Capítulos (Física de la Materia Condensada)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/10870

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Deuteration effect on tricritical phase transition of triglycine selenate: Calorimetric and dielectric measurements analyzed in the framework of Landau theory
(AIP Publishing, 2010) Romero Landa, Francisco Javier; Gallardo Cruz, María del Carmen; Martín Olalla, José María; Cerro González, Jaime del; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The ferroelectric phase transition of three single crystals of TGSe1−x DTGSex has been described by using specific heat, latent heat, and dielectric permittivity measurements. Pure, half-deuterated, and highly-deuterated TGSe single crystals were analyzed. Transition temperature and latent heat increase with increasing deuteration. Irrespective of the degree of deuteration, a 2-4-6 Landau model is suitable to describe the phase transition. The fourth-rank prefactor in Landau potential is found to be very sensitive to deuteration while the second-rank and the sixth-rank prefactors smoothly change with composition. The pyroelectric figure of merit for these materials has also been derived from the theoretical model.
Laser Dynamics Modelling and Simulation: An application of Dynamic Load Balancing of Parallel Cellular Automata
(Springer, 2010) Guisado Lizar, José Luis; Jiménez-Morales, Francisco de Paula; Guerra Pérez, José Manuel; Fernández de Vega, Francisco; Iskra, Kamil A.; Sloot, Peter M.A.; Lombraña González, Daniel; Universidad de Sevilla. Departamento de Arquitectura y Tecnología de Computadores; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Scaling Analysis of the Magnetocaloric Effect in Co/Au Nanoparticles
(Panstwowego Wydawnictwa Naukowego, 2017) Hrubovcák, P.; Zelenáková, Adriana; Zelenák, V.; Franco García, Victorino; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Slovak Research and Development Agency (APVV). Slovakia; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
The system of superparamagnetic Co/Au bimetallic nanoparticles of average diameter 7 nm was investigated with respect to its magnetocaloric properties. DC magnetic measurements revealed the presence of field dependent zero field cooled M(T) maximum (6–8 K) and significant zero field cooled/field cooled irreversibility at low temperatures in the system. Documented thermal hysteresis disallow standard magnetic entropy change calculation from isothermal M(H) data, thus we attempted to employ zero field cooled M(T) data for this purpose. Magnetic entropy change was calculated employing the Maxwell relation. In maximal field variation of 1 T relative high magnetic entropy change for nanoparticles ∆SM ≈ 0.7 J/(kg K) at T = 9 K was observed. The data collapsed onto single universal curve after proper axis rescaling.
Effect of the crystal chemistry on the hydration mechanism of swelling micas
(Elsevier, 2017) Pavón González, Esperanza; Alba Carranza, María Dolores; Castro Arroyo, Miguel Ángel; Osuna, Francisco J.; Pazos, M. Carolina; Universidad de Sevilla. Departamento de Química Inorgánica; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Junta de Andalucía; Ministerio de Economía y Competitividad (MINECO). España; European Union (UE)
Swelling and dehydration under minor changes in temperature and water vapor pressure is an important property that clays and clay minerals exhibit. In particular, their interlayer space, the solid-water interface and the layers’ collapse and re-expansion have received much attention because it affects to the dynamical properties of interlayer cations and thus the transfer and fate of water and pollutants. In this contribution, the dehydration and rehydration mechanism of a swelling high-charge mica family is examined by in situ X-ray Diffraction. The effect of the aluminosilicate layer charge and the physicochemical properties of the interlayer cations on these processes are analyzed. The results showed that the dehydration temperature and the number of steps involved in this process are related to the layer charge of the silicate and the physicochemical properties of the interlayer cations. Moreover, the ability to adsorb water molecules in a confined space with high electric field by the interlayer cations does not only depend on their hydration enthalpy but also on the electrostatic parameters of these cations.
Husos horarios españoles: racionalidad frente a leyenda
(Consello da Cultura Galega, 2017-03-22) Martín Olalla, José María; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Se describe la problemática del huso en España y se comparan los horarios españoles con los del resto de Europa para señalar su similitud.
A procedure to obtain the parameters of Curie temperature distribution from thermomagnetic and magnetocaloric data
(Elsevier, 2019) Manchón Gordón, Alejandro F.; Moreno Ramírez, Luis Miguel; Ipus Bados, Jhon Jairo; Blázquez Gámez, Javier Sebastián; Conde Amiano, Clara Francisca; Franco García, Victorino; Conde Amiano, Alejandro; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Agencia Estatal de Investigación. España; European Union (UE)
We propose a procedure for the determination of the parameters of the Curie temperature distribution (TCD)in a compositionally inhomogeneous ferromagnetic material. Assuming a Gaussian TCD and using a mean field approach based on the Brillouin function, we report that with respect to the average value of the distribution: a)both inflection point of magnetization, Tinf, and temperature at maximum magnetic entropy change curves, Tpk MCE, shift to lower temperatures and b)temperature at maximum paramagnetic susceptibility, Tpk χ, shifts to higher temperatures. Using these evolutions as a function of the TCD broadening and fitting them to a second order polynomial function, a self-consistent procedure to determine the parameters of the distribution is supplied. These predictions have been experimentally tested for a ball milled Fe70Zr30 amorphous alloy using thermomagnetic and magnetocaloric measurements. The obtained parameters using the proposed procedure agree with those directly measured using Mössbauer spectrometry.
Does grain size have an influence on intrinsic mechanical properties and conduction mechanism of near fully-dense boron carbide ceramics?
(Elsevier, 2019) Moshtaghion, Bibi Malmal; Laguna Bercero, Miguel Ángel; Gómez García, Diego; Peña, José I.; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Economía y Competitividad (MINECO). España
This work is concentrated on getting a reply to the following question: how does the grain size of boron carbide specimens influence on their mechanical and electrical response? It is a common issue that both essential properties are usually affected by the grain boundaries. To this purpose, a set of near fully-dense boron carbide specimens were prepared by spark plasma sintering. In order to reduce residual porosity and grain-size effects, nanoindentation tests at room temperature were conducted. DC conductivity was measured through four-point test technique from room temperature up to 800 °C. The results show that hardness can reach values as high as ∼60 GPa and plasticity onset takes place at around 23 GPa by dislocation nucleation. Regarding the conductivity, it is found that grain boundaries can block the mobility of bipolarons in an effective way. A simple additive law is provided to account for the resistivity of boron carbide polycrystals.
Casimir-Lifshitz Force Based Optical Resonators
(American Chemical Society, 2019) Esteso Carrizo, Victoria; Carretero Palacios, Sol; Míguez García, Hernán Ruy; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Ciencia, Innovación y Universidades (MICINN). España
We theoretically investigate the building of optical resonators based on the levitation properties of thin films subjected to strong repulsive Casimir-Lifshitz forces when immersed in an adequate medium and confronted with a planar substrate. We propose a design in which cavities supporting high Q-factor optical modes at visible frequencies can be achieved by means of combining commonly found materials, such as silicon oxide, polystyrene or gold, with glycerol as a mediating medium. We use the balance between flotation and repulsive Casimir-Lifshitz forces in the system to accurately tune the optical cavity thickness and hence its modes. The effects of other forces, such as electrostatic, that may come into play are also considered. Our results constitute a proof of concept that may open the route to the design of photonic architectures in environments in which dispersion forces play a substantial role and could be of particular relevance for devising novel microfluidic optical resonators.
Graphene nanoplatelets for electrically conductive 3YTZP composites densified by pressureless sintering
(Elsevier, 2019) López Pernía, Cristina; Gallardo López, Ángela María; Morales Rodríguez, Ana; Poyato Galán, Rosalía; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Economía y Competitividad (MINECO). España
3 mol% yttria tetragonal zirconia polycrystalline (3YTZP) ceramic composites with 2.5, 5 and 10 vol% graphene nanoplatelets (GNP) were pressureless sintered in argon atmosphere between 1350 and 1450 °C. The effects of the GNP content and the sintering temperature on the densification, microstructure and electrical properties of the composites were investigated. An isotropic distribution of GNP surrounding ceramic regions was exhibited regardless the GNP content and sintering temperature used. Electrical conductivity values comparable to the ones of fully dense composites prepared by more complex techniques were obtained, even though full densification was not achieved. While the composite with 5 vol% GNP exhibited electrical anisotropy with a semiconductor-type behaviour, the composite with 10 vol% GNP showed an electrically isotropic metallic-type behaviour.
Microstructure, interfaces and properties of 3YTZP ceramic composites with 10 and 20 vol% different graphene-based nanostructures as fillers
(Elsevier, 2019) Muñoz Ferreiro, Carmen; Morales Rodríguez, Ana; Rojas Ruiz, Teresa Cristina; Jiménez Piqué, Emilio; López Pernía, Cristina; Poyato Galán, Rosalía; Gallardo López, Ángela María; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Economía y Competitividad (MINECO). España
The graphene family comprises not only single layer graphene but also graphene-based nanomaterials (GBN), with remarkably different number of layers, lateral dimension and price. In this work, two of these GBN, namely graphene nanoplatelets (GNP) with n∼15–30 layers and few-layer graphene (FLG) with n < 3 layers have been evaluated as fillers in 3 mol% yttria stabilized tetragonal zirconia (3YTZP) ceramic composites. Composites with 10 and 20 vol% GNP or FLG have been fabricated by wet powder processing and spark plasma sintering (SPS) and the influence of the content and number of layers of the graphene-based filler has been assessed. For both graphene-based fillers, an intermediate zirconia oxycarbide has been detected in the grain boundaries. The lower stacking degree and much more homogeneous distribution of the FLG, revealed by transmission electron microscopy (TEM), can improve load transfer between the GBNs and the ceramic matrix. However, high FLG contents lower densification of the composites, due partly to the larger FLG interplanar spacing also estimated by TEM. The hardness (both Vickers and nanoindentation) and the elastic modulus decrease with increased GBN content and with improved graphene dispersion. The FLG greatly inhibit the crack propagation that occur perpendicular to their preferential orientation plane. The composites with thinner FLG have higher electrical conductivity than those with GNP. The highest electrical conductivity is achieved by composites with 20 vol% FLG in the direction perpendicular to the compression axis during sintering, σ⊥ = 3400 ± 500 Sm-1.
Tribological behavior of graphene nanoplatelet reinforced 3YTZP composites
(Elsevier, 2019) Gutiérrez Mora, Felipe; Morales Rodríguez, Ana; Gallardo López, Ángela María; Poyato Galán, Rosalía; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Economía y Competitividad (MINECO). España
The tribological behavior of graphene nanoplatelet (GNP) reinforced 3 mol% yttria tetragonal zirconia polycrystals (3YTZP) composites with different GNP content (2.5, 5 and 10 vol%) was analyzed and discussed. Their dry sliding behavior was studied using a ball-on-disk geometry with zirconia balls as counterparts, using loads between 2 and 20 N at ambient conditions and compared to the behavior of a monolithic 3YTZP ceramic used as a reference material. The composites showed lower friction coefficients and higher wear resistance than the monolithic 3YTZP. An outstanding performance was achieved at 10 N, where the friction coefficient decreased from 0.6 to 0.3 and the wear rates decreased 3 orders of magnitude in comparison with the monolithic ceramic. A layer adhered to the worn surface was found for all the composites, but it did not acted as a lubricating film. The composites with the lowest GNP content showed an overall improved tribological behavior.
Aprendizaje basado en el planteamiento de casos clínicos en contactología
(Editorial Universidad de Sevilla, 2019) Bautista Llamas, María José; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Este artículo describe la puesta en práctica de un ciclo de mejora en el aula aplicado en la asignatura Contactología II, que se imparte de ma- nera conjunta en el Grado en Óptica y Optometría y en el Doble Grado en Farmacia y en Óptica y Optometría de la Facultad de Farmacia de la Universidad de Sevilla. Este ciclo de mejora se centra en la docen- cia correspondiente a la selección de pacientes y la lente de contacto adecuada para cada uno de ellos, así como las complicaciones deri- vadas de las mismas. El modelo metodológico se basa en el planteamiento de una pregunta sobre el tema que se pretende aprender por parte del profesor, y que esa pregunta obtenga respuesta a través de la resolución de un pro- blema o caso práctico planteado y desarrollado por los alumnos, y ex- puesto en clase para discutir y extraer conclusiones sobre el mismo.
Phosphogypsum waste lime as a promising substitute of commercial limes: A rheological approach
(Elsevier, 2019) Romero Hermida, Isabel; Borrero-López, Antonio María; Alejandre Sánchez, Francisco Javier; Flores Alés, Vicente; Santos, A.; Franco, J. M.; Esquivias Fedriani, Luis María; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Universidad de Sevilla. Departamento de Construcciones Arquitectónicas II (ETSIE)
This paper presents the rheological properties of three types of lime putty, specifying the influence of their origin. The study aims to compare a special lime putty prepared from phosphogypsum with a commercial lime powder and an aged lime putty. The results obtained in terms of chemical composition, crystalline structure, grain size and rheological characterization, (linear viscoelasticity, shear rate and time-dependent flow behaviour) are presented in the study. Putties studied present a similar rheological response, which mainly depends on the particle size and water content. Lower values of the linear viscoelastic functions and viscosity were found for the phosphogypsum lime putty, in agreement with the higher particle size. Transient flow tests reveal a predominant elastic response with no significant shear-induced structural perturbations. However, either a thickening phenomenon over time, i.e. rheopexy, favoured at low shear rates, or a viscosity decrease, i.e. thixotropy, favoured at high shear rates, was observed.
Vault changes after cyclopentolate instillation in eyes with posterior chamber phakic intraocular lens
(Nature Research, 2020) Gargallo Martínez, Beatriz; García Medina, José Javier; Rubio Velázquez, Elena; Fernandes, Paulo; Villa Collar, César; Gonzalez Meijome, José M.; Gutiérrez Ortega, Ramón; Universidad de Sevilla. Departamento de Física de la Materia Condensada; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Fundação para a Ciência e a Tecnologia. Portugal
Posterior chamber phakic intraocular lens (pIOL) implantation is a common option for correcting moderate-to-high ocular refractive defects. Because this pIOL is implanted on ciliary sulcus, the distance between the back surface of the pIOL and the anterior surface of the crystalline lens, that it is known as vault, should be measured in diferent conditions to ensure the technique’s safety. Cyclopentolate is a drug that dilates the pupil and relaxes accommodation (cycloplegia). It is often used for diferent ocular examinations and for other medical purposes. However, there is no evidence of the efect of this drug on vault. This study quantifed central vault changes associated with cyclopentolate instillation. We measured the vault under normal conditions (pre-cycloplegic instillation) and after instilling cyclopentolate on 39 eyes of 39 patients with implanted pIOL. Our results suggest that cyclopentolate instillation may induce changes to vault in eyes with implanted pIOL. These changes seem safe and are mainly associated with vault under normal conditions, but also with anterior chamber depth, pupillary diameter and pIOL size.
Microstructure and Thermal Conductivity of Si-Al-C-O Fiber Bonded Ceramics Joined to Refractory Metals
(Elsevier, 2020) Vera García, María del Carmen; Martínez Fernández, Julián; Singh, M.; Casalegno, V.; Balagna, C.; Ramírez Rico, Joaquín; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Economía y Competitividad (MINECO). España
We explore joining Si-Al-C-O fiber-bonded ceramics to Cu-clad-Mo using an Ag-Ti-Cu brazing alloy. A temperature of 900 °C and times in the range of 10–20 min are required to obtain sound joints irrespectively of the fiber orientation. The reaction layer is 1–2 μm thick and free of pores and defects. The thermal conductivity of the joined samples is well described considering that the metal and the ceramic are in series for thermal resistance. This implies that the joint is highly conductive and forms an almost perfect thermal interface between the two materials, confirming the quality of the obtained brazing layer.
Mg2SiO4-MgAl2O4 Directionally Solidified Eutectics: Hardness Dependence Modelled Through an Array of Screw Dislocations
(Elsevier, 2020) Moshtaghion, Bibi Malmal; Gómez García, Diego; Peña, Jose I.; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Economía y Competitividad (MINECO). España; Gobierno de Aragón; Junta de Andalucía
Mg2SiO4-MgAl2O4 eutectic ceramics have been fabricated by means of the laser floating zone (LFZ) technique. The microstructure has revealed as an unusual one at lower growth rate, composed of broken lamellae of MgAl2O4 distributed randomly along one matrix, composed of Mg2SiO4. At higher growth rates, a cell structure with intra-cell lamella structure is dominant. Contrary to most eutectic systems, hardness is not dependent upon the inter-spacing, but it does depend on one characteristic length of lamellae: their perimeter. One simple model based upon the dislocation is proposed, which successfully accounts for such extraordinary hardness law. Accordingly, Mg2SiO4-MgAl2O4 eutectic ceramics fabricated at 50 mm/h growth rate with the smallest MgAl2O4 lamella perimeter favorably showed more elevated hardness (13.4 GPa from Vickers indentation and 15.3 GPa from nanoindentation) and strength (∼430 MPa) than those found in the monolithic Mg2SiO4 matrix.
Devitrification of Mechanically Alloyed Fe-Nb System: Mössbauer Study of the Intermetallic Phases
(Springer Nature, 2020) Manchón Gordón, Alejandro F.; Svec, P.; Ipus Bados, Jhon Jairo; Kowalczyk, M.; Blázquez Gámez, Javier Sebastián; Conde Amiano, Clara Francisca; Conde Amiano, Alejandro; Svec, P.; Kulik, T.; Universidad de Sevilla. Departamento de Física de la Materia Condensada; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
Intermetallic phases in the Fe-Nb system have been obtained as products of the devitrification of a homogeneous amorphous Fe70Nb30 alloy prepared by mechanical alloying. Besides Fe2Nb Laves and Fe7Nb6 intermetallic phases, α-Fe phase has been detected by X-ray diffraction (XRD). Hyperfine parameters for both Fe2Nb and Fe7Nb6 intermetallics have been obtained from Mössbauer spectroscopy in correlation with phase identification from XRD results. Thermomagnetic measurements show changes in the Curie temperatures of the amorphous and Fe2Nb phases during the crystallization, due to compositional variations related to the developing of the α-Fe phase. Kinetics of the crystallization process has been analyzed using the classical Johnson-Mehl-Avrami-Kolmogorov kinetic theory in both isothermal and non-isothermal regimes.
Novel Procedure for Laboratory Scale Production of Composite Functional Filaments for Additive Manufacturing
(Elsevier, 2020) Díaz García, Álvaro; Law, Jia Yan; Cota Reguero, Agustín; Bellido-Correa, A.; Ramírez Rico, Joaquín; Schäfer, R.; Franco García, Victorino; Universidad de Sevilla. Departamento de Física de la Materia Condensada; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Junta de Andalucía
Successful 3D printing by material extrusion of functional parts for new devices requires high quality filaments. Uniform homogeneity and good dispersion of particles embedded in filaments typically takes several cycles of extrusion or well-prepared feedstock by injection molding, industrial kneaders or twin-screw compounding. These methods need specific production devices that are not available in many laboratories non-specialized in polymer research, such as those working on different material science and technology topics that try to connect with additive manufacturing. Therefore, laboratory studies are usually limited to compositions and filler concentrations provided by commercial companies. Here, we present an original laboratory scale methodology to custom-prepare the feedstock for extruding magnetic composite filaments for fused filament fabrication (FFF), which is attainable by a desktop single-screw extruder. It consists in encapsulating the fillers in custom made capsules that are used as feedstock and reach the melting area of the extruder maintaining the same concentration of fillers. Results have shown that our approach can create smooth and continuous composite filaments with good homogeneity and printability with fine level of dimensional control. We further show the good dispersion of the particles in the composite filament using X-Ray Tomography, which enabled a 3D reconstruction of the spacial distribution of the embedded magnetic particles. The major advantage of this new way of preparing the composite feedstock is that it avoids the hassle of multiple extrusion runs and industrial machinery, yet providing uniform filaments of well controlled filler concentration, which is predictable and reproducible. The proposed methodology is suitable for different polymer matrices and applicable to other functional particle types, not just limited to magnetic ones. This opens an avenue for further laboratory scale development of novel functional composite filaments, useful for any community. This democratization of complex filament preparation, including consumers preparing their own desired uniform novel filaments, will facilitate to unify efforts nearing 3D printing of new functional devices.
An Electrochemical Evaluation of Nitrogen-doped Carbons as Anodes for Lithium Ion Batteries
(Elsevier, 2020) Gomez Martin, A.; Martínez Fernández, Julián; Ruttert, Mirco; Winter, Martin; Placke, Tobias; Ramírez Rico, Joaquín; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Economía y Competitividad (MINECO). España; Ministerium fur Wirtschaft, Innovation, Digitalisierung und Energie des Landes Nordrhein-Westfalen (Germany)
New anode materials beyond graphite are needed to improve the performance of lithium ion batteries (LIBs). Chemical doping with nitrogen has emerged as a simple strategy for enhancing lithium storage in carbon-based anodes. While specific capacity and rate capability are improved by doping, little is known about other key electrochemical properties relevant to practical applications. This work presents a systematic evaluation of electrochemical characteristics of nitrogen-doped carbons derived from a biomass source and urea powder as anodes in LIB half- and full-cells. Results show that doped carbons suffer from a continuous loss in capacity upon cycling that is more severe for higher nitrogen contents. Nitrogen negatively impacts the voltage and energy efficiencies at low charge/discharge current densities. However, as the charge/discharge rate increases, the voltage and energy efficiencies of the doped carbons outperform the non-doped ones. We provide insights towards a fundamental understanding of the requirements needed for practical applications and reveal drawbacks to be overcome by novel doped carbon-based anode materials in LIB applications. With this work, we also want to encourage other researchers to evaluate electrochemical characteristics besides capacity and cycling stability which are mandatory to assess the practicality of novel materials.
Temperature-FORC Analysis of a Magnetocaloric Heusler Alloy Using a Unified Driving Force Approach (T*FORC)
(American Institute of Physics, 2020) Franco García, Victorino; Universidad de Sevilla. Departamento de Física de la Materia Condensada; European Commission (EC). European Commission (FEDER); Junta de Andalucía; Army Research Laboratory
Temperature-first order reversal curve (FORC) distributions of thermomagnetic phase transitions are a fingerprinting tool to identify features of the phase transformations of the material. However, they have two major limitations: Qualitative character, due to the shift of the loops with increasing driving forces, and long experimental time. The use of an effective temperature that takes into account the different driving forces affecting the transformation allows for a more quantitative comparison of the features of the FORC distributions, as it eliminates the need for an ad hoc selection of the origin of the distribution axes. At the same time, experimental measurements as a function of this effective temperature are significantly faster than purely temperature loops, hinting at a future possibility of time and cost efficient FORC characterization of temperature dependent transitions.

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