R. Gómez - Academia.edu (original) (raw)
Papers by R. Gómez
Cornell University - arXiv, Nov 21, 2018
Polycrystalline samples of Fe2BiMO7 (M = Sb, Ta) compounds with pyrochlore-type structure were sy... more Polycrystalline samples of Fe2BiMO7 (M = Sb, Ta) compounds with pyrochlore-type structure were synthesized for the first time by the molten salts method. The compounds were obtained in one hour at 950ºC. The structures were determined by Rietveld refinement. Through Mössbauer spectroscopy and X-ray photoelectron spectroscopy, the site occupancies and ionic states of the cations in the pyrochlore structure were investigated.
… of Nanoscience and …, 2008
Sol-gel thin films containing Fe 2 O 3 were deposited onto glass substrates by the dip-coating me... more Sol-gel thin films containing Fe 2 O 3 were deposited onto glass substrates by the dip-coating method at room temperature. Fe 2 O 3 enriched with the isotope 57 Fe was embedded in two kinds of matrices: zinc oxide (ZnO) and silica (SiO 2 ). X-ray diffraction (XRD) was used for ...
European Journal of Physics
Journal of molecular modeling, Jan 4, 2017
First principles calculations have been performed for C60@C180 carbon double-layer endofullerenes... more First principles calculations have been performed for C60@C180 carbon double-layer endofullerenes with up to: three diatomic radioiodine molecules (131I2), two potassium radio-iodide (K131I), and three sodium radio-iodide (Na131I) inside. The plane-wave pseudopotential (PP) method within the general gradient approximation (GGA) in the framework of the density functional theory (DFT) and time-dependent DFT (TD-DFT) was used to perform geometric optimizations (GOs) and molecular dynamics (MD) at 310 K and atmospheric pressure. We found that the double-layer carbon nanocapsules formed by two concentric fullerenes (C180 surrounding C60) are very stable and may contain a radiodosis, without altering their configuration; that is, the 3(131I2)@C60@C180, 2(K131I)@C60@C180, and 3(Na131I)@C60@C180 systems constitute stable nanocapsules. We analyzed the interaction of double-layer endofullerene with radioactive content with some calcium, phosphorus, and strontium atoms, [n(X131I)@C60@C180 + mY...
Journal of Physics B: Atomic and Molecular Physics
High-resolution metastable excitation function measurements have been made in the doubly excited ... more High-resolution metastable excitation function measurements have been made in the doubly excited states region for Ne, Ar and Kr targets. Comparison of the spectra obtained suggests that the gross features are due to negative-ion resonances. Previous techniques which have proved successful in the identification and classification of resonances in the rare gases at energies below the first ionisation threshold are shown to be applicable in this energy region also and assignments for a number of resonances are suggested. Where appropriate, comparisons are made with data obtained by other techniques. The modified Rydberg formula has been used to predict energies for both doubly and triply excited configurations.
European Journal of Physics
Journal of Molecular Modeling, 2016
We report first-principles calculations carried out to analyze the adsorption of calcium on the o... more We report first-principles calculations carried out to analyze the adsorption of calcium on the outer surface of the fullerene C60, yielding [C60 + mCa]. Geometric optimization (GO) and molecular dynamics (MD) simulation were performed using the plane-wave pseudopotential method within the framework of density functional theory (DFT) and time-dependent DFT (TD-DFT) to investigate the configurations, the associated energies in the ground state, and the stabilities of fullerenes and endofullerenes doped with radioactive sodium iodide when they interact with calcium atoms on the outer fullerene surface (i.e., [nNa(131)I@C60 + mCa]). The reason for investigating these calcium-functionalized (endo)fullerene systems was to gauge their potential stability when used as vectors to deliver radioiodine to cancerous tissue in the human body. In the simulations, we found that the geometric limit on the number of calcium atoms that can be physisorbed on the outer surface of an empty fullerene while maintaining its structural stability is 28 calcium atoms, which also takes into account the proportional expansion of the fullerene as the number of absorbed calcium atoms increases. However, the stability of a fullerene system during calcium adsorption also strongly depends on whether any atoms or molecules are being encapsulated by the fullerene, as these encapsulated atoms/molecules can also interact with the fullerene and influence its stability. A Mulliken electronegativity analysis revealed that, when atoms inside and/or outside the fullerene donate charge (electrons) to the fullerene, the fullerene expands. The excess charge on the carbon atoms of the fullerene weakens some of the carbon-carbon bonds, potentially causing them to break, in which case the fullerene loses its ability to encapsulate molecules and releases them. Graphical Abstract DFT simulation of a endo fullerene doped with radioactive sodium iodide interacting with 28 calcium atoms in a geometric arrangement.
Boletin de la Sociedad Espanola de Ceramica y Vidrio
MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained sa... more MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained samples were characterized by X-ray and electron diffraction, Scanning and Transmission Electron Microscopy and Mössbauer spectroscopy. The transmission images show homogeneous shape and particle size ranging from 10 to 40 nm, depending on the nature of the M cation. Mössbauer spectroscopy yields to a ratio of occupancy between the A and B sites of 0.7 in the case of NiFe 2 O 4 oxide. DC magnetization (2-300 K) measurements reveal a superparamagnetic behaviour for the ZnFe 2 O 4 sample with a blocking temperature of 20 K. By contrast, in the case of the NiFe 2 O 4 ferrite the blocking temperature appears to be above 300 K and at lower temperature, it shows a ferrimagnetic behaviour arising from the superexchange interactions that take place in this inverse spinel. Mössbauer spectroscopy results confirm the bulk magnetic measurements.
Physical Review B
Moessbauer spectra of a YBaâCu/sub 2.9375/Fe/sub 0.0625/O/sub delta/ superconducting sample were ... more Moessbauer spectra of a YBaâCu/sub 2.9375/Fe/sub 0.0625/O/sub delta/ superconducting sample were obtained at different temperatures ranging from 50 to 120 K. The results clearly show that Fe substitutes for Cu in this complex. All the spectra showed a pair of superimposed quadrupole doublets with essentially the same splittings but different isomer shifts, corresponding to two different environments of the substituted atoms. The values of the isomer shifts obtained correspond to low-spin Fe atoms, which implies strong local fields, or strong bonding between the atoms.
Boletin de la Sociedad Espanola de Ceramica y Vidrio
MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained sa... more MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained samples were characterized by X-ray and electron diffraction, Scanning and Transmission Electron Microscopy and Mössbauer spectroscopy. The transmission images show homogeneous shape and particle size ranging from 10 to 40 nm, depending on the nature of the M cation. Mössbauer spectroscopy yields to a ratio of occupancy between the A and B sites of 0.7 in the case of NiFe 2 O 4 oxide. DC magnetization (2-300 K) measurements reveal a superparamagnetic behaviour for the ZnFe 2 O 4 sample with a blocking temperature of 20 K. By contrast, in the case of the NiFe 2 O 4 ferrite the blocking temperature appears to be above 300 K and at lower temperature, it shows a ferrimagnetic behaviour arising from the superexchange interactions that take place in this inverse spinel. Mössbauer spectroscopy results confirm the bulk magnetic measurements. Nanopartículas de ferrita MFe 2 O 4 (M = Ni y Zn): sínte...
MRS Proceedings, 1994
Magnetic susceptibility measurements and Mössbauer spectra (MS) were performed on a series of Nix... more Magnetic susceptibility measurements and Mössbauer spectra (MS) were performed on a series of NixFeyAlzB shape memory ribbons obtained by a melt spinning technique. The MS at room temperature show quadrupole splittings of two iron sites. At low temperatures (T<120 K) relaxed magnetic spectra begin to develop and, in one of the samples, a complete resolved magnetic spectrum at 13 K was observed. The overall magnetic susceptibility curves show non Curie-Weiss type behavior with peaks at around 60 K and 35 K. These curves also show magnetic hysteresis in the up-down temperature cycle used during the measurements. We relate our observations with a structural change occurring at temperatures between room temperature and 260 K, a second one around 200 K, and with the developing of spin-glass behavior at low temperatures, when the magnetic influences of Fe and Ni atoms almost compensate each other.
Physical Review B, 1987
... VOLUME 36, NUMBER 13 Indication of high local fields in the YBa2Cu2.9375Feo.062508 supercondu... more ... VOLUME 36, NUMBER 13 Indication of high local fields in the YBa2Cu2.9375Feo.062508 superconductor by Mossbauer spectroscopy R. Gomez, S. Aburto, ML Marquina, M. Jimenez, V. Marquina, and C. Quintanar Facultad de Ciencias ... 13R. D. Shannon, Acta Crystallogr. Sect. ...
Boletín de la Sociedad Española de Cerámica y Vidrio, 2008
MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained sa... more MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained samples were characterized by X-ray and electron diffraction, Scanning and Transmission Electron Microscopy and Mössbauer spectroscopy. The transmission images show homogeneous shape and particle size ranging from 10 to 40 nm, depending on the nature of the M cation. Mössbauer spectroscopy yields to a ratio of occupancy between the A and B sites of 0.7 in the case of NiFe 2 O 4 oxide. DC magnetization (2-300 K) measurements reveal a superparamagnetic behaviour for the ZnFe 2 O 4 sample with a blocking temperature of 20 K. By contrast, in the case of the NiFe 2 O 4 ferrite the blocking temperature appears to be above 300 K and at lower temperature, it shows a ferrimagnetic behaviour arising from the superexchange interactions that take place in this inverse spinel. Mössbauer spectroscopy results confirm the bulk magnetic measurements.
Physica B: Condensed Matter, 2014
Polycrystalline samples of LaFeO3 and GdFeO3 were synthesized by the molten salt method. Some pro... more Polycrystalline samples of LaFeO3 and GdFeO3 were synthesized by the molten salt method. Some properties and the quality of the resulting compounds were investigated. The crystal structure and purity of the samples was determined through X-ray diffraction and Rietveld analysis. The vibrational properties were characterized by Raman and IR spectroscopy. Mössbauer spectroscopy was used to determine the ionic state of the Fe ions and the internal hyperfine magnetic fields Considerable reduction of the heat treatment (temperature and time) for the reaction to take place was achieved without detriment of the quality of the compounds.
MRS Proceedings, 1993
ABSTRACTFT-Raman and infrared (IR) spectra of a series of TTF-fluorene derivative family were obt... more ABSTRACTFT-Raman and infrared (IR) spectra of a series of TTF-fluorene derivative family were obtained using a conventional IR spectrometer and a FT-Raman spectrometer. The Raman shifts of the observed band (ν3 stretching band) changes from sample to sample and we correlate these changes with the degree of charge transfer between the donor (TTF) and the acceptor (fluorene derivative) Molecules. These results are compared with those obtained from changes in the IR absorption frequencies of the C≡N stretching mode in the acceptor Molecule.
Journal of Materials Science, 2014
ABSTRACT Hematite and maghemite nanoparticles embedded in silica and titanium dioxide matrices we... more ABSTRACT Hematite and maghemite nanoparticles embedded in silica and titanium dioxide matrices were obtained by sol–gel method. A mixture of precursor solutions of SiO2 and TiO2 doped with Fe3O4 salt templated by the addition of PEO–PPO–PEO triblock copolymers in a concentration of 12.1 wt% PF127 (SiO2) and 4.1 wt% P123 (TiO2) produces very stable magnetic particles with average size between 5 and 10 nm. These neutral surfactants allow the control of the morphology and crystal phase of these magnetic nanoparticles, and stabilize the nanoparticles to avoid their aggregation. The samples were analyzed by X-ray diffraction, high-resolution transmission electron microscopy, and infrared and Mössbauer spectroscopies. Mössbauer results show that maghemite is the majority species in the SiO2 matrix (61.3 %) and TiO2 (63.0 %), respectively.
Superconductor Science and Technology, 2005
Samples of the Ru 1-x Fe x Sr 2 GdCu 2 O 8 system with x = 0, 0.025, 0.05, 0.075, 0.1, and 0.2, w... more Samples of the Ru 1-x Fe x Sr 2 GdCu 2 O 8 system with x = 0, 0.025, 0.05, 0.075, 0.1, and 0.2, were prepared and their structural, superconducting and magnetic properties were studied. Rietveld refinement of the X-ray diffraction patterns show that the Fe substitution occurs in both Ru and Cu sites. An increase of Fe concentration produces no significant changes in the bond angle Ru-O(3)-Ru, which is a measure of the rotation of the RuO 6 octahedra around the c-axis, and also in the bond angle φ, (Ru-O(1)-Cu), which is a measure of the canting of the RuO 6 octahedra. On the other hand, the bond angle Cu-O(2)-Cu, which is a measure of the buckling of the CuO 2 layer, has a slight tendency to decrease with the increase of Fe content. We found that both ferromagnetic and superconducting transition temperatures are reduced with the increase of Fe concentration. Analysis related to the decay of the superconducting and ferromagnetic states is presented.
Solid State Sciences, 2011
... J. Prado-Gonjal a , D. Ávila a , ME Villafuerte-Castrejón b , F. González-García c , L. Fuent... more ... J. Prado-Gonjal a , D. Ávila a , ME Villafuerte-Castrejón b , F. González-García c , L. Fuentes d , RW Gómez e , JL Pérez-Mazariego e , V. Marquina e , E. Morán a , Corresponding Author Contact Information , E-mail The Corresponding Author. ...
Cornell University - arXiv, Nov 21, 2018
Polycrystalline samples of Fe2BiMO7 (M = Sb, Ta) compounds with pyrochlore-type structure were sy... more Polycrystalline samples of Fe2BiMO7 (M = Sb, Ta) compounds with pyrochlore-type structure were synthesized for the first time by the molten salts method. The compounds were obtained in one hour at 950ºC. The structures were determined by Rietveld refinement. Through Mössbauer spectroscopy and X-ray photoelectron spectroscopy, the site occupancies and ionic states of the cations in the pyrochlore structure were investigated.
… of Nanoscience and …, 2008
Sol-gel thin films containing Fe 2 O 3 were deposited onto glass substrates by the dip-coating me... more Sol-gel thin films containing Fe 2 O 3 were deposited onto glass substrates by the dip-coating method at room temperature. Fe 2 O 3 enriched with the isotope 57 Fe was embedded in two kinds of matrices: zinc oxide (ZnO) and silica (SiO 2 ). X-ray diffraction (XRD) was used for ...
European Journal of Physics
Journal of molecular modeling, Jan 4, 2017
First principles calculations have been performed for C60@C180 carbon double-layer endofullerenes... more First principles calculations have been performed for C60@C180 carbon double-layer endofullerenes with up to: three diatomic radioiodine molecules (131I2), two potassium radio-iodide (K131I), and three sodium radio-iodide (Na131I) inside. The plane-wave pseudopotential (PP) method within the general gradient approximation (GGA) in the framework of the density functional theory (DFT) and time-dependent DFT (TD-DFT) was used to perform geometric optimizations (GOs) and molecular dynamics (MD) at 310 K and atmospheric pressure. We found that the double-layer carbon nanocapsules formed by two concentric fullerenes (C180 surrounding C60) are very stable and may contain a radiodosis, without altering their configuration; that is, the 3(131I2)@C60@C180, 2(K131I)@C60@C180, and 3(Na131I)@C60@C180 systems constitute stable nanocapsules. We analyzed the interaction of double-layer endofullerene with radioactive content with some calcium, phosphorus, and strontium atoms, [n(X131I)@C60@C180 + mY...
Journal of Physics B: Atomic and Molecular Physics
High-resolution metastable excitation function measurements have been made in the doubly excited ... more High-resolution metastable excitation function measurements have been made in the doubly excited states region for Ne, Ar and Kr targets. Comparison of the spectra obtained suggests that the gross features are due to negative-ion resonances. Previous techniques which have proved successful in the identification and classification of resonances in the rare gases at energies below the first ionisation threshold are shown to be applicable in this energy region also and assignments for a number of resonances are suggested. Where appropriate, comparisons are made with data obtained by other techniques. The modified Rydberg formula has been used to predict energies for both doubly and triply excited configurations.
European Journal of Physics
Journal of Molecular Modeling, 2016
We report first-principles calculations carried out to analyze the adsorption of calcium on the o... more We report first-principles calculations carried out to analyze the adsorption of calcium on the outer surface of the fullerene C60, yielding [C60 + mCa]. Geometric optimization (GO) and molecular dynamics (MD) simulation were performed using the plane-wave pseudopotential method within the framework of density functional theory (DFT) and time-dependent DFT (TD-DFT) to investigate the configurations, the associated energies in the ground state, and the stabilities of fullerenes and endofullerenes doped with radioactive sodium iodide when they interact with calcium atoms on the outer fullerene surface (i.e., [nNa(131)I@C60 + mCa]). The reason for investigating these calcium-functionalized (endo)fullerene systems was to gauge their potential stability when used as vectors to deliver radioiodine to cancerous tissue in the human body. In the simulations, we found that the geometric limit on the number of calcium atoms that can be physisorbed on the outer surface of an empty fullerene while maintaining its structural stability is 28 calcium atoms, which also takes into account the proportional expansion of the fullerene as the number of absorbed calcium atoms increases. However, the stability of a fullerene system during calcium adsorption also strongly depends on whether any atoms or molecules are being encapsulated by the fullerene, as these encapsulated atoms/molecules can also interact with the fullerene and influence its stability. A Mulliken electronegativity analysis revealed that, when atoms inside and/or outside the fullerene donate charge (electrons) to the fullerene, the fullerene expands. The excess charge on the carbon atoms of the fullerene weakens some of the carbon-carbon bonds, potentially causing them to break, in which case the fullerene loses its ability to encapsulate molecules and releases them. Graphical Abstract DFT simulation of a endo fullerene doped with radioactive sodium iodide interacting with 28 calcium atoms in a geometric arrangement.
Boletin de la Sociedad Espanola de Ceramica y Vidrio
MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained sa... more MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained samples were characterized by X-ray and electron diffraction, Scanning and Transmission Electron Microscopy and Mössbauer spectroscopy. The transmission images show homogeneous shape and particle size ranging from 10 to 40 nm, depending on the nature of the M cation. Mössbauer spectroscopy yields to a ratio of occupancy between the A and B sites of 0.7 in the case of NiFe 2 O 4 oxide. DC magnetization (2-300 K) measurements reveal a superparamagnetic behaviour for the ZnFe 2 O 4 sample with a blocking temperature of 20 K. By contrast, in the case of the NiFe 2 O 4 ferrite the blocking temperature appears to be above 300 K and at lower temperature, it shows a ferrimagnetic behaviour arising from the superexchange interactions that take place in this inverse spinel. Mössbauer spectroscopy results confirm the bulk magnetic measurements.
Physical Review B
Moessbauer spectra of a YBaâCu/sub 2.9375/Fe/sub 0.0625/O/sub delta/ superconducting sample were ... more Moessbauer spectra of a YBaâCu/sub 2.9375/Fe/sub 0.0625/O/sub delta/ superconducting sample were obtained at different temperatures ranging from 50 to 120 K. The results clearly show that Fe substitutes for Cu in this complex. All the spectra showed a pair of superimposed quadrupole doublets with essentially the same splittings but different isomer shifts, corresponding to two different environments of the substituted atoms. The values of the isomer shifts obtained correspond to low-spin Fe atoms, which implies strong local fields, or strong bonding between the atoms.
Boletin de la Sociedad Espanola de Ceramica y Vidrio
MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained sa... more MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained samples were characterized by X-ray and electron diffraction, Scanning and Transmission Electron Microscopy and Mössbauer spectroscopy. The transmission images show homogeneous shape and particle size ranging from 10 to 40 nm, depending on the nature of the M cation. Mössbauer spectroscopy yields to a ratio of occupancy between the A and B sites of 0.7 in the case of NiFe 2 O 4 oxide. DC magnetization (2-300 K) measurements reveal a superparamagnetic behaviour for the ZnFe 2 O 4 sample with a blocking temperature of 20 K. By contrast, in the case of the NiFe 2 O 4 ferrite the blocking temperature appears to be above 300 K and at lower temperature, it shows a ferrimagnetic behaviour arising from the superexchange interactions that take place in this inverse spinel. Mössbauer spectroscopy results confirm the bulk magnetic measurements. Nanopartículas de ferrita MFe 2 O 4 (M = Ni y Zn): sínte...
MRS Proceedings, 1994
Magnetic susceptibility measurements and Mössbauer spectra (MS) were performed on a series of Nix... more Magnetic susceptibility measurements and Mössbauer spectra (MS) were performed on a series of NixFeyAlzB shape memory ribbons obtained by a melt spinning technique. The MS at room temperature show quadrupole splittings of two iron sites. At low temperatures (T<120 K) relaxed magnetic spectra begin to develop and, in one of the samples, a complete resolved magnetic spectrum at 13 K was observed. The overall magnetic susceptibility curves show non Curie-Weiss type behavior with peaks at around 60 K and 35 K. These curves also show magnetic hysteresis in the up-down temperature cycle used during the measurements. We relate our observations with a structural change occurring at temperatures between room temperature and 260 K, a second one around 200 K, and with the developing of spin-glass behavior at low temperatures, when the magnetic influences of Fe and Ni atoms almost compensate each other.
Physical Review B, 1987
... VOLUME 36, NUMBER 13 Indication of high local fields in the YBa2Cu2.9375Feo.062508 supercondu... more ... VOLUME 36, NUMBER 13 Indication of high local fields in the YBa2Cu2.9375Feo.062508 superconductor by Mossbauer spectroscopy R. Gomez, S. Aburto, ML Marquina, M. Jimenez, V. Marquina, and C. Quintanar Facultad de Ciencias ... 13R. D. Shannon, Acta Crystallogr. Sect. ...
Boletín de la Sociedad Española de Cerámica y Vidrio, 2008
MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained sa... more MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained samples were characterized by X-ray and electron diffraction, Scanning and Transmission Electron Microscopy and Mössbauer spectroscopy. The transmission images show homogeneous shape and particle size ranging from 10 to 40 nm, depending on the nature of the M cation. Mössbauer spectroscopy yields to a ratio of occupancy between the A and B sites of 0.7 in the case of NiFe 2 O 4 oxide. DC magnetization (2-300 K) measurements reveal a superparamagnetic behaviour for the ZnFe 2 O 4 sample with a blocking temperature of 20 K. By contrast, in the case of the NiFe 2 O 4 ferrite the blocking temperature appears to be above 300 K and at lower temperature, it shows a ferrimagnetic behaviour arising from the superexchange interactions that take place in this inverse spinel. Mössbauer spectroscopy results confirm the bulk magnetic measurements.
Physica B: Condensed Matter, 2014
Polycrystalline samples of LaFeO3 and GdFeO3 were synthesized by the molten salt method. Some pro... more Polycrystalline samples of LaFeO3 and GdFeO3 were synthesized by the molten salt method. Some properties and the quality of the resulting compounds were investigated. The crystal structure and purity of the samples was determined through X-ray diffraction and Rietveld analysis. The vibrational properties were characterized by Raman and IR spectroscopy. Mössbauer spectroscopy was used to determine the ionic state of the Fe ions and the internal hyperfine magnetic fields Considerable reduction of the heat treatment (temperature and time) for the reaction to take place was achieved without detriment of the quality of the compounds.
MRS Proceedings, 1993
ABSTRACTFT-Raman and infrared (IR) spectra of a series of TTF-fluorene derivative family were obt... more ABSTRACTFT-Raman and infrared (IR) spectra of a series of TTF-fluorene derivative family were obtained using a conventional IR spectrometer and a FT-Raman spectrometer. The Raman shifts of the observed band (ν3 stretching band) changes from sample to sample and we correlate these changes with the degree of charge transfer between the donor (TTF) and the acceptor (fluorene derivative) Molecules. These results are compared with those obtained from changes in the IR absorption frequencies of the C≡N stretching mode in the acceptor Molecule.
Journal of Materials Science, 2014
ABSTRACT Hematite and maghemite nanoparticles embedded in silica and titanium dioxide matrices we... more ABSTRACT Hematite and maghemite nanoparticles embedded in silica and titanium dioxide matrices were obtained by sol–gel method. A mixture of precursor solutions of SiO2 and TiO2 doped with Fe3O4 salt templated by the addition of PEO–PPO–PEO triblock copolymers in a concentration of 12.1 wt% PF127 (SiO2) and 4.1 wt% P123 (TiO2) produces very stable magnetic particles with average size between 5 and 10 nm. These neutral surfactants allow the control of the morphology and crystal phase of these magnetic nanoparticles, and stabilize the nanoparticles to avoid their aggregation. The samples were analyzed by X-ray diffraction, high-resolution transmission electron microscopy, and infrared and Mössbauer spectroscopies. Mössbauer results show that maghemite is the majority species in the SiO2 matrix (61.3 %) and TiO2 (63.0 %), respectively.
Superconductor Science and Technology, 2005
Samples of the Ru 1-x Fe x Sr 2 GdCu 2 O 8 system with x = 0, 0.025, 0.05, 0.075, 0.1, and 0.2, w... more Samples of the Ru 1-x Fe x Sr 2 GdCu 2 O 8 system with x = 0, 0.025, 0.05, 0.075, 0.1, and 0.2, were prepared and their structural, superconducting and magnetic properties were studied. Rietveld refinement of the X-ray diffraction patterns show that the Fe substitution occurs in both Ru and Cu sites. An increase of Fe concentration produces no significant changes in the bond angle Ru-O(3)-Ru, which is a measure of the rotation of the RuO 6 octahedra around the c-axis, and also in the bond angle φ, (Ru-O(1)-Cu), which is a measure of the canting of the RuO 6 octahedra. On the other hand, the bond angle Cu-O(2)-Cu, which is a measure of the buckling of the CuO 2 layer, has a slight tendency to decrease with the increase of Fe content. We found that both ferromagnetic and superconducting transition temperatures are reduced with the increase of Fe concentration. Analysis related to the decay of the superconducting and ferromagnetic states is presented.
Solid State Sciences, 2011
... J. Prado-Gonjal a , D. Ávila a , ME Villafuerte-Castrejón b , F. González-García c , L. Fuent... more ... J. Prado-Gonjal a , D. Ávila a , ME Villafuerte-Castrejón b , F. González-García c , L. Fuentes d , RW Gómez e , JL Pérez-Mazariego e , V. Marquina e , E. Morán a , Corresponding Author Contact Information , E-mail The Corresponding Author. ...