Giornate sulla Termoelettricità

Giorna te sulla Te rm oe le ttricità
19-20 FEBBRAIO 2014
Au l a Bl u , Ar e a d e l l a Ri c e r c a d i Pa d ova
Cor s o St a t i Un i t i 4, 35127 Pa d ova
2° incontro sui materiali e dispositivi termoelettrici
e
assemblea costituente dell’Associazione Italiana di
Termoelettricità
Programma e abstract
Comitato Scientifico ed Organizzatore
Simone Battiston (CNR IENI PD), Stefano Boldrini (CNR IENI PD), Vincenzo Buscaglia
(CNR IENI GE), Matteo Codecasa (CNR IENI Lecco), Monica Fabrizio (CNR IENI PD),
Stefania Fiameni (CNR IENI PD), Dario Narducci (Univ. MI-Bicocca)
sito internet: gite.cnr.it
info: [email protected]
Programma Giornate sulla Termoelettricità 2014
Mercoledì 19 febbraio 2014
9:45 bus navetta da stazione ferroviaria di Padova ad Area della Ricerca CNR
10:00 registrazione
10:40 Apertura dei lavori (Monica Fabrizio, CNR-IENI Padova)
Sessione Materiali I (chairman: Monica Fabrizio, CNR-IENI Padova)
11:00 Dario Narducci (Università Milano-Bicocca) “Enhancement of the Power
Factor in Silicon-Silicon Boride Nanocomposites”.
11:20 Luciano Colombo (Università di Cagliari) “Lattice Thermal Conductivity of
SiGe Nanocomposites”.
11:40 Giovanni Pennelli (Università di Pisa) “Thermal Conductivity Measurements of
Silicon Nanostructures For Thermoelectric Applications”.
12:00 Stefano Cecchi (CNR-IMM, Agrate Brianza) “The Cross-Plane Thermoelectric
Properties of p-Ge/Si0.5Ge0.5 Superlattices”.
12:20 Andrea Tona (Politecnico di Torino) “A Comparison of Thermoelectric
Devices Evaluation Results Obtained with a Harman Method Based and a Porcupine
Method Based ZT Meters”.
12:40 Giovanna Trevisi (CNR-IMEM, Parma) “Cross-Plane Thermal Conductivity in
III-V Epitaxial Superlattices: The Role of Composition”.
13:00 pranzo
Sessione Materiali II (chairman: Giovanni Pennelli, Università di Pisa)
14:30 Guida Faglia (Università di Brescia) “Thermoelectrical Properties of ZnO(n)
and CuO(p) Nanowires for Micropower Generation”.
14:50 Alberto Castellero (Università di Torino) “Effect of Structure and
Microstructure on the Thermoelectric Properties of Yb0.19Co4Sb12 Alloy”.
15:10 Carlo Fanciulli (CNR-IENI, Lecco) “Improvement of Mechanical Properties of
Zn4Sb3 by Melt Spinning and Open Die Pressing”.
15:30 Riccardo Carlini (Università di Genova) “Preliminary Investigation on a New
Thermoelectric Device Based on Polymeric Materials”.
15:40 pausa caffè
16:10-19:00 Assemblea costituente dell’Associazione Italiana di Termoelettricità
(chairman Dario Narducci, Università Milano-Bicocca):
(a) Presentazione dell’Associazione
(b) Discussione e approvazione del Regolamento
(c) Elezione degli organi statutari
(d) Discussione sugli indirizzi operativi
19:10 bus navetta da Area della Ricerca CNR a centro di Padova
20:45 cena sociale (centro di Padova)
Giovedì 20 febbraio 2014
8:45 bus navetta da centro di Padova ad Area della Ricerca CNR
Sessione Dispositivi (chairman: Vincenzo Buscaglia, CNR-IENI Genova)
9:30 Alvise Miozzo (CNR-IENI, Padova) “Multiphysics modeling of silicide-based
thermoelectric generators”.
9:50 Andrea Montecucco (Università di Glasgow, Regno Unito) “Maximum Power
and Efficiency Converters without Battery for Thermoelectric Generators”.
10:10 Matteo Codecasa (CNR-IENI, Lecco) “Issues and Solutions for Testing and
Characterization of Unconventional Thermoelectric Devices”.
10:30 Alessandro Bellucci (CNR-IMIP, Montelibretti) “fs- and ns-Laser Deposition
of Thermoelectric Materials: An Unusual Approach for the Fabrication of Energy
Conversion Devices”.
10:50 pausa caffè
Sessione Materiali III (chairman: Stefano Boldrini, CNR-IENI Padova)
11:30 Vincenzo Buscaglia (CNR-IENI, Genova) “Transport and Thermoelectric
Properties of BaNbxTi1-xO3 (x = 0 – 0.1) Ceramics”.
11:50 Ilenia Giuseppina Tredici (Università di Pavia) “Synthesis and
Characterization of Some Thermoelectric Oxides”.
12:20 Paolo Mele (Università di Hiroshima, Giappone) “Nanostructured Thin Films
of Zinc Oxide for Thermoelectric Applications”.
12:40 Simone Battiston (CNR-IENI Padova) “Magnesium oxide uptake in Mg2Si
thermoelectric pellets and their protection by thin coating at middle-high temperatures”.
13:00 pranzo
14:00 – 16:00 Tavola rotonda: “Ricerca, progettualità e industrializzazione nel settore
termoelettrico in Italia” (con la partecipazione di Riello Group, Indesit e Confindustria
Emilia Romagna).
16:00 Candidature per l’organizzazione delle Giornate della termoelettricità 2015.
17:00 Chiusura dei lavori.
17:15 bus navetta da Area della Ricerca CNR a Stazione ferroviaria di Padova.
Mercoledì 19 Febbraio 2014
Abstract delle presentazioni
ENHANCEMENT OF THE POWER FACTOR IN SILICON-SILICON BORIDE
NANOCOMPOSITES
D. Narducci1*, B. Lorenzi1, R. Tonini2, S. Frabboni2,3, G.C. Gazzadi3, G. Ottaviani2, A. Roncaglia4,
M. Ferri4, and F. Suriano4
1
Dip.di Scienza dei Materiali, Univ. di Milano Bicocca, Milano, 2Dip. di FIM, Univ. di Modena e
Reggio Emilia, Modena, 3CNR, Istituto di Nanoscienze−S3, Modena, 4IMM–CNR, Bologna
*[email protected]
The precipitation of silicon boride around grain boundaries was anticipated to lead to an increase of
the power factor (PF) in nanocrystalline silicon [1-4]. Such an effect was modeled showing that the
formation of an interphase at the grain boundaries can actually lead to a concurrent increase of the
electrical conductivity σ and of the Seebeck coefficient S because of the microscopic distribution of
thermal gradients within the material [5-6]. In this communication we report recent evidence of the
key elements ruling such an unexpected effect. Nanocrystalline silicon films deposited onto a
variety of substrates were doped to nominal boron densities in excess of 1020 cm-3 and were
annealed up to 1000 °C to promote boride precipitation. Thermoelectric properties were measured
and compared with their microstructure. A concurrent increase of σ and S with the carrier density
was actually found only upon formation of an interphase. Its dependency on the film microstructure
and on the deposition and processing conditions will be discussed.
References
[1] D. Narducci et al., 8th Eur. Conf. on Thermoelectrics, Como, (2010), 141.
[2] D. Narducci et al., MRS Proc., 1314, mrsf10-1314-ll05-16.
[3] D. Narducci et al., J. Solid State Chem., 193 (2012) 19.
[4] D. Narducci et al., AIP Conf. Proc., 1449 (2012) 311.
[5] N. Neophytou et al., J. Electron. Mater., 42 (2013) 2393-2401.
[6] N. Neophytou et al., Nanotechnology, 24 (2013), 205402.
LATTICE THERMAL CONDUCTIVITY OF SiGe NANOCOMPOSITES
Luciano Colombo1*and Claudio Melis1
1
Dipartimento di Fisica, Universita' di Cagliari - 09042 Monserrato (Ca)
*[email protected]
We calculate the lattice thermal conductivity in model Si1-xGex nanocomposites by molecular
dynamics in a transient thermal conduction regime, simulating systems with unprecedented size.
Our simulations provide evidence that thermal transport depend only marginally by stoichiometry in
the range 0.2≤x≤0.8, while it is deeply affected by the granulometry. In particular, we show that
Si1-xGex nanocomposites have lattice thermal conductivity below the corresponding bulk alloy with
same stoichiometry.
The main role in affecting thermal conduction is provided by grain boundaries, which largely affect
vibrational modes with long mean free path, as quantitaively proved by the explicit calculation of
the thermal conductivity accumulation function.
THERMAL CONDUCTIVITY MEASUREMENTS OF SILICON NANOSTRUCTURES
FOR THERMOELECTRIC APPLICATIONS
G.Pennelli1*, A. Nannini1, M.Macucci1
1
Dipartimento di Ingegneria dell'Informazione, Universita' di Pisa
Via G.Caruso16, I-56122 PISA
*[email protected]
Silicon is the second most abundant element on the Earth surface, it is a very sustainable and
biocompatible material and it is very well known from the technological point of view for its
pervasiveness in the electronic market. However, the application of silicon to thermoelectric
conversion is currently limited by its high thermal conductivity (148 W/mK), principally due to the
lattice conductivity that can be strongly reduced by means of nanostructuring. Silicon nanowires
(SiNW) exhibit a thermal conductivity as low as 1 W/mK[1], and offer interesting prespectives for
high efficiency thermoelectric devices, that could exploit the high reliability of large-area
interconnected networks of nanostructures[2] (see the SEM images of figure 1). Our group used
these macroscopic devices for measuring the Seebeck coefficient S at the nanoscale, obtaining
relevant indications about the nanowire doping and electrical transport properties[3].
Several techniques for the reduction of thermal conductivity, such as the increase of the surface
roughness, have been suggested. However, techniques for the reliable measurement of the thermal
conductivity kt of nanowires still need to be developed. We will show that the application of
conventional 3w techniques to silicon structures is difficult, due to the strong non-linearity of the
electrical conductivity with respect to temperature. Here we present a measurement technique,
based on nanowire self-heating, which allows to estimate kt for a single nanowire, by applying a
numerical model to simple I-V measurements. We present kt measurements on top-down fabricated
silicon nanowires, that are not affected by any temperature drop due to the thermal resistance of
contacts. Figure 2 shows SEM images of a SiNW before and after the measurement, that has been
performed up to the SiNW local fusion for self-heating. The current and voltage values for which
the nanowire fails, due to local fusion, are coherent with the reduced thermal conductivity of the
nanowire.
Figure 1: Measurement of the macroscopic Seebeck
Figure 2: Local fusion of a SiNW due to self-heating,
coefficient of nanostructures, interconnected in a large
resulting from its reduced thermal conductivity
area array.
[1] A.I.Hochbaum, R.Chen, R.D.Delgado, W.Liang, E.C.Garnett, M.Najarian, A.Majumdar, P.Yang, Nature Letters 451, 163 (2008).
[2]M.Totaro, P.Bruschi, G.Pennelli, Microelectron. Eng. 97, 157 (2012).
[3]G.Pennelli, M.Totaro, M.Piotto, P.Bruschi, Nano Letters 13, 2593 (2013).
THE CROSS-PLANE THERMOELECTRIC PROPERTIES
OF P-GE/SI0.5GE0.5 SUPERLATTICES
S. Cecchi1*, L. Ferre Llin2, A. Samarelli2, T. Etzelstorfer3, E. Müller Gubler4,
D. Chrastina1, G. Isella1, J. Stangl3, J. Weaver2, P. Dobson2 and D. J. Paul2
1
L-NESS Politecnico di Milano, Polo Territoriale di Como, Como, Italy
2
Dept. of Electronics and Electrical Engineering, University of Glasgow, Glasgow, UK
3
Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Linz, Austria
4
Electron Microscopy ETH Zurich (EMEZ), Zurich, Switzerland
*[email protected]
The cross-plane electrical conductivities, Seebeck coefficients, and thermal conductivities of p-type
Ge/Si0.5Ge0.5 superlattices designed for thermoelectric generation at room temperature and grown
by low-energy plasma-enhanced chemical vapor deposition have been measured using microfabricated test structures [1]. Crystal quality and strain control have been investigated by means of
high resolution X-ray diffraction and transmission electron microscopy.
For superlattices featuring sub-nanometer thick barriers, the measured Seebeck coefficients are
comparable to bulk p-SiGe at similar doping levels, suggesting the holes see the material as a
random bulk alloy rather than a superlattice.
The thermoelectric properties as a function of the doping density have been studied for superlattices
with Ge quantum wells of nominally 2.85 nm and SiGe barriers of 1.5 nm. All investigated
structures have demonstrated higher Seebeck coefficients and lower thermal conductivities than
comparably doped bulk SiGe. A maximum ZT of 0.08 ± 0.011 has been measured at 300K.
A reduction in the strain between quantum wells and barriers has the potential to improve the
performances of the superlattices.
Figure 1. A STEM image of the grown Ge/Si0.5Ge0.5 superlattices
[1] L. Ferre Llin et al., Appl. Phys. Lett 103, 143507 (2013)
A COMPARISON OF THERMOELECTRIC DEVICES EVALUATION RESULTS
OBTAINED WITH A HARMAN METHOD BASED AND A PORCUPINE METHOD
BASED ZT METERS
Andrea De Marchi1, Valter Giaretto2, Simone Caron1, Andrea Tona1, Alberto Muscio3
1Dipartimento di Elettronica e Telecomunicazioni – Politecnico di Torino – Corso Duca degli
Abruzzi 24 – 10129 Torino
2Dipartimento Energia - Politecnico di Torino – Corso Duca degli Abruzzi 24 – 10129 Torino
3Dipartimento di Ingegneria “Enzo Ferrari”- Università di Modena e Reggio Emilia – Via
Vignolese 905 – 41125 Modena
e-mail: [email protected]
A comparison is presented of results obtained for the series resistance R and the dimensionless
figure of merit zT of a number of different thermoelectric devices with two instruments based on
alternative approaches. One is a commercial zT meter (DX 3065) manufactured by RMT and based
on the Harman method, and the other one is a prototype realized at the Politecnico di Torino and
based on the porcupine method1,2. All devices were evaluated with both instruments at three
different temperatures (20°C, 25°C and 30°C) in a climatic chamber, and results were compared. As
expected from the theoretical analysis1, the porcupine method consistently returned lower R values
than those obtained by the Harman approach. Values obtained for zT with the two instruments are
instead much more aligned, which is unexpected if thermoelectric effects are assumed to be
correctly accounted for. A discussion of such results is offered, with comments on extrapolations
which are introduced in both approaches in order to infer relevant quantities.
CROSS-PLANE THERMAL CONDUCTIVITY IN III-V EPITAXIAL SUPERLATTICES:
THE ROLE OF COMPOSITION
G. Trevisi1*, L. Seravalli1, P. Frigeri1, E. Buffagni1, F. Rossi1, C. Ferrari1, L. Nausner2, A. Rastelli2,
P.Chen2
1
CNR-IMEM Institute, Parma, Italy, 2Johannes Kepler University Linz, Austria
*[email protected]
Epitaxial superlattices (SL) offer an interesting model-system to study the dependence of thermal
transport on the characteristics of interfaces, also thanks to the great advancement in
characterization techniques that now allow the study of these mechanisms at the sub-µm scale.[1] A
deeper comprehension of phonon transport, together with the development of high ZT materials, is
highly desirable to allow the scalability of devices into local thermoelectric (TE) coolers integrated
into optoelectronic devices.[2] III-V compounds are appealing from both an applicative point of
view, for thermal management of III-V optoelectronic devices, and a fundamental one, since they
offer the possibility to study several parameters (interface roughness, atomic interdiffusion, strain)
by changing the SL composition and growth conditions.
We present the study of InAs/GaAs and AlAs/GaAs SLs grown on (100) GaAs substrates by
Molecular Beam Epitaxy with identical SL period; the results are compared to those obtained on
InxGa1-xAs and AlxGa1-xAs alloys with composition equivalent to that of the SLs (x = 0.058). The
structures’ properties are studied by low-temperature photoluminescence (PL) and high-resolution
X-ray diffraction (HRXRD) to evaluate their strain state, the atomic interdiffusion (typical of
InAs/GaAs SLs due to In segregation [3]) and the interface abruptness (typical of AlAs/GaAs SLs).
The cross-plane thermal conductivity (
200 K ≤ T ≤ 380 K range. Both types of SLs show a reduction of compared to the corresponding
bulk binaries and, in both cases, is not sensibly dependent on the number of periods composing
the SLs, suggesting that the phonon transport is incoherent.[1] When comparing the SLs to the
corresponding alloys, we observe that only the InAs/GaAs system allows a reduction of
with
respect to the InGaAs alloy, achieving a value of 8 W/(m*K) with only 5.8% of In in the structure.
Similarly to what happens in the SiGe system,[1] this behavior can be attributed to the effect of both
the SL interfaces and the atomic interdiffusion due to the large segregation of In in GaAs. The
AlAs/GaAs system, not characterized by the segregation phenomenon, does not show a distinct
reduction of (15-20 W/(m*K)) with respect to the alloy.
As a result of our work, we suggest that III-V SLs with reduced
can be effectively prepared
through suitable designs that aim at enhancing the atomic interdiffusion in the structures.
[1] P. Chen et al. Phys Rev Lett 111, 115901 (2013)
[2] I. Chowdhury et al. Nature Nanotech 4, 235 (2009)
[3] L. Seravalli et al. J Phys D-Appl Phys 46, 315101 (2013)
THERMOELECTICAL PROPERTIES OF ZNO(N) AND CUO(P) NANOWIRES FOR
MICROPOWER GENERATION
G. Faglia1*, S. Dalola2, E. Comini1, M. Ferroni1, D. Zappa1, V. Ferrari2, G. Sberveglieri1
1
SENSOR Lab, Dipartimento di Chimica e Fisica per l’Ingegneria e per i Materiali, Università
degli Studi di Brescia & INO CNR, Brescia, Italy
2
Dipartimento di Ingegneria dell’Informazione, Università degli Studi di Brescia, Brescia, Italy
*[email protected]
ZnO(n) and CuO(p) NWs have been investigated with the aim to build thermoelectric devices
based on NW arrays for energy harvesting and potential use in low-power portable electronics and
sensor systems. Until recently thermoelectric energy conversion was deemed less efficient than
steam engines and not suitable for energy harnessing. Latest results by Kraemer et al showed [1]
that solar thermoelectric generators may indeed become competitive with other solar power
conversion methods, demonstrating peak efficiency equal to 5.2%. Because of the very high
temperatures attained through concentrated sunlight, the results boosted the research of low cost
environmentally friendly materials for high temperature thermoelectrics.
Quasi 1D metal-oxide NWs (MOX) are formidable candidates to develop high-temperature
thermoelectrics as they provide reduced dimensionality and excellent durability at high temperature.
Five n-type (ZnO) and p-type (CuO) semiconducting thermoelectric element, wired electrically in
series and thermally in parallel have been deposited among the two sides of ceramic substrates.
Bundles of ZnO NWs have been deposited through Vapour-Phase (VP) and Vapour-Liquid-Phase
(VLS) growth. CuO NWs have been obtained on the same substrates starting from a metallic Cu
thin layer deposited by sputtering on alumina substrates. Thermal oxidation methods lead to copper
oxide NW with higher degree of crystallinity, as compared to others. The Seebeck coefficient of
ZnO and CuO NWs has been successfully measured with a purposely-developed experimental setup.
Authors gratefully acknowledge partial financial support by the IIT, Project Seed 2009 “Metal
oxide NANOwires as efficient high-temperature THERmoelectric Materials ”.
1. D. Kraemer et al Nature Materials 10 7 (2011), 532-538.
EFFECT OF STRUCTURE AND MICROSTRUCTURE ON THE THERMOELECTRIC
PROPERTIES OF Yb0.19Co4Sb12 ALLOY
A. Castellero1,*, M. Ostorero1, A. Ziggiotti2, M. Brignone2, M. Baricco1
1 Dipartimento di Chimica and NIS, Università di Torino, Torino, Italy
2 Centro Ricerche FIAT, Orbassano (TO), Italy
*[email protected]
In this work, we report results about the synthesis and characterization of the n-type Yb0.19Co4Sb12
thermoelectric alloy that is among the most promising materials for automotive applications with a
value of ZT ranging around 1 at about 330 °C.
Samples preparation consisted of a sequence of three steps: 1) solid/liquid reaction between the
pure elements at 660 °C in a resistance furnace; 2) complete melting in an induction furnace; 3)
annealing at 730 °C in a resistance furnace for 0.75h, 1.5h, 3h and 6h.
The non-annealed samples consist of a mixture of Sb, YbSb2, CoSb, CoSb2 and CoSb3 phases. Only
a fraction (about 50%) of the thermodynamically stable CoSb3 phase could be obtained by free
cooling of the melt. This is due to the complex solidification path, involving two peritectic
transformations, that did not allow the system to reach the equilibrium.
Annealing for 3-6 hours at 730 °C promotes the formation of the desired CoSb3-type phase up to
fractions around 98%.
Furthermore, the increase of the lattice parameter of CoSb3 with annealing time indicates that Yb is
progressively solubilized in the crystalline structure, as required for improving thermoelectric
properties.
After annealing the microstructure became more homogeneous and revealed the presence of
porosity that is independent on the annealing time.
Thermoelectric properties were measured between 30 °C and 230 °C. Increasing annealing times
brought to more negative values of the Seebeck coefficient, because of the higher fraction of the
Yb0.19Co4Sb12 thermoelectric phase. In the case of electrical conductivity, no clear trend as a
function of annealing time was observed.
The thermoelectric efficiency of the samples was estimated through the power factor. The values
obtained are between 2.0 and 3.7 mW K-1 m-1 at 230 °C, when the fraction of CoSb3 is around 98
%.
The brazing process of optimized Yb0.19Co4Sb12 ingots, coated with different diffusion barriers,
with a Cu electrode is under study.
IMPROVEMENT OF MECHANICANICAL PROPERTIES OF Zn4Sb3 BY MELT
SPINNING AND OPEN DIE PRESSING
C. Fanciulli1*, A. Castellero2, R. Carlini3, F. Passaretti1, M. Baricco2, G. Zanicchi3
1
CNR – Istituto per l'Energetica e le Interfasi, C.so Promessi Sopsi,29, Lecco, 2 Dipartimento di
Chimica e Chimica Industriale - Università di Genova and INSTM, Via Dodecaneso 31 16146
Genova, 3 Dipartimento di Chimica e Centro NIS - Università di Torino – via P. Giuria 9 - 10125
Torino
*Corresponding Author [email protected]
Recently, semiconducting intermetallic compounds, belonging to the Zintl’s Phases, have attracted
much attention due to their unexpectedly low thermal conductivity, which leads to improved
thermoelectric properties. The glass-like thermal conductivity of Zn4Sb3, originated in the
framework Zn position of its structure, make this compound one of the most studied phases in the
thermoelectric field. The reduction of grain size obtained by the melt spinning process can lead to
an improvement of Figure of the Merit-ZT but, unluckily, is associated with an increase of material
brittleness. This behavior is a heavy obstacle for its application in thermoelectric modules.
Here a new approach, aimed to obtain an improvement of the Zn4Sb3 mechanical performance is
proposed. The intermetallic, obtained through a simple route, have been processed using Open Die
Pressing (ODP) technique as bulk material or Melt Spun (MS) material. ODP has already been
successfully applied for fast chalcogenides powders sintering, the main feature of the process being
the low temperature involved and the short time required for sintering.
The stability of the pure β-phase Zn4Sb3 phase was investigated after both melt spinning and ODP
processes. All samples were studied in terms of crystal structure, phases composition, thermal
stability, mechanical resistance and thermoelectric properties.
The main result obtained, is the high improvement in mechanical behaviour of the material after
ODP processing: preserving thermoelectric properties of the material, we were able to increase
mechanical resistance of the bulk up to 11 times as respect to the starting as-cast bulk.
PRELIMINARY INVESTIGATION ON A NEW THERMOELECTRIC DEVICE BASED
ON POLYMERIC MATERIALS
Riccardo Carlini1,2,*, Roberto Masini3, Marina Alloisio1,2, PaoloMele4, Shrikant Saini4, Gilda
Zanicchi1,2, Giorgio Andrea Costa1,5
1
DCCI, University of Genoa, Via Dodecaneso 31, 16146 Genoa, Italy
INSTM – Genoa Research Unit of National Consortium of Materials Science and Technology, Via
Dodecaneso 31, 16146 Genoa, Italy
3
CNR-IMEM, Via Dodecaneso 33, 16146 Genoa, Italy
4
ISSD, Institute for Sustainable Sciences and Development, Hiroshima University, Kagamiyama 13-1 Higashi-Hiroshima, 739-8530 Japan
5
CNR-SPIN Genova, Corso Perrone 24, 16152 Genoa, Italy
2
*
Corresponding Author: [email protected]
Recently, organic materials have attracted much attention in the studies of thermoelectric
properties. The interest in thermoelectric properties of organic materials has been sparked for
several reasons. Conducting polymers possess several features that make them attractive: they are
lightweight, flexible, easy to process over large areas and cheap. In general, conjugated polymers
are semiconductors and show electrical conductivity after doping with suitable dopants. Through
modifications of their molecular structure, it is also possible to tune their physical and chemical
properties in a fairly large range, providing great material flexibility to meet the requirements of the
targeted applications. Finally, polymers generally possess a low thermal conductivity, which gives
them a potential advantage over conventional thermoelectric materials.
The main approaches in these researches are two: the design of thermoelectric devices composed of
conductive and polymeric elements and the design of modified metallorganic polymers.
Particularly in this work is considered and studied a thermoelectric device composed by a glass
support on which lays down a thin layer of polymer.
A poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) was selected as the
conductive polymer thank to its high conductivity, its significant thermal stability in the considered
temperature range and its strong solubility in water. Starting from an aqueous solution, it was
deposed onto the support using the Spin Coating technique. Afterwards a study on the thickness of
polymeric layer was carried out using the Ellipsometry Spectroscopy and Transmission
Spectroscopy. First results indicate layers thickness in the range of 100-500 nm. The polymer
stability depending on temperature was evaluated using Transmitted Light Spectrophotometry.
Thermoelectric evaluation of this preliminary device is in progress. Further step will be the addition
of nanoparticulate material to the polymeric matrix to improve the thermoelectric conversion of the
device.
Giovedì 20 Febbraio 2014
Abstract delle presentazioni
MULTIPHYSICS MODELING OF SILICIDE-BASED THERMOELECTRIC
GENERATORS
A. Miozzo1, S. Boldrini1, S. Battiston1, S. Fiameni1, A. Famengo1, A. Ferrario1, S. Barison1and M.
Fabrizio1
1
Institute for Energetics and Interphases - National Research Council of Italy
*[email protected]
The finite element method (FEM) represents an effective tool for solving coupled systems of partial
differential equations, performing multiphysics simulation. The thermoelectric effect can be
regarded as a multiphysics problem, since it involves different physical phenomena (heat transfer,
Joule heating, transport of electric charge) and further conditions may need to be taken into account
(heat flux between the thermoelectric material and the surrounding medium, elastic or inelastic
deformations with mid-high temperature, etc.) In this work, finite element analyses are performed
on uni-leg and multi-legs thermoelectric generators (TEG) with Mg2Si n-type and higher
manganese silicide (HMS) p-type elements. Thermal and electrical contact are taken into account
and defined in the models as boundary features. The simulation is carried out in two steps: (i)
evaluation of output power and conversion efficiency of uni-leg and multi-legs TEG; (ii) calculation
of thermal tensile stresses in the thermoelectric elements.
MAXIMUM POWER AND EFFICIENCY CONVERTERS WITHOUT BATTERY FOR
THERMOELECTRIC GENERATORS
A. Montecucco1,2,*, A. R. Knox1
1
TETRIC, School of Engineering, University of Glasgow, U.K., 2AMC.E3 LTD, U.K.
*[email protected]
This work aims at designing a small and low-cost power electronic converter to power a generic
electronic load from a temperature difference.
Thermoelectric generators (TEGs) are robust semiconductor devices able to produce electrical
energy from a temperature gradient. The quantity of electrical power and the voltage/current
characteristic depend on the temperature difference and the load applied to the TEG device.
Maximum Power Point Tracking converters can be employed to track the optimum electrical
operating point irrespective of the thermal operating point, at any time. They usually store the
harvested energy into supercapacitors or batteries. On the contrary the DC-DC converter presented
here does not make use of big storage devices. It provides a regulated output and maximises the
power produced by the TEGs only when the load is connected. When the load does not require
maximum power, the converter aims at running in maximum efficiency mode.
ISSUES AND SOLUTIONS FOR TESTING AND CHARACTERIZATION
OF UNCONVENTIONAL THERMOELECTRIC DEVICES
M.P. Codecasa1*, C. Fanciulli1, and F. Passaretti1
1
National Research Council of Italy (CNR), Institute for ENergetics and Interphases (IENI), Lecco,
Italy
*[email protected]
Thermoelectric materials may play a role in the large scale energy industry with the possibility to
effectively exploit waste heat recovery. Well established traditional thermoelectric material (based
on bulk Bi, Sb, Te, Se alloys), thermoelements ("p-Greek" p-n thermocouple, with p and n legs
thermally in parallel and electrically in series) and device configuration (thermopile of "p-Greek"
thermocouples) have been considered and evaluated in the past under this perspective, but their
success was considered unfeasible in the perspective of a potential mass production due to their
limits in conversion efficiency, high cost and low availability of raw material, and low specific
electrical output.
New thermoelectric devices (TEDs) based upon novel thermoelectric materials, thermoelement’s
new configurations and device’s new architectures are often proposed for their potential in
overcoming these limits thanks to improved conversion efficiency, improved specific electrical
output, extended material availability and reduced material cost.
The characterization of the performance of such TEDs often requires to update and adapt the
established methods, facilities and instruments, as well as to re-discuss the modelling of the
measure itself. Present work will discuss in detail all the issues faced for realization of a novel
characterization facility for properties and performance testing of new type of TEDs.
Fig. 1 - Panoramic view of the special characterization facility for thermoelectric devices (TEDs), and connected
instruments. From left to right: hydrostatic bath for liquid cooling; main framework (green painted) hosting the
calorimetric column of the flux meter (dismounted, in the picture), including the kinematics for the application of an
accurate, regulated and stable mechanical compression, and a precision scale for the measurement of the load; a multichannels multimeter datalogger for accurate monitoring of the temperature field and calorimetry in the flux meter;
power supplies for main and guard heaters in the flux meter, multi-scale electronic load for electric characterization of
the TEGs, and supplementary multimeter for manual checks; workstation for data logging and data analysis and post
processing.
FS- AND NS-LASER DEPOSITION OF THERMOELECTRIC MATERIALS: AN
UNUSUAL APPROACH FOR THE FABRICATION OF ENERGY CONVERSION
DEVICES.
A. Bellucci*1,2, P. Calvani1, E. Cappelli1, M. Girolami1, S. Orlando3, L. Medici4, A. Mezzi5, S.
Kaciulis5 and D.M. Trucchi1
1
2
CNR-IMIP, Via Salaria km 29.300, 00015 Monterotondo Scalo (RM) - Italy
Dipartimento di Fisica, Università di Roma la Sapienza, Piazzale A. Moro 2, I-00185 Rome, Italy
3
CNR – IMIP, U.O.S. Potenza, Zona Industriale di Tito Scalo, 85050 Tito Scalo (PZ), Italy
4) CNR–IMAA, Zona Industriale, 85050 Tito Scalo (PZ), Italy
5) CNR –ISMN, Via Salaria km 29.3, 00015 Monterotondo Stazione, Rome, Italy
*[email protected]
In this work, different PbTe-based thin films deposited by pulsed laser (fs-Ti:Sapphire and ns-ArF)
deposition (PLD) on Al2O3 and SiO2 were investigated. The aim of the work is to determine the
optimal conditions for the achievement of nano-structured thermoelectric materials with high
figure-of-merit ZT, exploiting the advantage of this deposition technique to realize complex native
nanostructured films with good stoichiometry. A detailed analysis of the best deposition parameters
will be shown as well as a study of the doping level (p-type and n-type), the substrate temperature
and the effects of post-deposition processes, such as thermal annealing. Moreover, a comparison
between the two pulsed laser sources will be presented. Chemical composition (X-ray Photoelectron
Spectroscopy, XPS), structure (X-ray diffraction, XRD), morphology (Atomic Force Microscopy,
AFM) and transport properties (Seebeck coefficient, electrical and thermal conductivity) will be
evaluated in order to point out the possible competitive thermoelectric thin-film structures
compared to the classical bulk systems for the fabrication of thermal-to-electrical devices.
TRANSPORT AND THERMOELECTRIC PROPERTIES OF BaNbxTi1-xO3 (x = 0 – 0.1)
CERAMICS
M.T. Buscaglia1, M. Viviani1, V. Buscaglia1*, I. Pallecchi2, D. Marrè2,3
1
IENI-CNR, Via De Marini 6, 16149 Genova, 2SPIN-CNR, C.so Perrone 24, 16152 Genoa,
3
Department of Physics, University of Genova, Via Dodecaneso 33, 16146 Genoa
*[email protected]
Nanostructuration is one of the most successful strategies to improve the performance of
thermoelectrics. In particular, the formation of small inclusions or precipitates with size of the order
of a few tens of nm determines a strong decrease of the thermal conductivity in conventional
thermoelectrics such as PbTe, Bi2Te3 and silicon. An efficient scattering of the thermal phonons can
be realized in a special kind of ferroelectric ceramics called relaxors and characterized by the
existence of polar nanoregions (PNRs) with a size up to 10 nm. The aim of this study is to verify if
PNRs survive when the ceramic is annealed in a reducing atmosphere resulting in a material with
lower thermal conductivity and high electronic conductivity. Nb-doped BaTiO3 has been selected as
a model system as it shows a ferroelectric to relaxor crossover for a dopant concentration of about 5
mol.% and is a good electronic conductor in the reduced state.
Ceramic disks with composition BaNbxTi1-xO3 (x = 0, 0.025, 0.05, 0.075 and 0.1) and high density
(rel. dens. >95%) were prepared by a conventional solid state process and sintered in air at 1450°C.
The ceramics were then annealed at 1350-1450°C in a reducing Ar-5%H2 atmosphere to increase
their electrical conductivity.
The electrical conductivity, Seebeck coefficient and thermal conductivity were measured in the
range 10-380K. All ceramics exhibit n-type semiconducting behaviour. The measurements
performed on ceramics annealed in Ar-5%H2 at 1350°C show a decrease of thermal conductivity
(down to 4 Wm-1K-1) and an increase of electrical conductivity (up to 20 Scm-1) with increasing Nb
concentration up to x = 0.075. The Seebeck coefficient is relatively high (-150 to -200 VK-1).
Measurements on ceramics annealed at 1450°C are in progress.
SYNTHESIS AND CHARACTERIZATION OF SOME
THERMOELECTRIC OXIDES
I. G. Tredici1*, A. Soffientini1, C. Ferrara1, A. S. Cattaneo1, T. Costanzo1,
P. Ghigna1, U. Anselmi Tamburini1, P. Mustarelli1, G. Spinolo1
1
University of Pavia, Department of Chemistry, Viale Taramelli 12, I27100 Pavia, Italy
*[email protected]
Thermoelectric materials based on crystalline oxides have been receiving a growing attention in the
past few years due to their low environmental impact, low toxicity, high thermal stability and low
cost. Oxide materials can be prepared using a large number of different approaches allowing a good
control of their stoichiometry, nano/microstructure and defectivity. Their figure of merit is generally
quite low, but it can be enhanced reducing their thermal conductivity through the nanostructure or
the introduction of high local disorder.
Layered cobalt oxides, such as Ca3Co4O9 or NaCoO2, and strontium barium niobates, such as SBN
(SrxBa1-xNb2O6), also doped on the Nb sites, represent good candidates for this approach. The
electrical conductivity of SBN, however, is quite low, so we started a preliminary investigation
aiming to understand the role of doping in controlling the structure and the electrical properties of
this material.
In order to investigate the role of the nanostructure the key challenge is represented by the
possibility to obtain fully dense sintered bodies without significant grain growth. To achieve this
goal we applied the High-Pressure Field Assisted Rapid Sintering (HP-FARS) method. The starting
nanopowders have been synthesized by wet chemistry methods.
The phase structure and purity of the obtained powders and sintered materials have been
characterized by X-ray diffraction, while the morphology was checked by scanning electron
microscopy. The differences between local and average structure have been investigated, where
possible, by means of solid state NMR. The electrical conductivity and power factor were
characterized in the temperature range of 25 °C - 800 °C.
The local chemical environment of doping atoms in the SBN structure was investigated by EXAFS
at the K edge of the pertinent elements.
NANOSTRUCTURED THIN FILMS OF ZINC OXIDE
FOR THERMOELECTRIC APPLICATIONS
P. Mele1*, S. Saini1, H. Honda1, K. Matsumoto2, K. Miyazaki2, H. Hagino2,A. Ichinose3, L. Molina4,
P. E. Hopkins5, J. E. Ihlefeld6
1
Hiroshima University, 2 Kyushu Institute of Technology, 3 CRIEPI, 4 Technical University of
Darmstadt, 5 University of Virginia, 6 Sandia National Laboratory
*[email protected]
We report on substrate dependence of thermoelectric properties for 2% Al-doped ZnO (AZO)
nanostructured thin films.
We fabricated ~500 nm thick films by means of Pulsed Laser Deposition on SrTiO 3 (STO) and
Al2O3 single crystals and fused silica amorphous substrates at Tdep = 300°C, 400°C, 500°C and
600°C keeping an oxygen pressure of 27 Pa. Dense AZO target was irradiated by Nd:YAG laser
(266 nm, 10 Hz) which energy density is about 4.2 J/cm2 for deposition period of 30 min. Electric
conductivity () and Seebeck coefficient (S) were evaluated in the interval T = 300 - 600 K. The
films deposited on Al2O3 are epitaxial and fully c-axis oriented showing only (002) peak in 
XRD patterns, independently of Tdep. Films deposited on STO are c-axis oriented for Tdep 
400°C, though at higher Tdep a-axis orientation (110 peak) also appears. Also on amorphous silica
thin films are fully c-axis oriented and epitaxy is reached for low deposition temperatures. TEM
images demonstrate typical columnar growth of the films independently from the substrate. 
presents a clear semiconducting behavior on STO and silica, while is almost constant with T for the
films grown on Al2O3. S sign is always negative, confirming the n-type conduction due to Al3+
substitution, and his absolute value increases with Tdep. At the same Tdep, films deposited on silica
always shows much higher values of S2 (power factor) in comparison with films deposited on
Al2O3 and STO. For example, at Tdep= 300 °C and T = 600 K, (S2)silica = 1.2 W/m.K2, (S2)STO =
0.55 W/m.K2 and (S2)Al2O3 = 0.02 W/m.K2.
To justify the behaviour of film deposited on crystalline substrates, we invoked the epitaxial strain
effect: AZO film has larger epitaxial strain (caxis ~ 18%) and larger concentration of dislocations
[1] (N ~ 1011 cm-2) on Al2O3, while caxis ~ 6%, aaxis ~ 2% and N ~1010 cm-2 for AZO on STO.  is
reported to decrease and S to increase with N [2]: this consideration explains the different behavior
of the two films. Since silica is amorphous, is not possible to calculate epitaxial strain; however
dislocations density is expected to be lower than on crystalline substrates [3], which explains the
enhancement of thermoelectric performance.
[1] P. Mele et al, Appl. Phys. Lett. 102 (2013) 253903
[2] J. M. Woodall et al, Phys. Rev. Lett. 51 (1983) 1783
[3] M Novotny et al, J. Phys. D: Appl. Phys. 45 (2012) 225101
MAGNESIUM OXIDE UPTAKE IN Mg2Si THERMOELECTRIC PELLETS AND THEIR
PROTECTION BY THIN COATING AT MIDDLE-HIGH TEMPERATURES
S. Battiston1,*, S. Boldrini1, T. Sakamoto2, A. Famengo1, A. Miozzo1, S. Fiameni1, A. Ferrario1, S.
Barison1, T. Iida2, M. Fabrizio1.
1
CNR - IENI, Corso Stati Uniti 4, 35127 Padova, Italy; 2Department of Materials Science and
Technology, Tokyo University of Science, 6-3-1, Niijuku, Katsushika-ku, Tokyo 125-8585, Japan.
*[email protected]
The magnesium silicide (Mg2Si) based alloys are promising candidates for thermoelectric (TE)
energy conversion in the middle-high temperature range. These materials are a candidate to replace
lead-based TE materials due to the abundance of their constituent elements in the earth’s crust, their
nontoxicity and their low density [1].
The drawback of such kind of materials is their oxygen sensitivity at high temperature [2, 3] that
entails their use under vacuum or inert atmosphere. In this work, the influence of pellet features on
the MgO uptake and the protection of the silicide pellets, coated via magnetron sputtering, are
discussed.
X-Ray Diffraction, Energy Dispersive Spectroscopy, Field Emission Scanning Electron microscope
(FE-SEM), themorgravimetric analysis, and electrical measurement at high temperature were
carried out in order to obtain, respectively, the structural, compositional, morphological and
electrical characterization of the pellets and coatings. The mechanical behavior of the system thin
film/Mg2Si-substrate as a function of temperature and the coating barrier properties for oxygen
protection were qualitatively evaluated by FE-SEM after thermal treatment in air at high
temperature.
References
[1] T. Sakamoto, T. Iida, N. Fukushima, Y. Honda, M. Tada, Y. Taguchi, Y. Mito, H. Taguchi, Y.
Takanashi, Thin Solid Films, 519 (2011) 8528-8531.
[2] J. Tani, M. Takahashi, H. Kido, Thermoelectric properties and oxidation behaviour of
Magnesium Silicide, in, Osaka, 2011.
[3] S. Battiston, S. Boldrini, S. Fiameni, A. Famengo, M. Fabrizio, S. Barison, Thin Solid Films,
526 (2012) 150-154.
Acknowledgments.
The authors are grateful to Dr Rosalba Gerbasi (CNR-ICIS) for XRD spectra.
This work has been funded by the Italian National Research Council - Italian Ministry of Economic
Development Agreement “Ricerca di sistema elettrico nazionale” and a Grant-in-Aid for JSPS
Fellows awarded by the Japan Society for the Promotion of Science.
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