Person: Sáez Puche, Regino
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First Name
Regino
Last Name
Sáez Puche
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Inorgánica
Area
Química Inorgánica
Identifiers
18 results
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Now showing 1 - 10 of 18
Item Single phase, electrically insulating, multiferroic La-substituted BiFeO3 prepared by mechanosynthesis(Journal of Materials Chemistry C, 2014) Perejón, Antonio; Sánchez-Jiménez, Pedro E.; Pérez-Maqueda, Luis A.; Criado, José M.; Romero de Paz, Julio; Sáez Puche, Regino; Masó, Nahum; West, Anthony R.Single phase, electrically insulating samples of Bi1-xLaxFeO3 solid solutions have been prepared by mechanosynthesis over the whole compositional range for the first time. Lanthanum substitution influenced the kinetics of the mechanochemical reaction and crystallite size of the products. For 0 <= x <= 0.15, an increase in the La content produced a significant decrease in the weight-normalized cumulative kinetic energy required to obtain the final product and an increase in the resulting crystallite size. Larger La contents did not affect either the reactivity or the crystallite size. The effect of x on the structure has been identified. Samples in the ranges x <= 0.15 and x >= 0.45 gave single phase solid solutions with R3c and Pnma space groups, respectively, while for the intermediate range, a non-centrosymetric Pn2(1)a(00 gamma)s00 super structure was obtained. For 0 <= x <= 0.30, differential scanning calorimetry showed two endothermic effects corresponding to the Neel temperature (T-N, antiferromagnetic-paramagnetic transition) and the Curie temperature (T-C, ferroelectric-paraelectric transition), demonstrating their multiferroic character. Compositions with a larger La content only showed T-N. Dilatometric and permittivity measurements confirmed the results obtained by DSC for the ferroelectric-paraelectric transition. The composition dependence of T-N and T-C showed that, at low x, T-N < T-C, but a cross-over, or isoferroic transition occurred at x similar to 0.28, when T-N = T-C = 386 degrees C. Ceramics with 0 <= x <= 0.15 were highly insulating at room temperature with a resistivity, extrapolated from the Arrhenius plots, of similar to 7 x 10(16) to 8 x 10(14) Omega cm and an activation energy similar to 1.14-1.20 eV. Magnetization of the samples improved with La substitution.Item Tuning the magnetic properties of transition metal MOFs by metal–oxygen condensation control: the relation between synthesis temperature, SBU nuclearity and carboxylate geometry(CrystEngComm, 2012) Bernini, María ; Platero-Prats, Ana; Snejko, Natalia; Gutiérrez-Puebla, Enrique; Labrador, Ana; Sáez Puche, Regino; Romero de Paz, Julio; Monge, M. ÁngelesFive novel metal organic frameworks, belonging to three structural types, have been obtained hydrothermally. Three of them, with formula [M-3(hfipbb)(2)(OH)(2)(H2O)] (M = Mn, Co, Ni; hfipbb = 4,4'-(hexafluoroisopropylidene)bis(benzoate) dianion) belong to the first structural type. The crystal structure of the Mn-based compound was obtained from single crystal synchrotron X-ray diffraction data, while the isostructural compounds of Co and Ni were studied by means of Rietveld analysis using powder X-ray diffraction data. The magnetic behavior of the compounds with M = Co and Ni is characterized by the onset of long-range ferromagnetic order at very low temperature with Curie temperatures near 8 and 2.5 K, respectively. Such spontaneous magnetization seems to be preceded by low-dimensional magnetic interactions, due to the nature of the secondary building units (SBUs) of the structure, which are triple chains built by M3O14 units. Structural and topological analyses of [Mn-2(hfipbb)(2)(H(2)hfipbb)] and [Co-2(hfipbb)(2)(H(2)hfipbb)] (2 and 3 structural types, respectively; H(2)hfipbb = 4,4'-(hexafluoroisopropylidene)bis(benzoic acid)) demonstrate that the packing of the rod-shaped SBUs in 2 prevents the framework interpenetration giving rise to a bnn net whereas 3 is a 2-fold interpenetrated pcu net with isolated paddle-wheel clusters as SBUs pcu. Concerning the magnetic behavior of 2 and 3, antiferromagnetic interactions observed at very low temperature (magnetic susceptibility maximum at 2.8 and 18 K, respectively) are confined to the secondary building units.Item Structural characterisation and spin glass behaviour of the new oxide Ba2ScCoO5(Journal of Materials Chemistry, 1999) Julián Ortega, Inmaculada; Sáez Puche, Regino; Romero de Paz, Julio; Martínez, José LuisThe new oxide Ba 2 ScCoO 5 has been synthesised by solid state reaction and characterised by using both X-ray and electron diffraction techniques. It crystallises in a perovskite-type structure, showing cubic symmetry, space group Pm[3 with combining macron]m [a=4.1400(9) Å]. χ dc and χ ac magnetic susceptibility have been measured down to 1.6 K and analysed, indicating the existence of a freezing phenomenon corresponding to a spin glass state. In the high temperature range, χ dc shows a Curie-Weiss like behaviour, with magnetic correlations starting around T C =50 K. Below this temperature, a strong irreversibility in χ vs. T curves obtained by zero field cooled and field cooled processes (ZFC/FC) has been detected. A second magnetic transition to a spin-glass phase is observed at T F =35 K in the ZFC curve. χ ac measurements performed at different frequencies and magnetic fields also show all the common features characteristic of re-entrant spin-glasses. A possible origin of this magnetic behaviour is proposed and discussed.Item High pressure synthesis of polar and non-polar cation ordered polymorphs of Mn2ScSbO6(Dalton Transactions, 2015) Solana Madruga, Elena; Dos Santos García, Antonio Juan; Arévalo-López, Ángel ; Ávila Brande, David; Ritter, Clemens; Attfield, Paul; Sáez Puche, ReginoTwo new cation-ordered polymorphs of Mn2ScSbO6 have been synthesised at high-pressure. At 5.5 GPa and 1523 K Mn2ScSbO6 crystallizes in the Ni3TeO6-type structure with the polar R3 space group and cell parameters a = 5.3419 (5) Å and c = 14.0603 (2) Å. Below TC = 42.0 K it exhibits ferrimagnetic order with a net magnetization of 0.6μB arising from unusual site-selective Mn/Sc disorder and is thus a potential multiferroic material. A double perovskite phase obtained at 12 GPa and 1473 K crystallizes in the nonpolar P21/n monoclinic space group with cell parameters a = 5.2909 (3) Å, b = 5.4698 (3) Å, c = 7.7349 (5) Å and β = 90.165 (6) °. Magnetization and neutron diffraction experiments reveal antiferromagnetic order below TN = 22.3 K with the spins lying in the ac plane.Item One-step Sustainable Preparation of Superparamagnetic Iron Oxide Nanoparticles Supported on Mesoporous SiO2(Journal of Supercritical Fluids, 2020) Chamorro, Elena; Granados García Tenorio, María José; Calvo Garrido, María Lourdes; Torralvo Fernández, María Josefa; Sáez Puche, Regino; Cabañas Poveda, AlbertinaSuperparamagnetic iron oxide nanoparticles (SPIONs) supported on high surface area mesoporous SiO2 are advanced materials of great interest in catalysis, adsorption and biomedicine. Here we present a new process to prepare SPION/SiO2 materials by the impregnation and insitu decomposition of Fe(NO3)3.9H2O on mesoporous SiO2 supports in a 25-50% mol ethanol + CO2 mixture at 523 K and 25.0 MPa. -Fe2O3 nanoparticles (NPs) of average size between 6-9 nm were distributed homogeneously on the supports. NPs deposited into the SBA-15 mesopores but mostly on the external surface of MCM-41. Materials prepared with the highest ethanol content were very homogeneous. Magnetic measurements confirmed the superparamagnetic nature of the materials at room temperature. The process proposed is sustainable and scalable, avoids tedious preparations and the additional high temperature treatment under a controlled atmosphere, as the metal decomposition is performed insitu in the CO2-expanded liquid mixture.Item Magnetic and crystal structure determination of Mn2FeSbO6 double perovskite(Journal of Physics: Condensed Matter, 2013) Dos Santos García, Antonio Juan; Ritter, Clemens; Solana Madruga, Elena; Sáez Puche, ReginoThe perovskite form of the Mn2FeSbO6 oxide has been obtained at 5.5 GPa and 1523 K. X-ray and neutron diffraction data reveal that this compound crystallizes in the monoclinic P21/n space group with a = 0.5234 nm, b = 0.5389 nm, c = 0.7642 nm and β = 90.372° lattice parameters. AC and DC magnetic susceptibility measurements suggest the existence of a complex magnetic behavior below 200 K. The magnetic structure has been determined and can be described on the basis of an elliptical spiral with an incommensurate propagation vector, k = [0,0.426,0], where the magnetic moments of 2Mn2+ and Fe3+ cations are confined to the ac-plane.Item Mesoporous Silica Matrix as a Tool for Minimizing Dipolar Interactions in NiFe2O4 and ZnFe2O4 Nanoparticles(Nanomaterials, 2017) Virumbrales del Olmo, Maider; Sáez Puche, Regino; Torralvo Fernández, María Josefa; Blanco Gutiérrez, VerónicaNiFe2O4 and ZnFe2O4 nanoparticles have been prepared encased in the MCM (Mobile Composition of Matter) type matrix. Their magnetic behavior has been studied and compared with that corresponding to particles of the same composition and of a similar size (prepared and embedded in amorphous silica or as bare particles). This study has allowed elucidation of the role exerted by the matrix and interparticle interactions in the magnetic behavior of each ferrite system. Thus, very different superparamagnetic behavior has been found in ferrite particles of similar size depending on the surrounding media. Also, the obtained results clearly provide evidence of the vastly different magnetic behavior for each ferrite system.Item Structural characterization and magnetic properties of divanadates ZnMV2O7 (M = Co, Ni and Cu)(Journal of Alloys and Compounds, 2005) Salah, Ait; Benkhouja, Khalil; Jaafari, Kamal; Romero de Paz, Julio; Climent Pascual, Esteban; Sáez Puche, ReginoDivanadates of general formula ZnMV2O7 (M = Co, Ni and Cu) have been prepared as powdered samples and the X-ray structural determination and magnetic studies have been carried out. Both ZnCoV2O7 and ZnNiV2O7 crystallize with the so-called dichromate structure type, showing monoclinic symmetry, space group P21/c, while the third member of this family of vanadates ZnCuV2O7 shows the thortveitite structure type with monoclinic symmetry, space group C2/c. Magnetic susceptibility and specific heat measurements reveal that these derivatives behave as antiferromagnets and the estimated Néel temperatures are 4.5, 3.5 and 5.3K for cobalt, nickel and copper vanadates, respectively. In all cases, the one-dimensional magnetic behavior that present the M2V2O7 vanadates is broken down when the magnetic cation M is half replaced by the diamagnetic Zn2+ to give the ZnMV2O7 samples studied in the present work.Item Anisotropic magnetic structures of the MnRMnSbO6 high pressure double double perovskites(Physical Review B, 2018) Solana Madruga, Elena; Arévalo-López, Ángel ; Dos Santos García, Antonio Juan; Ritter, Clemens; Cascales, Concepción; Sáez Puche, Regino; Attfield, PaulA new type of doubly ordered perovskite (also reported as double double perovskite, DDPv) structure combining columnar and rock-salt orders of the cations at the A and B sites, respectively, was recently found at high pressure for MnRMnSbO6 (R = La–Sm). Here we report further magnetic structures of these compounds. Mn2+ spins align into antiparallel ferromagnetic sublattices along the x axis for MnLaMnSbO6, while the magnetic anisotropy of Pr3+ magnetic moments induces their preferential order along the z direction for MnPrMnSbO6. The magnetic structure of MnNdMnSbO6 was reported to show a spin-reorientation transition of Mn2+ spins from the z axis towards the x axis driven by the ordering of Nd3+ magnetic moments. The crystal-field parameters for Pr3+ and Nd3+ at the 4e C2 site of their DDPv structure have been semiempirically estimated and used to derive their energy levels and associated wave functions. The results demonstrate that the spin-reorientation transition in MnNdMnSbO6 arises as a consequence of the crystal-field-induced magnetic anisotropy of Nd3+.Item Lithium Storage Mechanisms and Effect of Partial Cobalt Substitution in Manganese Carbonate Electrodes(Inorganic Chemistry, 2012) Mirhashemihaghighi, Shadi; León, Bernardo; Pérez Vicente, Carlos; Tirado Fernández, José Francisco; Stoyanova, Radostina; Yoncheva, Meglena; Zhecheva, Ekaterina; Sáez Puche, Regino; Arroyo De Dompablo, María Elena; Romero de Paz, JulioA promising group of inorganic salts recently emerged for the negative electrode of advanced lithium-ion batteries. Manganese carbonate combines low weight and significant lithium storage properties. Electron paramagnetic resonance (EPR) and magnetic measurements are used to study the environment of manganese ions during cycling in lithium test cells. To observe reversible lithium storage into manganese carbonate, preparation by a reverse micelles method is used. The resulting nanostructuration favors a capacitive lithium storage mechanism in manganese carbonate with good rate performance. Partial substitution of cobalt by manganese improves cycling efficiency at high rates.