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

Structural-elastic relationships of Zr-TL (TL = Cu, Co, Ni) thin films metallic glasses

International audienceIn this study, we investigated the structural and elastic properties of Zr-TL (late transition metal TL = Cu, Co, Ni) thin films metallic glasses (TFMG) deposited by dc magnetron co-sputtering from pure TL targets in Ar plasma discharge. The influence of the deposition parameters on the microstructure, chemical composition and elastic properties of the thin films has been explored. Advanced non-destructive techniques such as the picosecond ultrasonics and the Brillouin light scattering were employed to selectively measure the longitudinal V L and the transversal V T sound velocities, leading to the determination of the elastic constants C 11 , C 44 , respectively. From these data sets, the elastic constants of metastable amorphous single elements a-Zr, a-Cu, a-Co and a-Ni have been extrapolated. Some relationships between elastic moduli (Young's modulus E and shear modulus G = C 44) and the structural state either crystalline or amorphous are established. Predicted ductility/brittleness character was emphasized based on the Blackman's diagram, Pugh's ratio and the Pettifor criteria. Equivalently, the newly introduced δ parameter termed as 'the cooperation parameter' and related uniquely to the Poisson's ratio ν, confirmed the improvement of ductility with TL alloying

Thermal stability of Zr-O-N(:Ti) thin films prepared by magnetron sputtering

Metallic oxynitrides are materials of interest, since they represent the combination between the properties of the respective nitrides and oxides. The thermal stability of the oxynitride films is important for different applications, but it has to be differentiated from oxidation resistance. For this evaluation, x-ray diffraction (XRD) patterns have been acquired in situ during heating under two different atmospheres selected to avoid external oxidation (vacuum and a He/H2 mixture). Such tests were performed on selected Zr-O-N films presenting different chemical compositions and phases (metal-rich N-deficient nitride, (oxy)nitride, and O-rich disordered oxynitride). The influence of the addition of Ti has been studied in films including also TiN-like phases. To facilitate the phase identification, the intensity of the different peaks in the XRD patterns was tuned to highlight the weaker ones. In addition, the intensity of representative peaks of the main phases has been monitored to represent the overall behavior under heating. It has been found that the structure of the films evolves to the formation of ZrO2, the phase with tetragonal symmetry at lower temperature and the monoclinic one at higher temperature. Films including Ti showed an improved thermal stability, without the formation of the monoclinic oxide even at 1000 ºC.The financial support of Portuguese Foundation of Science and Technology (FCT), under the project number IF/00671/2013 is gratefully acknowledged

A comparative study of the oxidation behaviour of cathodic arc evaporated AlCrN and AlCrYN coatings: a microstructural and physic-chemical investigation

International audienc

A comparative study of the oxidation behaviour of cathodic arc evaporated AlCrN and AlCrYN coatings: a microstructural and physic-chemical investigation

International audienc