High quality thin films of thermoelectric misfit cobalt oxides prepared by a chemical solution method

Misfit cobaltates ([Bi/Ba/Sr/Ca/CoO]nRS[CoO2]q) constitute the most promising family of thermoelectric oxides for high temperature energy harvesting. However, their complex structure and chemical composition makes extremely challenging their deposition by high-vacuum physical techniques. Therefore, many of them have not been prepared as thin films until now. Here we report the synthesis of high-quality epitaxial thin films of the most representative members of this family of compounds by a water-based chemical solution deposition method. The films show an exceptional crystalline quality, with an electrical conductivity and thermopower comparable to single crystals. These properties are linked to the epitaxial matching of the rock-salt layers of the structure to the substrate, producing clean interfaces free of amorphous phases. This is an important step forward for the integration of these materials with complementary n-type thermoelectric oxides in multilayer nanostructuresThis research was supported by the European Research Council (ERC StG-2DTHERMS), Ministerio de Economía y Competitividad of Spain (MAT2010-16157 & MAT2013-44673-R) and Xunta de Galicia (2012-CP071). J.M.V-F acknowledges the MINECO for support with a PhD grant of the FPI programS

Sub-µL measurements of the thermal conductivity and heat capacity of liquids

We present the analysis of the thermal conductivity, κ, and heat capacity, Cp, of a wide variety of liquids, covering organic molecular solvents, ionic liquids and water–polymer mixtures. These data were obtained from ≈0.6 μL samples, using an experimental development based on the 3ω method, capable of the simultaneous measurement of κ and Cp. In spite of the different type and strength of interactions, expected in a priori so different systems, the ratio of κ to the sound velocity is approximately constant for all of them. This is the consequence of a similar atomic density for all these liquids, notwithstanding their different molecular structures. This was corroborated experimentally by the observation of a Cp/V ≈ 1.89 × 106 J K−1 m−3 (≈3R/2 per atom), for all liquids studied in this work. Finally, the very small volume of the sample required in this experimental method is an important advantage for the characterization of systems like nanofluids, in which having a large amount of the dispersed phase is sometimes extremely challengingThis work was supported by the Ministry of Science of Spain (Projects No. MAT2016-80762-R), the Consellería de Cultura, Educación e Ordenación Universitaria (ED431F 2016/008, and Centro singular de investigación de Galicia accreditation 2016-2019, ED431G/09), and the European Regional Development Fund (ERDF)S

¿Es generalizable la existencia de una transición de primer orden ferromagnética-paramagnética en los materiales con magnetorresistencia colosal R2/3B1/3MnO3 (R=lantanido; B=alcalinoterreo)?

En este trabajo se examina la naturaleza de la transición de fase ferromagnética de materiales de manganeso con estructura de perovskita, de gran interés tecnológico por sus enormes variaciones de resistividad eléctrica ante la presencia de un campo magnético aplicado (magnetorresistencia colosal). Se encuentra que, en contra de la opinión generalizada, no todos estos materiales presentan un comportamiento cualitativamente similar. En concreto, el carácter de primer orden de la transición ferromagnética no es un factor común. Las implicaciones físicas de este resultado son discutidasIn this work, the nature of the ferromagnetic phase transition of manganese-based materials with perovskite structure, is examined. These are materials of great technological interest due to the enormous variations of their electrical resistivity under the presence of an applied magnetic field (colossal magnetoresistance). lt is found that, contrary to the assumed belíef, not all these materials present a qualitatively similar behaviour. Concretely, the first order character of the ferromagnetic transition is not a common factor. The physical implications of this result are discussedS

Analysis of the temperature dependence of the thermal conductivity of insulating single crystal oxides

The temperature dependence of the thermal conductivity of 27 different single crystal oxides is reported from ≈20 K to 350 K. These crystals have been selected among the most common substrates for growing epitaxial thin-film oxides, spanning over a range of lattice parameters from ≈3.7 Å to ≈12.5 Å. Different contributions to the phonon relaxation time are discussed on the basis of the Debye model. This work provides a database for the selection of appropriate substrates for thin-film growth according to their desired thermal properties, for applications in which heat management is importantThis work was supported by the European Research Council (Grant No. ERC StG-259082, 2DTHERMS), and MINECO of Spain (Project No. MAT2013-44673-R) and Xunta de Galicia (Project No. EM2013/037). V.P. acknowledges support from the Ramon y Cajal Program (No. RYC-2011-09024) and E.F.V. from Xunta de Galicia through the I2C planS

Strain-induced enhancement of the thermoelectric power in thin films of hole-doped La2NiO4+δ

We propose a novel route for optimizing the thermoelectric power of a polaronic conductor, independent of its electronic conductivity. This mechanism is exemplified here in thin-films of La2NiO4+δ. Tensile stress induced by epitaxial growth on SrTiO3 doubles the thermoelectric power of ≈15 nm thick films relative to ≈90 nm films, while the electronic conductivity remains practically unchanged. Epitaxial strain influences the statistical contribution to the high temperature thermopower, but introduces a smaller correction to the electronic conductivity. This mechanism provides a new way for optimizing the high temperature thermoelectric performance of polaronic conductorsThis work was supported by the European Research Council (ERC StG-259082, 2DTHERMS), and Ministerio de Economía y Competitividad of Spain through the project MAT2010-16157, and a Ph.D. grant of the FPI program (J.M.V.-F.)S

Quantification of the interfacial and bulk contributions to the longitudinal spin Seebeck effect

This article appeared in P. Jiménez-Cavero et al. Applied Physics Letters 118, 092404 (2021) and may be found at https://aip.scitation.org/doi/10.1063/5.0038192We report the disentanglement of bulk and interfacial contributions to the thermally excited magnon spin current in the spin Seebeck effect under static heating. For this purpose, we have studied the dependence of the inverse spin Hall voltage and the thermal conductivity on the magnetic layer thickness. Knowledge of these quantities allows us to take into account the influence of both sources of thermal spin current in the analysis of the voltage dependence. The magnetic layer thickness modulates the relative magnitude of the involved thermal drops for a fixed total thermal difference throughout the sample. In the end, we attain the separate contributions of both sources of thermal spin current—bulk and interfacial—and obtain the value of the thermal magnon accumulation length scale in maghemite, which we find to be 29(1) nm. According to our results, bulk magnon accumulation dominates the spin Seebeck effect in our studied range of thicknesses, but the interfacial component is by no means negligibleThis work was supported by the Spanish Ministry of Science [through Project Nos. MAT2014-51982-C2-R, MAT2016-80762-R, MAT2017-82970-C2-R, and PID2019-104150RB-I00 (including FEDER funding) and the Aragón Regional government (Project No. E26)]. P.J.-C. acknowledges Spanish MECD for support through FPU program (Reference No. FPU014/02546). D.B. acknowledges support from MINECO (Spain) through an FPI program (No. BES-2017-079688). R.R. also acknowledges support from the European Commission through the Project No. 734187-SPICOLOST (H2020-MSCA-RISE-2016), the European Union's Horizon 2020 research and innovation program through the Marie Sklodowska-Curie Actions Grant Agreement SPEC No. 894006, and the Spanish Ministry of Science (No. RYC 2019-026915-I). Authors acknowledge the Advanced Microscopy Laboratory-INA University of Zaragoza for offering access to their instruments. C. L-B. acknowledges Xunta de Galicia and ESF for a PhD Grant (ED481A-2018/013)S

Apparent auxetic to non-auxetic crossover driven by Co2+ redistribution in CoFe2O4 thin films

Oxide spinels of general formula AB2O4 (A = Mg2+, Fe2+; B = Al3+, Cr3+, etc.) constitute one of the most abundant crystalline structures in mineralogy. In this structure, cations distribute among octahedral and tetrahedral sites, according to their size and the crystal-field stabilization energy. The cationic arrangement determines the mechanical, magnetic, and transport properties of the spinel and can be influenced by external parameters like temperature, pressure, or epitaxial stress in the case of thin films. Here, we report a progressive change in the sign of the Poisson ratio, ν, in thin films of CoFe2O4, defining a smooth crossover from auxetic (ν 0) behavior in response to epitaxial stress and temperature. Microstructural and magnetization studies, as well as ab initio calculations, demonstrate that such unusual elastic response is actually due to a progressive redistribution of Co2+ among the octahedral and tetrahedral sites of the spinel structure. The results presented in this work clarify a long standing controversy about the magnetic and elastic properties of Co-ferrites and are of general applicability for understanding the stress-relaxation mechanism in complex crystalline structures.This work has received financial support from Ministerio de Economía y Competitividad (Spain) under Project No. MAT2016-80762-R and MAT2017-82970-C2-R, Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016-2019, No. ED431G/09), the European Union (European Regional Development Fund-ERDF), and the European Commission through the Horizon H2020 funding by H2020-MSCA-RISE-2016-Project No. 734187–SPICOLOST. I.L.d.P. and B.R.-M. thank the funding under the ESTEEM2 project and the researchers L.A. Rodríguez and E. Snoeck for preliminary Lorentz Microscopy (L.M.) and electron holography (EH) studies in CoFe2O4 samples synthesized by PAD method performed at CEMES (Toulouse)S

Light-induced bi-directional switching of thermal conductivity in azobenzene-doped liquid crystal mesophases

The development of systems that can be switched between states with different thermal conductivities is one of the current challenges in materials science. Despite their enormous diversity and chemical richness, molecular materials have been only scarcely explored in this regard. Here, we report a reversible, light-triggered thermal conductivity switching of ≈30–40% in mesophases of pure 4,4′-dialkyloxy-3-methylazobenzene. By doping a liquid crystal matrix with the azobenzene molecules, reversible and bidirectional switching of the thermal conductivity can be achieved by UV/Vis-light irradiation. Given the enormous variety of photoactive molecules and chemically compatible liquid crystal mesophases, this approach opens unforeseen possibilities for developing effective thermal switches based on molecular materialsS

Tuning coherent-phonon heat transport in LaCoO3/SrTiO3 Superlattices

Accessing the regime of coherent phonon propagation in nanostructures opens enormous possibilities to control the thermal conductivity in energy harvesting devices, phononic circuits, etc. In this paper we show that coherent phonons contribute substantially to the thermal conductivity of LaCoO3/SrTiO3 oxide superlattices, up to room temperature. We show that their contribution can be tuned through small variations of the superlattice periodicity, without changing the total superlattice thickness. Using this strategy, we tuned the thermal conductivity by 20% at room temperature. We also discuss the role of interface mixing and epitaxial relaxation as an extrinsic, material dependent key parameter for understanding the thermal conductivity of oxide superlatticesThis work has received financial support from Ministerio de Economía y Competitividad (Spain) under project Nos. MAT2016-80762-R and PID2019-104150RB-I00, Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2019-2022, ED431G 2019/03), the European Union (European Regional Development Fund-ERDF), and the European Commission through the Horizon H2020 funding by H2020-MSCA-RISE-2016- Project No. 734187-SPICOLOST. E.L. is a Serra Húnter Fellow (Generalitat de Catalunya). D.B. acknowledges financial support from MINECO (Spain) through an FPI fellowship (BES-2017-079688). V.P. and A.O.F. were supported by the MINECO of Spain through the project PGC2018-101334-B-C21. A.O.F. thanks MECD for the financial support received through the FPU grant FPU16/02572. This work was carried out in part through the use of the INL User FacilitiesS

MSIMEP : Predicting microsatellite instability from microarray DNA methylation tumor profiles

Altres ajuts: Xunta de Galicia (ED481A-2017/299); Xunta de Galicia (ED481A 2022/491)Deficiency in DNA MMR activity results in tumors with a hypermutator phenotype, termed microsatellite instability (MSI). Beyond its utility in Lynch syndrome screening algorithms, today MSI has gained importance as predictive biomarker for various anti-PD-1 therapies across many different tumor types. Over the past years, many computational methods have emerged to infer MSI using either DNA- or RNA-based approaches. Considering this together with the fact that MSI-high tumors frequently exhibit a hypermethylated phenotype, herein we developed and validated MSIMEP, a computational tool for predicting MSI status from microarray DNA methylation tumor profiles of colorectal cancer samples. We demonstrated that MSIMEP optimized and reduced models have high performance in predicting MSI in different colorectal cancer cohorts. Moreover, we tested its consistency in other tumor types with high prevalence of MSI such as gastric and endometrial cancers. Finally, we demonstrated better performance of both MSIMEP models vis-à-vis a MLH1 promoter methylation-based one in colorectal cancer