Instituto de Ciencia de Materiales de Sevilla (ICMS) – CIC Cartuja

URI permanente para esta comunidadhttps://hdl.handle.net/11441/10963

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Autocalibrating quasistatic M‐H hysteresis loop tracer with negligible drift
(AIP Publishing, 1996) Franco García, Victorino; Conde Amiano, Alejandro; Ramos Martos, J.; Universidad de Sevilla. Departamento de Física de la Matería Condensada; Gobierno de España
A computer‐controlled system for measuring M‐Hhysteresis loops of soft magnetic materials is described. It overcomes many of the problems associated with these kinds of measurements of low coercivity materials. The combination of ‘‘low drift’’ hardware and measurement procedure makes software correction unnecessary. At every field step, the homemade integrator is reset in order to minimize the drift and to provide a way of separating the sample contribution to the signal from the field contribution and, consequently, to allow M‐H plots. Furthermore, to avoid the residual drift of the hardware, the method of ‘‘two‐way measurement’’ is applied, giving drifts of 0.01% per hour. Results obtained for a FINEMET alloy filmannealed at different temperatures are presented, illustrating the ability of the system to measure soft magnetic materials.
First order transitions by conduction calorimetry: Application to deuterated potassium dihydrogen phosphate ferroelastic crystal under uniaxial pressure
(AIP Publishing, 1997) Gallardo Cruz, María del Carmen; Jiménez Fernández, Justo; Koralewski, M.; Cerro González, Jaime del; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Cerro González, Jaime del
The specific heat c and the heat power W exchanged by a Deuterated Potassium Dihydrogen Phosphate ferroelectric-ferroelastic crystal have been measured simultaneously for both decreasing and increasing temperature at a low constant rate (0.06 K/h) between 175 and 240 K. The measurements were carried out under controlled uniaxial stresses of 0.3 and 4.5±0.1 bar applied to face (110). At Tt=207.9 K, a first order transition is produced with anomalous specific heat behavior in the interval where the transition heat appears. This anomalous behavior is explained in terms of the temperature variation of the heat power during the transition. During cooling, the transition occurs with coexistence of phases, while during heating it seems that metastable states are reached. Excluding data affected by the transition heat, the specific heat behavior agrees with the predictions of a 2-4-6 Landau potential in the range of 4–15 K below Tt while logarithmic behavior is obtained in the range from Tt to 1 K below Tt. Data obtained under 0.3 and 4.5 bar uniaxial stresses exhibit the same behavior.
Photonic crystal properties of packed submicrometric SiO2 spheres
(American Institute of Physics, 1997) Míguez García, Hernán Ruy; López, C.; Meseguer, Francisco; Blanco Montes, Álvaro; Vázquez, Luis; Mayoral, R.; Ocaña Jurado, Manuel; Fornés, Vicente; Mifsud, A.; Universidad de Sevilla. Departamento de Química Inorgánica; Comisión Interministerial de Ciencia y Tecnología (CICYT). España
In this letter, we investigate the optical properties of packed monodisperse silica submicron spheres by means of optical transmission measurements. The results are compatible with a three dimensional face centered cubic order in these solid structures. The lattice parameter of these structures, and therefore their optical properties, can be easily tuned through the sphere size (between 200 and 700 nm) thus covering the whole visible and near infrared spectrum.
Evidence of spin disorder at the surface–core interface of oxygen passivated Fe nanoparticles
(AIP Publishing, 1998) Bianco, Lucia del; Hernando, A.; Multigner, M.; Prados, Clara; Sánchez López, Juan Carlos; Fernández, A.; Conde Amiano, Clara Francisca; Conde Amiano, Alejandro; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Bianco, Lucia del
Hysteresis, thermal dependence of magnetization, and coercivity of oxide coated ultrafine Fe particles prepared by inert gas condensation and oxygen passivation have been studied in the 5–300 K range. The results are found to be consistent with a spin-glasslike state of the oxide layer inducing, through exchange interaction with the ferromagnetic core, a shift of the field cooled hysteresis loops at temperatures below the freezing at approximately 50 K.
Estudio científico de los libros de coro de la abadía del sacromonte de Granada
(Universidad de Sevilla, 1999) Martínez Blanes, José María; Bueno-Vargas, Javier; Pérez Rodríguez, José Luis; Universidad de Sevilla. Departamento de Pintura; Instituto de Ciencia de Materiales de Sevilla (ICMS) – CIC Cartuja
El objetivo de esta comunicación es dar a conocer el estudio científico que se está realizando sobre el más de medio centenar de los Libros de Coro reali zados en pergamino, expresamente para esta institución, entre los ss. XVII al XX que se encuentran en la Abadía del Sacromonte en Granada. Se efectúa una pe queña introducción histórica de lo que es la Abadía y su localización. A conti nuación .se describen los libros estudiados (tipologías y características generales) y sobre todo de las miniaturas con las que están decorados algunos de ellos.
Dependence of exchange anisotropy and coercivity on the Fe–oxide structure in oxygen-passivated Fe nanoparticles
(American Institute of Physics, 1999) Prados, C.; Multigner, M.; Hernando, Antonio; Sánchez López, Juan Carlos; Fernández Camacho, Asunción; Conde Amiano, Clara Francisca; Conde Amiano, Alejandro; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Ultrafine Fe particles have been prepared by the inert gas condensation method and subsequently oxygen passivated. The as-obtained particles consist in an Fe core surrounded by an amorphous Fe-oxide surface layer. The antiferromagnetic character of the Fe-oxide surface induces an exchange anisotropy in the ferromagnetic Fe core when the system is field cooled. Samples have been heat treated in vacuum at different temperatures. Structural changes of the Fe–O layer have been monitored by x-ray diffraction and transmission electron microscopy. Magnetic properties as coercivity, hysteresis loop shift, and evolution of magnetization with temperature have been analyzed for different oxide crystallization stages. A decrease of the exchange anisotropy strength is reported as the structural disorder of the surface oxide layer is decreased with thermal treatment.
Aplicacion de la tecnica PIXE (Particle Induced X-Ray Emision) a la caracterización no destructiva de una pieza de ajuar funerario (siglo I d.c.) procedente de una excavacion arqueologica (antiguo Hospital de las Cinco Llagas, Sevilla)
(Sociedad Española de Cerámica y Vidrio, 2002) Enrique Magariño, María Esther; Ramírez de Arellano López, Antonio; Tabales Rodríguez, Miguel Ángel; Ruiz Conde, Antonio; Sánchez Soto, Pedro José; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Universidad de Sevilla. Departamento de Construcciones Arquitectónicas II (ETSIE); Junta de Andalucía
En el presente trabajo se ha realizado la caracterización de una pieza de ajuar funerario del Siglo I d.C. (anillo con pieza incrustada y grabada), encontrado en una excavación arqueológica en el antiguo Hospital de las Cinco Llagas de Sevilla, de la que inicialmente se desconocía su naturaleza cerámica o vítrea, utilizando las posibilidades que brindan una serie de técnicas instrumentales no destructivas ampliamente conocidas, como son microscopía óptica convencional, MEB-EDX, DRX y FRX. En este caso concreto se ha aplicado, además, la técnica de Emisión de Rayos X inducidos por partículas (Particle Induced X-ray Emision, PIXE). Dicha técnica permite extraer información de la composición química de una muestra para un análisis rápido de múltiples elementos traza. El estudio de esta interesante pieza pone de manifiesto la extrema calidad y precisión de la talla de las figuras o motivos, en particular algunos de ellos (garza y palma) a pesar del tamaño reducido de la misma, con efectos de relieve en el tallado del material aprovechando su propia constitución. El análisis de fases por DRX indica que la única fase cristalina constituyente del material es cuarzo y puede considerarse la pieza estudiada como una gema: cuarzo azul. La composición química de la gema determinada por FRX ha permitido comprobar que además de los elementos mayoritarios (Si y O), existen otros minoritarios, como son Ca y Fe (< 1,5 %), Na y Al (próximos al 0,3 %); otros elementos como Cl, K y P aparecen en porcentajes similares (0.2-0,25 %), además de Mg y S en porcentajes inferiores (ca. 0,08 %). Sin embargo, la aplicación de la técnica PIXE basada en haces de iones ha permitido determinar la presencia de Ti y V en la gema, lo que explicaría su coloración azul. Estos elementos deben encontrarse en forma iónica formando parte de la estructura cristalina del cuarzo. En consecuencia, esta técnica no destructiva permite encontrar una diferencia química importante entre zonas de una misma pieza, que no se aprecian mediante la aplicación de técnicas convencionales, con la ventaja añadida de utilizar directamente el objeto del análisis.
Determination of texture by infrared spectroscopy in titanium oxide–anatase thin films
(American Institute of Physics, 2003) Pecharromán, Carlos; Gracia Torres, Francisco; Holgado Vázquez, Juan Pedro; Ocaña Jurado, Manuel; Rodríguez González-Elipe, Agustín; Bassas, J.; Santiso, José; Figueras, Albert; Universidad de Sevilla. Departamento de Química Inorgánica
A theoretical model to determine the effective dielectric tensor of heterogeneous materials composed by anisotropic microcrystallites has been introduced to explain the infrared spectral features of textured thin films of uniaxial materials as the function of a textural parameter. This theoretical treatment is able to satisfactorily reproduce the experimental absorbance spectra of TiO2–anatase thin films chosen as a model system. Comparison of texture data obtained from infrared spectroscopy and x-ray diffraction are in good agreement which support the validity of the proposed model.
Acicular iron nanoparticles protected against sintering with aluminium oxide
(Sociedad Española de Cerámica y Vidrio, 2004) Pozas, R.; Morales, M. P.; Serna Pereda, Carlos J.; Ocaña Jurado, Manuel; Universidad de Sevilla. Departamento de Química Inorgánica; Comisión Interministerial de Ciencia y Tecnología (CICYT). España
Acicular iron nanoparticles have been obtained by thermal reduction with hydrogen of a goethite precursor protected against sintering with Al cations, either by doping during the synthesis or by a further coating and the relation between microstructure and magnetic properties of the final Fe particles has been studied in order to evaluate the efficiency of both protecting methods. Uniform goethite and Al-doped goethite precursors were prepared by oxidation with air of FeSO4 solutions, containing Al(NO3)3 when required, previously precipitated with Na2CO3, while the Al oxide coating on the undoped goethite precursor was carried out by heterocoagulation. In both protecting methods, Al cations were mainly concentrated in the particle outer layers of the goethite precursors and the final iron. Due to this Al enrichment, the growth of iron crystals during the reduction process is minimised resulting Fe particles with improved coercivity and squareness. Nevertheless, the coating procedure seems to be more effective giving rise to the iron particles with the largest coercivity, probably due to a better preservation of the acicular morphology in this case.
Reforming of ethanol in a microwave surface-wave plasma discharge
(American Institute of Physics, 2004) Yanguas Gil, Alejandro; Hueso Martos, José Luis; Cotrino Bautista, José; Caballero Martínez, Alfonso; Rodríguez González-Elipe, Agustín; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Ministerio de Ciencia y Tecnología (MCYT). España
Hydrogen production through plasma reforming of ethanol at room temperature and moderate pressure has been carried out in a microwave surface-wave reactor. Both pure ethanol and mixtures ethanol-water have been studied. The reforming yield was almost 100% in all conditions with H2, solid carbon, CO and CO2 as the main reaction products. In the mixture ethanol-water the formation of solid C was avoided. The optical emission spectroscopy analysis has shown that the formation of the excited species CO*, CH* and C depends on the plasma mixture. The temperature of the OH* species was determined by analyzing the shape profile of its emission band.
Analysis of wave propagation in a two-dimensional photonic crystal with negative index of refraction: plane wave decomposition of the Bloch modes
(Optical Society of America, 2005) Martínez, Alejandro; Míguez García, Hernán Ruy; Sánchez Dehesa, José; Martí, Javier; Ministerio de Ciencia y Tecnología (MCYT). España
This work presents a comprehensive analysis of electromagnetic wave propagation inside a two-dimensional photonic crystal in a spectral region in which the crystal behaves as an effective medium to which a negative effective index of refraction can be associated. It is obtained that the main plane wave component of the Bloch mode that propagates inside the photonic crystal has its wave vector k⃗′ out of the first Brillouin zone and it is parallel to the Poynting vector (S⃗·k⃗′>0), so light propagation in these composites is different from that reported for left-handed materials despite the fact that negative refraction can take place at the interface between air and both kinds of composites. However, wave coupling at the interfaces is well explained using the reduced wave vector (k⃗) in the first Brillouin zone, which is opposed to the energy flow, and agrees well with previous works dealing with negative refraction in photonic crystals
Electronic state characterization of SiOx thin films prepared by evaporation
(American Institute of Physics, 2005) Barranco Quero, Ángel; Yubero Valencia, Francisco; Espinós Manzorro, Juan Pedro; Groening, P.; Rodríguez González-Elipe, Agustín; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Ciencia y Tecnología (MCYT). España
SiOx thin films with different stoichiometries from SiO1.3 to SiO1.8 have been prepared by evaporation of silicon monoxide in vacuum or under well-controlled partial pressures of oxygen (P<10–6 Torr). These thin films have been characterized by x-ray photoemission and x-ray-absorption spectroscopies, this latter at the Si K and L2,3 absorption edges. It has been found that the films prepared in vacuum consists of a mixture of Si3+ and Si+ species that progressively convert into Si4+ as the partial pressure of oxygen during preparation increases. From this spectroscopic analysis, information has been gained about the energy distribution of both the full and empty states of, respectively, the valence and conduction bands of SiOx as a function of the O/Si ratio. The characterization of these films by reflection electron energy-loss spectroscopy (REELS) has provided further evidences about their electronic structure (band gap and electronic states) as a function of the oxygen content. The determination of the plasmon energies by REELS has also shown that the films prepared by evaporation in vacuum consist of a single phase which is characterized by a density (1.7 g cm–3) lower than that of SiO2 (i.e., 2.2 g cm–3) or Si (i.e., 2.4 g cm–3). The optical properties (n and k) of the films as a function of the O/Si content have been deduced from the analysis of REELS spectra in the energy range from 4 to 20 eV. It has been also shown that the O/Si ratio in the films and several spectroscopic parameters such as the Auger parameter or the energy of bulk plasmons present a linear relationship and that this linear dependence can be used for a rapid characterization of SiOx materials. By contrast, the band-gap energy changes differently with the O/Si ratio, following a smooth linear increase from about 3.8 eV for SiO1.3 to ca. 5.0 eV for SiO1.7 and a jump up to 8.7 eV for SiO2. These results indicate that the random-bonding model does not apply to thin films prepared by evaporation under our experimental conditions. Other distributions of Sin+ states can be induced if the films are excited with an external source such as heat or photon irradiation. In this case the electronic properties vary and the previous linear correlations as a function of the oxygen content do not hold any longer.
Vapor swellable colloidal photonic crystals with pressure tunability
(Royal Society of Chemistry (Great Britain), 2005) Arsenault, André C.; Kitaev, Vlamidir; Manners, Ian; Ozin, G.A.; Mihi, Agustín; Míguez García, Hernán Ruy; Generalitat Valenciana
Polyferrocenylsilane gel photonic crystals have been reversibly swollen using solvent vapors, and exhibit precise pressure tunability over a wavelength range of greater than 100 nm
Dependence of the preexponential factor on temperature
(Springer Verlag, 2005) Criado Luque, José Manuel; Pérez Maqueda, Luis Allan; Sánchez Jiménez, Pedro Enrique; Universidad de Sevilla. Departamento de Química Inorgánica
The dependence of the preexponential factor on the temperature has been examined and the errors involved in the activation energy calculated from isothermal and non-isothermal methods without considering such dependence have been estimated. It has been shown that the error in the determination of the activation energy calculated ignoring the dependence of Aon Tcan be rather large and it is dependent on x=E/RT, but independent of the experimental method used. It has been also shown that the error introduced by omitting the dependence of the preexponential factor on the temperature is considerably larger than the error due to the Arrhenius integral approach used for carrying out the kinetic analysis of TG data.
Kinetic analysis of solid-state reactions: Precision of the activation energy calculated by integral methods
(Wiley, 2005) Pérez Maqueda, Luis Allan; Sánchez Jiménez, Pedro Enrique; Criado Luque, José Manuel; Universidad de Sevilla. Departamento de Química Inorgánica
The integral methods are extensively used for the kinetic analysis of solid-state reactions. As the Arrhenius integral function [p(χ)] does not have an exact analytical solution, different approximated equations have been proposed in the literature for performing the kinetic analysis of experimental integral data. Since the first approximation of Van Krevelen, a large number of equations have been proposed with the objective of increasing the precision in the determination of the Arrhenius integral, as checked from the standard deviation of the approximated function with regard to the real exact value of the integral. However, the main application of these equations is the determination of the kinetic parameters, in particular activation energies, and not the computation of the Arrhenius integral. A systematic analysis of the errors involved in the determination of the activation energy from these integral methods is still missing. A comparative study of the precision of the activation energy as a function of χ and T computed from the different integral methods has been carried out.
Surface resonant modes in colloidal photonic crystals
(American Physical Society, 2005) Míguez García, Hernán Ruy; Rodríguez, I.; Rubio, S; Meseguer, Francisco; Mihi Cervello, Agustín
Herein we report an experimental and theoretical optical analysis of the effect of growing a dielectric slab on the surface of photonic colloidal crystals. Optical spectroscopy shows an enhancement of the transmitted intensity for certain frequencies within the photonic pseudogap. Simulations based on a scalar wave approximation fairly reproduce the experimental results and provide a description of the interplay between the features arising from the presence of the surface slab and the finite size of the photonic crystal. The experimental observations are explained by the excitation of photon resonant states at the crystal boundary. Our work demonstrates that the amplitude of light waves penetrating the crystal with frequencies lying within the pseudogap range can be greatly modified by rather simple means.
Evaluation of the integral methods for the kinetic study of thermally stimulated processes in polymer science
(Elsevier, 2005) Pérez Maqueda, Luis Allan; Sánchez Jiménez, Pedro Enrique; Criado Luque, José Manuel; Universidad de Sevilla. Departamento de Química inorgánica
This paper reports on the accuracy of the integral methods used for the kinetic analysis of degradation and crystallization of polymers. Integral methods are preferred by many authors over the differential ones because often the experimental data obtained, such as thermal degradation studied by thermogravimetry, are integral and the differentiation of the integral data usually produces an unwilling increase of the noise. A problem of the integral methods is the fact that Arrhenius integral function does not have an exact analytical solution. Thus, several approximated equations have been proposed in literature. Some of these approximations lead to a linear relation between the logarithm of g(α) and a predetermined function of T, in such a way that the activation energy can be determined from the slope of the plot of ln g(α) versus the predetermined T function. The most popular approximations to the Arrhenius integral in polymer science are those of van Krevelen et al., Horowitz and Metzger, and Coats and Redfern. Although these three approaches where proposed 50 years ago, they are extensively used nowadays and several hundreds of citations to the original papers can be found in recent polymer science publications. Despite their popularity, there are cast doubts on the accuracy of these approximations, because they provide significant deviations in the determination of the actual values of the Arrhenius integral when used for simulating α–T plots. Nevertheless, a comprehensive study of the systematic errors in the activation energy calculated from these integral methods is still missing. In this paper a comparative study of the accuracy of the different integral methods is performed. The calculated errors are tested with simulated and experimental results.
Measuring the electron temperature by optical emission spectroscopy in two temperature plasmas at atmospheric pressure: A critical approach
(American Institute of Physics, 2006) Yanguas Gil, Alejandro; Cotrino Bautista, José; Rodríguez González-Elipe, Agustín; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Ministerio de Ciencia y Tecnología (MCYT). España
The measurement of the electron mean kinetic energy by identifying the electron temperature and the excitation temperature obtained by optical emission spectroscopy is theoretically studied for two temperature argon plasmas at atmospheric pressure. Using a 32-level collisional radiative model in which both electron impact and argon-impact inelastic collisions are taken into account, it has been found that under certain conditions the argon inelastic collisions may cause a decrease of the argon excitation temperature so that the relation Te>Texc>T0 is satisfied. This inequality also appears when electron losses due to diffusion are important and the electron density is lower than its equilibrium value.
The influence of chain length and ripening time on the self-assembly of alkylamines on mica
(American Institute of Physics, 2006) Benítez Jiménez, José Jesús; Salmerón, Miquel
The influence of chain length and ripening time on the self-assembly of tetradecyl C 14 , hexadecyl C 16 , and octadecylamine C 16 on mica has been studied by atomic force microscopy. The overall process can be described in three stages characterized by different time scales. First, alkylamine molecules adsorb in a process controlled by water mediated interactions of the NH 2 head groups and mica. Second, surface diffusion and aggregation into islands takes place, driven by energy interactions between alkyl chains. The third stage consists of a progressive tilt of the self-assembled molecules towards the surface, driven by relaxation of the electrostatic repulsion between protonated amino groups due to water uptake from atmosphere.
Modificaciones de las propiedades texturales y estructurales de una zeolita USY y de sus mezclas con "caolín Clay" y clorhidrol como consecuencia del tratamiento hidrotémico
(Universidad Nacional de Colombia, 2006) Agámez Pertuz, Yazmin Yaneth; Oviedo Aguiar, Luis Alfredo; Navarro Uribe, Uriel; Centeno Gallego, Miguel Ángel; Odriozola Gordón, José Antonio; Universidad de Sevilla. Departamento de Química Inorgánica
El catalizador de FCC está constituido por partículas de composición compleja donde el componente activo es una zeolita-Y. En este trabajo se presentan los resultados tex- turales y estructurales de una zeolita USY comercial lixiviada, de una serie de catali - zadores con 7, 15, 25, 35 y 45% de mate - rial activo, y los de estos materiales desac - tivados hidrotérmicamente. Las muestras se caracterizaron por fluorescencia de ra - yos X (FRX), difracción de rayos X (DRX), resonancia magnética nuclear de silicio ( 29 Si RMN) y fisiadsorción de nitró - geno a 77 K. A partir de estos resultados se hallaron correlaciones entre el volumen de microporo y el contenido de zeolita, y en - tre el grado de cristalinidad y el porcentaje de zeolita. Además, se encontró que un tratamiento con sólo 20% de vapor de agua a 1033 K durante 16 horas destruye los grupos estructurales Si(2Al) y Si(3Al) como reflejo de la dealuminización drásti- ca que sufre el material

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