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82 results on '"Sapiña, F."'

1. Compressibility and structural stability of ultra-incompressible bimetallic interstitial carbides and nitrides

Author

Errandonea, D., Ruiz-Fuertes, J., Sans, J. A., Santamaria-Perez, D., Gomis, O., Gomez, A., and Sapina, F.

Subjects
Condensed Matter - Materials Science, Physics - Chemical Physics
Abstract

We have investigated by means of high-pressure x-ray diffraction the structural stability of Pd2Mo3N, Ni2Mo3C0.52N0.48, Co3Mo3C0.62N0.38, and Fe3Mo3C. We have found that they remain stable in their ambient-pressure cubic phase at least up to 48 GPa. All of them have a bulk modulus larger than 330 GPa, being the least compressible material Fe3Mo3C, B0 = 374(3) GPa. In addition, apparently a reduction of compressibility is detected as the carbon content increased. The equation of state for each material is determined. A comparison with other refractory materials indicates that interstitial nitrides and carbides behave as ultra-incompressible materials., Comment: 14 pages, 3 figures, 1 table

Published
2012
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2. High-pressure x-ray diffraction and ab initio study of Ni2Mo3N, Pd2Mo3N, Pt2Mo3N, Co3Mo3N, and Fe3Mo3N: Two families of ultra-incompressible bimetallic interstitial nitrides

Author

Errandonea, D., Ferrer-Roca, Ch., Martinez-Garcia, D., Segura, A., Gomis, O., Munoz, A., Rodriguez-Hernandez, P., Lopez-Solano, J., Alconchel, S., and Sapina, F.

Subjects
Condensed Matter - Materials Science, Physics - Chemical Physics
Abstract

We have studied by means of high-pressure x-ray diffraction the structural stability of Ni2Mo3N, Co3Mo3N, and Fe3Mo3N. We also report ab initio computing modeling of the high-pressure properties of these compounds, Pd2Mo3N, and Pt2Mo3N. We have found that the nitrides remain stable in the ambient-pressure cubic structure at least up to 50 GPa and determined their equation of state. All of them have a bulk modulus larger than 300 GPa. Single-crystal elastic constants have been calculated in order to quantify the stiffness of the investigated nitrides. We found that they should have a Vickers hardness similar to that of cubic spinel nitrides like gamma-Si3N4, Comment: 25 pages, 6 figures, 3 tables

Published
2010
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3. Raman and infrared studies of La_1-ySr_yMn_1-xM_xO_3 (M=Cr, Co, Cu, Zn, Sc or Ga): Oxygen disorder and local vibrational modes

Author

Dubroka, A., Humlicek, J., Abrashev, M. V., Popovic, Z. V., Sapina, F., and Cantarero, A.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We present results of our study of polarized Raman scattering and infrared reflectivity of rhombohedral ceramic La_1-ySr_yMn_1-xM_xO_3 manganites in the temperature range between 77 and 320K. In our samples, a part of the Mn atoms is substituted by M = Cr, Co, Cu, Zn, Sc, or Ga with x in the range 0 -- 0.1. The hole concentration was kept at the optimal value of about 32% by tuning the Sr content y. We have monitored the distortions of the oxygen sublattice by the presence of broad bands in the Raman spectra, the increase of d.c. resistivity extracted from the infrared reflectivity, and the change of the critical temperature of the ferromagnetic transition. Our results support the idea, that these properties are mainly determined by the radius of the substituent ion, its electronic and magnetic structure playing only a minor role. Furthermore, the Raman spectra exhibit an additional A_g-like high frequency mode attributed to the local breathing vibration of oxygens surrounding the substituent ion. Its frequency and intensity strongly depend on the type of the substituent. In the Co-substituted sample, the mode anomalously softens when going from 300 to 77K. The frequency of the bulk A_{1g} mode depends linearly on the angle of the rhombohedral distortion., Comment: 11 pages, 11 Figures, best-fit values table added, a discussion added

Published
2005
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4. The effect of Cu substitution on the A1g mode of La(0.7)Sr(0.3)MnO3 manganites

Author

De Marzi, G., Trodahl, H. J., Bok, J., Cantarero, A., and Sapina, F.

Subjects
Condensed Matter - Materials Science
Abstract

We report on the first Raman data of Cu substituted La(1-y)Sr(y)Mn(1-x)Cu(x)O3 (0 < x < 0.10 and 0.17 < y < 0.3, accordingly in order to have the same Mn(4+)/[Mn(4+)+Mn(3+)] ratio), collected in the frequency range 100-900 cm-1 and at room temperature, with parallel and crossed polarizations of the incident and scattered light. Spectra were fitted with a Drude-Lorentz model, and peaks at 190-220 and 430 cm-1, together with two broad structures centered at near 500 and 670 cm-1, have been found. We also have observed that the A1g mode is substantially shifted with increasing Cu substitution. The A1g phonon shift is a linear function of the tolerance factor t and the rhombohedral angle, thus following the structural changes of the MnO6 octahedra in the system., Comment: 6 pages, 4 figures, SSC (accepted)

Published
2003
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11. The ferrimagnetic compounds CoM[M’(EDTA)]2·4H2O(M,M’=Co,Ni): Magnetic characterization of CoCo[Ni(EDTA)2]·4H2O.

Author

Sapiña, F., Coronado, E., Gomez-Romero, P., Beltran, D., Burriel, R., and Carlin, R. L.

Subjects
*LAMINATED metals, *MAGNETISM, MAGNETIC properties of complex compounds
Abstract

Discusses a study which examined the magnetic properties of the ordered bimetallic compound CoCo(NiEDTA)[sub2]4H[sub2]O. Structure of the bimetallic compound; Conditions that influence magnetic behavior; Computational equations for the transfer matrix of the bimetallic compound.

Published
1990

12. Crystal structure and magnetism of Co(HPO3)·H2O: A novel layered compound of Co(II).

Author

Marcos, M. D., Gómez-Romero, P., Amorós, P., Sapiña, F., Beltrán-Porter, D., Navarro, R., Rillo, C., and Lera, F.

Subjects
METAL crystals, MAGNETISM
Abstract

Discusses a study which determined the crystal structure and magnetic properties of the layered compound Co(HPO[sub3]) H[sub2]O. Formation and refinement of the structure; Description of the structure; Characterization of the magnetic properties of the sample.

Published
1990
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13. Compressibility and structural stability of ultra-incompressible bimetallic interstitial carbides and nitrides

Author

Universitat Politècnica de València. Departamento de Física Aplicada - Departament de Física Aplicada, Universitat Politècnica de València. Centro de Tecnologías Físicas: Acústica, Materiales y Astrofísica - Centre de Tecnologies Físiques: Acústica, Materials i Astrofísica, Errandonea, D., Ruiz-Fuertes, J., Sans, J. A., Santamaría-Perez, D., Gomis Hilario, Oscar, Gómez, A., Sapiña, F., Universitat Politècnica de València. Departamento de Física Aplicada - Departament de Física Aplicada, Universitat Politècnica de València. Centro de Tecnologías Físicas: Acústica, Materiales y Astrofísica - Centre de Tecnologies Físiques: Acústica, Materials i Astrofísica, Errandonea, D., Ruiz-Fuertes, J., Sans, J. A., Santamaría-Perez, D., Gomis Hilario, Oscar, Gómez, A., and Sapiña, F.

Abstract

We have investigated by means of high-pressure x-ray diffraction the structural stability of Pd 2Mo 3N, Ni 2Mo 3C 0.52N 0.48, Co 3Mo 3C 0.62N 0.38, and Fe 3Mo 3C. We have found that they remain stable in their ambient-pressure cubic phase at least up to 48 GPa. All of them have a bulk modulus larger than 330 GPa, the least compressible material being Fe 3Mo 3C, B 0 = 374(3) GPa. In addition, apparently a reduction of compressibility is detected as the carbon content is increased. The equation of state for each material is determined. A comparison with other refractory materials indicates that interstitial nitrides and carbides behave as ultra-incompressible materials. © 2012 American Physical Society.

Published
2012

15. High-pressure x-ray diffraction andab initiostudy ofNi2Mo3N,Pd2Mo3N,Pt2Mo3N,Co3Mo3N, andFe3Mo3N: Two families of ultra-incompressible bimetallic interstitial nitrides

Author

Errandonea, D., primary, Ferrer-Roca, Ch., additional, Martínez-Garcia, D., additional, Segura, A., additional, Gomis, O., additional, Muñoz, A., additional, Rodríguez-Hernández, P., additional, López-Solano, J., additional, Alconchel, S., additional, and Sapiña, F., additional

Published
2010
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20. Ordered Mesoporous Silicon Oxynitrides

Author

El Haskouri, J., primary, Cabrera, S., additional, Sapiña, F., additional, Latorre, J., additional, Guillem, C., additional, Beltrán-Porter, A., additional, Beltrán-Porter, D., additional, Marcos, M. D., additional, and Amorós, P., additional

Published
2001
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26. The ferrimagnetic compounds CoM[M'(EDTA)]2.4H2O (M,M'=Co,Ni): Magnetic characterization of CoCo[Ni(EDTA)]2.4H2O

Author

Generalitat Valenciana, National Science Foundation (US), Ministerio de Educación y Ciencia (España), Comisión Interministerial de Ciencia y Tecnología, CICYT (España), Sapiña, F., Coronado, Eugenio, Gómez-Romero, P., Beltrán-Porter, Daniel, Burriel, Ramón, Carlin, Richard L., Generalitat Valenciana, National Science Foundation (US), Ministerio de Educación y Ciencia (España), Comisión Interministerial de Ciencia y Tecnología, CICYT (España), Sapiña, F., Coronado, Eugenio, Gómez-Romero, P., Beltrán-Porter, Daniel, Burriel, Ramón, and Carlin, Richard L.

Abstract

We report on the magnetic properties of the ordered bimetallic compound CoCo(NiEDTA)2⋅4H2O (abbreviated as [CoCoNi]). The structure consists of ordered bimetallic layers formed by alternating octahedral sites of Co and Ni(II); tetrahedral Co sites connect different Co‐Ni layers. We discuss the low‐dimensional ferrimagnetic behavior of this compound in terms of a model that assumes three spin sublattices exchange coupled by an Ising interaction.

Published
1990

35. Polymer solution processing of (Bi, Pb)SrCaCuO

Author

de la Fuente, G.F., primary, Sotelo, A., additional, Huang, Y., additional, Ruiz, M.T., additional, Badia, A., additional, Angurel, L.A., additional, Lera, F., additional, Navarro, R., additional, Rillo, C., additional, Ibañez, R., additional, Beltran, D., additional, Sapiña, F., additional, and Beltran, A., additional

Published
1991
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39. Structural effects of Co and Cr substitution in LaMnO<SUB>3 + <SUB>δ</SUB></SUB>

Author

El-Fadli, Z., Metni, M. R., Sapiña, F., Martinez, E., Folgado, J. V., Beltrán, D., and Beltrán, A.

Abstract

Series of perovskite oxides with the composition LaMn1 − xMxO3 + δ (M = Cr, Co; 0 ≤ x ≤ 1) have been synthesized by thermal treatment of precursors obtained by freeze-drying of acetic acid solutions. The oxides have been characterized by X-ray diffraction, and the Mn4+ content and, thus, the oxygen excess, δ, has been determined by redox back-titration. LaMnO3.14 and LaCrO3 phases have the rhombohedral-LaAlO3 and the orthorhombic-GdFeO3 structures, respectively. The LaMn1 − xCrxO3 + δ phases have the rhombohedral structure for x ≤ 0.3, and the orthorhombic structure for x ≥ 0.5. LaCoO3 has, as LaMnO3.14, the rhombohedral structure. However, the LaMn1 − xCoxO3 + δ phases have orthorhombic structure for 0.05 ≤ x ≤ 0.55. The evolution of the crystal symmetry has been interpreted by considering the effect of the size of the substituting ion on the capability of the perovskite network to accommodate the oxygen excess (δ).

Published
2000

40. Low temperature synthesis, structure and magnetic properties of La0.85(Na1–xKx)0.15MnO3 perovskites: the role of A cation size disparity in the electronic properties of mixed-valence manganates

Author

El-Fadli, Z., Coret, E., Sapiña, F., Martinez, E., Beltrán, A., Beltrán, D., and Lloret, F.

Abstract

Single-phase perovskites in the solid solution series La0.85(Na1–xKx)0.15MnO3 (0≤x≤1) have been obtained using a soft treatment, which makes possible strict stoichiometric control. X-Ray powder diffraction patterns of these compounds have been completely indexed with a rhombohedral perovskite cell. The crystal structures have been refined in space group R-3c, in the hexagonal setting, from room-temperature data. Substitution of Na+ by larger K+ ions produces a cell expansion and a decrease in the structural distortion from the ideal cubic structure. The critical temperature for the paramagnetic-ferromagnetic transition, Tc, is found to be practically constant, ca. 333 K, along the entire series. This behaviour is unexpected, taking into account previous correlations established for the alkaline-earth La0.7(Ca1–xSrx)0.3MnO3 series (Tc increases with the mean size of cations at the A positions, 〈rA〉) which expands over a similar 〈rA〉 range. We can therefore discuss these results in terms of two counterweighting contributions: increasing Tc values could be expected as a consequence of the increase with x of the 〈rA〉 value, but the concomitant disorder introduced at the A positions [as represented by the variance of the A cations radial distribution, σ2(〈rA〉)] would cause a decrease in Tc. An approach to the understanding of the contribution that the electronic energy makes to this last effect is advanced.

Published
1999
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41. Precursor-based synthetic pathways to nanometer NdNiO3−xparticles

Author

García, J., González, A., Sanchis, M.J., Marcos, M.D., Martínez, E., Sapiña, F., Beltrán, D., and Beltrán, A.

Abstract

The oxygen deficient neodymium nickel perovskite, NdNiO3−x, has been obtained by different low temperature-low oxygen pressure synthetic procedures. Besides a solid-matrix based route, both ordered and disordered chemical-precursors have been used as starting products. X-ray powder diffraction shows that the structure of this defective perovskite is orthorhombic. The study of the grain morphology of the products as resulting from the different synthetic procedures indicates that the main parameter determining the average particle size, which is in the nanometer range, is the maximum temperature achieved in the synthesis. Resistivity and DSC measurements show the existence of a metal to insulator transition at ca. 175 K. The anomalous behaviour of the resistivity in the insulator zone is discussed.

Published
1993
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42. Fast synthesis of single-phased 110 K bismuth superconductor by freeze-drying of acetic precursors. Kinetic role of calcium and copper oxides

Author

Primo, V., Sapiña, F., Sanchis, M.J., Ibáñez, R., Beltrán, A., and Beltrán, D.

Abstract

Although the usefulness of solution procedures to improve the synthesis of bismuth HTSC has been argued, an adequate control of the procedural variables has allowed us to isolate the 110 K phase as the only superconducting phase after such a short sintering time as 22 h. The precursors used have been freeze-dried powders resulting from acetic solutions containing excess Ca and Cu. TGA-DTA and XRD experiments have been performed to follow the subsequent solid-state reaction processes. The initial formation of a mixed bismuth-lead oxoacetate, as intermediate to (Bi1−yPby)2CuO4, and the presence of an excess of Ca2CuO 3in the last reaction step are two of the main factors driving the fast synthesis of the 110 K phase.

Published
1993
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