtained from the ramsdellite Li 2 Ti 3 O 7 : the large reversibility, low polarization and relatively high capacity (235 A h/kg) make this compound a promising material as negative electrode for lithium ion cells. However, the relatively high average potential, close to 1.4 V, would reduce considerably the performance of a rocking-chair battery using this ramsdellite instead of carbon.

The compound Bi 4 V 2 O 11 has been tested as a positive electrode in room temperature electrochemical lithium cells. When the cells are discharged down to 0.5 V the reaction of Bi 4 V 2 O 11 with 28 lithium ions develops a theoretical specific capacity of 700 A h kg −1 . Hence, this compound could be used as cathode in primary lithium batteries. Besides, we consider the fact that in the low voltage region (1.3–0.5 V) Li 28 Bi 4 V 2 O 11 develops about 360 A h kg −1 at 0.7 V, and, therefore, this material is proposed as a negative electrode in lithium ion batteries. The mechanism of the reaction of Bi 4 V 2 O 11 with 28 lithium ions is not yet fully understood, although some guidelines can be given.

The stoichiometric range, crystal chemistry, ionic conductivity and electrochemical window of the La1/3−xLi3xNbO3 solid solution with a perovskite-related structure have been studied. The range of existence of the solid solution appears to be 0≤x≤0.06. These niobates have a basic diagonal unit cell a≈√2ap b√2ap c≈2ap. Ionic conductivity of the materials and its dependence with the composition and temperature have been examined. We have found that the highest conductivity value is 4.3×1O−5 S cm−1 at 300 K for x=0.04. The electrochemical window of the compounds has been investigated by potentiostatic discharge and charge. Electrochemical experiments show that the use of the materials as solid electrolytes in secondary batteries is limited down to 1.75 V using Li metal as anode.

6 páginas, 10 figuras, 3 tablas., Superconducting thick films of Y-Ba-Cu-O have been prepared via an electrodeposition procedure of the constituent metals on metallic substrates (Cu, Ag) followed by an oxidative thermal treatment. The films were electrodeposited at a constant potential of –3.5 V (vs. Ag/AgCl) from a single electrolyte bath, which contains the nitrates of the cations in dimethyl sulfoxide. The initial state of the precursor film and the formation process of the final superconducting film have been followed by IR spectroscopy, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy. In the precursor film, yttrium and copper are present as metals while barium forms a carbonate. Dimethyl sulfoxide (DMSO) is not inert under the experimental conditions and oxidises to the sulfone. The superconducting transition temperature (Tc) of the final film was ≈92 K and the critical current density (Jc) values were ≈9 500 A cm–2 at 77 K and zero field, the highest so far obtained by electrodeposition., This work was financially supported by CICYT Program 32 MAT95–0809 and MAT98–0729. J.G.J. wishes to thank the Basque Government/Eusko Jaurlaritza for a postdoctoral fellowship.

5 páginas, 5 figuras, 2 tablas., Electrodeposition techniques provide a way of synthesising oxide superconductor thick films in two steps: (a) electrodeposition of the cations and (b) oxidation of the deposit at high temperatures. This method is fast, economic and enjoys the benefits of a well known technology. We have performed the preparation of several copper containing superconductors (YBa2Cu3O7–δ, Bi2Sr2CaCu2O8+δ) and a copper-free one (Ba1–xK x BiO3) from electrolytes containing nitrate salts dissolved in dimethyl sulfoxide using chronoamperometric techniques. The quality of the films strongly depends on the experimental conditions such as substrate, bath composition and thermal annealing. Characterisation of the initial deposit and the final superconducting oxide was made by means of infrared spectroscopy, thermal analysis, X-ray diffraction and scanning electron microscopy. The best critical current (Jc) values, in A cm–2, for the different phases were: YBa2Cu3O7–δ (13000/5 K and 400/77 K), Bi2Sr2CaCu2O8+δ (12000/77 K) and Ba1–xK x BiO3 (2700/5 K).

A large amount of 16 lithium ions reacts with the phase Bi4V2O11 between 3 and 1 Volts. From the structural characterisation of inserted compounds LixBi4V2O11 (0

The insertion of an excess of oxygen within the structure of La 2− x Ca x CuO 4 ( x ≤0.12) by means of room temperature chemical oxidation modifies the physical properties and the crystal structure of these cuprates. The superconducting features of the starting La 2− x Ca x CuO 4 samples improve considerably upon oxidation. The oxidized Ca-doped materials with x ≤0.08 show an almost constant T c of ∼38 K, close to that corresponding to the optimum hole-doping in La 2− x M x CuO 4 ; however, the oxidized samples with higher Ca contents present slightly lower T c s. This decrease of T c is connected with the ability of these compounds to incorporate extra oxygen, which decreases as the Ca-doping increases and is controlled by a structural limit. The behavior of the La 2− x Ca x CuO 4 materials under the oxidation process and the changes induced by the interstitial oxygen are strongly conditioned by the smaller size of Ca 2+ with respect to La 3+ . Indeed, this peculiarity clearly differentiates the oxidized La 2− x Ca x CuO 4+ y series from the Sr 2+ and the Ba 2+ substituted systems, where the size of the dopant is larger than that of La 3+ . In the present work the analogies and the differences concerning the insertion of oxygen and the modifications induced in La 2− x M x CuO 4+ y (M=Ca, Sr, Ba) are presented and discussed.

The electrochemical sodium insertion and extraction of the phosphomolybdates Na 2 (MoOPO 4 ) 2 (HPO 4 )·yH 2 O (y=2, 0) is reported. Both compounds show a similar behaviour upon electrochemical sodium extraction, while the insertion reaction is notably different for each host compound. During the charge/discharge of electrochemical cells the existence of new phases Na 2+x (MoOPO 4 ) 2 (HPO 4 )·2H 2 O with compositions –0.7

The influence of oxygenation in the magnetism, superconductivity and electronic states for the Mo0.3Cu0.7Sr2RECu2Oy (RE = Y, Er and Tm) compounds are discussed here. The magnetic measurements on the as-prepared (AP) samples suggest the existence of short-range magnetic correlations due to the presence of the paramagnetic MoV cations in the copper chain site. On the other hand, all the oxygenated samples are not magnetic but superconducting. The high pressure oxygenated sample shows the highest superconducting transition temperature of TC = 84 K. The influence of oxygenation in the electronic states for the Mo0.3Cu0.7Sr2YCu2Oy system associated with an oxidation reaction leading from a non-superconducting to a superconducting state has also been investigated by means of X-ray photoelectron spectroscopy (XPS). XPS measurements show the predominance of the MoV oxidation state over the MoVI one in the AP material; annealing under flowing oxygen enhances both the MoVI and CuII amounts. A detailed study of the electronic states for the Mo0.3Cu0.7Sr2YCu2Oy samples has been performed and is also discussed.

Room temperature chemical oxidation has been used for the insertion of oxygen into the T/O phase of La2−xNdxCuO4 (x ≤ 0.5). The influence of interstitial oxygen on both the structural features and the physical properties of this series of cuprates is worth a study. The excess of oxygen introduced in the semiconducting starting materials relieves partially the distortion of the structure, which increases for increasing Nd content, and provides the hole doping required for superconductivity. The extra oxygen content decreases along this series of compounds as the Nd-doping increases, probably due to the progressive contraction of the structure along the c-axis. Analogies and differences in the modification induced by the oxidation process in the present La2−xNdxCuO4+y materials and in related compounds La2−x(Ca/Sr/Ba)xCuO4+y (x ≤ 0.15) are reported and discussed.

Sodium removal from Na0.875Fe0.875Ti1.125O4by means of oxidizing agents leads to the formation of the defect solid solution Na0.875−δFe0.875−δTi1.125O4(0≤δ≤0.44). A systematic increase in theaparameter of the orthorhombic unit cell is observed as the sodium content is reduced, while thebparameter decreases only slightly. The cell volume remains almost constant as a consequence of the irregular change in thecparameter and the different behavior of both theaandbparameters. Structural changes have been followed by Rietveld powder diffraction analysis. Room- and low-temperature Mossbauer studies confirm the increase in the Fe4+state with decreased sodium content in the less extracted samples withδ=0.10 and 0.15, whereas a maximum Fe4+content (about 21%) is reached in a sample withδ=0.25. Surprisingly, the amount of Fe4+does not increase with further sodium extraction. This is thought to be related to the greater oxidative power of the more oxidized materials, which facilitates a subsequent partial backreduction of Fe4+formed during the oxidation procedure. Results of both Mossbauer spectroscopy and structure refinements indicate that the Fe4+cations randomly occupy both octahedral metal positions,M(1) andM(2), of each quadruple rutile unit.

The structure of room temperature chemically oxidized La 2 CuO 4+ y [ y = 0.103(4)] has been refined from powder neutron diffraction data using the space group Bmab . The modifications induced in the CuO 2 and the LaO planes by the insertion of oxygen are consistent with the high T c measured for this material. The thermogravimetric analysis (TGA) of La 2 CuO 4.103(4) evidences an unexplained two-step mass loss process. Based on this observation, three samples obtained by different thermal treatments of the fully oxidized material were studied by TGA, X-ray diffraction and AC magnetic susceptibility. After a short treatment at 433 K, La 2 CuO 4.103(4) undergoes a phase separation into two phases: phase 1, with estimated y 1 = 0.086(4) and T c1 = 30 K, and phase 2, with estimated y 2 = 0.12(1) and T c2 = 17 K. By increasing the annealing times, phase 2 transforms to phase 1 and finally disappears. Therefore, it seems likely that the plateau observed in the TGA curve of La 2 CuO 4.103(4) might be due to the formation on heating of a stable phase with a fixed oxygen stoichiometry, i.e. La 2 CuO 4.086(4) . The stability of this phase could be related to the presence of one-dimensional interstitial oxygen ordering along the c -axis (stage 3), although no experimental evidence for this has been found.

In this work some members of the La 2-x Sr x Cu 1- x/2 Ti x/2 O 4-δ and La 2-x Sr x Cu 0.5 Ti 0.5 O 4-δ families have been synthesised in the composition ranges 0.1≤x≤1.5 and 1.0≤x≤1.5, respectively. A complete solid solution between La 2 CuO 4 and Sr 2 TiO 4 , has been found by X-ray powder diffraction and no evidence of Cu/Ti ordering has been found either by these means or by electron diffraction, compositions being checked by energy dispersive analysis by X-rays (EDAX). Samples were compared before and after oxidation with BrO - and only materials with stoichiometries close to LaSrCu 0.5 Ti 0.5 O 4-δ and La 1.9 Sr 0.1 Cu 0.95 Ti 0.05 O 4-δ could be oxidised in these conditions. Paramagnetic susceptibilities showed the presence of small fractions of superconducting phases (T c values close to 30 K) for samples with low titanium content (x≤0.2).

International audience; A detailed study of the structure and properties for the as-prepared and oxygen annealed Mo0.3Cu0.7Sr2TmCu2Oy material is reported. The Cu/Mo cationic distribution is established using a combination of x-ray/neutron powder diffraction refinement. The chemical substitution of the Mo ions for the Cu ions in the CuYSr2Cu2O7−δ structure is found to occur in both of the copper sites for the as-prepared sample. Interestingly, no trace of Mo substitution in the copper plane site is found to occur after oxygenation. The as-prepared Mo0.3Cu0.7Sr2TmCu2Oy material is found to be a spin glass (SG) system and explained on the basis of the cluster-by-cluster freezing model. On the other hand, the oxygen annealed material is superconducting (SC) (TSC,onset = 31 K). A peak has been observed in the critical current density plot and can be explained on the basis of field induced pins. The influence of oxygen annealing in the structure and properties of this material are presented and discussed. This seems to be the first case of a SG-SC transformation following an oxidation reaction in cuprates.

The insertion of oxygen within the structure of La 2− x Ba x CuO 4+ y ( x ≤ 0.15), by means of room-temperature chemical oxidation, modifies both the physical and the structural features of these materials. Concerning the superconducting properties, the extra oxygen gives rise to an increase of T c . Regarding the crystal structure, the phase transitions HTT (F4/mmm) ⇔ LTO(Bmab) ⇔ LTT(P4 2 /ncm), that unoxidized materials undergo as the temperature decreases, seem to be hindered by the presence of the interstitial oxygen. Similarities and differences concerning the modifications induced by this oxidation process in the present series of La 2− x Ba x CuO 4+ y compounds and in equivalent La 2− x Sr x CuO 4+ y materials are discussed.

In the search for new intercalation electrode materials, several phases related to the compound Bi 4 V 2 O 11 have been tested as positive electrodes in room temperature electrochemical lithium cells. Bi 4 V 2 O 11 , Bi 3.6 Pb 0.4 V 2 O 11− y and Bi 4 V 1.8 Cu 0.2 O 11− y are structurally similar compounds differing only from a microstructural point of view. Electrochemical lithium intercalation is not affected by such structural and compositional differences, since the performance of all these phases is equivalent. The surprising amount of 8 lithium ions per vanadium atom inserted in Bi 4 V 2 O 11 during the first discharge at an average potential of 1.7 V implies a theoretical specific energy of 655 W h/Kg. In spite of this promising value, the irreversibility found after the first discharge slightly reduces the possibilities of these materials as positive electrodes in room temperature rechargeable lithium batteries. Even so, the energy density is high enough to consider the materials for future improvements.

The microstructure of La0.5 Li0.5TiO3 can be considered as being formed by microdomains of a diagonal perovskite where the c-axis is oriented along the three space directions. The coalescence of some of these microdomains produces in some places a double 2ap × 2ap cell. Lithium can be intercalated in La0.5 Li0.5TiO3 through a reversible intercalation reaction to form La0.5 Li0.5TiO3. On the way to this phase another two phase regions are detected. The occupancy of three different sites for intercalated lithium is likely at the origin of these three phases.

Sodium removal from Na x Fe x Ti 2 − x O 4 by means of the oxidising agent nitrosonium tetrafluoroborate (NO 2 BF 4 ) leads to the formation of the solid solution Na x − δ Fe x Ti 2 − x O 4 . The homogeneity range of Na x − δ Fe x Ti 2 − x O 4 was determined from the results of single-crystal X-ray structure analyses of several specimens. The sodium content in the as-grown crystals ranges from 0.58 up to 0.87, while the upper level of sodium extraction was δ ≈ 0.30 for a sodium content of 0.79 in the starting sample. When sodium is removed from the material a considerable change in the lattice parameters and a rearrangement of the framework are observed. No evidence was found for the splitting of the unique sodium position for low sodium content.

New tungsten bronzes, Mg x WO 3 and Mg x W 18 O 49 , have been synthetized by magnesium chemical insertion reaction. For the former case, two blue bronzes with composition Mg 0.09 WO 3 and Mg 0.15 WO 3 have been isolated through a topotactic reaction that keeps the parent hexagonal structure unaltered. In the case of W 18 O 49 , a new compound with composition Mg 0.9 W 18 O 49 and lattice parameters close to those of W 18 O 49 has been synthetized. We have also studied the electrochemical lithium insertion in h-Mg x WO 3 and Mg itx W 18 O 49 . In this way, different phases have been detected in the systems Li-Mg x WO 3 and Li-Mg x W 18 O 49 and a relationship between the maximum quantity of lithium inserted and the magnesium content is deduced and discussed in terms of the ionic potential of the intercalated ions.