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[Abstract] In this work we focus in setting the limits of the tolerance factor and the size of the A-cations that stabilize the perovskite structure in hybrid dicyanamide compounds [A][Mn(dca)3]. For this purpose, we propose an alternative, simple approach to calculate a more realistic effective ionic radius for the large and anisotropic A-cations often present in these type of compounds. We test the proposed procedure by analysing the crystal structures of [A][Mn(dca)3] dicyanamide hybrids reported in the literature and recalculating the tolerance factors of such compounds, as well as by preparing five new [A][Mn(dca)3] members, discussing also the influence of the A-cation shape in the stability limits of the perovskite structure. Interestingly, such methodology is not only useful to develop new compounds of the emerging family of (multi)functional multi(stimuli)-responsive dicyanamide materials but can also be applied to other hybrid organic-inorganic perovskites and related materials. As for financial support, the authors thank Ministerio de Economía y Competitividad MINECO and EU-FEDER (projects MAT2017-86453-R and PDC2021-121076-I00), and Xunta de Galicia for the collaboration agreement “Development of research strategic actions Universidade da Coruña I ​+ ​D ​+ ​i 2021–2022: CICA-Disrupting Projects 2021SEM-A3 (NanoCool). J.G.-B. and J.M.B.-G. acknowledge Xunta de Galicia for Predoctoral and Postdoctoral Fellowships, respectively. I.D.-F thanks Ministerio de Universidades for a FPU Predoctoral Fellowship. A. G.-F. and U.B.C thank the Carl Tryggers foundation and the Göran Gustafsson foundation for financial support

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.

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG [Abstract] In this work, “breathing-caloric” effect is introduced as a new term to define very large thermal changes that arise from the combination of structural changes and gas adsorption processes occurring during breathing transitions. In regard to cooling and heating applications, this innovative caloric effect appears under very low working pressures and in a wide operating temperature range. This phenomenon, whose origin is analyzed in depth, is observed and reported here for the first time in the porous hybrid organic–inorganic MIL-53(Al) material. This MOF compound exhibits colossal thermal changes of ΔS ∼ 311 J K–1 kg–1 and ΔH ∼ 93 kJ kg–1 at room temperature (298 K) and under only 16 bar, pressure which is similar to that of common gas refrigerants at the same operating temperature (for instance, p(CO2) ∼ 64 bar and p(R134a) ∼ 6 bar) and noticeably lower than p > 1000 bar of most solid barocaloric materials. Furthermore, MIL-53(Al) can operate in a very wide temperature range from 333 K down to 254 K, matching the operating requirements of most HVAC systems. Therefore, these findings offer new eco-friendly alternatives to the current refrigeration systems that can be easily adapted to existing technologies and open the door to the innovation of future cooling systems yet to be developed. This work was financially supported by Ministerio de Economía y Competitividad MINECO and EU-FEDER (projects MAT2017-86453-R and PDC2021-121076-I00), Xunta de Galicia and IACOBUS Programme. Funding for open access fee was provided by Universidade da Coruña/CISUG

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.

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.

Cs23Mn16O23 was synthesized via the azide/nitrate route from mixtures of Mn2O3, CsNO3, and CsN3. This manganese(II/III) mixed-valent oxide, which contains only one Mn3+ besides 15 Mn2+ cations, was studied by single-crystal X-ray diffraction and magnetic susceptibility measurements. Its crystal structure [P1, Z = 1, a = 1114.26(2), b = 1185.53(2), c = 1205.39(2) pm, α = 70.596(1), β = 80.377(2), γ = 83.072(2)°, R1 = 0.033] is based on a honeycomb-like arrangement of cesium atoms, providing the space for two different types of one-dimensional polyoxomanganate anions, illustrated by the syntax Cs23[MnO2]4[Mn3O5]4. Magnetic susceptibility measurements indicate dominant antiferromagnetic intra-chain interactions present already at ambient temperature and long range inter-chain magnetic ordering at 11 K.

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.

In this work, the incorporation of dicyanamide building blocks in organic–inorganic hybrid compounds is found to be a promising strategy for the synthesis of multiwalled carbon nanotubes embedded with magnetic nanoparticles (M@CNTs). Following a novel one-step, scalable and fast synthetic route, M@CNTs are obtained by simple calcination of the organic–inorganic hybrid perovskite [TPrA][M(dca)3] (TPrA = tetrapropylammonium, M = Ni2+ and Co2+, dca = dicyanamide). The resulting M@CNTs (M = Ni and Co) display a regular morphology and an essentially mesoporous network of ∼250 m2 g−1, whereas the Co@CNT composite displays a broad pore size distribution (PSD) up to 6 nm, Ni@CNTs show a strictly controlled unimodal PSD, centered at around 5 nm. Monitoring of their thermal decomposition by X-ray diffraction, electron microscopy, thermogravimetric and spectroscopic analyses allows proposing a calcination mechanism and establishing the conditions to obtain optimal materials. Moreover, magnetization studies reveal a ferromagnetic behaviour of the obtained M@CNTs, with small coercive fields due to the size of the magnetic nanoparticles. In addition, preliminary assays of oil adsorption–desorption capacity reveal a promising potential for spilled oil recovery using this easily-synthesized materials. All these physicochemical properties make these composites good candidates for other nitrogen-rich CNT common applications., The authors are grateful for the financial support from Ministerio de Economía y Competitividad MINECO and EU‐FEDER under project ENE2014‐56237‐C4‐4‐R and Xunta de Galicia under project GRC2014/042. J. M. B.‐G. wants to thanks Barrié Foundation for a predoctoral fellowship and S. Y.‐V. to the Xunta de Galicia for a postdoctoral fellowship

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).

In this work we use molecular dynamics simulations to study the diffusion of N,N-dimethylformamide (DMF) and H2O as a function of temperature within the well-known metal–organic framework Co2(dobdc)·[G] (G = 2DMF·1H2O), also known as Co-MOF-74. The molecular dynamics simulations show that the diffusivity of guest molecules, which is almost negligible at low temperatures (T < 200 K), increases in the range of 200 < T (K) < 400 up to 3 and 4 orders of magnitude for DMF and H2O, respectively. This molecular diffusion can be easily detected by dielectric spectroscopy as it gives rise to extrinsic interfacial polarization effects that result in an apparent “colossal” dielectric constant at room temperature, er′ ∼ 42 000 (T = 300 K, ν = 10 Hz). Furthermore, the measured dielectric constant exhibits a thermal dependence similar to that of the diffusion coefficient, revealing the parallelism of the dielectric response and the molecular diffusion as a function of temperature. These results highlight: (a) the great utility of the fast and non-destructive dielectric and impedance spectroscopy techniques for the study and detection of the molecular transport of small polar molecules within porous metal-organic frameworks and related materials; (b) the peculiarity and uniqueness of MOF materials with “medium” size nanopores containing guest molecules as they are solid materials in which the guest molecules display a liquid state-like behaviour close to room temperature; and (c) the potential of these materials for molecular transport applications.

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.

We investigate the magnetic ordering and the magnetization dynamics (from kHz to THz time scales) of the double perovskite Lu2MnCoO6 using elastic neutron diffraction, muon spin relaxation, and micro-Hall magnetization measurements. This compound is known to be a type II multiferroic with the interesting feature that a ferromagneticlike magnetization hysteresis loop couples to an equally hysteretic electric polarization in the bulk of the material despite a zero-field magnetic ordering of the type ↑↑↓↓ along Co-Mn spin chains. Here we explore the unusual dynamics of this compound and find extremely strong fluctuations, consistent with the axial next-nearest-neighbor Ising (ANNNI) model for frustrated spin chains. We identify three temperature scales in Lu2MnCoO6 corresponding to the onset of highly fluctuating long-range order below TN = 50 ± 3 K identified from neutron scattering, the onset of magnetic and electric hysteresis, with change in kHz magnetic and electric dynamics below a 30 K temperature scale, and partial freezing of ∼MHz spin fluctuations in the muon spin relaxation data below 12 ± 3 K. Our results provide a framework for understanding the multiferroic behavior of this compound and its hysteresis and dynamics.

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.

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

Se han conseguido preparar monocristales de 10 oxidos mixtos de la serie LnMn2O5 (Ln= Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho y Er) mediante sintesis hidrotermal optimizada, en un unico paso y sin tratamientos termicos posteriores partiendo de las correspondientes sales metalicas en disolucion acuosa a 240 oC. Los monocristales obtenidos son relativamente grandes, de varias micras y su morfologia varia a lo largo de la serie: es poligonal en el caso de los compuestos de los lantanidos del inicio de la serie (Ln= Pr, Nd, Sm, Eu y Gd) y acicular en el caso de los compuestos de Y y de los lantanidos del final de la serie (Ln= Tb, Dy, Ho y Er). Tras el analisis de los productos obtenidos empleando distintas condiciones de sintesis atribuimos la diferente morfologia a una mayor velocidad de crecimiento cristalino a lo largo del eje c cuando intervienen los iones mas pequenos (Y, Tb, Dy, Ho y Er) debido a la mejor adaptacion de estos ultimos a la estructura cristalina del compuesto.

We report the magneto-transport properties of the layered mixed oxides Nd1−xSr1+xCoO4 (0 ≤ x ≤ 0.3) compounds. These materials are found to evolve towards an anomalous “cluster-glass” like behavior as x increases. The onset of the ferromagnetic order in the bidimensional phase is seen to occur in the x = 0.30 sample at Tc(2D) ≈ 125 K, followed by a blocking process around TB (2D) ≈ 55 K. In addition, present in the magnetic response of these materials is the paramagnetic contribution coming from the Nd3+ ions μ eff-N d 3+ = 3.62 μ B together with the signal coming from a minority perovskite phase, that is nevertheless not detected by powder X-ray diffraction. From the electrical point of view these materials are semiconducting and their resistivitiy decreases upon doping. In addition, at low temperatures T

We present the first example of magnetic ordering-induced multiferroic behavior in a metal-organic framework magnet. This compound is [CH3NH3][Co(HCOO)3] with a perovskite-like structure. The A-site [CH3NH3](+) cation strongly distorts the framework, allowing anisotropic magnetic and electric behavior and coupling between them to occur. This material is a spin canted antiferromagnet below 15.9 K with a weak ferromagnetic component attributable to Dzyaloshinskii-Moriya (DM) interactions and experiences a discontinuous hysteretic magnetic-field-induced switching along [010] and a more continuous hysteresis along [101]. Coupling between the magnetic and electric order is resolved when the field is applied along this [101]: a spin rearrangement occurs at a critical magnetic field in the ac plane that induces a change in the electric polarization along [101] and [10-1]. The electric polarization exhibits an unusual memory effect, as it remembers the direction of the previous two magnetic-field pulses applied. The data are consistent with an inverse-DM mechanism for multiferroic behavior.

A multistimuli response to temperature and pressure is found in the hybrid inorganic–organic perovskite-like [TPrA][Mn(dca)3] compound, which is related to a first-order structural phase transition near room temperature, Tt ≈ 330 K. This phase transition involves a transformation from room temperature polymorph I, with the noncentrosymmetric space group P4̅21c, to the high temperature polymorph II, with the centrosymmetric space group I4/mcm, and it implies ionic displacements, order–disorder phenomena, and a large and anisotropic thermal expansion (specially along the c-axis). As a consequence, [TPrA][Mn(dca)3] exhibits a dielectric anomaly, associated with the change from a cooperative to a noncooperative electric behavior (antiferroelectric (AFE)–paraelectric (PE) transition). The former implies an AFE distribution of electric dipoles in polymorph I, related to the described off-shift of the apolar TPrA cations and the order–disorder of the polar dca ligands mechanisms, that are different from those reported, up to now, for others perovskite-type hybrid compounds. Such cooperative electric order, below Tt ≈ 330 K, coexisting with long-range antiferromagnetic ordering below T = 2.1 K render the [TPrA][Mn(dca)3] a new type-I multiferroic material. In addition, the obtained experimental results reveal that this compound is also a multistimuli-responsive material, with a very large sensitivity toward temperature and applied external pressure, δTt/δP ≈ 24 K kbar–1, even for small values of pressure (P < 2 kbar). Therefore, this material opens up a potential interest for future technological applications, such as temperature/pressure sensing., The authors are grateful for the financial support from Ministerio de Economia 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).

After half a century of intensive and extensive studies on ferrocene [Fe(C5H5)2] and ammonia-borane (H3N·BH3), it is very exciting to observe that these “classical” compounds still hide interesting properties never described before. Despite it being well-known that they both experience phase transitions as a function of temperature, here, for the first time, we give experimental evidence for the dielectric transitions they experience associated to the former, results that we support with DFT calculations. In that context, we report that ferrocene displays a temperature-induced paraelectric to antiferroelectric transition associated with the monoclinic–triclinic transition, which implies order–disorder of the cyclopentadienyl (Cp) ligands and displacement of the Fe atoms within the ferrocene molecules. As for the ammonia-borane, we report a sharp dielectric transition at T ≈ 232 K, associated with a structural transition that combines ordering and atomic displacement of the H3N·BH3 molecules. In this case, we attribute such behaviour to the temperature dependent displacement of the H3N·BH3 molecules out-of the crystal polar c-axis The authors are grateful for financial support from Ministerio de Economía y Competitividad (MINECO) ENE2014-56237-C4-4-R and Xunta de Galicia under the project GRC2014/042. S. Y.-V. acknowledges Xunta de Galicia for a Postdoctoral fellowship SI

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 report the dielectric response of Ca2?xPrxMnO4 (x = 0 and 0.25). Specifically, their intrinsic dielectric constants are calculated by impedance spectroscopy from the values of the obtained bulk capacitances. For Ca2MnO4, that does not show charge-order, the measured intrinsic dielectric constant is 14. The Pr doping induces charge-order in the system, and also a noteworthy increase in , that reaches a value of ~220 for x = 0.25, unusual in these kind of oxides. This result provides a new link between both phenomena.

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

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

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 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

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.

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

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

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

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.

[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