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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.

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.

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 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.

We have prepared two new lead halides with the novel general formula of DMA7Pb4X15 (DMA = [(CH3)2NH2]+ and X = Cl– or Br–) by using an easy route under mild conditions at room temperature. These compounds exhibit an unprecedented crystal structure, are formed by layers of distorted [PbX6] octahedra, which share corners and faces, and contain intercalated DMA cations. Very interestingly, they display dielectric transitions, which are related to a partial order–disorder process of the DMA cations between 160 and 260 K. Additionally, these new layered hybrids exhibit a broadband photoluminiscent emission, which is related to the structural distortions of the [PbX6] octahedra. These findings not only open up large possibilities for future optoelectronic applications of these materials, but they also offer a novel playground for an easy modulation of electrical and optical properties of hybrid organic–inorganic materials. We anticipate that this novel A7Pb4X15 formula can be adequate to tune the family of the ...

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

By a wet-chemistry route we have been able to effectively dope the CHA2PbBr4 compound, a ferroelectric compound with photovoltaic effect, with different amounts of Mn2+ obtaining three pure compounds CHA2Pb1-xMnxBr4 with x = 0.05, 0.07 and 0.11. At room temperature the crystal structure of these new Mn-doped compounds present an orthorhombic symmetric with polar space group Cmc21, as in the case of the undoped compoud (x = 0). Very interestingly, the doped compounds exhibit a broad PL emissions at room temperature, with a maximum around 605 nm and a long PL lifetime (~0.55 ms), whose intensity increases further upon cooling. The observed PL emission is induced from an energy transfer from host semiconductor to the d-orbitals of Mn2+ cation. In addition, we have explored the capability of these materials to act as chemical sensors for volatile organic compounds and report the selective luminescence vapochromic response in this family of compounds. Therefore, the here presented Mn-doped CHA2Pb1-xMnxBr4 compounds belong to the scarce and desirable group of multifunctional materials, where not only ferroelectric and photovoltaic properties can coexist but also photoluminescence and vapochromic properties, rendering them extremely interesting for a large number of potential practical applications.

The perovskite azido compound [(CH3)4N][Mn(N3)3], which undergoes a first-order phase change at Tt=310 K with an associated magnetic bistability, was revisited in the search for additional ferroic orders. The driving force for such structural transition is multifold and involves a peculiar cooperative rotation of the [MnN6] octahedral as well as order/disorder and off-center shifts of the [(CH3)4N]+ cations and bridging azide ligands, which also bend and change their coordination mode. According to DFT calculations the latter two give rise to the appearance of electric dipoles in the low-temperature (LT) polymorph, the polarization of which nevertheless cancels out due to their antiparallel alignment in the crystal. The conversion of this antiferroelectric phase to the paraelectric phase could be responsible for the experimental dielectric anomaly detected at 310 K. Additionally, the structural change involves a ferroelastic phase transition, whereby the LT polymorph exhibits an unusual and anisotropic thermal behavior. Hence, [(CH3)4N][Mn(N3)3] is a singular material in which three ferroic orders coexist even above room temperature. Triple-ferroic hybrid perovskite: The azido perovskite compound [(CH3)4N][Mn(N3)3] is a singular multiferroic material in which the three ferroic orders (electric, elastic, and magnetic) coexist even above room temperature (see figure).

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.

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.

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.

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.

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

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.

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).

We report the magnetic and transport properties of the cobalt layered mixed-oxides La1−xSr1+xCoO4 ( 0 ⩽ x ⩽ 0.40 ) . An evolution towards an anomalous “cluster-glass”-like behavior as x increases has been found. The onset of the ferromagnetic order in the layered phases occurs at around 150 K followed by a blocking process around 125 K. Also, present in the magnetic response of these materials is the signal coming from small intergrowths of a perovskite phase, also detected by TEM, although invisible for powder-X-ray diffraction. From the electrical point of view these materials are semiconducting and their resistivity decreases upon doping. Most interestingly, at low temperature these layered compounds show rather large magnetoresistance (MR). The highest effect is found in the sample with x = 0.20 that shows a magnetoresistance MR max = − 24 % at T = 15 K under a field H max = 50 kOe .

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

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

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).

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

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.

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

[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

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.

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

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