Unified modelling of the thermoelectric properties in SrTiO3

Thermoelectric materials are opening a promising pathway to address energy conversion issues governed by a competition between thermal and electronic transport. Improving the efficiency is a difficult task, a challenge that requires new strategies to unearth optimized compounds. We present a theory of thermoelectric transport in electron doped SrTiO3, based on a realistic tight binding model that includes relevant scattering processes. We compare our calculations against a wide panel of experimental data, both bulk and thin films. We find a qualitative and quantitative agreement over both a wide range of temperatures and carrier concentrations, from light to heavily doped. Moreover, the results appear insensitive to the nature of the dopant La, B, Gd and Nb. Thus, the quantitative success found in the case of SrTiO3, reveals an efficient procedure to explore new routes to improve the thermoelectric properties in oxides.Comment: 5 figures, manuscript submitte

Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nanometer to micrometer and mosaicity effects

High-quality thermoelectric LaxSr1-xTiO3 (LSTO) layers (here with x = 0.2), with thicknesses ranging from 20 nm to 700 nm, have been epitaxially grown on SrTiO3(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1{\deg}), and present very low electrical resistivity (<5 x 10-4 ohm.cm at room temperature), one order of magnitude lower than commercial Nb-doped SrTiO3 single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of around -60 microV/K have been found for all films, accordingly. Finally, a correlation is given between the mosaicity and the (thermo)electric properties. These functional LSTO films can be integrated on Si in opto-microelectronic devices as transparent conductor, thermoelectric elements or in non-volatile memory structures

Functional behaviour of TiO2films doped with noble metals

To evaluate the effects of different concentrations of noble metal in a TiO2 matrix, different films of both Ag:TiO2 and Au:TiO2 systems were prepared. Mechanical and tribological characterization was carried out to evaluate the coatings response as a function of the noble metals composition and (micro)structure of the films. The overall set of results indicates that the amorphous films reveal better results than the crystalline ones. For the amorphous samples, the reduced Young’s modulus and the adhesion critical loads followed similar tendencies in both sets of films. Wear rates were similar for all samples except for the one with the highest silver content. To improve brittleness of TiO2 films, the results seem to indicate that a slight metal doping is preferred, and Au showed to be a better choice than Ag. In fact, the sample with the lowest Au content revealed a better mechanical behaviour than the pure TiO2 film.This research was sponsored by FEDER funds through the COMPETE program (Programa Operacional Factores de Competitividade) and by FCT (Fundação para a Ciência e a Tecnologia), under the projects PEST-C/FIS/UI607/2013 and PEst-C/EME/UI0285/2013. The authors also acknowledge the financial support by the project Nano4color – Design and develop a new generation of color PVD coatings for decorative applications (FP7 EC R4SME Project No. 315286)

A time discretization scheme for a nonlocal degenerate problem modelling resistance spot welding

This is the author's PDF version of an article published in Mathematical Modelling of Natural Phenomena© 2015. The definitive version is available at http://www.mmnp-journal.org/articles/mmnp/abs/2015/06/mmnp2015106p90/mmnp2015106p90.htmlIn the current work we construct a nonlocal mathematical model describing the phase transition occurs during the resistance spot welding process in the industry of metallurgy. We then consider a time discretization scheme for solving the resulting nonlocal moving boundary problem. The scheme consists of solving at each time step a linear elliptic partial differential equation and then making a correction to account for the nonlinearity. The stability and error estimates of the developed scheme are investigated. Finally some numerical results are presented confirming the efficiency of the developed numerical algorithm

Crystallization and hardening of Zr-40at.% Cu thin film metallic glass: Effects of isothermal annealing

cited By 6International audienceEffects of isothermal annealing on structural relaxation, crystallization and mechanical behavior of Zr-40at.% Cu thin film metallic glass (TFMG) are reported. Two annealing temperatures have been chosen in the supercooled liquid region (δT) and one below the glass transition temperature (Tg). During annealing the free volume decreased and nanocrystals nucleated into the matrix. Results show that the nanocrystalline CuZr2 intermetallic phase precipitates in the glassy matrix with respect to the annealing temperature and duration. When annealed below Tg, the structural relaxation induces a slight improvement of the mechanical properties with a hardness and Young's modulus variation of about 2.5% and 9.0% compared with the as-deposited values. At higher temperatures, it is shown that hardness increases of about 5.5% and 25.0% after a heat treatment of 60min at 350°C and 380°C, respectively. The elastic modulus follows a time dependent increase from ~100GPa (as-deposited) up to ~105GPa after a one-hour annealing at 350°C and ~125GPa at 380°C, respectively. © 2015 Elsevier Ltd

Preface to the Issue Nonlocal Reaction-Diffusion Equations

1. Nonlocal reaction-diffusion equations in population dynamics Nonlocal reaction-diffusion equations are intensively studied during the last decade in relation with prob-lems in population dynamics and other applications. In comparison with traditional reaction-diffusion equations they possess new mathematical properties and richer nonlinear dynamics. Many studies are devoted to the nonlocal reaction-diffusion equation ∂u ∂

Impact of local nanocrystallization on mechanical properties in the Zr-59 at.% Cu metallic glass thin film

International audienceZr-59 at.% Cu glassy filmwas deposited by co-magnetron sputtering using pure metal targets. The film exhibits anXRD-amorphous structure and smooth surface morphology. Isothermal annealing at 370 °C, for 30 and 60 min,modify the local structural ordering and promote nucleation of Cu10Zr7 nanocrystalline-like domains as confirmedby TEM analysis. The mechanical properties of the film are far higher than those of pure metals, and arestill improved after nanocrystallization

Modulated IR radiometry for determining thermal properties and basic characteristics of titanium thin films

cited By 5International audienceTitanium thin films of different thicknesses were prepared by direct current magnetron sputtering to study modulated infrared (IR) radiometry as a tool for analyzing film thickness. Thickness was varied by regularly increasing the deposition time, keeping all the other deposition parameters constant. The influence of film thickness on morphological, structural, and electrical properties of the titanium coatings also was investigated. The experimental results revealed a systematic grain growth with increasing film thickness, along with enhanced film crystallinity, which led to increased electrical conductivity. Using the results obtained by modulated IR radiometry, the thickness of each thin film was calculated. These thickness values were then compared with the coating thickness measurements obtained by scanning electron microscopy. The values confirmed the reliability of modulated IR radiometry as an analysis tool for thin films and coatings, and for determining thicknesses in the micrometer range, in particular. © 2014 American Vacuum Society

Zr-Cu thin film metallic glasses: An assessment of the thermal stability and phases' transformation mechanisms

cited By 13International audienceThe PVD co-sputtering technology is an efficient way to deposit Zr-Cu thin film metallic glass in a wide composition range. The structural stability and crystallization behavior of metallic glass films are investigated by in situ X-ray diffraction (XRD) via heating up to 873 K. The glassy films within the 33.3-89.1 at.% Cu range maintained their amorphous structure at temperatures higher than 550 K. Within this chemical composition range, films exhibit a smooth and dense surface morphology with 100 nm-sized grains and vein-like features. Glassy films revealed a high thermal stability as reflected by differential scanning calorimetry experiments and in situ high temperature XRD analysis. It was found that the structure evolved with the temperature and copper contents from a highly textured 1 1 1 crystallized fcc-Zr to intermetallic CuZr2, Cu10Zr7, Cu51Zr14phases to finally 1 1 1 crystallized fcc-Cu. Mechanisms involved in the structural changes of the glassy films together with the multi-stage crystallization process are discussed in the light of the copper contents. © 2014 Elsevier B.V. All rights reserved

Binary Zr-Ni/Co metallic glass films: Role of the structural state on their durability

cited By 5International audienceThin film metallic glasses are a new class of promising materials for advanced structural applications. In this work, binary Zr-based thin film metallic glasses (TFMGs) were deposited by the magnetron co-sputtering process from pure metal targets. Two similar enrichments were investigated (44 at.% for the nickel, 43 at.% for the cobalt), in order to determine the effect of the alloying element's nature on the structural, mechanical and electrochemical behaviors. Structure of films was determined by in situ XRD measurements carried out during heating up to 600 °C, while their morphology was characterized by SEM observations. Mechanical properties of amorphous and crystallized films (hardness and Young's modulus) were measured by nanoindentation. Intrinsic electrochemical properties are deduced from polarization curves and electrochemical impedance spectroscopy measurements carried out in Na2SO4 aqueous solution. It is found that the surface morphology of TFMGs was very smooth with a compact and dense microstructure. When heated, glassy films exhibit a high structural stability (up to 440 °C) with crystallization occurring through a multistage process for the Co-containing film. Whatever the coating, Zr affords its beneficial passive-ability, while crystallization process accelerates the global corrosion kinetics. Corrosion mechanisms of the Zr-based TFMGs were discussed in the light of the alloying element (Ni or Co) and the structure of films (amorphous or crystallized). © 2015 Acta Materialia Inc