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We report giant reversible barocaloric effects in [(CH3)4N]Mn[N3]3 hybrid organic–inorganic perovskite, near its first-order cubic-monoclinic structural phase transition at T0 ∼ 305 K. When driving the transition thermally at atmospheric pressure, the transition displays a large change in entropy of ∼80 J K−1 kg−1 and a small thermal hysteresis of ∼7 K, as well as a large change in volume of ∼1.5%. When driving the transition with pressure near room temperature, the transition displays large changes in entropy of ∼70 J K−1 kg−1, which represent a giant barocaloric response. Hybrid perovskites with similar barocaloric response and lower operating temperatures may find applications in environmentally friendly cooling.

In this work, we report a new halometallate [(CH3)3S][FeCl4] with plastic crystal behaviour as a new material for multi-energy storage. This material undergoes a first-order solid–solid plastic crystal phase transition near room temperature with a relatively large latent heat (∼40 kJ kg−1) and an operational temperature for storing and releasing thermal energy between 42 °C (315 K) and 29 °C (302 K), very appropriate for solar thermal energy storage. In addition, the dielectric, magnetization and electron spin resonance studies reveal that this material exhibits multifunctional properties with temperature-induced reversible changes in its dielectric, conducting and magnetic behaviour associated with the phase transition. Also, the dielectric permittivity increases sharply up to 5 times when inducing the phase transition, which can be exploited to store electric energy into a capacitor. Therefore, [(CH3)3S][FeCl4] is a very interesting compound with the coexistence of multifunctional properties that can be useful for both solar thermal and electric energy storage.

In this work, we introduce a new family of barocaloric hybrid organic-inorganic compounds with colossal barocaloric effects. The here reported hybrid materials, [(CH3)3(CH2Cl)N]FeCl4 and [(CH3)3S]FeCl4, exhibit a molecular structure composed by discrete inorganic anions and organic cations with weak elestrostatic interactions. Our calorimetric studies reveal colossal barocaloric effects of similar magnitude than organic plastic crystals (ΔS > 100 J K-1 kg-1) near room temperature and under smaller pressures (p ≤ 1000 bar), which leads to higher barocaloric strengths. Furthermore, these materials exhibit densities similar to barocaloric hybrid perovskites enhancing the volumetric barocaloric effects (ΔS ~ 200 J K-1 l-1), which could provide more compact cooling devices. Therefore, the colossal values of the mass and volumetric barocaloric effects and large barocaloric strength, in addition to the low working pressure and near-room-temperature operation, offer a new family of compounds to further explore in the search for improved barocaloric materials.

We have been able to prepare two new lead halides with the formula DMAPbX3 (where DMA is dimethylammonium and X is Cl− or Br−), which display a 4H-hexagonal perovskite polytype, an unusual crystal structure in hybrid organic–inorganic perovskites. Both compounds experience a first-order phase transition, the chloride at ∼320 K and the bromide at ∼250 K, which involves two cooperative processes: an off-center shift of the lead cations and an order–disorder process of the DMA cations. Additionally, a sharp dielectric transition is associated with this structural transition in both hybrids. Both compounds are semiconductors with band gap values of 3.5 eV (X: Cl−) and 3.0 eV (X: Br−). Also, the LT-phase of the Br− compound displays a broad red light photoluminescence (PL) emission (620 nm) and PLE excitation with the maximum at a soft UV wavelength (360 nm). This broadband emission and large Stokes-shifted PL seem to be related to a self-trapped exciton mechanism. Therefore, the uncommon 4H-hexagonal perovskite is a promising crystal structure for understanding and designing new hybrid materials with broad photoluminescent emission and dielectric properties.

In this work, we study the structural changes of the polar [NH4][Cd(HCOO)3] hybrid perovskite under external hydrostatic pressure. We report a reversible framework rearrangement as a function of pressure characterized by: (i) a gradual modification of one formate ligand, which changes its coordination mode from a bridging syn–anti mode at atmospheric pressure (LP-phase) to a chelating-anti mode at high-pressure (HP-phase) and (ii) a change in the coordination of the Cd2+ cations from six-coordinated (LP-phase) to hepta-coordinated (HP-phase). Very interestingly, this unprecedented framework arrangement displays a large electrical polarization. For instance, the polarization value observed at p = 17.7 GPa is about four times the polarization at atmospheric pressure. Therefore, we report that the external pressure induces a novel framework rearrangement in the polar [NH4][Cd(HCOO)3] hybrid perovskite with enhanced electrical polarization. This structure–property relationship offers new insights for designing novel ferroelectric materials based on pressure-responsive hybrid perovskite materials.

A systematic study of the thermal decomposition of hybrid perovskites of formula [AH][M(HCOO)3] under inert atmosphere was performed by means of thermogravimetry and simultaneous infrared spectroscopy of the evolved gases. The influence of: (i) the metal ion of the [M(HCOO)3]- framework and (ii) the guest [AH]+ cation, in the composition of the final residue was evaluated. In this work, it has been demonstrated that these materials can be used as precursors of metal or metal-oxide compounds—obtained free of carbon—, and that the composition of the final residue is determined by the standard reduction potential of the metal cation of the framework.

Temperature-dependent Raman scattering and differential scanning calorimetry were applied to the study of the hybrid organic-inorganic azide-perovskite [(CH3)4N][Cd(N3)3], a compound with multiple structural phase transitions as a function of temperature. A significant entropy variation was observed associated to such phase transitions, |∆S| ~ 62.09 J&middot, kg&minus, 1 K&minus, 1, together with both a positive high barocaloric (BC) coefficient |&delta, Tt/&delta, P| ~ 12.39 K kbar&minus, 1 and an inverse barocaloric (BC) coefficient |&delta, P| ~ &minus, 6.52 kbar&minus, 1, features that render this compound interesting for barocaloric applications. As for the obtained Raman spectra, they revealed that molecular vibrations associated to the NC4, N3&ndash, and CH3 molecular groups exhibit clear anomalies during the phase transitions, which include splits and discontinuity in the phonon wavenumber and lifetime. Furthermore, variation of the TMA+ and N3&ndash, modes with temperature revealed that while some modes follow the conventional red shift upon heating, others exhibit an unconventional blue shift, a result which was related to the weakening of the intermolecular interactions between the TMA (tetramethylammonium) cations and the azide ligands and the concomitant strengthening of the intramolecular bondings. Therefore, these studies show that Raman spectroscopy is a powerful tool to gain information about phase transitions, structures and intermolecular interactions between the A-cation and the framework, even in complex hybrid organic-inorganic perovskites with highly disordered phases.

In this work, we report a new halometallate [(CH3)3S][FeCl4] with plastic crystal behaviour as a new material for multi-energy storage. This material undergoes a first-order solid-solid plastic crystal phase transition near room temperature with a relatively large latent heat (~40 kJ kg-1) and an operational temperature for storing and releasing thermal energy between 42 oC (315 K) and 29 oC (302 K), very appropriate for solar thermal energy storage. In addition, the dielectric, magnetization and electron spin resonance studies reveal that this material exhibits multifunctional properties with temperature-induced reversible changes in its dielectric, conducting and magnetic behaviour associated with the phase transition. Also, the dielectric permitivity increases sharply up to 5 times when inducing the phase transition, which can be exploited to store electric energy into a capacitor. Therefore, [(CH3)3S][FeCl4] is a very interesting compound with coexistence of multifunctional properties that can be useful for both solar thermal and electric energy storage.

In large quantities, water is detrimental to lead halide perovskite solar cells, mainly because of the decomposition of the perovskite layer. In contrast, the presence of small quantities of water has been observed to play a key role in the crystallization of the perovskite and in the performance of the corresponding devices. However, the exact role of water during the operation of perovskite solar cells is still under debate. In this paper, impedance spectroscopy is used to analyze the changes produced by environmental humidity in the electronic properties of methylammonium lead triiodide perovskite. Our results show that water absorbed from environmental humidity induces a huge increase in the capacitance of this material. This capacitance can reach values as large as the accumulation capacitance found in devices based on perovskite, which is responsible for the characteristic large hysteresis observed between forward and reverse J–V curves. In parallel to this outstanding rise of the capacitance, water absorption produces a significant rise of the conductivity, in agreement with previous reports in the literature. An activation energy of 0.52 eV is found for electronic transport, a value in line with the activation energy of ionic transport found in the literature, which suggests ambipolar diffusion as the transport mechanism that links these two phenomena.

The fast growing family of organic–inorganic hybrid compounds has recently been attracting increased attention owing to the remarkable functional properties (magnetic, multiferroic, optoelectronic, photovoltaic) displayed by some of its members. Here we show that these compounds can also have great potential in the until now unexplored field of solid-state cooling by presenting giant barocaloric effects near room temperature already under easily accessible pressures in the hybrid perovskite [TPrA][Mn(dca)3] (TPrA: tetrapropylammonium, dca: dicyanamide). Moreover, we propose that this will not be an isolated example for such an extraordinary behaviour as many other organic–inorganic hybrids (metal-organic frameworks and coordination polymers) exhibit the basic ingredients to display large caloric effects which can be very sensitive to pressure and other external stimuli. These findings open up new horizons and great opportunities for both organic–inorganic hybrids and for solid-state cooling technologies., Designing mechanically and chemically robust liquid-repellent surfaces remains a long-standing challenge. Here, Wang and colleagues report a microfluidic emulsion templating strategy to fabricate bioinspired omniphobic porous membranes with remarkable durability.

Spin-phonon coupling in rare-earth based manganites with double perovskite structure plays a crucial role in the magnetoelectric properties of these ferromagnetic materials. Particularly, on Y2CoMnO6 (YCMO), it is assumed that spin-phonon coupling is related to the induced ferroelectric polarization. This confers to YCMO a multiferroic characteristic. In this work, we probed the spin-phonon coupling in YCMO by temperature-dependent Raman spectroscopy measurements in ceramic samples obtained by the nitrate decomposition method. Raman scattering revealed some anomalies that could be attributed to a weak spin-phonon coupling, an unconventional behavior for rare-earth based manganites with double perovskite structure, in which the coupling does not fit with the quadratic magnetization.

The hybrid inorganic–organic [TPrA][M(dca)3] (M: Fe2+, Co2+ and Ni2+) compounds, where TPrA is the tetrapropylammonium cation and dca is the dicyanamide anion, are unique multi-sensitive compounds that display multiple phases and dielectric transitions. These materials exhibit up to three first-order structural transitions (between the polymorphs I, Ia, Ib and II) associated with the same number of dielectric transitions in the temperature range of 210–360 K. The mechanisms responsible for these dielectric responses are found to be novel within the hybrid perovskites, involving ionic displacements of the A-site cations (TPrA) and order/disorder processes of the X anions (dca). In addition, the phase transitions and dielectric transition temperatures can be tuned by applying external hydrostatic pressure or by inducing internal pressure by modifying the tolerance factor through ionic substitution in the B-sites. This multi-sensitive response towards temperature, external and internal pressure opens up promising technological applications for this family of materials, such as dielectric transductors or multistimuli-sensors, whose response can be modulated in a wide range of temperatures and pressures., The authors are grateful for the financial support from Ministerio de Economía y Competitividad MINECO (MINECO) ENE2014-56237-C4-4-R and Xunta de Galicia under the project GRC2014/042. J. M. B.-G. also wants to thank Barrié Foundation for a predoctoral fellowship and S. Y.-V. to the Xunta de Galicia for a postdoctoral grant (Plan I2C).

We report the barocaloric performance of cadmium-dicyanamide perovskite [(CH3CH2CH2)4N]Cd[N(CN)2]3 ([TPrA]Cd[dca]3). The introduction of Cd, a large second-row post-transition metal, into this hybrid organic–inorganic perovskite structure leads to three separate thermally driven phase transitions and four polymorphs, which we characterize in full using temperature-dependent X-ray diffraction and temperature-dependent calorimetry. Amongst these transitions, the non-isochoric orthorhombic to tetragonal phase transition at high temperatures, with a large volume change of ∼0.4%, leads to a large reversible pressure-driven isothermal change in entropy of ∼11.5 J K−1 kg−1, and a giant barocaloric tunability of the transition temperature with pressure of ∼38.2 K kbar−1, which are both desirable for future low-pressure barocaloric cooling applications.

Here we present an in-depth study of the magnetic properties of a family of metal–organic perovskites ABX3, [CH3NH3][M(HCOO)3] in which A = CH3NH3+ is the methylammonium cation, B = M is a divalent metal cation (Mn2+, Co2+, Ni2+ or Cu2+), and X is the formate anion (HCOO−). The magnetic properties have been measured on powdered samples and along the different orientations of mm-sized single crystals. They display spin-canted weak ferromagnetism with Néel temperatures of 8.0 K (Mn2+), 15.7 K (Co2+) and 34 K (Ni2+), which are inversely proportional to the ionic radii of the metal cations. The Cu2+ member displays low-dimensional magnetism as a result of orbital ordering of the Cu2+ d orbitals originating from a Jahn–Teller distortion. Pulsed-field magnetization experiments (fields of up to 60 T at temperatures down to 0.6 K) show that Mn2+, Co2+ and Ni2+ formates display cation-characteristic spin flop transitions. A saturation magnetization value of 5 μB (at 12.5 T) was observed for Mn2+, meanwhile the Co2+ formate shows an orientation dependent quasi saturation (5.1 μB at 21 T along [101] vs. 5.8 μB at 26 T along [010]). The different isotropic/anisotropic behaviour can be explained by the orbital contribution to the magnetic response The Spanish authors are grateful for financial support from Ministerio de Economía y Competitividad (MINECO) (Spain) and EU under the project ENE2014-56237-C4-4-R, and Xunta de Galicia under the project GRC2014/042. L. C. G.-A. acknowledges UDC for a predoctoral fellowship and Fundación Barrié for the research stay grant at LANL. Work at LANL, A. P. H. and B. P.-D.'s visit to LANL were funded by the Laboratory Directed Research and Development program at LANL. The NHMFL pulsed-field facility is funded by the U.S. National Science Foundation through Cooperative Grant No. DMR-1157490, the State of Florida, and the U.S. Department of Energy SI

[Abstract] In this work, we show that the hybrid material Co2(1,4-bdc)2(dabco)•[4DMF•1H2O], shows an apparent colossal dielectric constant at room temperature (r5000 at 300 K for =100 Hz). Nevertheless, such response does not imply colossal polarizability processes, as its dielectric constant is not purely intrinsic, but is greatly enhanced by the activation of extrinsic dielectric effects close to room temperature associated to the diffusion of numerous guest molecules through the channels. If such extrinsic contributions are eliminated or reduced, the values of the dielectric constant turn to be much smaller, as observed in the closely related Co2(1,4-bdc-NH2)2(dabco)•[7/2DMF•1H2O], Co2(1,4-ndc)2(dabco) •[3DMF•2H2O] and Ni2(1,4-bdc)2(dabco)•[3DMF•1/2H2O] compounds. Therefore, we warn about the imperious necessity of distinguishing between intrinsic and extrinsic effects in electrically inhomogenous MOF materials that display a certain conductivity in order to adequately interpret their dielectric behavior Ministerio de Economía y Competitividad; MAT2010-21342-C02-01 Xunta de Galicia; PGIDIT10PXB103272PR

In this work, we present the new compounds Pr 0.50 Ln 0.50 BaCo 2 O 5+ δ (Ln: Pr, Nd, Sm, Eu, Gd, Tb and Dy) that we have synthesized as pure phase polycrystalline materials by the Pechini method. Doping the A site with a second heavier lanthanide promotes smaller oxygen stoichiometry, providing an alternative way to modify the oxygen content of these Pr-cobalt oxides by means of changing the PrLn ratio. According to powder X-Ray diffraction the compounds display an average tetragonal structure. The presence of smaller Ln ions together with a smaller amount of oxygen gives rise to higher Seebeck coefficients, specially from PrEu to PrDy, and to a substantial increase of the resistivity below 200 K. As a result the highest power factor is displayed by the Pr 0.50 Eu 0.50 BaCo 2 O 5.69 sample at ∼125 K, PF max ∼0.154 μW K −2 cm −1 , value that is two orders of magnitude higher than that shown by the starting PrBaCo 2 O 5.76 sample at the same temperature.

In this work, we focus on the influence of the oxygen content and the preparation method on the power factor of different PrBaCo2O 5+δ samples (0.54 ≤ δ ≤ 0.84). The samples have been initially synthesized by the Pechini method. Their oxygen content has been subsequently modified by annealing under argon/oxygen flow or by electrochemical oxidation/reduction. The oxygen stoichiometry has a high impact on the electrical conductivity and Seebeck coefficient of the resulting materials. Moreover, by adequately reducing their oxygen content while increasing their intergrain conductivity (by increasing the particle size and degree of sintering) the power factor of these samples can be drastically improved. The best result is shown by the PrBaCo2O5.54 sample, that was annealed at high temperature under argon flow, whose power factor is as high as 6.5 μW/K2 cm-1 at ∼135 K, more than two orders of magnitude higher than that shown by the initial PrBaCo2O 5.76 reference sample. © 2011 Elsevier B.V.

We are reporting on the dielectric properties of NaCu3(Ti3Nb)O12 and Na(Cu2.5Ti0.5)Ti4O12 which are related to the perovskite CaCu3Ti4O12 compound. The NaCu3(Ti3Nb)O12 perovskite, that is doped with Nb cations at the Ti B-site, shows high values of dielectric constant. Using impedance spectroscopy (IS), we have observed that this compound is electrically inhomogeneous, showing a semiconductive bulk and insulating grain boundaries. The presence of a semiconductive bulk seems to indicate that a charge delocalization process is taking place through the Cu A′-site. In the case of the Na(Cu2.5Ti0.5)Ti4O12 perovskite, the dielectric response comes from the bulk material and the IS results show an intrinsic homogeneous material. In this compound, the large doping of Ti cations at the Cu A′-site prevents a charge delocalization process and the material becomes insulating. These results highlight the importance of the A′-sites in the charge delocalization process. In addition, Na(Cu2.5Ti0.5)Ti4O12 provides evidence of a soft-mode behavior that could be responsible for the relatively high intrinsic dielectric constant of CaCu3Ti4O12 and related compounds. © 2009 Elsevier B.V. All rights reserved.

This is the accepted manuscript of the following article: Sánchez-Andújar, M., Yáñez-Vilar, S., Biskup, N., Castro-García, S., Mira, J., Rivas, J., & Señarís-Rodríguez, M. (2009). Magnetoelectric behavior in the complex CaMn7O12 perovskite. Journal Of Magnetism And Magnetic Materials, 321(11), 1739-1742. doi: 10.1016/j.jmmm.2009.02.018 We report a magnetoelectric effect in the double perovskite CaMn7O12, that shows a complex magnetic behavior below 90 K with two magnetic phases coexisting (one ferrimagnetic and the other modulated). A second magnetic transition, associated with changes in the magnetic modulation and magnetic ordering coherence lengths of the two magnetic phases occurs at 50 K (TN2). A detailed structural characterization of this compound, that we have carried out by means of high-resolution X-ray powder diffraction, reveals an anisotropic thermal expansion of its lattice parameters at 50 K (TN2). In addition, our study of the complex permittivity of this sample as a function of temperature, frequency and magnetic field shows very interesting results below 90 K and specially below 50 K: the dielectric constant ε′r that was decreasing continuously on cooling experiences an upturn, and even more, on application of a magnetic field it shows a moderate magnetoelectric response. We attribute such dielectric behavior to the formation of electric dipoles by magnetostriction in this charge and spin ordered system, that are sensible to the presence of an external magnetic field The authors are grateful from financial support for MEC (Spain) under project FEDER MAT 2007-66696 and Xunta de Galicia under project PGIDIT06PXB103298PR. S. Yáñez-Vilar want to thank to MEC of Spain for her FPI fellowship and M. Sánchez-Andújar acknowledges to Xunta de Galicia for support under program Parga Pondal SI

The La0.85Sr0.15CoO3 compound has been synthesized under different annealing temperatures. It has been observed that the transport properties and magnetoresistance of this compound depend on such temperatures. This response is discussed in the framework of a model of electronic phase segregation.

In this work we have measured the complex dielectric permittivity of a polycrystalline material using samples of different thickness (frequency range 20–1 MHz). The results reveal that the CaMn 7 O 12 material is electrically heterogeneous as it consists of regions of different conductivities. In this kind of electrically heterogeneous materials the variation of the dielectric permittivity as a function of temperature can be fitted to a Maxwell–Wagner model. In the case of the CaMn 7 O 12 sample this model fits only partially the experimental data and we need to include three regions of different conductivities to explain the obtained dielectric response.

We present the synthesis and dielectric characterization of core–shell LaMn0.5Co0.5O3-based composites that we have prepared with the aim of improving the dielectric properties of the pure mixed oxide, especially reducing its high dielectric losses. For this purpose we have coated the LaMn0.5Co0.5O3 particles with SiO2 nanoshells ~20 nm thick. From the practical point of view, the composite material obtained shows at room temperature a still rather high dielectric constant (e'r~200 at ν = 106 Hz) while its dielectric losses are at least one order of magnitude smaller than those of the base oxide (tanδ = 0.8 at ν = 106 Hz).

In this work, we study the dielectric properties of the layered perovskites La 3/2 Sr 1/2 NiO 4 and La 5/3 Sr 1/3 NiO 4 in the frequency range 20 Hz-1 MHz and in the temperature range 110-350 K. For this study, we have synthesized single phase polycrystalline samples by a conventional solid-state reaction. These nickelates show very high values of the dielectric constant at room temperature (e' r ∼ 10 5 ), that make them very attractive for potential applications, provided that their rather high losses can be minimized. The obtained results reveal that even if their dielectric behavior is strongly enhanced by extrinsic polarization effects, there is also a very interesting correlation between their dielectric response and their electronic state.

We present in this paper a detailed investigation of the dielectric properties of the mixed oxide CaMn7O12 that shows a charge-ordering transition at TCO = 440 K. Surprisingly, this compound presents a high dielectric constant at room temperature. Data taken at several frequencies and temperatures point to relaxor dielectric behaviour, that can be attributed to the electronic inhomogeneities present in the material. Extrinsic Maxwell–Wagner effects make a significant contribution to this dielectric response, as revealed by the studies made on samples of different particle size and using different types of contact. The intrinsic dielectric constant of this material is e �(intrinsic) ∼ 30 at room temperature, a value that is relatively high for this type of compound and that we relate to the presence of the electronic process of charge ordering in this material.

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, 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.

[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

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.

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

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

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.

[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

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 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

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.