Thermoelectric properties of Bi2Te3 nanowire array in thickness direction

Comunicación presentada en la 12th European Conference on Thermoelectricity (ECT2014), celebrada en Madrid del 24 al 26 de septiembre de 2014.Theoretical studies have predicted a possibility of increasing thermoelectric efficiency of nanos tructure materials, owing to quantum confinement effect on the charge carriers and lattice vibrations. On the other hand, Bi2Te3 is well known to be the most efficient thermoelectric material that can be operated around room temperatureThis work has been supported by the bilateral Spanish–Japanese NANOTHERMA projects of Strategic International Reserch Cooperative Program and KAKENHI for Challenging Exploratory.Peer Reviewe

Enhanced Power Factor of PANI/GNP nanocomposites

Comunicación presentada en la 11th European Conference on Thermoelectrics (ECT2013), celebrada en Noordwijk (Holanda) del 18 al 20 de noviembre de 2013.Nowadays, the inorganic compounds (like Bi2Te3) are the best thermoelectric materials due to their suitable thermoelectric properties for room temperature applications. Nevertheless, organic materials, like conjugated polymers, are becoming more important recently due to their increasing Figure of Merit (0.25‐0.42). Polymers generally have low thermal conductivity (©§≈0.1‐0.5W/m∙K), flexibility, environmental stability, easily doping and de‐doping, non‐toxicity, potential processing advantages (e.g. printing) and straightforward preparation in comparison with inorganic semiconductors. The increase in the Power Factor of this materials, which is given by S2¥ò, is being achieved by two mechanisms: doping the polymers or blending them with different kinds of filling materials, such as carbon nanotubes, graphene nanosheets (GN) or graphene nanoplatelets.Peer Reviewe

El efecto fotoacústico como técnica de medida de conductividad térmica

Ponencia presentada en las IV Jornadas de Jóvenes Investigadores, celebradas en Madrid el 9 de julio de 2015.La conductividad térmica es una propiedad de los materiales de gran importancia en muchos campos de investigación como por ejemplo, la termoelectricidad. Sin embargo, es una magnitud muy compleja de determinar, especialmente a escala nanométrica. En este trabajo se ha desarrollado un sistema experimental basado en el efecto fotoacústico capaz de medir conductividad térmica de materiales de muy diferentes estructuras, dimensiones y propiedades térmicas. La técnica fotoacústica es una técnica óptica de no contacto que permite obtener la conductividad térmica de diferentes tipos de estructuras desde materiales en volumen, películas delgadas, estructuras multicapa o incluso matrices de nanohilos. En esta técnica, una radiación periódica modulada calienta la muestra de tal forma que el aire en contacto con la superficie de la muestra se caliente y enfría y por tanto se expande y se contrae periódicamente de forma similar a un pistón térmico. Este efecto provoca ondas acústicas que son detectadas por un micrófono. Comparando la onda incidente proveniente del láser con la onda acústica registrada, se pueden extraer las propiedades térmicas de la muestra. El análisis de la señal depende del tipo de muestra que se esté analizando. En este trabajo, se usan dos tipos diferentes de normalización. En el caso de estructuras multicapa, la muestra es iluminada en configuración frontal (o de reflexión) y la señal es normalizada con una muestra de referencia que permite eliminar la contribución de la celda fotoacústica. Para el cálculo de la conductividad térmica se emplea un modelo multicapa desarrollado por Hu et al. En el caso de muestras en volumen, la normalización se lleva a cabo midiendo la muestra tanto en configuración de reflexión como transmisión. El sistema experimental, que se muestra en la figura, fue desarrollado en el laboratorio y consiste en una celda fotoacústica hecha de metacrilato diseñada de tal forma que se evitan posibles resonancias acústicas. En este trabajo, se muestran las capacidades y límites de la técnica junto con algunos resultados experimentales que se han obtenido.Peer Reviewe

Thermoelectric properties of tellurium thick films prepared by electrodeposition

Póster presentado en la 12th European Conference on Thermoelectricity (ECT2014), celebrada en Madrid del 24 al 26 de septiembre de 2014.Tellurium is a p-type semiconductor with a narrow bandgap (0.34eV) and highly anisotropic crystal structure. It consists of helical chains which are bounded by covalent unions between the atoms and bound with other chains by Van der Waals interactions. These chains turn into a hexagonal lattice whose c axis is perpendicular to the hexagonal base or parallel to the helical chains.RC StG NANO-TEC EU 240497. PHOtoacoustic MEasurements of Nanostructures for Thermoelectric Applications (PHOMENTA).Peer Reviewe

Optimization of bismuth telluride films and nano-wire arrays via electrodeposition for thermoelectric applications

Comunicación presentada en el 3rd Early Stage Researchers Workshop in Nanoscience, celebrado en Madrid el 27 y 28 de junio de 2013.Due to the current world’s demand for energy, there is a great interest in thermoelectricity, which offers the possibility of increasing the sustainability of our electrical system. Thermoelectric materials can convert heat into electricity and vice versa, and thus they offer a way of recovering wasted heat produced in engines, industrial processes and others into usable power. However, one of the main problems for their actual use is their low efficiency in this conversion. This efficiency is directly related with what is called the thermoelectric figure of merit, described by ZT=(S2·σ·T)/κ ,where S, σ, κ, and T stand for the Seebeck coefficient, electrical and thermal conductivities, and the absolute temperature, respectively. Given that in classical physics S, σ, and κ, are correlated, the improvement of the efficiency is not straightforward. Nevertheless, in 1993 a theoretical work suggested that the efficiency could be greatly enhanced by reducing the dimensionality of the structures under studied and working in the nano-scale. Therefore, much experimental effort has been done to achieve these kind of structures and in some cases, an enhancement of the ZT value has been achieved, although this has not been due to the quantum confinement to the charge carriers, as it was theoretically predicted, but to an increase of the κ due to the increased number of interface boundaries in nanostructures. Among the most efficient thermoelectric materials used for applications at room temperature, bismuth telluride (Bi2Te3) and its different alloys stand out, with a ZT for Bi2Te3of around 1 at RT [2]. We present here an optimized method of obtaining films and nanowire arrays via electrochemical deposition in a conventional three-electrode cell. Different ways of improving the quality of the obtained films have been studied (working electrode, constant and pulsed potentials, different chemical baths, etc.) in order to obtain highly oriented (110) films, which are the most favorable for out-of-plane applications. Then, nanostructuration has been achieved by changing the working electrode to porous alumina templates and realizing the electrochemical deposition inside the pores. The samples produced have been characterized using SEM, EDX, AFM, XRD, and Raman spectrometry, and in the case of the films, their transport properties have also been measured.Peer Reviewe

Tailoring the thermoelectric properties of Skutterudites by nanocomposites

Póster presentado en la 34th Annual International Conference on Thermoelectrics (ICT) y en la 13th European Conference on Thermoelectrics(ECT), celebradas en Dresden del 28 de junio al 2 de julio de 2015.Skutterudites have attracted great attention for their promising potential on thermoelectric applications, such as harvesting the heat generated in industrial processes and automotive operations. To improve their thermoelectric figure of merit ,emphasis has gone into modifying the band structure through doping to enhance the Power Factor and reducing thermal conductivity through increasing phonon scattering by filling and in-situ nanocomposites formation.Depending on the nature of the nanoinclusions and the proportion in the matrix, it is possible to tailor the thermoelectric properties. In this work, different concentrations of oxides were included in a one-step synthesis mechanism, obtaining the Skutterudite phase with nanoinclusions and therefore, achieving lower thermal conductivities than those reported in literature.Peer Reviewe

Effectiveness of an intervention for improving drug prescription in primary care patients with multimorbidity and polypharmacy:Study protocol of a cluster randomized clinical trial (Multi-PAP project)

This study was funded by the Fondo de Investigaciones Sanitarias ISCIII (Grant Numbers PI15/00276, PI15/00572, PI15/00996), REDISSEC (Project Numbers RD12/0001/0012, RD16/0001/0005), and the European Regional Development Fund ("A way to build Europe").Background: Multimorbidity is associated with negative effects both on people's health and on healthcare systems. A key problem linked to multimorbidity is polypharmacy, which in turn is associated with increased risk of partly preventable adverse effects, including mortality. The Ariadne principles describe a model of care based on a thorough assessment of diseases, treatments (and potential interactions), clinical status, context and preferences of patients with multimorbidity, with the aim of prioritizing and sharing realistic treatment goals that guide an individualized management. The aim of this study is to evaluate the effectiveness of a complex intervention that implements the Ariadne principles in a population of young-old patients with multimorbidity and polypharmacy. The intervention seeks to improve the appropriateness of prescribing in primary care (PC), as measured by the medication appropriateness index (MAI) score at 6 and 12months, as compared with usual care. Methods/Design: Design:pragmatic cluster randomized clinical trial. Unit of randomization: family physician (FP). Unit of analysis: patient. Scope: PC health centres in three autonomous communities: Aragon, Madrid, and Andalusia (Spain). Population: patients aged 65-74years with multimorbidity (≥3 chronic diseases) and polypharmacy (≥5 drugs prescribed in ≥3months). Sample size: n=400 (200 per study arm). Intervention: complex intervention based on the implementation of the Ariadne principles with two components: (1) FP training and (2) FP-patient interview. Outcomes: MAI score, health services use, quality of life (Euroqol 5D-5L), pharmacotherapy and adherence to treatment (Morisky-Green, Haynes-Sackett), and clinical and socio-demographic variables. Statistical analysis: primary outcome is the difference in MAI score between T0 and T1 and corresponding 95% confidence interval. Adjustment for confounding factors will be performed by multilevel analysis. All analyses will be carried out in accordance with the intention-to-treat principle. Discussion: It is essential to provide evidence concerning interventions on PC patients with polypharmacy and multimorbidity, conducted in the context of routine clinical practice, and involving young-old patients with significant potential for preventing negative health outcomes. Trial registration: Clinicaltrials.gov, NCT02866799Publisher PDFPeer reviewe

Thermal conductivity of Anodic Aluminium Oxide (AAO) membranes with different pore diameters

Póster presentado en la 34th Annual International Conference on Thermoelectrics (ICT) y en la 13th European Conference on Thermoelectrics(ECT), celebradas en Dresden del 28 de junio al 2 de julio de 2015.Peer Reviewe

The effect of electrolyte impurities on the thermoelectric properties of electrodeposited Bi2Te3 films

An increase of up to 2.5 times in the power factor can be obtained just by using different high purity Te reagents from different suppliers. The obtained results demonstrate that the incorporation of trace impurities from the Bi2Te3 electrochemical bath play an important role in the thermoelectric properties of the film. To make that observation, bismuth telluride (Bi2Te3) films were electrodeposited under the same conditions, but using three different Te powder sources. All the powders tested have a nominal purity equal to or higher than 99.99%. In all the cases, we could achieve films with highly oriented along the [110] direction, with the same 2 to 3 Bi/Te ratio, and similar surface, and cross-sectional morphology. However, the thermoelectric properties (electrical conductivity, Seebeck coefficient, and thermal conductivity) depended strongly on the used tellurium powders sources used. Inductively coupled plasma mass spectrometry measurements were performed to determine which elements influence the final thermoelectric properties of Bi2Te3 films.Peer reviewe