Search

The dielectric properties of mixed-oxide CaMn7O12 are reported. This compound exhibits a high dielectric constant at room temperature (er >1 0 4 ), for frequencies up to 10 4 Hz, values that make it very attractive for potential applications provided that its rather high losses can be minimized. Complex plane analysis of the obtained data reveal an important extrinsic contribution to these high er values; and also that the

Polycrystalline samples of the charge ordered mixed oxide LaMn0.5Co0.5O3−δ (TCO = 400 K) have been prepared by the nitrate decomposition method. These samples are biphasic, according to XRPD, and except one, oxygen defficient (δ ≈ 0.04-0.05). The study of the dielectric properties of these samples reveal that LaMn0.5Co0.5O3−δ displays a high dielectric constant, specially at room temperature and low frequencies. This e′r is seen to be strongly dependent on the particle size and not so much on the oxygen defficiency and the best properties are found in the sample with biggest particle size (ϕ = 7 μm) for which e′r (300 K) ≈ 105 up to 2x104 Hz. Analysis of the role of the grain size and the electrode contacts on the obtained data reveal that this mixed oxide has an intrinsic dielectric constant that is rather high for this type of compounds (e′r,∞ ≈ 30) and that is further enhanced by extrinsic Maxwell-Wagner effects. We relate such enhanced intrinsic dielectric constant to the electronic process of charge ordering present in this material below 400 K.

We have prepared Ca2−xPrxMnO4 ( x = 0 , 0.25 , 0.33 and 0.50) compounds by the so-called “liquid-mix” method. X-ray powder diffraction indicated that these compounds are single-phase materials and resistivity measurements showed that the Pr-doped samples experience charge-ordering (CO) transitions at 275 K ( x = 0.25 ), 330 K ( x = 0.33 ) and 315 K ( x = 0.50 ). The intrinsic dielectric constants calculated by impedance spectroscopy (IS) from the values of the obtained bulk capacitances were remarkably high: 217, 37 and 80 for the x = 0.25 , 0.33 and 0.50 samples, respectively. In addition, extrinsic factors play an important role on their dielectric response, especially at T > 150 K , giving rise to very high dielectric constants at room temperature ( ɛ r ′ ∼ 10 6 ). Also, and for comparison, we have studied the dielectric response of Ca2MnO4 (non charge-ordered compound), finding much smaller dielectric constant values and an intrinsic contribution ɛ r ′ (bulk)=14, remarkably lower than in the case of Pr-doped compounds. These results could be a new evidence of the link between the charge ordered state and the increase of the dielectric constant.

In this work we have prepared, by a sol-gel method, LiCo 1-x M x O 2 compounds (M= Ni, Al and Mg), in order to study the doping effect in their electrochemical behaviour as cathodes in lithium-batteries. We have studied the influence of the synthesis conditions (using various chelating agents for the formation of the gel) on their morphologic, structural and electrochemical properties. We have obtained monophasic materials: LiCo 1-x Ni x O 2 (0≤x≤0.8), LiCo 1-x Mg x O 2 (0≤x≤0.05), LiCo 1-x Al x O 2 (0≤x≤0.3) and LiCo 0.5 Ni 0.5-x Al x O 2 (0≤x≤0.3). In general, the samples obtained with succinic acid have better ordered lithium layers than malic samples.The capacity of the Li//LiCo 1-x M x O 2 batteries decrease upon doping. However, more stable charge-discharge cycling performances have been obtained as compared to those displayed by the native oxides. In LiCo 1-x Mg x O 2 , small amounts of MgO appear as secondary phases for 0.05

By using the nitrate decomposition method in the presence of KNO 3 , we have been able to enlarge the compositional range of the cobalt-layered compounds Ln 1-x Sr 1+x CoO 4 (Ln: La, Nd, Gd) to 0≤x≤0.40 in the case of lanthanum, to 0≤x≤0.30 for neodymium, and to 0≤x≤0.20 in the case of gadolinium. In this work we present the results of their structural characterization by means of powder X-ray diffraction (PXD) and Rietveld analysis as a function of composition (x) and the rare earth (Ln), information that has been complemented by infrared spectroscopy (IR), electron diffraction (ED) and electron microscopy.

In this work, the behaviour of the real and imaginary components of the dielectric permittivity of layered perovskite La 1 5 Sr 0 . 5 CoO 4 have been studied, in the frequency range 20 Hz-1 MHz and in the temperature range 115-350 K. Polycrystalline samples were prepared by the ceramic method. The powder diffraction results showed the pattern of the desired phase together with a small quantities of La 2 O 3 impurities. A comparative study of the electrical and magnetic properties of this charge-ordered compound (T C O ∼750 K) has revealed a basically semiconductor behaviour with a complex bidimensional antiferromagnetism which can be explained on the basis of a thermally activated evolution of the spin state of the Co 3 + ions. A detailed investigation of the dielectric properties of this system has allowed us to identify two superimposed relaxation processes: the first one in the low frequency range (f

By using the nitrate decomposition method in the presence of KNO3, we have been able to enlarge the compositional range of the solid solution of the layered compounds with K2NiF4 structure Ln1−x Sr1+xCoO4 (Ln: La, Nd, Gd) to 0 x 0.40 in the case of Ln = La, to 0 x 0.30 for Ln = Nd and to 0 x 0.20 for Ln = Gd. In this paper we present the results of their structural characterization by means of powder X-ray diffraction and Rietveld analysis as a function of composition (x) and the rare earth (Ln), information that has been complemented by the results obtained from electron diffraction and transmission electron microscopy.  2003 Elsevier SAS. All rights reserved.

We report the synthesis of the Ruddlesden–Popper material Sr 3 Fe 1.5 Co 0.5 O 6.67 (a compound usually obtained under high-pressure conditions) by a simpler normal pressure liquid-mix method and its structural characterization by means of X-ray powder diffraction. In this material—which is semiconducting and shows a glassy magnetic behavior—the combination of the reduced dimensionality of the structure compared to 3D perovskites, the small grain size obtained by our synthesis method and the selected stoichiometry, results in a record magnetoresistance in these kind of compounds, −47% at T =5 K and H =50 kOe, that is explained on the basis of intragranular and intergranular effects.

We have prepared LiNi1−yCoyO2 (0 ≤ y ≤ 1) compounds as polycrystalline nanomaterials (d ≈ 400 nm) using a low-temperature sol–gel method. XRD studies indicate that these materials are single phase for 0.2 ≤ y ≤ 1 with an ordered distribution of Li and Ni/Co in the layered structure. Nevertheless, as this technique provides only averaged structural information, it is still possible that locally there are some defects, among them disorder, that could affect the electrochemical behaviour of these materials. In fact, through FTIR spectroscopy we observe for the Li–O band a slight deviation from a linear behaviour for high nickel content (y ≤ 0.2), that is attributed to the presence of Ni cations in the predominantly lithium layers (octahedral interstices). In addition, by means of magnetic measurements, χm (T) and M(H), we detect in all the samples a ferrimagnetic signal, that gets smaller and smaller as the Co content increases, but that indeed reveals the presence of some Ni2+ ions occupying Li+ places, that would lead to the formation of small ferromagnetic islands. From those magnetic measurements we have estimated the size of those nanometric magnetic inhomogenities that decreases upon Co doping from R(y = 0) = 3.5 nm to R(y = 0.4) = 0.5 nm. This result confirms that the addition of Co3+ inhibits the presence of interlayer Ni2+ and therefore favours a better lamellar structure, only obtained for y > 0.4.

LiCo1−xNixO2 materials having the layeredα-NaFeO2-type structure are promising positive electrodes for advanced lithium-ion batteries. Their electrochemical performance is very much conditioned by the integrity of the lamellar structure that needs to be stable enough to stand many charge/discharge cycles. LiNi0.5−xAlxCo0.5O2 (0≤x≤0.3) samples have been prepared by a low-temperature route, the sol-gel method assisted by succinic acid as chelating agent. We study in detail their crystallographic structure by XRD, their chemical composition by ICP and their morphology by SEM. Their local cationic environment is also carried out by means of FTIR spectroscopy.

We introduce the magnetotransport properties of Gd 1-x Sr x CoO 3 (0 < x ≤ 0.30) materials. These compounds are semiconducting and show a magnetic transition at T c 160 K associated with the onset of magnetic order of cobalt ions within superparamagnetic clusters, which have a freezing point T B < T c . Very remarkably, the more resistive samples showed rather large magnetoresistance at the lowest available temperature: MR max (x = 0.10) -16% at T = 4.2 K under H max = 40 kOe. We relate these results to the inhomogeneous electronic structure of these cobaltates and to the presence of the paramagnetic Gd 3+ sublattice, which at low temperatures influences the cobalt ions of the superparamagnetic clusters, provoking an increase in the size of the hole-rich regions and in the hopping probability of the charge carriers, and gives rise to the negative magnetoresistance observed.

We have prepared polycrystalline, single-phase Nd1−xSrxCoO3 materials (0≤x≤0.40) using the nitrate decomposition method and we have studied how their structural, magnetic and transport properties change upon Sr2+ doping. In this context we find that these series of compounds crystallize in GdFeO3-type perovskite structures whose cell volume increases as x gets higher. From the magnetic point of view, this doping makes the materials evolve towards a ferromagnetic behavior as x increases, so that for x>0.20 the samples are already ferromagnetic below a Tc∼225 K. Also, their electrical conductivity progressively increases with x. Nevertheless the materials remain semiconducting for x≤0.30 and only the sample with x=0.40 displays a M–I transition as a function of temperature (TMI∼160 K).

[Abstract] Lithiated metal oxides LiCo1−yNiyO2 were synthesized by a sol–gel method using succinic acid as chelating agent. Microcrystalline materials were formed by calcination in oxygen at 800°C. The physicochemical properties of the powders (crystallinity, lattice constants, size grain) has been investigated in the compositional range 0≤y≤1. Structural studies show that a layered single phase was obtained. The local cationic environment has been studied by Raman and FTIR spectroscopy. The changes in the vibrational spectra are well related to those observed by X-ray diffraction. It is shown that the lithium predominant layers are preserved in the entire range of substitution. Pelletized LiCo1−yNiyO2 powders (0.2≤y≤1.0) were tested in Li//LiCo1−yNiyO2 cells by galvanostatic titration. These cells have an initial capacity of 140 mAh/g in the voltage range 2.8–4.2 V and show attractive charge–discharge profiles upon cycling. Spanish and French Foreign Office; PAI Picasso 00717TC Spanish and French Foreign Office; HF1999-0101

High-resolution transmission electron microscopy observations and magnetic ac susceptibility measurements have been carried out to study the changes in the magnetic properties of La1-xSrxCoO3 samples (x≤0.3) processed at different annealing temperatures, ranging from 1273 to 1573 K. Although neutron diffraction excludes the coexistence of distinct phases with different chemical composition, room temperature micrographs taken along the [0,-1,1] rhombohedral zone-axis show bright fringes of different widths, extending over regions with sizes ranging from 8 to 40 nm. These regions are detected in all the samples, whatever the Sr content or the annealing temperature Ta. However, their number depends strongly on the processing conditions and becomes smaller and smaller as Ta increases. The periodicity of the bright fringes cannot be accounted for, either by variations in the sample thickness or by crystallographic defects, but it can be simulated if the presence of aperiodically alternate Sr-rich and La-rich (0,1,1) planes is assumed. On the other hand, the susceptibility measurements show that the amount of ferromagnetic phase present in each specimen depends on its thermal history. This suggests that the segregation of a second electronic phase takes place, the nucleation of which is influenced by the spatial homogeneity of the dopant distribution.

We have synthesized LiNi1−yCoyO2 powders by a sol-gel method using malic acid as a chelating agent. The dependence of physico-chemical properties of the powders (crystallinity, lattice constants, grain size) has been investigated by changing the malic acid quantity and the calcination temperature for the different LiNi1−yCoyO2 oxides in the composition range 0 ≤ y ≤1. Structural studies show that a layered single phase was obtained for the y values 0.2 ≤ y ≤ 1.0. The local cationic environment has been studied by Raman and FTIR spectroscopy. Using acid-assisted LiNi1−yCoyO2 powders (with compositions y=0.8 and y=0.6) calcined at 800 °C, Li//LiNi1−yCoyO2 cells were assembled and tested by galvanostatic titration. These cells had an initial capacity of 140 mAh/g in the voltage range 2.8-4.2 V and showed attractive charge-discharge profiles upon cycling.

We prepared in this work La1−xBaxCoO3−δ (0 0.15, Tc≈200 K) in the temperature range 77 K≤T≤300 K. We find that while for x 0.20 they show metallic behavior for T>100 K, with a transition to semiconducting behavior being observed for T ≤ 100 K. For x=0.20, small changes in the oxygen stoichiometry of the samples - due to slight variations in the thermal treatments - greatly affect the transport properties of the materials that can show either two metal-insulator transitions as the temperature increases or a semiconducting behavior. Very interestingly all these ferromagnetic samples are very sensitive to the polarity of the applied electrical current, and display peculiar “diodic” behaviors. All these observations are explained on the basis of an inhomogeneous electronic structure in the Ba-doped cobalt perovskites.

Neutron diffraction and small-angle scattering on La1 − xSrxCoO3 (0 < x ≤ 0.30) show that for x = 0.3 the system is near a two-phase percolation threshold and undergoes a transition from itinerant to polaronic conduction at the Curie temperature TC. The stabilization of superparamagnetic clusters on warming through TC is revealed by an anomalous thermal expansion of the volume and a deviation of the paramagnetic susceptibility from the Curie-Weiss law. The development of a temperature-dependent small-angle-scattering signal confirms that regions of short-range ferromagnetic order are present above TC.

The crystallographic structure and the magnetic order of the distorted perovskite ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{3}$ $(0.10l~xl~0.30)$ has been studied by neutron diffraction, high-resolution electron microscopy, and magnetic-susceptibility measurements. The results give direct evidence for an inhomogeneous distribution of the ${\mathrm{Sr}}^{2+}$ ions and the segregation of the material into hole-rich ferromagnetic regions and a hole-poor semiconducting matrix at lower values of x. The holes introduced by Sr doping are attracted to the ${\mathrm{Sr}}^{2+}$ ions where they stabilize to lowest temperatures an intermediate-spin state at neighboring trivalent cobalt. The antibonding e electrons so stabilized increase the mean unit-cell volume and are delocalized over the cobalt atoms of the cluster where they couple the localized ${t}^{5}$ configurations ferromagnetically. Long-range ferromagnetic order between clusters is realized even for Sr doping as low as $x=0.10.$ The transition to a spin glass state is observed only for Sr concentrations smaller than 0.10. The volume of a hole-rich cluster grows in a magnetic field, and the origin of the large negative magnetoresistance observed near ${T}_{C}$ for $0.15l~xl~0.25$ appears to be due to a growth of the clusters to a percolation threshold. For $x=0.30,$ the ${\ensuremath{\sigma}}^{*}$ band of the intermediate-spin state below ${T}_{C}$ is at the threshold of a transition from itinerant to polaronic conduction and, above ${T}_{C},$ the system transforms smoothly to a cluster state.

The critical exponents of the second-order ferromagnetic-paramagnetic phase transition of (Formula presented) (Formula presented) compounds are obtained. The results (Formula presented) (Formula presented) and (Formula presented) are qualitatively different than those reported in the literature for parent manganites, and are taken as the indication of the absence of long-range interactions below the Curie point. Electronic phase segregation in hole-rich ferromagnetic and hole-poor (Formula presented)-like regions is supposed to explain the observations. The hole-poor regions would dilute the magnetic lattice and prevent the occurrence of long-range order. Also, a spin transition of the (Formula presented) ions at (Formula presented) or the hole-poor regions (acting equivalently to missed spin clusters in amorphous ferromagnets) could be the reason for the high β value in the framework of a Heisenberg model. © 1999 The American Physical Society.

We have used three soft-chemistry methods for the efficient preparation of Ln1−xSrxCoO3 samples, adapting the combustion and the liquid-mix methods for the synthesis of the Ln = La and Gd compounds, respectively, and the preparation of Nd1−xSrxCoO3 by the nitrate decomposition method. We report the magnetic and electrical properties of these relatively small particle-size materials, specially in the case of the Ln = La and Ln = Nd series (d≈0.2 µm and 0.5 µm, respectively), and we compare them to those displayed by the corresponding compounds prepared at higher temperatures. The compounds here obtained are ferromagnetic for x≥0.15 when Ln = La and for x≥0.20 when Ln = Nd and Gd. Their resistivity decreases as the doping degree increases. And, very interestingly, for compositions 0.20

HREM, EDX and EELS techniques have been used to study the transformations that occur in the high-temperature superconductors YBa 2 Cu 3 O 7 − δ (commonly referred to as ‘123’) and YBa 2 Cu 4 O 8 (‘124’) in their reaction with the lithiating agent n-BuLi. This study confirms that the original ‘123’ and ‘124’ materials transform into a heterogeneous product that mainly consists of higher members of the Y 2 Ba 4 Cu 6 + n O 14 + n homologous series of compounds. The amount of lithium present in these new phases is quantified through systematic EELS experiments. Study of the energy-loss near-edge structures (ELNES) of the Li-K edge shows that Li is present in the main phases of the lithiated YBaCuO materials under two different forms: (i) in an ionic state (ii) in a more metallic-like state. These results allow to rationalize both the high lithium ionic conductivity displayed by these materials and the influence of lithium on the superconducting properties of these cuprates.

This is the accepted manuscript of the following article: Pato-Doldán, B., Gómez-Aguirre, L., Bermúdez-García, J., Sánchez-Andújar, M., Fondado, A., & Mira, J. et al. (2013). Coexistence of magnetic and electrical order in the new perovskite-like (C3N2H5)[Mn(HCOO)3] formate. RSC Advances, 3(44), 22404. doi: 10.1039/c3ra43165g In this work we further the structural characterization of the recently discovered (C3N2H5)[Mn(HCOO)3] metal–organic framework with perovskite-like structure, and we present its magnetic and dielectric properties up to 350 K. At low temperature, the C3N2H5+ imidazolium cations, that sit oblique within the cavities of the [Mn(HCOO)3]− framework structure, show a cooperative order resulting in an antiparallel arrangement of their electrical dipole moments. Very interestingly, it is only above 220 K that thermal energy seems to be able to break this antiferroelectric order, resulting in a linear increase of its dielectric constant with temperature. In addition, this Mn(II) compound is antiferromagnetic below TN = 9 K, with a slightly non-collinear arrangement of its magnetic moments, yielding to a weak ferromagnetism. Therefore, this is a new multiferroic material which exhibits coexistence of magnetic and electric ordering The authors are grateful for financial support from Ministerio de Economía y Competitividad MINECO (Spain) under project FEDER MAT2010-21342-C02-01 and from Xunta de Galicia under project PGIDIT10PXB103272PR. B.P.-D. also wants to thank MICINN for a FPI fellowship SI

Magnetic and transport measurements on the system La{sub 1-x}Sr{sub x} CoO{sub 3-{delta}}(0 < x {le} 0.50, {delta} = 0 for 0 {le} x < 0.30, and {delta} (x) {le} 0.06 for 0.30 {le} x {le} 0.50) have led to a phase diagram for this system. Upon Sr doping, the material segregates into hole-rich, metallic ferromagnetic regions and a hole-poor matrix similar to LaCoO{sub 3}. The Co ions of the ferromagnetic phase are in intermediate-spin configurations; the hole-poor matrix experiences a thermally induced low-spin to high-spin transition. For low Sr doping (x < 0.20), the hole-rich regions are isolated from one another and show superparamagnetic behavior below T{sub c}{approx}240 K; longrange magnetic order via frustrated intercluster interactions occurs below a superparamagnetic freezing temperature T{sub g} that increases with x. At x = 0.20, the coupling between the intermediate-spin, metallic ferromagnetic clusters within an interpenetrating matrix reaches a magnetic percolation threshold that orders the clusters ferromagnetically below T{sub c}{approx} 250 K. However, the electrical conduction in the ferromagnetic regions is modulated by the matrix, which has a spin state that varies with temperature. This causes a reentrant semiconductive behavior in the samples with 0.20 {le} x {le} 0.25. Metallic ferromagnetic behavior ismore » found for 0.30 {le} x {le} 0.50 even though the presence of an interpenetrating hole-poor matrix persists to x = 0.50. A ferromagnetic fraction less than unity leads to peculiar magnetic properties that have been attributed in the literature to a magnetic {open_quotes}cluster glass.{close_quotes}« less

The title compound is synthesized by the azide/nitrate route from Mn2O3, CsNO3, and CsN3 (closed steel vessel, 773 K, 30 h) and characterized by powder and single crystal XRD, magnetic susceptibility measurements, and DFT calculations.

We report that the hybrid organic-inorganic compound [(CH(3))(2)NH(2)][Mg(HCOO)(3)] shows a marked dielectric transition around T(t) ∼ 270 K, associated to a structural phase transition from SG R3[combining macron]c (centrosymmetric) to Cc (non-centrosymmetric). This is the highest T(t) reported so far for a perovskite-like formate that is thus a promising candidate to display electric order very close to room temperature.

We present Lu${}_{2}$MnCoO${}_{6}$, a multiferroic member of the double perovskites that we have investigated using x-ray and neutron diffraction, specific heat, magnetization, electric polarization, and dielectric constant measurements. This material possesses a net electric polarization strongly coupled to a net magnetization below 35 K, despite the antiferromagnetic ordering of the $S=3/2$ Mn${}^{4+}$ and Co${}^{2+}$ spins in an $\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}$ configuration along the $c$ direction. We discuss the magnetic order in terms of a condensation of domain boundaries between $\ensuremath{\uparrow}\ensuremath{\uparrow}$ and $\ensuremath{\downarrow}\ensuremath{\downarrow}$ ferromagnetic domains, with each domain boundary producing an electric polarization due to spatial inversion symmetry breaking. In an applied magnetic field the domain boundaries slide, controlling the size of the magnetization, electric polarization, and magnetoelectric coupling.

[Abstract] We have prepared polycrystalline single-phase ACo2+xRu4−xO11 (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10−5 Ωm and their Seebeck coefficients are positive and range from 1 μV K−1 (T = 100 K) to 20 μV K−1 (T = 450 K). The maximum power factor at room temperature is displayed by BaCo2Ru4O11 (P.F.: 0.20 μW K−2 cm−1), value that is comparable to that shown by compounds such as SrRuO3 and Sr6Co5O15. Ministerio de Ciencia e Innovación; Project FEDER MAT 2007-66696

We report here a study on the electrical and magnetic properties of La1-xBaxCoO3 in the re-entrant semiconducting region (x = 0.20). We find that in this material: (i) the insulator-metal-insulator sequence is unstable and evolves toward a purely semiconducting behavior; the initial ρ versus T curve can be reinstated upon appropriate annealing treatments; (ii) there are relaxation effects that can be seen by changing the polarity of the electrodes; (iii) there is a negative magnetoresistance Δρ/ρ approx. 2-3%, for a field as low as 9 kOe, especially at the metal-insulating transition temperatures; and (iv) there are important fluctuations in the electrical resistivity. Taking into account these experimental observations, we can interpret this material as an inhomogeneous system where two thermodynamic phases, one semiconducting and the other metallic and ferromagnetic, coexist, although they are crystallographically indistinguishable. Fil: Sanchez, Rodolfo Daniel. Universidad de Santiago de Compostela. Facultad de Física; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Mira, J.. Universidad de Santiago de Compostela. Facultad de Física; España Fil: Rivas, J.. Universidad de Santiago de Compostela. Facultad de Física; España Fil: Breijo, M. P.. Departamento de Química Fundamental E Industrial; España Fil: Señarís Rodríguez, M. A.. Departamento de Química Fundamental E Industrial; España

Superconducting La 1.78 K 0.22 CuO 4− y has been studied by means of X-ray diffraction, scanning electron microprobe and transmission electron microscopy, in order to characterize the relative distribution of K within these samples. From microprobe and X-ray diffraction data, these materials appear to be homogeneous and show a tetragonal structure ( a≃ 3.77 A , c≃ 13.3 A ). Nevertheless, as shown below, X-ray microanalysis, electron diffraction and low resolution electron microscopy studies indicate that, on a local scale, the situation is more complex and different modulated structures based on a tetragonal La 2 CuO 4 subcell are present.

This is the accepted manuscript of the following article: Yáñez-Vilar, S., Sánchez-Andújar, M., Gómez-Aguirre, C., Mira, J., Señarís-Rodríguez, M., & Castro-García, S. (2009). A simple solvothermal synthesis of MFe2O4 (M=Mn, Co and Ni) nanoparticles. Journal Of Solid State Chemistry, 182(10), 2685-2690. doi: 10.1016/j.jssc.2009.07.028 Nanoparticles of MFe2O4 (M=Mn, Co and Ni), with diameters ranging from 5 to 10 nm, have been obtained through a solvothermal method. In this synthesis, an alcohol (benzyl alcohol or hexanol) is used as both a solvent and a ligand; it is not necessary, therefore, to add a surfactant, simplifying the preparation of the dispersed particles. We have studied the influence of the synthetic conditions (temperature, time of synthesis and nature of solvent) on the quality of the obtained ferrites and on their particle size. In this last aspect, we have to highlight that the solvent plays an important role on the particle size, obtaining the smallest diameters when hexanol was used as a solvent. In addition, the magnetic properties of the obtained compounds have been studied at room temperature (RT). These compounds show a superparamagnetic behaviour, as was expected for single domain nanoparticles, and good magnetization values. The maxima magnetization values of the MFe2O4 samples are quite high for such small nanoparticles; this is closely related to the high crystallinity of the particles obtained by the solvothermal method The authors are grateful for financial support from the MEC of Spain (Project CSD2006-00012 of Consolider-Ingenio 2010 Programme and FPI fellowship to S. Yáñez-Vilar), from the Xunta de Galicia (Project PGIDIT06PXIB103298PR, Rede Galega de Nanomedicina and Parga Pondal Programme) and from the EU (FEDER) SI

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.

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”.

Measurements of the temperature dependence of the magnetization (and parameters like coercivity and susceptibility) of La1-xSrxCoO3 (0.20 ≤ x ≤ 0.30) perovskites are presented. Particular attention is given to the interval of temperatures containing the ferro-paramagnetic phase transition. Curie temperature values lower than those reported previously and critical exponents are given. Additionally, the coercivity as well as the parameters of the law of approach to magnetic saturation are experimentally determined. Anomalies in Curie temperature, coercivity and law of approach to saturation are introduced confirming a non-conventional transition from ferromagnetic to paramagnetic states. © 1999 Elsevier Science B.V. All rights reserved.

[Abstract] The Pr0.79Na0.21MnO3 perovskite has been prepared in polycrystalline form by a ceramic method. We have carried out its structural characterization by synchrotron X-ray powder diffraction (SXRPD) at room temperature and at 150 K (T

We report the structure and microstructure of the Ruddlesden-Popper (RP) series n=2 Gd2−2xSr1+2xCo2O7 (x = 0 and 0.10). X-ray powder diffraction, electron diffraction and HRTEM indicate that these compounds have a tetragonal structure (space group: P42/mnm) with cell parameters a ≈ 5.3749A c ≈ 19.3591A, in which the [CoO6] octahedra are distorted and tilted. Also, very interestingly, according to the obtained results these compounds presents A-site cation ordering where the divalent and bigger Sr2+ cation selectively prefers the 12-coordinated P site while the smaller and trivalent Gd3+ cation prefers the 9-coordinated R site. From the electrical point of view these materials are semiconducting and their resistivitiy decreases upon doping. In addition, the highest doped sample presents a small magnetoresistive effect MRmax = −3.2 % under Hmax = 50 kOe at T = 55 K.

We are reporting the dielectric response of La1.5Sr0.5NiO4, a system that presents a charge-ordered state above room temperature and a rearrangement of its charge-order pattern in the temperature region 160-200 K. A careful analysis of the role of the electric contacts used, sample thickness and grain size on the experimental data allows us to determine that this material exhibits high values of intrinsic dielectric constant. The variation of the dielectric constant with temperature shows a maximum in the region of the rearrangement of the charge-order pattern, which constitutes an evidence of the link between both phenomena., The original version, submitted on 31 July 2003, has been replaced, because the role of extrinsic effects is now taken into account in the calculation of the dielectric constant

We have prepared LiCo1−yAlyO2 and LiNi0.5−yAlyCo0.5O2 (0≤y≤0.3) powder samples by a low temperature sol–gel method using succinic acid as chelating agent. We have studied the details of their crystallographic and local structure by X-ray diffraction (XRD) and FTIR spectroscopy, respectively; we have analyzed their chemical composition by ICP and obtained information about the morphology of the polycrystalline particles by SEM. Also, we have studied the electrochemical performance of the as-prepared materials in the LiLiNi0.5−yAlyCo0.5O2 cells cycled in the potential range 2.5–4.2 V finding that the overall capacity of the oxides has been reduced due to the metal substitution. For example, at 4.2 V cut-off, the charge capacity of the LiLiNi0.35Al0.15Co0.5O2 cell is ca. 115 mA h/g. However, more stable charge–discharge cycling performances have been obtained as compared to those displayed by the native oxides. Finally, we have characterized the kinetics of Li-diffusion by the galvanostatic intermittent titration technique and, according to our results, Al substitution provides an increase in the chemical diffusion coefficients of Li ions in the LiNi0.5−yAlyCo0.5O2 matrix. Spanish and French Foreing Office; PAI Picasso 00717TC Spanish and French Foreing Office; HF 1999-0101

LiCo1-xMxO2 materials, having the layered α-NaFeO2 type structure, are promising cathodes for advanced lithium batteries. Their good performance is very much conditioned by the presence of a good lamellar structure that needs to be stable enough to stand many charge/discharge cycles. In our case, we focus on LiCo1-xMxO2 samples (M=Ni, A1) prepared by a low temperature route: we synthesize them by a sol-gel method using succinic acid as chelating agent. We study the details of their crystallographic structure by XRD, we analyse their chemical composition by ICP and get information about the morphology of the powders by SEM. Also, we carry out a study of their local structure by means of FTIR spectroscopies. Finally, we show the results of the electrochemical studies of the Li//LiNi0.5-xAlxCo0.5O2 prepared cells

[ES] En este trabajo se ha llevado a cabo el tratamiento de partículas de pizarra en medio ácido. Los resultados han sido analizados en función de los iones extraídos y de la variación que dicho tratamiento ocasiona en los valores de la superficie específica de las muestras estudiadas. Se han empleado también las técnicas de espectroscopía infrarroja (FT-IR) y difracción de rayos X. Se ha comprobado que la pizarra está compuesta fundamentalmente por cuarzo, moscovita y clorita, siendo ésta última extraída durante el ataque ácido. Los valores de la superficie específica disminuyen con el tratamiento ácido, lo que corrobora los resultados de las otras técnicas experimentales, es decir, la extracción de clorita de las partículas de pizarra., [EN] Slate particles were treated in liquid acid medium. The results were analyzed as a function of the disolved ions and specific surface area values. Infrared spectroscopy (FT-IR) and X- ray difraction were also used in this study. Slate particles are composed by quartz, muscovite and chlorite. Chlorite is the mainly phase leached during the acid attack. The specific surface area of the treated particles decreases with the intensity of the treatment, being this result assigned to the elimination of chlorite from the slate particles. FT-IR, X- ray diffraction and the analysis of the leached ions confirms this assumption.

In this letter, we investigated the temperature-dependent Raman spectra of CaMn7O12 helimagnet from room temperature down to 10 K. The temperature dependence of the Raman mode parameters shows remarkable anomalies for both antiferromagnetic and incommensurate transitions that this compound undergoes at low temperatures. The anomalies observed at the magnetic ordering transition indicate a spin-phonon coupling at higher-temperature magnetic transition in this material, while a magnetostriction effect at the lower-temperature magnetic transition.

In this work we explore the overall structural behaviour of the [(CH 3)2NH2][Mn(HCOO)3] multiferroic compound across the temperature range where its ferroelectric transition takes place by means of calorimetry, thermal expansion measurements and variable temperature powder and single crystal X-ray diffraction. The results clearly prove the presence of a structural phase transition at Tt ~ 187 K (the temperature at which the dielectric transition occurs) that involves a symmetry change from R3c to Cc, twinning of the crystals, a discontinuous variation of the unit cell parameters and unit cell volume, and a sharp first-order-like anomaly in the thermal expansion. In addition, the calorimetric results show a 3-fold order-disorder transition. The calculated pressure dependence of the transition temperature is rather large (dTt/dP = 4.6 ± 0.1 K kbar-1) in that it should be feasible to shift it to room temperature under adequate thermodynamic conditions, for instance by application of an external pressure. © 2014 the Partner Organisations.

[Abstract] We have recorded the FTIR spectra of powder samples of Ln2−xSrxCoO4 (Ln=La, Nd) at room temperature. We have identified the infrared active modes (3A2u+4Eu), and analyzed how they change as a function of Ln and the Sr doping. We correlate the obtained results with structural data obtained from powder X-ray diffraction studies and with the electronic properties displayed by these samples.

Various methods for the preparation of LiNi1-yCoyO2 solid solution have been proposed because the synthetic condition gives great impact on the electrochemical characteristics of cathode materials [1–3]. Traditionally, compounds are synthesized using solid-state reactions which require prolonged process of the reacting species at high temperatures. Wet chemistry based sol-gel and colloidal precipitation techniques for synthesizing oxides has been applied recently [4–8]. The low-temperature route of preparation (aqueous solution chemistry) develops materials with submicron sized grains which favor the rate capability on charging/discharging the electrochemical cells [9].

Thermoelectric, electrical resistivity and thermal conductivity studies reveal the remarkable influence of lead doping onto formation and improving properties of the Pb x Bi 2- x Sr 2 Ca 2 Cu 3 O y superconductors.

Measurements of thermoelectric power and electrical resistivity of granular Bi1.5Pb0.5Sr2Ca2Cu 3Oy are reported. Rounding of thermoelectric power near and above the critical temperature is analysed in terms of thermodynamic fluctuations of the superconducting order parameter.

This is the accepted manuscript of the following article: Señarís-Rodríguez, M. et al. (1999). Peculiarities in the electrical and magnetic properties of cobalt perovskites Ln1−xMxCoO3 (Ln3+: La3+, M2+: Ca2+, Sr2+, Ba2+; Ln3+: Nd3+, M2+: Sr2+). International Journal Of Inorganic Materials, 1(3-4), 281-287. doi: 10.1016/s1466-6049(99)00042-2 We refer here to the electrical and magnetic properties of the Ln1−xMxCoO3 systems (Ln3+: La3+, M2+: Ca2+, Sr2+, Ba2+; Ln3+: Nd3+, M2+: Sr2+), paying special attention to those ferromagnetic compounds that display M–I transitions as temperature rises: La1−xMxCoO3 (M2+: Ca2+, Sr2+, Ba2+) in the compositional interval x=0.2–0.3, and Nd1−xSrxCoO3, with x=0.40. The magneto-transport properties of such materials are peculiar and interesting: they show diodic behavior and large relaxation effects — these latter being specially important in the Nd compound — they display magnetoresistive effects specially at the M–I transition temperatures, and they age with time. All these results are discussed on the basis of the inhomogeneous electronic structure of these doped cobalt perovskites and taking into account the influence of the lanthanide ion on their magnetic and electrical properties We thank the Spanish DGICYT for financial support under project MAT98-0416-C03-02 SI

In this work we report magnetically modulated microwave absorption experiments performed at 9.4 GHz from 110 up to 300 K on samples of Pr 1−x Ba x CoO 3−δ (0.10 which were prepared by the “Pechini” method.

We have studied the AC and DC magnetic properties of the lamellar compounds La 1− x Sr 1+ x CoO 4 (0⩽ x ⩽0.4). These materials are found to evolve towards an anomalous “cluster-glass”-like behaviour as x increases. The onset of the ferromagnetic order in the bidimensional phases is seen to occur at around 150 K, followed by a blocking process around 125 K. Also, present in the magnetic behaviour of these materials is the signal coming from small intergrowths of a perovskite phase, also detected by TEM, although invisible for powder-X-ray diffraction.