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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

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.

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 full rare earth chromite series LnCrO3 and the isostructural compound YCrO3 are prepared from mixtures of appropriate amounts of Cr(NO3)3 and Ln(NO3)3 with amorphous carbon as microwave absorber (porcelain crucible, microwave irradiation for 10 min, followed by heating at 500 and 800 °C for 2 h each, and sintering at 1300 °C for 15 h).

We report the effect of oxygen-annealing in the superconductivity and electronic states for the Mo0.3Cu0.7Sr2YCu2O y compound. The influence of oxygen annealing in the electronic states for Mo0.3Cu0.7Sr2YCu2O y associated with a nonsuperconducting to superconducting state transformation has been investigated by means of X-ray photoelectron spectroscopy, powder X-ray diffraction, magnetic susceptibility, and resistivity measurements. We unambiguously show the preeminence of the MoV state over the MoVI one; annealing under an oxygen atmosphere enhances both the MoVI and CuII amounts. The enhancement of MoVI after oxygen annealing is in close relation with the decrease in the O 2p→Cu 3d charge-transfer energy resulting in superconducting properties. Oxygen annealing is then seemed to reduce the copper plane hole concentration of the overdoped as-prepared sample, which induces superconductivity in the Cu–O planes.

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.

A three-dimensional antiferromagnetic ordering 3D-AF atT N ≈12K has been observed in these nonsuperconducting phases. In the compounds where a partial trivalent-divalent cationic substitution (Y by Ca or La by Sr) has been performed, this antiferromagnetic ordering is not observed above 4 K. Mossbauer spectroscopy studies indicate a unique iron environment and magnetic ordering; the spectra are consistent with the classic high spin Fe3+ although in an unusual fivefold coordination. Both the herein described transition and the formerly reported one at ∼460 K are affected upon doping.

The full rare-earth (RE) chromites series (RE)CrO(3) with an orthorhombic distorted (Pnma) perovskite structure and the isostructural compound YCrO(3) can be synthesized through a simple microwave-assisted technique, yielding high-quality materials. Magnetization measurements evidence that the Néel temperature for antiferromagnetic Cr(3+)-Cr(3+) ordering strongly depends on the RE(3+) ionic radius (IOR), and a rich variety of different magnetic spin interactions exists. Dielectric spectroscopy on sintered pellets indicates electronic inhomogeneity in all samples as manifested by the presence of at least two dielectric relaxation processes associated with grain boundary and grain interior bulk contributions. X-ray diffraction, Raman spectroscopy, and temperature-dependent dielectric permittivity data do not indicate potential noncentrosymmetry in the crystal or concomitant ferroelectricity. Strong correlations between the magnetic and dielectric properties were not encountered, and microwave-synthesized (RE)CrO(3) may not be classified as magnetoelectric or multiferroic materials.

The primary focus of our work has been on the development of a stable mixed ionic and electronic conducting (MIEC) oxide electrode that is catalytic for application as an air electrode in reversible solid oxide fuel cells (RSOFCs). For this purpose, our recently developed La0.3Sr0.7Fe0.7Cr0.3O3-δ (LSFCr) material [1], shown to be active as both an anode and cathode material in symmetrical SOFCs, has been modified by replacing the Sr in the A site with Ca, producing La0.3Ca0.7Fe0.7Cr0.3O3- δ (LCFCr), which has been shown to be a very promising oxygen and fuel electrode for reversible SOFCs [2-4]. In the present work, we are working towards a solid oxide fuel cell/electrolysis cell that is fabricated entirely with the use of MW techniques, starting with the synthesis of the electrode/electrolyte powders and including the sintering of the full cell. We have already demonstrated that the LCFCr material can be produced from the precursor salts by microwave (MW) methods, showing that the pure phase can be obtained at a much lower synthesis temperature (300 oC) and that the synthesis time can be cut down by ca. 50% as compared to conventional solid-state processing methods [5]. Another outcome is that there is a significant increase in its surface area (10.4 m2 g-1) vs. what is obtained using standard methods, i.e., 0.89 m2 g-1 ) [5]. More recently, we have developed an effective method for the MW co-sintering of the anode-electrolyte-cathode combination in one simple step. This approach, in which sintering temperatures as high as 1000 oC can be achieved in just a few minutes, would have a significant impact on both lowering material and cell manufacturing costs and on further enhancing the performance of these cells. In this work, the LCFCr perovskite powders were first formed using MW methods and were then screen-printed on both sides of a gadolinia-doped ceria (GDC) electrolyte, followed by MW-assisted sintering of the cell. It is worth noting that there were no MW susceptors added in any of the fabrication steps and the normal pre-sintering steps used in conventional furnaces were also not needed. We show that these LCFCr/GDC/LCFCr cells, sintered using only MW methods, gave performances that were very similar to cells fabricated using normal ceramic processing methods. However, the time required to achieve this was decreased by ca. ten times, thus translating to significant savings in manufacturing costs. References [1] M. Chen, S. Paulson, V. Thangadurai, V. Birss, Sr-rich chromium ferrites as symmetrical solid oxide fuel cell electrodes, Journal of Power Sources, 236 (2013) 68-79. [2] P.K. Addo, B. Molero-Sanchez, A. Buyukaksoy, S. Paulson, V. Birss, Sulfur Tolerance of La0.3M0.7Fe0.7Cr0.3O3 -δ (M= Sr, Ca) Solid Oxide Fuel Cell Anodes, ECS Transactions, 66 (2015) 219-228. [3] B. Molero-Sánchez, P.K. Addo, A. Buyukaksoy, V. Birss, GDC-Infiltrated La0.3Ca0.7Fe0.7Cr0.3O3-δ Symmetrical Oxygen Electrodes for Reversible SOFCs, ECS Transactions, 66 (2015) 185-193. [4] B. Molero-Sánchez, J. Prado-Gonjal, D. Ávila-Brande, M. Chen, E. Morán, V. Birss, High performance La0.3Ca0.7Cr0.3Fe0.7O3−δ air electrode for reversible solid oxide fuel cell applications, International Journal of Hydrogen Energy, 40 (2015) 1902-1910. [5] B. Molero-Sánchez, J. Prado-Gonjal, D. Ávila-Brande, V. Birss, E. Morán, Microwave-assisted synthesis and characterization of new cathodic material for solid oxide fuel cells: La0.3Ca0.7Fe0.7Cr0.3O3−δ, Ceramics International, 41 (2015) 8411-8416.

High-Tc superconducting YBa2Cu3O7 ceramic samples are lithiated by the reaction with n-butyllithium. For lithium nominal contents less than unity per formula the presence of '123' and '124' phases are deduced from X-ray diffraction and high-resolution electron microscopy experiments. NMR and impedance spectroscopy techniques have been conducted in a sample with a nominal Li content of 0.9 per formula. Spin-lattice relaxation times and electrical conductivity relaxation (ECR) are measured as a function of temperature. NMR and ECR data are interpreted in terms of a stretched exponential decay function in the time domain. Microscopic activation energies for lithium motion of 0.49 eV (NMR measurements) and of 0.41 eV (ECR) are deduced for short range motion. Activation energies for long range motion of 0.98 eV (NMR) and 1.03 eV (ECR) are also deduced.

There is great interest in the development of SOFCs that can be operated in reverse in the electrolysis mode, thus producing fuels and oxygen, while also serving as an electricity storage medium for renewable energy. In the solid oxide electrolysis cell (SOEC), steam can be converted to H2 and O2 while steam together with CO2 can generate syngas and O2. High temperature operation (700-950 oC) of water electrolysis cells significantly increases the performance of SOECs, as compared to PEM-based electrolysis systems. However, an obstacle for operating at high temperatures is the lower stability of materials, although the significant progress made in the development of SOFC materials is a significant asset to SOECs as well [1]. Even so, the operating conditions in SOECS are quite different than in SOFCs, and thus new problems are emerging, including the delamination of the SOEC anode from the electrolyte, oxidation of Ni in the SOEC cathode as a result of the high levels of steam present, and sulfur poisoning of the Ni cathode [2]. Therefore, research is this field is moving towards the use of mixed ionic and electronic conducting oxides, which have been shown to be more stable as oxygen electrodes than conventional LSM materials [3]. Previous research in our group has been focused on the development of robust sulfur and coke tolerant electrode-supported SOFCs, based primarily on very promising metal oxide materials currently being developed in our group, which have shown very good catalytic activity for both H2/CO oxidation and O2 reduction. These are based on a La0.3Sr0.7Fe0.7Cr0.3O3-δ (LSFCr) mixed ionic-electronic conducting (MIEC) perovskite material [4, 5]. Because of the excellent performance of LSFC, efforts have been made to further improve its properties. Thus, the A-site of the perovskite was doped with Ca instead of Sr, producing La0.3Ca0.7Fe0.7Cr0.3O3-δ (LCFCr), shown to be a very promising oxygen and fuel electrode for reversible SOFCs [6-8]. The main goal of the introduction of Ca was to decrease the thermal expansion coefficient of this derivative of LSFCr, in order to more closely match that of a Gd-doped ceria (GDC) electrolyte[8].The partial substitution of Sr by Ca may also enable the introduction of structural inhomogeneities, as Ca doping of LaFeO3 is known to promote oxygen-vacancy ordering [9]. We have also demonstrated that the LCFCr material can be produced by microwave (MW) methods, showing that the pure phase can be obtained at a much lower synthesis temperature of only 300 oC, the synthesis time can be cut down by ca. 50%, and there is a significant increase in its surface area (10.4 m2 g-1 vs 0.89 m2 g-1 ) [10]. In this work, we are focussed on working towards a solid oxide fuel cell/electrolysis cell that is fabricated entirely with the use of MW techniques, starting with the synthesis of the electrode/electrolyte powders and including the sintering of the full cell. An effective method has been developed for the MW co-sintering of the anode-electrolyte-cathode combination in one simple step. This approach, in which sintering temperatures as high as 1000 oC can be achieved in just a few minutes, would have a significant impact on both lowering material and cell manufacturing costs and on further enhancing the performance of these cells. Thus, the LCFCr perovskite powders were first formed using MW methods and were then screen-printed on both sides of a gadolinia-doped ceria (GDC) electrolyte, followed by MW-assisted sintering of the cell. It is shown that these LCFCr/GDC/LCFCr cells, sintered using only MW energy, gave performances that were very similar to cells fabricated using normal ceramic processing methods. However, the time required to achieve this was decreased by ca. ten times, thus translating to significant manufacturing cost savings. Acknowledgements: We are very grateful to the SOFC Canada NSERC Strategic Research Network, as well as Carbon Management Canada, for the support of this work. . References: [1] A. Hauch et al., Solid State Ionics, 192 547-551. [2] A. Hauch et al., Journal of Materials Chemistry, 18 (2008) 2331-2340. [3] M.A. Laguna-Bercero et al., Journal of Power Sources, 203 4-16. [4] M. Chen et al., Journal of Power Sources, 236 (2013) 68-79. [5] P. Addoet al., 11th Europeand SOFC and SOE forum, Luzerne, Switzerland, 2014, pp. B0314. [6] P.K. Addo et al., ECS Transactions, 66 (2015) 219-228. [7] B. Molero-Sánchez et al., ECS Transactions, 66 (2015) 185-193. [8] B. Molero-Sánchez et al.,International Journal of Hydrogen Energy, 40 (2015) 1902-1910. [9] V.V. Kharton et al.,Chemistry of Materials, 20 (2008) 6457-6467. [10] B. Molero-Sánchez et al., Ceramics International, 41 (2015) 8411-8416.

Electrochemical lithium insertion into W18O49 has allowed the determination of the existence of a range of intercalated phases, LixW18O49. For x < 22 the phases form through an intercalation reaction and four single-phase regions are detected: x= 0–2.6, 3.4–10, 11–15, 15.5–22. In the last of these composition ranges and by reaction with n-butyllithium, a new phase, Li17W18O49, can be isolated that has a multiple cell, with respect to the starting phase. By following this chemical route, the maximum lithium content corresponds to Li40W18O49. Electrochemical experiments showed that lithium is not reversibly intercalated in this last phase.

By exposure of YBa2Cu3O7 to hydrogen at moderate temperatures, the superconductivity properties, Tc and Meissner volume fraction, are, depending on the treatment conditions, differently affected. Although no major changes are detected by X-ray diffraction, the microstructure of the obtained products is quite complex, and a significant amount of disorder is produced. The results are also compared with those produced in the reduction performed with n-butyllithium.

The new complex oxide (V0.5Re0.5)O2 has been synthesized under high pressure of 60 kbar at 1000°C, and its crystal structure determined by single crystal X-ray diffraction data analysis (S.G.: P42/mnm, a = 4.6357(4) Å, c = 2.8292(3) Å, V = 60.80(1) Å3). This compound adopts a rutile-type structure with random cat ion distribution on one crystallographic site. The substitution of 50 vanadium by rhenium stabilizes the high temperature form of VO2 at room temperature. The cation ratio of 1 : 1 was confirmed by EDX analysis performed by electron microscopy on the same crystals used for X-ray diffraction.

A systematic study is reported on the range of stability of molybdenum substituted Sr-based 123 compounds with Mo-Sr-Y-Cu system, synthesized under ambient pressure. All materials crystallize in the space group: P4/mmm and the observed solubility limit of Mo is rather low in this structure because secondary phases start to form as soon as x>0.3 in nominal composition is reached. The antiferromagnetic property in all superconducting multiphase samples can be attributed to the secondary phase Y{sub 2}Cu{sub 2}O{sub 5}. The influence of oxygen annealing on the changes in electronic structure for the pure Mo{sub 0.3}Cu{sub 0.7}Sr{sub 2}YCu{sub 2}O{sub y} system associated with a non-superconductor to superconductor transition has been investigated by means of X-ray photoelectron spectroscopy, powder X-ray diffraction, magnetic susceptibility and specific-heat measurements. We unambiguously show the predominance of the Mo{sup 5+} state over the Mo{sup 6+} one on both as-synthesized and annealed phases; annealing under an oxygen atmosphere enhances both the Mo{sup 6+} and Cu{sup 2+} amounts. We suggest that the enhancement of Mo{sup 6+} under oxygen annealing is in close relation with the decrease in the O 2p{yields}Cu 3d charge-transfer energy resulting in superconducting properties. - Graphical abstract: A study on the ambient-pressure synthesis and the range ofmore » stability of complex perovskites in the system Y-Sr-Cu-Mo shows that the solubility limit of Mo is rather low in this structure ({approx}30%). Secondary phases (detected by XRD) start to form for x>0.3 in nominal composition. All materials crystallize in the space group: P4/mmm. Antiferromagnetism in all superconducting multiphase samples is attributed to the secondary phase Y{sub 2}Cu{sub 2}O{sub 5}. Pure Mo{sub 0.3}Cu{sub 0.7}Sr{sub 2}YCu{sub 2}O{sub y} studied by means of powder X-ray diffraction, magnetic susceptibility and specific-heat measurements. Changes in electronic structure for the pure Mo{sub 0.3}Cu{sub 0.7}Sr{sub 2}YCu{sub 2}O{sub y} system associated with a non-superconductor to superconductor transition have been investigated by means of X-ray photoelectron spectroscopy (XPS). Highlights: Black-Right-Pointing-Pointer Solubility limit of Mo is rather low in Mo{sub x}Cu{sub 1-x}Sr{sub 2}YCu{sub 2}O{sub y} (x{approx}0.3). Black-Right-Pointing-Pointer Antiferromagnetism and superconductivity do not coexist. Black-Right-Pointing-Pointer Pure Mo{sub 0.3}Cu{sub 0.7}Sr{sub 2}YCu{sub 2}O{sub y} (T{sub c} Almost-Equal-To 30 K) prepared and characterized. Black-Right-Pointing-Pointer XPS shows that Mo{sup 5+} predominates over Mo{sup 6+}. Black-Right-Pointing-Pointer Annealing under O{sub 2} enhances Mo{sup 6+} and Cu{sup 2+} states.« less

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.

A series of oxidized La2−xSrxCuO4+y\((0.05 \preccurlyeq x \preccurlyeq 0.3)\) compounds has been prepared by treating the starting materials with a solution of Br2 in NaOH at room temperature. The structural modifications due to the oxidation of the materials have been studied by X-ray diffraction. Some of the observed changes are: (i) a large increase in the long parameter of the unit cell for samples with Sr content\(0.05 \preccurlyeq x \preccurlyeq 0.15\) and (ii) a slight decrease in a along the whole range ofx. Interesting features have been observed regarding the critical temperatures of these materials: transition temperatures are higher for those containing lower Sr amounts (some of them were even nonsuperconducting before the oxidation treatment) in contrast to materials with x≻0.15, whoseTc's do not change very much. The influence of both oxygen and strontium contents on the structural modifications and the superconducting properties of the oxidized materials will be discussed.

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.

The title solid solution is synthesized by calcination of a gel (900 °C, 12 h) obtained from a mixture of Bi(NO3)3, La(NO3)3, Fe(NO3)3, Cr(NO3)3, and 2-methoxyethanol.

The title compound is prepared from stoichiometric mixtures of SrCO3, CaCO3, and Sb2O3 (1200 °C, 120 h) and characterized by XRD, TEM, and SAED.

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.

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.

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.

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.

Hydrolysis reactions of the title compound have been performed under different experimental conditions followed by thermal treatments at moderate temperatures of the hydrolysis products. Different magnetic oxides such as γ-Fe 2 O 3 or Fe 3 O 4 are produced and, due to particle size effects, even α-Fe 2 O 3 shows a weak ferromagnetic behaviour.

The corundum-type In(2-2x)Zn(x)Sn(x)O(3) solid solution (cor-ZITO, x ≤ 0.7) was synthesized at 1000 °C under a high pressure of 70 kbar. cor-ZITO is a high-pressure polymorph of the transparent conducting oxide bixbyite-In(2-2x)Zn(x)Sn(x)O(3) (x ≤ 0.4). Analysis of the extended X-ray absorption fine structure suggests that significant face-sharing of Zn and Sn octahedra occurs, as expected for the corundum structure type. In contrast to the ideal corundum structure, however, Zn and Sn are displaced and form oxygen bonds with lengths that are similar to those observed in high-pressure ZnSnO(3). Powder X-ray diffraction patterns of cor-ZITO showed the expected unit cell contraction with increased cosubstitution, but no evidence for ilmenite-type ordering of the substituted Zn and Sn. A qualitative second harmonic generation measurement, for the solid solution x = 0.6 and using 1064 nm radiation, showed that Zn and Sn adopt a polar LiNbO(3)-type arrangement.

In this paper we present the structural, magnetic and dielectric properties of ceramic nickel manganite NiMn2O4+δ produced by using nickel permanganate Ni(MnO4)2xH2O as a precursor. We have characterized the NiMn2O4+δ stoichiometry using quantitative energy-dispersive analysis of X-rays and thermal gravimetry under reducing conditions. Increased oxygen and Mn4+ contents were detected. X-ray diffraction and Rietveld refinement of X-ray data were carried out. Temperature dependent magnetization measurements were performed and the ferri-magnetic transition was identified at ≈100K. The ferri-magnetic moment was found to be ≈1μB and hysteretic magnetization vs applied field curves were obtained. Dielectric properties were measured using impedance spectroscopy. Two dielectric relaxation processes were detected, which were associated with grain boundary and bulk contributions. The Arrhenius plots of resistivity and the temperature dependent dielectric permittivity were obtained for the two relaxations by means of an equivalent circuit model based on a series of two parallel RC elements. © 2010 Elsevier Ltd. Fil: Díez, Alejandra. Universidad Nacional del Sur. Departamento de Química; Argentina Fil: Schmidt, Rainer. Universidad Complutense de Madrid; España Fil: Sagua, Aurora Estela. Universidad Nacional del Sur. Departamento de Química; Argentina Fil: Frechero, Marisa Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Matesanz, Emilio. Universidad Complutense de Madrid; España Fil: Leon, Carlos. Universidad Complutense de Madrid; España Fil: Morán Emilio, E.. Universidad Complutense de Madrid; España

A polycrystalline sample of the monoclinic phase Bi 2 Sr 2 CuO 6 has been prepared. The displacive modulation, also present in other compounds of the Bi−Sr−Ca−Cu−O system, has been investigated by means of both electron diffraction and electron microscopy. The modulation is commensurate but it is affected by a strong instability. Discommensurations produce an incommensurate modulation that, in our sample, does not have a well ordered periodicity; this is likely due to a partial disorder of the excess oxygen atoms. A higher-order superstructure (eightfold), also found in the same preparation, is also affected by discommensurations.

The structure of the Ba 2 PrPtO 6 compound has been determined by X-ray powder diffraction and profile analysis and has been confirmed by TEM and HREM. The structure of this material is made up of alternating [PtO 6 ] and [PrO 6 ] octahedra along the three a, b , and c directions. Magnetic properties are also presented and discussed.

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.

HREM has been used to study the process induced by the reaction of the HTSC YBa{sub 2}Cu{sub 3}O{sub 7{minus}y} (commonly referred to as '123') with the lithiating agent n-BuLi. High resolution electron micrographs reveal that this reaction promotes, at room temperature, irreversible microstructural modifications into the '123' structure leading to a rather heterogeneous product. In this respect, both '247' (Y{sub 2}Ba{sub 4}Cu{sub 7}O{sub 15{minus}z}) and the '124' (YBa{sub 2}Cu{sub 4}O{sub 8}) structures appear as either extended defects within the '123' matrix or disordered intergrowths. A structural model is proposed to justify the high lithium conductivity displayed by these materials.

We have measured the resistivity of two series of ceramics samples of nominal composition Bi2SrXCuOy (1.2 ≦ x ≦ 2.1) prepared with different synthesis times. In one of the series, all the samples obtained are insulating, while in the other a transition from superconducting onset at 10 K to insulating behaviour is observed as the Sr content is lowered. In the low-temperature region the resistivity of the insulating samples follows the expression ϱ ( T ) = ϱ O exp [(T o /T) 1 4 ], characteristic of Mott variable-range hopping (VRH) conduction in three dimensions.

We present a comprehensive analysis of Raman spectra in the ${\mathit{R}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ system (R=Gd,Sm,Nd,Pr) as a function of doping, temperature, rare-earth atomic radius, and Raman resonance conditions. Phonon frequencies as well as their temperature dependences behave anomalously for R=Pr: The ${\mathit{B}}_{1\mathit{g}}$ phonon, for instance, softens by as much as 11 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ when the crystal is cooled from room temperature to 10 K, while it hardens by 11 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for R=Nd. These observations are attributed to the fact that Pr, as the largest rare-earth atom that can give rise to the T' structure, is already close to the T' stability limit, yielding large phonon anharmonicities in this compound. The dependence of the phonon frequencies on doping is strong only for the oxygen ${\mathit{E}}_{\mathit{g}}$ mode, which can thus be used for sample characterization. We also present and discuss phonon resonance profiles for ${\mathrm{Nd}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4}$ and ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4}$, which yield electronic structural information that should be compared with future calculations of the resonance profiles. Finally, we also discuss the origin of an additional large ${\mathit{A}}_{1\mathit{g}}$-symmetry peak that shows a dramatic, rare-earth-dependent resonance behavior and gives a possible explanation on the grounds of a partial T'\ensuremath{\rightarrow}T transition. We always observe several well-defined, unexpected vibrational peaks that seem to be intrinsic to the ${\mathit{R}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ system, indicating crystal distortions that have not been conclusively identified by x-ray- or neutron-diffraction experiments so far.

Following our work on lithium insertion into YBa 2 Cu 3 O 7− δ (commonly referred to as “123”) in which we observed the room-temperature formation of YBa 2 Cu 4 O 8 (“124”) [1,2], we have now found, by the same procedure using “124” as starting material, a novel phase with Y:Cu:Ba in the ratio 1:2:6 (“126”), intergrown in different proportions with YBa 2 Cu 4 O 8 and YBa 2 Cu 5 O 9 (“125”). Powder X-ray diffraction patterns and electron microscopy and diffraction suggest a unit cell of ≈ 3.80 × 3.86 × 33.4 A containing four [CuO 4 ] chain layers instead of the two observed in the original “124”.

The thermodynamic stability of Li2MnSiO4 polymorphs and their electrochemical properties as electrode for Li batteries are investigated combining experimental and computational methods. Three possible Li2MnSiO4 forms have been considered crystallizing in Pmnb, Pmn21 (β-Li3PO4 derivatives) and P21/n (γ-Li3PO4 derivative) space groups (S.G.). We have first demonstrated that the relative stability of β- and γ-Li3PO4 polymorphs is well-reproduced by density functional theory (DFT) methods (LDA, GGA). For Li2MnSiO4, the Pmnb form is predicted to be 2.4 meV/f.u. and 65 meV/f.u. more stable than the Pmn21 and P21/n forms, respectively (GGA + U results). Computational results indicate that the denser Pmn21 polymorph can be obtained by high pressure/high temperature treatment of the other polymorphs or their mixtures. A sample of Li2MnSiO4 prepared at 900 °C consists of a mixture of polymorphs, as detected by XRD and confirmed by means of SAED and 6Li MAS-NMR. As expected from DFT results, exposing the as-prepared...

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 .

Ternary oxides of formula ABO4 adopt various crystal structures depending on the relative size of the A and B cations. For some ABO4 compounds it is reasonable to expect pressure-induced transformations resembling those of dioxides provided that the A and B cationic sizes are similar [1]. For instance, in the case of A = Al, or if A and B are disordered Ga, and B = P, As, these compounds crystallize at ordinary pressure in the berlinite structure (α-quartz-like), or in a 2-fold superstructure of it if A and B are ordered along the c axis [2]. Other related compounds, such as boron phosphate or arsenate, prefer the cristobalite structure which, under high-pressure / high-temperature conditions, transform into the α-quartz modification [3]. On the other hand, it is well known that silica transforms under very high pressures (approx. 10 GPa) into stishovite, the rutile form of silica where the coordination number of Si changes from 4 (tetrahedra) to six (octahedra) and, associated with this, the density increases dramatically [4]. Therefore, by analogy to the rich phase diagram of silicon dioxide, one would expect that the above mentioned ternary oxides will finally transform into rutiles upon sufficiently increasing the pressure and temperature applied, but that other intermediate high-pressure phases would also be possible. In this paper we focus on the different reported polymorphs of GaAsO4 where some controversy ex