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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.

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.

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.

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.

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.

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.

The ionic conductivity of some double rate-earth chromates MLn(CrO 4 ) 2 (M=Na, K, Rb; Ln=La, Eu, Lu) has been analyzed by means of admittance spectroscopy. Real and imaginary part of the permittivity show the frequency power dependence characteristic of many-body interactions between mobile ions. Ac conductivity parameters are correlated with structural details of the compounds studied.

Novel materials, LixBa2YCu3O7-y(0≤x≤2), have been obtained by reaction of Ba2YCu3O7-y with n-butyl lithium. The most striking feature of these materials is the coexistence of both ionic conductivity and superconductivity for 0

A novel procedure for growing single crystals of the title phases has been found by dissolving (RE) 2 CuO 4 in appropriate liquid mixtures of BaO-CuO. The soaking conditions are, in each cases, different and the crystals were further annealed in pure oxygen. Symmetry, contamination from the crucible and superconducting properties are related to the growth conditions which are presented and discussed. Magnetic susceptibility measurements have been carried out down to 4.2 to both determine T c and the oxidation states of the rate earths.

New BPB materials have been obtained by cationic sunbstitution in the B sublattice of the perovskite type structure. Both, non magnetic (Ga, In, Y) and magnetic (Eu, Ho, Yb) trivalent cations have been used to partially substitute lead. The structure remains tetragonal, like the parent BPB-albeit T c gets lower.