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In this work, we examine the benefits of alternative powder processing methods, with a primary focus on microwave-based synthesis, that could both lower material manufacturing costs and further enhance cathode performance for solid oxide fuel cell applications. La 0.3 Ca 0.7 Fe 0.7 Cr 0.3 O 3− δ (LCFCr), formed using conventional solid-state methods, has been shown in earlier work to be a very promising catalyst for the oxygen reduction reaction. To further increase its performance, microwave methods were used to increase the surface area of LCFCr and to decrease the synthesis time. It was found that the material could be obtained in crystalline form in only 7 h, with the synthesis temperature lowered by roughly 300 °C as compared to conventional methods.

A novel mixed-conducting perovskite oxide (La0.3Ca0.7Fe0.7Cr0.3O3−δ, LCFCr), prepared using the combustion method, has been developed as a new air electrode material for reversible solid oxide fuel cells (RSOFCs) applications. XRD analysis showed that the LCFCr powder is a pure crystalline phase with an orthorhombic perovskite structure and that its thermal expansion coefficient matches closely with several commonly used solid electrolytes, while TEM analysis confirmed the high purity of the LCFCr powders. The electrochemical activity of LCFCr, screen-printed on a gadolinium doped ceria electrolyte, towards both the oxygen reduction (ORR) and oxygen evolution (OER) reactions, was examined at 600–800 °C in stagnant air using a symmetrical RSOFC configuration. Under open circuit conditions, LCFCr showed a very low polarization resistance (Rp) of only 0.07 Ω cm2 at 800 °C, comparable to some of the best-performing oxide materials reported by others. The LCFCr air electrode was also found to be very stable, with very little loss in performance and no interfacial damage observed, even after 100 h at a 0.4 V (OER) and −0.4 V (ORR) overpotentials.

We describe the synthesis, crystal structure, magnetic and electrochemical characterization of new rock salt-related oxides of formula, Li{sub 3}M{sub 2}RuO{sub 6} (M=Co, Ni). The M=Co oxide adopts the LiCoO{sub 2} (R-3m) structure, where sheets of LiO{sub 6} and (Co{sub 2}/Ru)O{sub 6} octahedra are alternately stacked along the c-direction. The M=Ni oxide also adopts a similar layered structure related to Li{sub 2}TiO{sub 3}, where partial mixing of Li and Ni/Ru atoms lowers the symmetry to monoclinic (C2/c). Magnetic susceptibility measurements reveal that in Li{sub 3}Co{sub 2}RuO{sub 6}, the oxidation states of transition metal ions are Co{sup 3+} (S=0), Co{sup 2+} (S=1/2) and Ru{sup 4+} (S=1), all of them in low-spin configuration and at 10 K, the material orders antiferromagnetically. Analogous Li{sub 3}Ni{sub 2}RuO{sub 6} presents a ferrimagnetic behavior with a Curie temperature of 100 K. The differences in the magnetic behavior have been explained in terms of differences in the crystal structure. Electrochemical studies correlate well with both magnetic properties and crystal structure. Li-transition metal intermixing may be at the origin of the more impeded oxidation of Li{sub 3}Ni{sub 2}RuO{sub 6} when compared to Li{sub 3}Co{sub 2}RuO{sub 6}. Interestingly high first charge capacities (between ca. 160 and 180 mAh g{sup −1})more » corresponding to ca. 2/3 of theoretical capacity are reached albeit, in both cases, capacity retention and cyclability are not satisfactory enough to consider these materials as alternatives to LiCoO{sub 2}. - Graphical abstract: Two new rock salt related oxides of formula, Li{sub 3}M{sub 2}RuO{sub 6}, (M=Co, Ni) have been prepared. The M=Co oxide adopts the LiCoO{sub 2} (R-3m) structure and the M=Ni oxide adopts a similar layered structure related to Li{sub 2}TiO{sub 3,} monoclinic (C2/c), with partial mixing of Li and Ni/Ru atoms. For Li{sub 3}Co{sub 2}RuO{sub 6}, oxidation state for Ru is 4+ and antiferromagnetic (AFM) order is found below 10 K while for the analogous Li{sub 3}Ni{sub 2}RuO{sub 6} , Ru oxidation state is 5+ and a ferrimagnetic (FM) behavior with a Curie temperature of 100 K is found. Electrochemical studies correlate well with both magnetic properties and crystal structure. - Highlights: • New Ruthenium rock salt-related oxides of formula, Li{sub 3}M{sub 2}RuO{sub 6} (M=Co, Ni) were studied. • Structurally different: rhombohedral α-NaFeO{sub 2}-type (Co) and monoclinic Li{sub 2}TiO{sub 3}-type (Ni) • Magnetic behavior is different: the Co sample is AFM while the Ni one is ferrimagnetic. • Ruthenium oxidation states are different: 4+ in the Co sample and 5+ in the Ni one. • Electrochemical studies correlate well with magnetic properties and crystal structures.« less

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.

Ce 0.85 RE 0.15 O 1.925 (RE = Gd, Sm), Ce 0.8 (Gd 0.1 Sm 0.1 )O 1.9 and CeO 2− δ nano-powders were synthesized by microwave-assisted hydrothermal synthesis in a time and energy efficient way. The fluorite-type crystal structure of the synthesized nano-powders was confirmed by X-ray diffraction (XRD) and Rietveld refinement, and the nano-metric particle sizes calculated from the XRD line width broadening were consistent with transmission electron microscopy observations. The Brunauer–Emmett–Teller method was used to confirm large powder surface area. Scanning electron microscopy confirmed high density and low surface porosity of the sintered ceramics as a result of the high sintering activity of the large surface area nano-powders. Impedance spectroscopy was carried out to separately analyze grain boundary (GB) and bulk dielectric relaxations where GB areas were found to constitute ionic charge transport barriers, because their resistance was larger than that of the bulk. Such barriers were found to be comparatively low due to high GB and bulk ceramic ionic conductivities, with the highest values encountered in the composition Ce 0.85 Sm 0.15 O 1.925 . The optimal ionic conductivities encountered were associated with the effect of high sintering activity of the nano-powders.

The title compound has been synthesized by the hydroxide route. The crystal structure has been investigated at room temperature from high-resolution neutron powder diffraction (NPD) data. It crystallizes in a cubic spinel structure, space group F d 3 ¯ m , Z = 8, with a = 8.3940(2) A at 295 K. The crystallographic formula is (Ni 0.202(1) Mn 0.798(1) ) 8a (Ni 0.790(1) Mn 1.210(1) ) 16d O 4 where 8 a and 16 d stand for the tetrahedral and octahedral sites of the spinel structure, respectively. There is a significant inversion degree of the spinel structure, λ = 0.80. In fact, the variable parameter for the oxygen position, u = 0.2636(4), is far from that expected ( u = 0.25) for normal spinels. From a bond-valence study, it seems that the valence distribution in NiMn 2 O 4 spinel is not as trivial as expected (Ni 2+ and Mn 3+ ), but clearly the tetrahedral Mn ions are divalent whereas the octahedral Mn and Ni are slightly oxidized from the expected +3 and +2 values, respectively. The mixed valence observed at the octahedral sites provides the charge carriers that, by a hopping mechanism between Mn 3+ /Mn 4+ adjacent sites, leads to a significant conductivity, up to 0.85 S cm −1 at 800 °C in air.

Rare-earth chromite ErCrO 3 powder was synthesized from metal nitrate precursors using microwave synthesis. (Micro-) structural characterizations were performed using X-ray diffraction, Rietveld refinement, High Resolution Transmission Electron Microscopy and Electron Micro-Diffraction. Magnetization vs. temperature measurements revealed anti-ferromagnetism with T Neel ≈ 135 K. An anti-ferrimagnetic moment of ≈0.4 μ B was determined from magnetization vs. applied field measurements. Temperature dependent impedance spectroscopy (IS) indicated 3 dielectric relaxation processes: electrode interface, grain boundary and bulk. The intrinsic bulk activation energy was found to be 0.27 eV and the dielectric permittivity ɛ r was ≈23 in excellent agreement with Clausius–Mossotti predictions and showed no perceptible temperature dependence. This and the low ɛ r value suggested that ErCrO 3 is a dielectric rather than ferroelectric compound. IS measurements with applied dc bias revealed the signs of an unconventional type of Schottky barrier at the metallic Au electrode/ceramic ErCrO 3 interface.

Multiferroic BiFeO3 has been rapidly synthesized by a microwave – hydrothermal method using nitrates as the metallic source. Structural characterization was performed by thermal analysis, X-ray diffraction and transmission electron microscopy. Generally accepted trigonal space group R3c, as well as recently suggested monoclinic symmetries, were assayed in the search for the best fit. Due to the ambiguity of the Rietveld refinement to distinguish between crystal systems, a micro-diffraction and HRTEM study has been performed. The best solution was obtained with the trigonal model. The room-temperature Mossbauer spectra reveal the presence of a small fraction (2%) of iron in low spin configuration.

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.

Microstructural, magnetothermal and dielectric properties of YCrO3 powders prepared by combustion and solid state methods have been studied by a combination of XRD, specific heat, magnetization and permittivity measurements. The TEM and XRD characterization confirm that the combustion powders are amorphous plate-like agglomerates of nano-sized crystalline particles. A more uniform grain size along with an increase of the relative density is observed by SEM in the sintered samples prepared by combustion route with respect to those produced by solid state reaction. Similar to the material obtained through solid state synthesis, the material prepared by the combustion method also shows spin canted antiferromagnetic ordering of Cr+3 (S=3/2) at ∼140 K, which is shown by magnetization as well as λ-type anomaly in the total specific heat. Furthermore, the magnetic contribution to the total specific heat reveals spin fluctuations above TN and a spin reorientation transition at about 60 K. Both YCrO3 compounds show a diffuse phase transition at about 450 K, typical of a relaxor ferroelectric, which is characterized by a broad peak in the real part of the dielectric permittivity as a function of temperature, with the peak decreasing in magnitude and shifting to higher temperature as the frequency increases. The relaxor dipoles are due to the local non-centrosymmetric structure. Furthermore, the high loss tangent in a broad range of temperature as well as conductivity analysis indicates a hopping mechanism for the electronic conductivity as we believe it is a consequence of the outer d3-shell, which have detrimental effects on the polarization and the pooling process in the YCrO3 bulk material. The more uniform particle size and higher density material synthesized through the combustion process leads to an improvement in the dielectric Properties.

Nanocrystalline (between 30 and 40 nm) LiCoO2 and LiCo1−xGaxO2 (0 ≤ x ≤ 0.15) powders have been prepared by using a standard microwave furnace. Depending on the power and irradiation time, nanosized LT-LiCo1−xGaxO2 (cubic) or HT-LiCo1−xGaxO2 (hexagonal) (0 ≤ x ≤ 0.15) materials have been obtained and studied by means of X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrochemical characterization and magnetic behaviour of the electrochemical active polymorphs (HT-phases) have also been investigated.

In this work, three different methods for preparing BiFeO3 polycrystals are compared: hydrothermal synthesis, microwave heating in the solid state and the combination of both, that is a hydrothermal method using microwave heating. The best materials, without high purity reactants, are obtained in few minutes by the last procedure, a new, very fast, reproducible and environment-friendly method of synthesis, which is described and discussed here.

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.

Olivine-LiCoXO4 (X = P, As) compounds might transform to the denser spinel-type and Na2CrO4-type structures under pressure. In this work, the relative energetic stability of the three polymorphs and the pressure of the possible polymorphic transformations are investigated combining experiments and first principles calculations. Olivine-LiCoAsO4 is predicted to transform to the Na2CrO4-like structure at 0.4 GPa and to the spinel structure at 5.8 GPa (0 K). Quenching HP/HT experiments show that olivine-LiCoAsO4 treated at 6 GPa/1173 K transforms to the spinel-like structure. Computational results indicate that olivine-LiCoPO4 transforms to the Na2CrO4-like form at around 4 GPa (0 K), the latter being the stable form till very high pressures (21.6 GPa). In good agreement with this, olivine-LiCoPO4 when subjected to 6 GPa/1173 K and 15 GPa/1173 K is converted to the Na2CrO4-type polymorph. Crystallographic data of the new compound LiCoPO4 within the Na2CrO4 structural type are provided.

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.

Iron oxychloride has been lithiated by the reaction with n -butyllithium and thereafter exposed to air. Lithium intercalation increases several orders of magnitude of the electrical conductivity of the pristine material although the intercalate remains a semiconductor. This phase, after being exposed to atmospheric humidity becomes an ionic conductor, with a conductivity comparable to that of some molten salts, and does not show electronic conduction in the whole range of temperatures of measurement (150–300 K), a strong non-Arrhenius behaviour being observed. Impedance spectroscopy and NMR techniques, among others, have been used to follow this behaviour.

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.

The effects of zinc substitution in the structural and magnetic properties of the orthorhombic solid solution SeCu1� xZnxO3 have been studied. Rietveld refinements of the X-ray diffraction patterns indicate that the zinc ions occupy the copper sites. This replacement induces some changes in the Cu–O bond lengths and /Cu–O–CuS bond angles. Magnetization vs temperature measurements show a fast decrease in the Weiss constant that reveals a direct quadratic relationship with the increase of the average /Cu–O–CuS bond angle. Besides, the introduction of a non-magnetic cation in the B-positions in the structure of SeCu1� xZnxO3 system, progressively decreases the ferromagnetic interactions. # 2002 Elsevier Science (USA)

The reaction of iron oxychloride with n-butyl-lithium has been re-examined, important changes being found in the structure and properties of the lithiated compounds as compared to the pristine material. Lithium intercalation by these means increases several orders of magnitude the electrical conductivity of FeOCl although the intercalate remains semiconductor. From the structural and microstructural point of view the lithiation results in complex changes, including inter alia staging, superstructures, etc., and it seems to be quite an heterogeneous process.

A new oxygen-deficient and ordered perovskite-type structure with the formula Sr(Sr 0.5 Sb 0.5 )O 3− y has been synthesized readily by a solid state reaction in air at 1200°C. The structure of the Sr(Sr 0.5 Sb 0.5 )O 3− y phase as determined by Rietveld analysis using X-ray diffraction data, corresponds to an ordered perovskite with face-centered cubic symmetry, space group Fm 3 m (no. 225) and lattice parameters, a =8.3136(3) A, V =574.602(3) A 3 and Z =8. An important structural feature of Sr(Sr 0.5 Sb 0.5 )O 3− y is the oxygen deficiency and the displacements of oxygen atoms from their ideal positions toward the Sb 5+ cations. This fact leads to an alternating arrangement of larger [SrO 6 ] and smaller [SbO 6 ] octahedra (B-sites), the remaining Sr 2+ being in the larger 12-fold coordinated A-sites. The thermal stability of the Sr(Sr 0.5 Sb 0.5 )O 3− y phase is pointed out, its melting point being 1480°C, and the subsequent quenching giving rise to a glass material.

We present results of an electrochemical intercalation study of Zn into β-ZrNCl, β-ZrNBr and β-HfNCl. For β-ZrNCl an intercalation reaction takes place, leading to the final compound Zn0.04ZrNCl with a superconducting transition temperature Tc of 15 K. A similar behaviour is observed for β-ZrNBr where the insertion reaction produces the superconducting compound Zn0.04ZrNBr with a Tc of 14 K, whereas attempts to obtain ZnxHfNCl superconductors applying the same conditions failed. In comparison to β-MNX compounds with monovalent inserted ions, superconductivity in Zn doped β-MNX occurs at much lower levels of electron doping, although the values of Tc are similar.

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.

Several compositions in the system Sr (1.45–x) Ca x Sb 0.55 O 3–y (0 ⩽ x ⩽ 1.45) have been synthesized by solid state reaction in air at 1000°C and investigated by powder X-ray diffraction and EDS microanalysis. They exhibit good thermal stability up to 1200°C. The solid solution range was delimited in the composition 0 ⩽ x ⩽ 1.1. For quantities of Ca 2+ higher than 1.1, the amount of solid solution decreases and another phase, Ca 6 Sb 2 O 10 , appears. The lattice parameters of the system Sr (1.45–x) Ca x Sb 0.55 O 3–y decrease with increasing Ca 2+ content.

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.

ZrW 2 O 8 samples have been prepared from ZrO 2 and WO 3 precursors by a ceramic method. Different portions of this material were subjected to non cumulative pressure treatments within the 2–65 Kbar range; the metastable high-pressure phase, γ-ZrW 2 O 8 , has been isolated by quenching from 6 Kbar. Further pressure increases up to 10 Kbar produced the volume reduction of the γ-phase; a minimum volume was found even after having released the pressure. Otherwise, heating above 600°C, followed by quenching at 77 K leads to the high-temperature phase, β-ZrW 2 O 8 , which is stable at room temperature. Finally, when γ-ZrW 2 O 8 was subjected to pressure and temperature, γ-ZrW 2 O 8 could also be quenched with a still larger volume reduction at 6 Kbar and 600°C.

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.

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.

In the present work, the evolution of an oxidised sample of composition La 2 CuO 4.103(4) along a thermal treatment has been studied and the stabilisation of a novel phase with a well-defined excess of oxygen has been proven by means of real-time synchrotron X-ray diffraction experiments. The stability of this phase, La 2 CuO 4.086(4) , seems to be due to the presence of one-dimensional interstitial oxygen ordering along the c -axis, as suggested by the appearance of a pair of superlattice satellite peaks around the mixed parity (012) peak position in a synchrotron X-ray diffractogram collected at 110 K.

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.

Complex admittance measurements are performed on Na{sub x{minus}{delta}}Fe{sub x}Ti{sub 2{minus}x}O{sub 4} (x = 0.875, 0 {le} {delta} {le} 0.40) polycrystalline samples, which have been prepared by the standard ceramic method and further treated by soft chemistry extraction reactions. The parent, nonextracted sample has a Na content of 0.875 ions per formula and shows a single activation energy in the dc conductivity of 1.1 eV. The conduction process is due to ion motion along the double tunnels parallel to the short b axes of the quadruple rutile structure. When Na is removed, a decrease in the activation energy is observed. This can be interpreted in terms of an increased ion mobility due to the increased number of vacancies created on sodium extraction. In addition, a second, less activated process, which is attributed to an electronic contribution produced by the partial oxidation of Fe{sup 3+} to Fe{sup 4+}, appears on Na removal.

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.

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.

The crystallographic structure of a hyperstoichiometric Ni 1+ x Fe 2−2 x /3 O 4 ( x =0.30) spinel-like material, obtained by a soft chemistry synthetic route, has been refined by combining X-ray and neutron powder diffraction data. This compound shows a structure intermediate between the rocksalt and the spinel structure types. The results of the refinement of the magnetic structure are also presented and discussed.

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.

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.

The crystal structure, superconducting properties and oxygen stoichiometry of room temperature chemically oxidized La 2− x Sr x CuO 4 + y ( x = 0.05, 0.09) have been studied by means of powder neutron diffraction, magnetic susceptibility and thermogravimetric analysis. The presence in these materials of interstitial oxygen located at ( 1 4 , y, 3 4 ; y ≈ 1 4 , as previously observed in oxygen-rich La 2 CuO 4 + y , is proposed from neutron diffraction data at different temperatures. This is supported by the excess of mass loss detected by TG for the oxidized materials relative to the starting ones. Besides, an important improvement in the superconducting properties ( T c and superconducting volume fraction) of these compounds is observed after oxidation. On the other hand, no phase separation into two phases with different oxygen content is observed at low temperature.

The coexistence of superconductivity and magnetic order seems to take place in the so called ruthenate-cuprates. Previous work has mainly focused on RuSr 2 GdCu 2 O 8 where a magnetic transition is observed at 133 K and superconductivity has been claimed below T c ∼46 K. 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 pressures and temperatures allows one to replace gadolinium by other lanthanide cations, although it is difficult to get pure samples. In order to better understand this, rather unusual behaviour, we have performed some substitutions in the title compound. The synthesis at high pressures (∼60 kbar) and high temperatures (∼1100 °C) of the title new ruthenates has been achieved and the materials compared to the gadolinium analogue. The structure remains tetragonal (Space group: P 4/ m m m ) and the cell parameters linearly decrease following the lanthanide contraction. We have succeeded in replacing Gd by Tb, Dy, Y, Ho and Er, magnetic susceptibility measurements reveal the existence of interesting phenomena. The microstructure of these compounds has been studied by high-resolution electron microscopy. Also, at room pressure, we have replaced up to 10% calcium for strontium and observed that, in consonance with the difference in ionic radii, the unit cell contracts. On the other hand, the calcium-doped sample shows a positive magnetic susceptibility at 5 K.

New mixed conductors have been obtained by the reaction of n -BuLi with Pb 2 Sr 2 Y 1−x Ca x Cu 3 O 8+δ (0.5 ⩽ x ⩽0.7). In these materials lithium ionic and electronic conductivity coexist at high temperature, superconductivity remaining below 80 K. A method to separate the electronic and ionic components of the conductivity is proposed.

Synthesis and characterization of nickel and magnesium ferrites obtained by ionic exchange reactions in molten salts are presented. Although their structure is quite close to the spinel one, the ideal composition MFe 2 O 4 (M:Ni, Mg) is not obtained. Instead, some extra octahedral sites are occupied thus, the structure is better described as intermediate between the spinel and defective NaCl one.

New phases of the title family of compounds have been prepared and the synthesis conditions have been optimized. In spite that iron and copper are located in different crystallographic positions, as deduced from Mossbauer analysis, doping of the copper-oxygen planes induced by partial cationic substitution in the trivalent site does not produce superconductivity.

Experiments on the chemical lithiation of Ba2YCu3O7 and related materials have been performed previously by the authors [1–4]. One of the main results of that work is the room temperature formation of “124” from “123”. Here a simple ionic model is used to give an estimate of the activation energy for lithium motion which is in good agreement with experimental values obtained from conductivity measurements. Lithium diffusion seems to be favoured in the “124” compared with “123”. This result is discussed on the basis of the structure of these phases.