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Miguel Lagos

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Arturo Domínguez-rodríguez

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University of the Basque Country, Euskal Herriko Unibertsitatea

Universidad Rey Juan Carlos

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Papers by Miguel Lagos

Superplastic Deformation of Alumina Composites Reinforced with Carbon Nanofibers and with Graphene Oxide Sintered by SPS—Experimental Testing and Theoretical Interpretation

Materials, 2022

The superplastic behavior of alumina-based nanostructured ceramics (Al2O3) is an important issue ... more The superplastic behavior of alumina-based nanostructured ceramics (Al2O3) is an important issue in the world of materials. The main body of this paper is an analysis of the creep behavior of polycrystals, with grain boundary sliding as the main deformation mechanism at high temperatures. Concomitant accommodation of grain shapes to preserve spatial continuity has a comparatively small effect on the strain rate. The constitutive equations for small deformations, relating strain and strain rate, derived from two models for grain sliding, are compared with the experimental data with their respective uncertainties. The data follow from experiments on the plastic deformation of alumina composites reinforced, on the one hand by graphene oxide, and on the other hand by carbon nanofibers sintered by SPS. The results show good agreement between experiment and theory for these advanced ceramics, particularly for one of the assumed models. The values obtained of ξ2 for model A were in the int...

Fourier Transform Spectrometry with Fourier Analysis of the Interferogram as Just an Optional Tool

ACS Omega, 2018

Fourier transform spectrometers replace the traditional dispersive frequency analyzer by a Michel... more Fourier transform spectrometers replace the traditional dispersive frequency analyzer by a Michelson interferometer. The spectrum is the Fourier transform of the interferogram constituting the raw output. The method is a primary tool for chemical analysis because it has decisive advantages over the dispersive one for analyzing infrared electromagnetic radiation (Fourier transform infrared, FTIR). A new procedure for dealing with the raw interferometric output of the instrument, not needing Fourier transformation and having additional advantages, is put forward here. It rests on recent advances in the theory of the interaction of matter with electromagnetic radiation yielding first principles analytic expressions for the Fourier transform of the spectral lineshapes, which can be fitted directly to the experimentally measured interferogram. The relevant physical information, as the integrated intensities of the electronic transitions and their net energy release, not affected by Stokes shifts, is readily obtained in the fitting procedure. Ulterior analysis of the spectra, introducing phenomenological standard interpolation functions to deconvolute and integrate peaks, becomes unnecessary. Both methods, standard FTIR and the one outlined here, demand little computer time and can be used simultaneously with synergistic effects.

High precision energy measurements from the analysis of wide spectral features. Application to the fluorescence of YAG:Ce 3+

Journal of Photochemistry and Photobiology A: Chemistry, 2017

Advantage is taken of a complete and precise experimental study of the luminescent properties of ... more Advantage is taken of a complete and precise experimental study of the luminescent properties of yttrium aluminium garnet doped with Ce 3+ , previously accomplished by other authors, to confirm the accuracy of the invoked theoretical methods for dealing with the realistic calculation of the electromagnetic spectra of condensed phases. The fluorescent spectra at T = 0 and T = 250 K of YAG:Ce 3+ were calculated with no adjustable parameter, giving complete agreement with experiment. The energy released by the electronic transitions was determined with precision better than 5% the full width at half maximum of the spectral features. Thermal quenching of the fluorescent yield is discussed and calculated in a less accurate way, but anyway showing good agreement with experiment.

The Role of a Threshold Stress on the Superplasticity of Ceramics Revisited

Materials Science Forum, 2016

This paper is a brief review of the concept of superplasticity, which has been extensively used t... more This paper is a brief review of the concept of superplasticity, which has been extensively used to explain the superplastic behavior of yttria-tetragonal zirconia polycrystals. The diverse theories develop to account for the origin of this quantity are outlined. In addition to that, a modern approach to this concept is reported. This new contribution can give rise to a revision of the until-now established concept of invariant microstructure associated to superplasticity.

The semiconducting state of conjugated polymers

arXiv: Mesoscale and Nanoscale Physics, 2019

Recently a variety of pi-conjugated polymers have been developed and essayed for a number of appl... more Recently a variety of pi-conjugated polymers have been developed and essayed for a number of applications such as organic light--emitting diodes (OLEDs), organic field-effect transistors (OFETs), organic photovoltaics (OPVs), and sensors. Some of them are now in mass production. Is central for these applications the semiconductor character of the pure materials, which can turn into metallic conductivity by local oxydation or reduction. The issue is that $\pi$--electrons are paired in covalent highly localized stable orbitals and interact strongly between them and with the ionic cores, thus being far from the extended quasi--free independent electron states assumed by the theory of inorganic semiconductors. A model yielding a mechanism for many--body conduction of charge and semiconducting properties of the undoped material is introduced here.

Fourier transform spectrometry without Fourier analysis of the interferogram

arXiv: Instrumentation and Detectors, 2018

It is shown here that precision is gained by analyzing the interferometric spectra directly from ... more It is shown here that precision is gained by analyzing the interferometric spectra directly from the interferograms, with no previous Fourier transformation to put them in the standard frequency domain. The method is based on the theoretical calculation of the lineshape, which gives a general closed--form expression for the spectrum in the time domain and is directly assimilable to the experimental interferogram. Error sources in Fourier integrals, apodization, peak fitting with standard interpolation functions, choice of background level, Stokes energy shifts, etc., are neatly avoided.

Why old tires are still being preferred as dock bumpers in harbours

arXiv: Classical Physics, 2012

The usage of old tires as dock and tugboat bumpers has been a common practice from long ago, prov... more The usage of old tires as dock and tugboat bumpers has been a common practice from long ago, proving to be safe for docking even the largest freighters. The reaction force and stored energy of an axially compressed tire is studied in order to determine the specific features of these variables that make tires so adequate as docking protections. The reaction force is attributed to the elastic deformation of the tread, which is modeled as a not too thin cylindrical shell. Most energy absorption takes place after tread buckling, which bends tread and increases its circumference, inducing strong tensile forces that contribute to stabilize the buckled structure. Results shed light on the mechanical properties that a designed dock bumper should exhibit.

An alternate theoretical approach to diffusion bonding

arXiv: Materials Science, 2010

On the basis of a previous theoretical approach to the plastic flow of highly refined materials, ... more On the basis of a previous theoretical approach to the plastic flow of highly refined materials, a physical explanation for diffusion bonding is essayed, which yields closed--form equations relating the bonding progress with time, temperature, applied pressure and the constants characterizing the material. Excellent agreement with experiment is attained, with no adjustable parameter. In the novel scheme, diffusion bonding is caused by the interpenetration of the two sufaces at the grain level. The process is driven by the strong tensile stress field induced in the plane of the interface by the plastic deformation in the normal direction. The grain boundaries of each joining surface yield to host grains of the other surface, releasing this way the internally generated tensile stresses. Voids gradually close with the increment of the interpenetrated areas. In this scheme bonding is not a matter of contacting and atomic interdiffusion, but of grain exchange.

Evidence of a two--dimensional grain sliding regime in the plastic deformation of micron and sub--micron films

arXiv: Materials Science, 2012

Copper and aluminium sub-micron films are structured as columnar arrays of grains traversing the ... more Copper and aluminium sub-micron films are structured as columnar arrays of grains traversing the entire film, and hence are virtual two-dimensional polycrystalline solids. A closed-form solution for the two-dimensional plastic flow is obtained assuming that grain boundary sliding is the dominating mechanism for deformation. The theoretical results obtained here are in close agreement with experimental data appeared in the literature, which suggests further work on the subject.

$Research paper thumbnail of Theoretical approach to the ductile fracture of polycrystalline solids$

Theoretical approach to the ductile fracture of polycrystalline solids

It is shown here that fracture after a brief plastic strain, typically of a few percents, is a ne... more It is shown here that fracture after a brief plastic strain, typically of a few percents, is a necessary consequence of the polycrystalline nature of the materials. The polycrystal undergoing plastic deformation is modeled as a flowing continuum of random deformable polyhedra, representing the grains, which fill the space without leaving voids. Adjacent grains slide with a relative velocity proportional to the local shear stress resolved on the plane of the shared grain boundary, when greater than a finite threshold. The polyhedral grains reshape continuously to preserve matter continuity, being the forces causing grain sliding dominant over those reshaping the grains. It has been shown in the past that this model does not conserve volume, causing a monotonic hydrostatic pressure variation with strain. This effect introduces a novel concept in the theory of plasticity because determines that any fine grained polycrystalline material will fail after a finite plastic strain. Here the ...

High Precision Energy Measurements from the Analysis of Wide Spectral Features. Application to the fluorescence of YAG:Ce 3

Advantage is taken of a complete and precise experimental study of the luminescent properties of ... more Advantage is taken of a complete and precise experimental study of the luminescent properties of yttrium aluminium garnet doped with Ce 3+ , previously accomplished by other authors, to confirm the accuracy of the invoked theoretical methods for dealing with the realistic calculation of the electromagnetic spectra of condensed phases. The fluorescent spectra at T = 0 and T = 250 K of YAG:Ce 3+ were calculated with no adjustable parameter, giving complete agreement with experiment. The energy released by the electronic transitions was determined with precision better than 5% the full width at half maximum of the spectral features. Thermal quenching of the fluorescent yield is discussed and calculated in a less accurate way, but anyway showing good agreement with experiment.

A new approach to the grain-size dependent transition of stress exponents in yttria tetragonal zirconia polycrystals. The theoretical limit for superplasticity in ceramics

Ceramics International, 2015

Abstract Superplastic behavior of fine-grained zirconia ceramics (YTZP) is still a major issue on... more Abstract Superplastic behavior of fine-grained zirconia ceramics (YTZP) is still a major issue on the ceramic science. This work presents a theoretical approach to the deformation mechanism yielding superplastic response in YTZP. In this paper we prove that, in the absence of any relaxation mechanism of internal stresses, a linear dependence of strain rate with stress is obtained, but the invariance of the microstructure cannot be assured. On the other hand, if the grain dynamics is controlled by the relaxation mechanism, a parabolic dependence is expected. This model predicts a transition between parabolic to linear dependence as the grain size increases, in quantitative agreement with the experimental data reported in the literature for YTZP.

Quantum mechanism of hydrogen diffusion in tantalum

Solid State Communications, Feb 29, 1988

LETTER TO THE EDITOR: Quantum diffusion in FCC metals

J Phys Condens Matter, 1990

Subsurface bonding of hydrogen in transition metals: dependence on surface orientation

Surface Science, Oct 10, 1994

Singlet excitations in the anisotropic S=1/2 antiferromagnetic Heisenberg model

Solid State Communications, Mar 1, 1992

ABSTRACT We generalize to arbitrary exchange anisotropy an analytic approach to the ground state ... more ABSTRACT We generalize to arbitrary exchange anisotropy an analytic approach to the ground state and excitations of the Heisenberg antiferromagnet previously formulated for exchange anisotropy toward the Ising limit. This way we obtain a theory of antiferromagnetism that takes in from the Ising to the XY extreme models, yields more precision than linear spinwave theory and, in opposition to the latter, is expressed in terms of excitations carrying no spin.

Thermal quenching of fluorescence in condensed media

Solid State Communications, 2016

Method and device for the generation of printed graphic patterns for exhibiting movie pictures to moving observers by means of a static optical apparatus

Brittle and Ductile Character of Amorphous Solids

Advances in Applied Mathematics and Mechanics, 2016

.Common silicate glasses are among the most brittle of the materials. However, on warming beyond ... more .Common silicate glasses are among the most brittle of the materials. However, on warming beyond the glass transition temperatureTgglass transforms into one of the most plastic known materials. Bulk metallic glasses exhibit similar phenomenology, indicating that it rests on the disordered structure instead on the nature of the chemical bonds. The micromechanics of a solid with bulk amorphous structure is examined in order to determine the most basic conditions the system must satisfy to be able of plastic flow. The equations for the macroscopic flow, consistent with the constrictions imposed at the atomic scale, prove that a randomly structured bulk material must be either a brittle solid or a liquid, but not a ductile solid. The theory permits to identify a single parameter determining the difference between the brittle solid and the liquid. However, the system is able of perfect ductility if the plastic flow proceeds in two dimensional plane layers that concentrate the strain. Insight is gained on the nature of the glass transition, and the phase occurring between glass transition and melting.

Mechanical instability of stressed grain boundaries during plastic deformation of zirconium carbide

Journal of the European Ceramic Society, 2016

Superplastic Deformation of Alumina Composites Reinforced with Carbon Nanofibers and with Graphene Oxide Sintered by SPS—Experimental Testing and Theoretical Interpretation

Materials, 2022

The superplastic behavior of alumina-based nanostructured ceramics (Al2O3) is an important issue ... more The superplastic behavior of alumina-based nanostructured ceramics (Al2O3) is an important issue in the world of materials. The main body of this paper is an analysis of the creep behavior of polycrystals, with grain boundary sliding as the main deformation mechanism at high temperatures. Concomitant accommodation of grain shapes to preserve spatial continuity has a comparatively small effect on the strain rate. The constitutive equations for small deformations, relating strain and strain rate, derived from two models for grain sliding, are compared with the experimental data with their respective uncertainties. The data follow from experiments on the plastic deformation of alumina composites reinforced, on the one hand by graphene oxide, and on the other hand by carbon nanofibers sintered by SPS. The results show good agreement between experiment and theory for these advanced ceramics, particularly for one of the assumed models. The values obtained of ξ2 for model A were in the int...

Fourier Transform Spectrometry with Fourier Analysis of the Interferogram as Just an Optional Tool

ACS Omega, 2018

Fourier transform spectrometers replace the traditional dispersive frequency analyzer by a Michel... more Fourier transform spectrometers replace the traditional dispersive frequency analyzer by a Michelson interferometer. The spectrum is the Fourier transform of the interferogram constituting the raw output. The method is a primary tool for chemical analysis because it has decisive advantages over the dispersive one for analyzing infrared electromagnetic radiation (Fourier transform infrared, FTIR). A new procedure for dealing with the raw interferometric output of the instrument, not needing Fourier transformation and having additional advantages, is put forward here. It rests on recent advances in the theory of the interaction of matter with electromagnetic radiation yielding first principles analytic expressions for the Fourier transform of the spectral lineshapes, which can be fitted directly to the experimentally measured interferogram. The relevant physical information, as the integrated intensities of the electronic transitions and their net energy release, not affected by Stokes shifts, is readily obtained in the fitting procedure. Ulterior analysis of the spectra, introducing phenomenological standard interpolation functions to deconvolute and integrate peaks, becomes unnecessary. Both methods, standard FTIR and the one outlined here, demand little computer time and can be used simultaneously with synergistic effects.

High precision energy measurements from the analysis of wide spectral features. Application to the fluorescence of YAG:Ce 3+

Journal of Photochemistry and Photobiology A: Chemistry, 2017

Advantage is taken of a complete and precise experimental study of the luminescent properties of ... more Advantage is taken of a complete and precise experimental study of the luminescent properties of yttrium aluminium garnet doped with Ce 3+ , previously accomplished by other authors, to confirm the accuracy of the invoked theoretical methods for dealing with the realistic calculation of the electromagnetic spectra of condensed phases. The fluorescent spectra at T = 0 and T = 250 K of YAG:Ce 3+ were calculated with no adjustable parameter, giving complete agreement with experiment. The energy released by the electronic transitions was determined with precision better than 5% the full width at half maximum of the spectral features. Thermal quenching of the fluorescent yield is discussed and calculated in a less accurate way, but anyway showing good agreement with experiment.

The Role of a Threshold Stress on the Superplasticity of Ceramics Revisited

Materials Science Forum, 2016

This paper is a brief review of the concept of superplasticity, which has been extensively used t... more This paper is a brief review of the concept of superplasticity, which has been extensively used to explain the superplastic behavior of yttria-tetragonal zirconia polycrystals. The diverse theories develop to account for the origin of this quantity are outlined. In addition to that, a modern approach to this concept is reported. This new contribution can give rise to a revision of the until-now established concept of invariant microstructure associated to superplasticity.

The semiconducting state of conjugated polymers

arXiv: Mesoscale and Nanoscale Physics, 2019

Recently a variety of pi-conjugated polymers have been developed and essayed for a number of appl... more Recently a variety of pi-conjugated polymers have been developed and essayed for a number of applications such as organic light--emitting diodes (OLEDs), organic field-effect transistors (OFETs), organic photovoltaics (OPVs), and sensors. Some of them are now in mass production. Is central for these applications the semiconductor character of the pure materials, which can turn into metallic conductivity by local oxydation or reduction. The issue is that $\pi$--electrons are paired in covalent highly localized stable orbitals and interact strongly between them and with the ionic cores, thus being far from the extended quasi--free independent electron states assumed by the theory of inorganic semiconductors. A model yielding a mechanism for many--body conduction of charge and semiconducting properties of the undoped material is introduced here.

Fourier transform spectrometry without Fourier analysis of the interferogram

arXiv: Instrumentation and Detectors, 2018

It is shown here that precision is gained by analyzing the interferometric spectra directly from ... more It is shown here that precision is gained by analyzing the interferometric spectra directly from the interferograms, with no previous Fourier transformation to put them in the standard frequency domain. The method is based on the theoretical calculation of the lineshape, which gives a general closed--form expression for the spectrum in the time domain and is directly assimilable to the experimental interferogram. Error sources in Fourier integrals, apodization, peak fitting with standard interpolation functions, choice of background level, Stokes energy shifts, etc., are neatly avoided.

Why old tires are still being preferred as dock bumpers in harbours

arXiv: Classical Physics, 2012

The usage of old tires as dock and tugboat bumpers has been a common practice from long ago, prov... more The usage of old tires as dock and tugboat bumpers has been a common practice from long ago, proving to be safe for docking even the largest freighters. The reaction force and stored energy of an axially compressed tire is studied in order to determine the specific features of these variables that make tires so adequate as docking protections. The reaction force is attributed to the elastic deformation of the tread, which is modeled as a not too thin cylindrical shell. Most energy absorption takes place after tread buckling, which bends tread and increases its circumference, inducing strong tensile forces that contribute to stabilize the buckled structure. Results shed light on the mechanical properties that a designed dock bumper should exhibit.

An alternate theoretical approach to diffusion bonding

arXiv: Materials Science, 2010

On the basis of a previous theoretical approach to the plastic flow of highly refined materials, ... more On the basis of a previous theoretical approach to the plastic flow of highly refined materials, a physical explanation for diffusion bonding is essayed, which yields closed--form equations relating the bonding progress with time, temperature, applied pressure and the constants characterizing the material. Excellent agreement with experiment is attained, with no adjustable parameter. In the novel scheme, diffusion bonding is caused by the interpenetration of the two sufaces at the grain level. The process is driven by the strong tensile stress field induced in the plane of the interface by the plastic deformation in the normal direction. The grain boundaries of each joining surface yield to host grains of the other surface, releasing this way the internally generated tensile stresses. Voids gradually close with the increment of the interpenetrated areas. In this scheme bonding is not a matter of contacting and atomic interdiffusion, but of grain exchange.

Evidence of a two--dimensional grain sliding regime in the plastic deformation of micron and sub--micron films

arXiv: Materials Science, 2012

Copper and aluminium sub-micron films are structured as columnar arrays of grains traversing the ... more Copper and aluminium sub-micron films are structured as columnar arrays of grains traversing the entire film, and hence are virtual two-dimensional polycrystalline solids. A closed-form solution for the two-dimensional plastic flow is obtained assuming that grain boundary sliding is the dominating mechanism for deformation. The theoretical results obtained here are in close agreement with experimental data appeared in the literature, which suggests further work on the subject.

$Research paper thumbnail of Theoretical approach to the ductile fracture of polycrystalline solids$

Theoretical approach to the ductile fracture of polycrystalline solids

It is shown here that fracture after a brief plastic strain, typically of a few percents, is a ne... more It is shown here that fracture after a brief plastic strain, typically of a few percents, is a necessary consequence of the polycrystalline nature of the materials. The polycrystal undergoing plastic deformation is modeled as a flowing continuum of random deformable polyhedra, representing the grains, which fill the space without leaving voids. Adjacent grains slide with a relative velocity proportional to the local shear stress resolved on the plane of the shared grain boundary, when greater than a finite threshold. The polyhedral grains reshape continuously to preserve matter continuity, being the forces causing grain sliding dominant over those reshaping the grains. It has been shown in the past that this model does not conserve volume, causing a monotonic hydrostatic pressure variation with strain. This effect introduces a novel concept in the theory of plasticity because determines that any fine grained polycrystalline material will fail after a finite plastic strain. Here the ...

High Precision Energy Measurements from the Analysis of Wide Spectral Features. Application to the fluorescence of YAG:Ce 3

Advantage is taken of a complete and precise experimental study of the luminescent properties of ... more Advantage is taken of a complete and precise experimental study of the luminescent properties of yttrium aluminium garnet doped with Ce 3+ , previously accomplished by other authors, to confirm the accuracy of the invoked theoretical methods for dealing with the realistic calculation of the electromagnetic spectra of condensed phases. The fluorescent spectra at T = 0 and T = 250 K of YAG:Ce 3+ were calculated with no adjustable parameter, giving complete agreement with experiment. The energy released by the electronic transitions was determined with precision better than 5% the full width at half maximum of the spectral features. Thermal quenching of the fluorescent yield is discussed and calculated in a less accurate way, but anyway showing good agreement with experiment.

A new approach to the grain-size dependent transition of stress exponents in yttria tetragonal zirconia polycrystals. The theoretical limit for superplasticity in ceramics

Ceramics International, 2015

Abstract Superplastic behavior of fine-grained zirconia ceramics (YTZP) is still a major issue on... more Abstract Superplastic behavior of fine-grained zirconia ceramics (YTZP) is still a major issue on the ceramic science. This work presents a theoretical approach to the deformation mechanism yielding superplastic response in YTZP. In this paper we prove that, in the absence of any relaxation mechanism of internal stresses, a linear dependence of strain rate with stress is obtained, but the invariance of the microstructure cannot be assured. On the other hand, if the grain dynamics is controlled by the relaxation mechanism, a parabolic dependence is expected. This model predicts a transition between parabolic to linear dependence as the grain size increases, in quantitative agreement with the experimental data reported in the literature for YTZP.

Quantum mechanism of hydrogen diffusion in tantalum

Solid State Communications, Feb 29, 1988

LETTER TO THE EDITOR: Quantum diffusion in FCC metals

J Phys Condens Matter, 1990

Subsurface bonding of hydrogen in transition metals: dependence on surface orientation

Surface Science, Oct 10, 1994

Singlet excitations in the anisotropic S=1/2 antiferromagnetic Heisenberg model

Solid State Communications, Mar 1, 1992

ABSTRACT We generalize to arbitrary exchange anisotropy an analytic approach to the ground state ... more ABSTRACT We generalize to arbitrary exchange anisotropy an analytic approach to the ground state and excitations of the Heisenberg antiferromagnet previously formulated for exchange anisotropy toward the Ising limit. This way we obtain a theory of antiferromagnetism that takes in from the Ising to the XY extreme models, yields more precision than linear spinwave theory and, in opposition to the latter, is expressed in terms of excitations carrying no spin.

Thermal quenching of fluorescence in condensed media

Solid State Communications, 2016

Method and device for the generation of printed graphic patterns for exhibiting movie pictures to moving observers by means of a static optical apparatus

Brittle and Ductile Character of Amorphous Solids

Advances in Applied Mathematics and Mechanics, 2016

.Common silicate glasses are among the most brittle of the materials. However, on warming beyond ... more .Common silicate glasses are among the most brittle of the materials. However, on warming beyond the glass transition temperatureTgglass transforms into one of the most plastic known materials. Bulk metallic glasses exhibit similar phenomenology, indicating that it rests on the disordered structure instead on the nature of the chemical bonds. The micromechanics of a solid with bulk amorphous structure is examined in order to determine the most basic conditions the system must satisfy to be able of plastic flow. The equations for the macroscopic flow, consistent with the constrictions imposed at the atomic scale, prove that a randomly structured bulk material must be either a brittle solid or a liquid, but not a ductile solid. The theory permits to identify a single parameter determining the difference between the brittle solid and the liquid. However, the system is able of perfect ductility if the plastic flow proceeds in two dimensional plane layers that concentrate the strain. Insight is gained on the nature of the glass transition, and the phase occurring between glass transition and melting.

Mechanical instability of stressed grain boundaries during plastic deformation of zirconium carbide

Journal of the European Ceramic Society, 2016