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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.

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.

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.

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

In this work we prepare and study the M(dca) 2 pyz compounds, where dca = polar dicyanamide N(CN) 2 − ligand, pyz = pyrazine (C 4 H 4 N 2 ) ligand and M = Fe 2+ , Co 2+ and Zn 2+ that, according to DSC display a first order phase transition, at T t ∼ 270 K (Fe), ∼250 K (Co) and ∼240 K (Zn). Very interestingly these compounds, which consist of a rather robust framework with incorporated polar dca ligands, and which does not host guest species in the cavities of the structure, display a dielectric anomaly associated to such phase transition. This latter in fact corresponds to the structural transition from the disordered HT-phase (space group Pnma ) to the ordered LT-phase (space group P 2 1 / n ). From a detailed analysis of the dipole distributions in each of these crystal structures we conclude that the polar dca ligands, which bridge two transition metal cations, display a cooperative electrical arrangement, in which the dipoles of each of the two interpenetrated networks show a ferroelectric (FE) arrangement; nevertheless, the relative antiparallel orientation of both networks finally results in net antiferroelectric (AFE) arrangements both in the LT- and HT-polymorphs. Very interestingly, the dynamic disorder of the dca ligands at T t gives rise to the observed dielectric anomaly. These materials constitute, therefore, an example of hybrid organic–inorganic compounds where the dielectric response directly arises from the framework –and not from polar guest species– which is a very interesting and novel approach in the search for materials in which the dielectric and magnetic properties can couple more strongly.

In this work, we have successfully synthesized hollow microtubular crystals of the metal–organic framework (MOF) [Co2(NH2-bdc)2(dabco)]·[G] {G = H2O, N,N-dimethylformamide (DMF); NH2-bdc =2-amino-1,4-benzenedicarboxylate; dabco = 1,4-diazabicyclo[2.2.2]octane} by a very simple coordination-modulation method that avoids the use of an external modulator. Additionally, we have obtained the corresponding hollow microtubular crystals of Co3O4 through the solid-state thermolysis of the Co-MOF material at 400 °C. The as-prepared Co3O4 crystals exhibit the typical magnetic behavior for a nanostructured material with good crystallinity. Thus, this coordination-modulation method provides a simple route for the preparation of nanostructured porous frameworks and derived oxides and opens a way to prepare new materials with advanced properties.

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 on the hybrid inorganic-organic ammonium compound [NH4][Cd(HCOO)3], which displays a most unusual framework structure: instead of the expected 4(9)·6(6) topology, it shows an ABX3 perovskite architecture with the peculiarity and uniqueness (among all the up-to-date reported hybrid metal formates) that the Cd ions are connected only by syn-anti formate bridges, instead of anti-anti ones. This change of the coordination mode of the formate ligand is thus another variable that can provide new possibilities for tuning the properties of these versatile functional metal-organic framework materials. The room-temperature crystal structure of [NH4][Cd(HCOO)3] is noncentrosymmetric (S.G.: Pna21) and displays a polar axis. DFT calculations and symmetry mode analysis show that the rather large polarization arising from the off-center shift of the ammonium cations in the cavities (4.33 μC/cm(2)) is partially canceled by the antiparallel polarization coming from the [Cd(HCOO)3](-) framework, thus resulting in a net polarization of 1.35 μC/cm(2). As shown by second harmonic generation studies, this net polarization can be greatly increased by applying pressure (Pmax = 14 GPa), an external stimulus that, in turn, induces the appearance of new structural phases, as confirmed by Raman spectroscopy.

[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

We have found that the hybrid organic-inorganic perovskite-like formate Mn(HCOO)(3)[(CH(3))(2)NH(2)] shows a dielectric transition around 190 K. According to single crystal X-ray diffraction, the compound shows rhombohedral symmetry at room temperature and monoclinic symmetry at low temperature (100 K), and the main difference between both structures is that the (CH(3))(2)NH(2)(+) (DMA) cations are disordered in the high temperature phase but cooperatively ordered in the low temperature one. The vibrational spectra of this compound reveal that significant changes take place in the vibrations ascribed to the DMA cation (changes in the frequency of certain vibrations, splitting of particular vibrations, and changes in the intensities), while no significant changes have been observed in those attributed to the formate anion. On the basis of all this information, we attribute the origin of the dielectric transition to the dynamics of the DMA cations: above 190 K these cations can rotate inside the cubooctahedral cavity created by the [Mn(HCOO)(3)](-) framework, while for lower temperatures such rotation gets frozen, and their cooperative arrangement inside the cavities give rise to the observed dielectric transition.

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

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.

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.

[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.

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

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

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

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