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In this work the effect of different processing routes on the kinetics of formation of Co4Sb12 phase and Yb filling in the skutterudite cage, as well as thermoelectric behaviour was evaluated. As prepared slowly cooled ingot and rapidly solidified ribbons show the presence of multiple phases, as a consequence of the complex solidification path characterized by two peritectic reactions. As solidification rate increases, grain refinement is promoted. Annealing of rapidly solidified ribbons induces a faster solubilisation of Yb due to increased grain boundary diffusivity. For this reason, rapid solidification can be considered a promising intermediate step for lowering the total processing time of skutterudites. Sintering of powders obtained from the slowly cooled ingot and rapidly solidified ribbons leads to the formation of massive samples with different densities, depending on the particle size distributions of the starting powders. The effect of Yb content on the thermoelectric properties was critically analysed, considering both data from the literature and this work.

Efficient protection against degradation process of tetrahedrite-based thermoelectric materials was obtained employing AlTiN based thin films. The coatings were deposited via reactive direct current physical vapour deposition magnetron sputtering. The composition, thermal and electrical behaviour of thin films were investigated by X-ray diffraction, energy dispersive spectroscopy associated to field emission scanning electron microscopy, thermogravimetric analyses and electrical conductivity measurements. The barrier features for oxygen protection during thermal treatment in air at 500 °C were qualitatively evaluated, studying the coating behaviour over the higher operating temperature of tetrahedrite based thermoelectric devices.

A compositional and crystallographic study was carried out on the Smy(FexNi1&minus, x)4Sb11.5Sn0.5 filled skutterudite system (0.40 &le, x &le, 0.80) with the aim to determine the equilibrium Sm filling fraction (y) within the considered x range. The relevance of the material lies in its potential thermoelectric properties: in analogy with similar skutterudites systems, these features should in fact result as being improved with respect to the ones of the corresponding Sn-free system thanks to the partial substitution of Sn for Sb, which is expected to lower the phonon thermal conductivity. The results of Rietveld refinements allowed us to study the skutterudite structural properties and to discuss them, adopting a comparative approach with respect to the ones of the Sn-free system Smy(FexNi1&minus, x)4Sb12. Relying on the refined Sm occupancy factors, the p/n crossover is shown to be located at x ⁓ 0.53, meaning that the introduction of Sn induces an enlargement of the p-region, moreover, at variance with the Sn-free system, the coefficient of thermal expansion does not show any significant mismatch between n- and p- compositions, which should ensure a prolonged lifetime of a device made of n- and p- legs that both derive from the studied system.

Spiral and serpentine channels are a very interesting solution to enhance heat transfer in small or miniaturized heat exchangers. In order to properly design these devices, of course, it is essential having a good knowledge of heat transfer characteristics of forced flow through this kind of ducts. However, the data base in open literature is rather lacking being investigations concerning flow mainly restricted to Dean number less than 500 and specific geometric parameters. In order to overcome these limits, a CFD analysis of a laminar forced flow through serpentine mini-channels has been started using a commercial code at finite volumes, namely Ansys Fluent. In this paper, after discussing the preliminary CFD analysis carried out on a straight pipe to tune the tool, we present the results on a flow through a half- stadium serpentine mini-channel with Reynolds number ranging between 200 and 2000. As thermal boundary conditions, a uniform wall temperature is assumed on the flat wall of the half-stadium duct, whereas the others are adiabatic. Finally, simultaneously developing flow condition is adopted. Heat transfer performances and pressure drops have been compared with ones in the straight tube, with the same length and hydraulic diameter as the serpentine duct. The results show heat transfer capability increases due to the presence of curvature as well as an earlier transition from laminar to turbulent flow.

A structural study was performed by high temperature x-ray diffraction on samples of the filled skutterudite Smβ(FeαNi1-α)4Sb12 between 303 K and 773 K, i.e. in the range including the highest values of the dimensionless figure of merit ZT for this system. Samples were prepared by direct reaction of the pure elements at 1223 K, followed by an annealing treatment at 873 K. Morphology and composition of the obtained alloys were checked by SEM-EDS; the coefficient of thermal expansion (CTE) was calculated from the refined values of the cell parameter, and its trend as a function of the Fe amount revealed a discontinuity in proximity of the composition separating p- and n-skutterudites. Since the reduction of thermal stresses is a fundamental requirement for the lengthening of the thermoelectric devices lifetime, this evidence suggests useful hints for the choice of the most proper skutterudite compositions to be used in p- and n-legs. The effect of increasing temperature on other structural parameters, such as the shape of the Sb4 rings, is considered too and discussed in terms of filling degree of the cell.

Samples of a TiNiSn half-Heusler thermoelectric alloy were prepared using arc melting and rapid solidification by planar flow casting. On the one hand, arc melted samples show multiple phases and need long annealing time to be homogenized into a single phase. On the other hand, rapidly solidified samples show an almost single phase, with a grain refined microstructure. This result is a consequence of the melt undercooling, that allows to bypass the primary solidification of TiNi2Sn full-Heusler and to hinder grain growth. Rapidly solidified samples were consolidated into dense bulk samples by means of open die pressing. The grain refined microstructure obtained by rapid solidification is maintained after sintering, leading to a reduced lattice thermal conductivity, due to a scattering of phonons at grain boundaries. The role of the residual secondary phases (Ni3Sn4, TiNi2Sn and Sn) on the electrical conductivity and thermopower is discussed in the framework of the effective medium theory and related models, explaining the dispersion of thermoelectric properties observed in the literature for nominally stoichiometric TiNiSn. Thermal cycling above 700 K causes surface oxidation, leading to altered thermoelectric properties.

Tetrahedrite mineral family (Cu12Sb4S13), one of the most widespread sulfosalts on Earth's crust, seems to be an attractive sustainable source for p-type thermoelectric materials[1-3]. Unfortunately, beside phase decomposition with sulphur volatilization, oxidation of the tetrahedrite usually occurs in air atmosphere at its operating temperature range (RT- 450 °C)[4]. One way to overcome the problem of thermal degradation and consider tetrahedrite-based materials for practical devices operating in air atmosphere is material protection with oxidation-resistant thin films. In this work, an efficient protection against oxidative processes was obtained employing AlTiN based thin films. The coatings were deposited via reactive direct current physical vapour deposition magnetron sputtering. The composition, thermal and electrical behaviour of thin films were investigated by X-ray diffraction, energy dispersive spectroscopy associated to field emission scanning electron microscopy, thermogravimetric analyses, and electrical conductivity measurements. The barrier features for oxygen protection during thermal treatment in air at 500 °C were qualitatively evaluated, studying the coating behaviour over higher operating temperature of tetrahedrite based thermoelectric devices. [1]Battiston S, Fanciulli C, Fiameni S, Famengo A, Fasolin S, Fabrizio M. One step synthesis and sintering of Ni and Zn substituted tetrahedrite as thermoelectric material. J Alloys Compd 2017;702:75-83. doi:10.1016/j.jallcom.2017.01.187. [2]Fasolin S, Fiameni S, Fanciulli C, Battiston S, Famengo A, Fabrizio M. Nanostructured tetrahedrite synthesis for thermoelectric applications. J Nanosci Nanotechnol 2016;accepted:1645-9. doi:10.1166/jnn.2017.13733. [3]Lu X, Morelli DT. Natural mineral tetrahedrite as a direct source of thermoelectric materials. Phys Chem Chem Phys 2013;15:5762-6. doi:10.1039/c3cp50920f. [4]Gonçalves AP, Lopes EB, Montemor MF, Monnier J, Lenoir B. Oxidation Studies of Cu12Sb3.9Bi0.1S10Se3 Tetrahedrite. J Electron Mater 2018;47:2880-9. doi:10.1007/s11664-018-6141-9.

Skutterudites are a class of compounds promising in thermoelectric field. They are among the most studied thermoelectric materials of the last decade because related to the concept of electron-phonon-glass crystal. In literature there are many studies on Co-based skutterudites filled with Rare Earths (RE) (Ballikaya et al. 2012, Daniel et al. 2015, Zhang et al. 2015, Lili et al. 2015, Bhaskar et al. 2015) and Fe,Co-based (REFe4 -xCoxSb12) (Jacobsen et al. 2014, Zhang et al. 2015, Rogl et al. 2010a), while very few are the studies on Fe,Ni–based skutterudites (REFe4-xNixSb12) (Tan et al. 2013a, Kaltzoglou et al. 2012, Morimura et al. 2003). The name “Skutterudite” comes from a small mining town, Skutterud, in Norway where it was extracted and classified for the first time in 1845. The natural Skutterudite is a cobalt arsenide mineral that contains variable amounts of Ni and Fe, substituting for cobalt, having the general formula: (Co,Ni,Fe)As3. Its orogeny is hydrothermal, in moderate-high temperature; it is often found associated with other minerals such as Arsenopyrite, native Silver, Erythrite, Annabergite, Nickeline, Cobaltite, Silver sulfosalts, native Bismuth, Calcite, Siderite, Barite and Quartz. Its density is about 6.5 g/cm3 and the Mohs hardness is 6 but these values strictly depend on the composition. Synthetic skutterudites are now produced in laboratory. They include compounds having the composition MX3, where M is a transition metal of the VIII, IX, X group and X represents a pnitogen atom belonging to the XV group. Oftedal in 1928 identified CoAs3 as the first synthetic skutterudites and determined its structure as a cubic body-centered cell and space group . CoAs3 is now reported as the prototype compound for skutterudites. The modelling of skutterudite properties has been the subject of a large number of publications over the past decades. In this review we will only consider a limited set of results pertaining to Fe- or Ni-based skutterudites. This choice aims at preserving coherence with the experimental section of this chapter that mainly deals with these types of compounds.

The Half-Heusler phases within the Density Functional Theory (DFT) could be divided into three parts. The first part consists of chemical bonding evaluation using semi-empirical extended Hückel tight-binding method. The second part contains thermodynamic calculations using heat of formation obtained from the total energy calculations and temperature dependences of the entropy, free energy and enthalpy from phonon calculations in quasiharmonic approximation. The third part includes physical properties calculation using the linear response techniques in Korringa-Kohn-Rostocker method with Coherent Potential Approximation and analysis of Density of States spectrum (DOS). The interpretation of the chemical bonding is made via the analysis of the distribution of the DOS and defining the overlapping states of each element. The complex utilization of different DFT methods allows predicting the main thermoelectric properties of half-Heusler materials. Combination of theoretical DFT methods with experimental techniques gives the key for better understanding the nature of thermoelectric phenomena in half-Heusler materials.

We present a systematic study of the superconducting properties of high quality V3Si thin films, grown by high vacuum pulsed laser deposition from a stoichiometric target, a technique never reported in literature for this compound. By changing both the substrate (crystal structure and orientation) and the deposition conditions (substrate temperature, target-substrate distance, laser frequency and pulse energy) the critical temperature and the resistivity values of the samples have been finely tuned. Best results (TC = 16.1 K and Residual Resistivity Ratio RRR = 8.5) are obtained for deposition temperatures higher than 1200degC on both LaAlO3 and MgO substrates. All the samples are polycrystalline, that however does not affect the good quality of the transport properties. The possibility of multiband superconductivity in this compound is investigated, probing as a function of temperature: (i) the critical field up to 28 T using voltamperometric measurements, and (ii) the superfluid density via magnetic penetration depth measurements with a single coil inductive technique operating in the MHz region.

Skutterudites form a class of promising compounds in the field of thermoelectrics. They are among the most studied thermoelectric materials of the last decade because related to the concept of electron-phonon-glass crystal. In literature there are many studies on Co-based skutterudites filled with Rare Earths (RE) (Ballikaya et al. 2012; Daniel et al. 2015a; Zhang et al. 2015; Lili et al. 2015; Bhaskar et al. 2015) and Fe, Co-based (REFe4-x Co x Sb12) (Jacobsen et al. 2014; Zhang et al. 2015; Rogl et al. 2010a), while there 325are very few the studies on Fe, Ni-based skutterudites (REFe4-x Ni x Sb12) (Tan et al. 2013a; Kaltzoglou et al. 2012; Morimura et al. 2003).

The risk factors and clinical features of patients with Candida tropicalis fungaemia have not been fully defined. We performed a case-control study comparing 59 cases of C. tropicalis fungaemia with 177 episodes of fungaemia caused by other species of Candida in our hospital over a 24-year period (January 1985 to December 2008). Patients with C. tropicalis fungaemia were more likely to be older (median age, 67 vs. 56 years; p0.01), to have cancer (45.5% vs. 31.6%, p0.04), and to have the abdomen as the portal of entry (32.2% vs. 11.9%, p0.001), and had a higher in-hospital mortality rate (61% vs. 44%, p0.03). Multivariate analysis showed that the independent risk factors for C. tropicalis fungaemia were cancer (OR 4.5; 95% CI 1.05-3.83; p0.03) and the abdomen as the portal of entry (OR 13.6; 95% CI 1.9-8.2; p

The solid state magnetic properties of two new molecular organic materials based on polyfluoro- acridines functionalised with the 2,2,6,6-tetramethyl piperidine-1-oxyl radical (TEMPO) have been ana- lyzed. After a first characterisation of the two materials by electron paramagnetic resonance and by X-ray diffraction, magnetisation measurements were performed from room temperature down to 2 K and the paramagnetic behaviour due to the unpaired spin on the radical TEMPO observed. Both compounds show some ferro-magnetic interactions down to 40 K, while at lower temperatures an antiferro-magnetic contribution switches on, possibly related to the reduction of intermolecular distances.

In dc and ac practical applications of MgB2 superconducting wires, an important role is represented by the material sheath that has to provide, among other things, a suitable electrical and thermal stabilization. One way to obtain a large-enough amount of low-resistivity material into the conductor architecture is to use it as the external sheath. In this paper, we study ex situ multifilamentary MgB2 wires fabricated with oxide-dispersion-strengthened copper (GlidCop) as the external sheath in order to reach a good compromise between critical current density and thermal properties. We prepared three GlidCop samples with different contents of dispersed submicroscopic Al2O3 particles. We characterized the superconducting and thermal properties, and we showed that the good thermal conductivity, together with the good mechanical properties and a reasonable critical current density, makes the GlidCop composite wire a useful conductor for applications where high thermal conductivity is required at temperatures above 30 K, such as superconducting fault-current limiters.

A structural study of the filled skutterudite Smy(FexNi1-x)4Sb12 was performed by means of X-ray powder diffraction and μ-Raman spectroscopy with the aim to unveil the correlations between structural and electronic properties of this material and to favor the improvement of its thermoelectric performance. Samples were prepared by direct reaction of the elements at 1223 K, followed by quenching and subsequent sintering at 873 K; microstructure and composition of the obtained products were determined by SEM-EDS. The position of the boundary separating regions that obey hole- and electron-based conduction mechanisms was found by X-ray diffraction at x ≈ 0.63 and y ≈ 0.30, confirmed by measurements of room-temperature Seebeck coefficient, and discussed on the basis of crystallographic data. The presence of a discontinuity is observed in several structural and spectroscopic parameters at the p/n crossover; it is interpreted as associated with the change in the conduction mechanism. The role of the rare earth filling fraction in driving the structural response of the material is investigated too. The advantage of using X-ray diffraction and μ-Raman spectroscopy as aids in the study of electronic properties of this material is highlighted, as well as the complementarity of the two techniques.

Many conventional thermoelectric materials are anisotropic: the structural complexity, useful to improve the material efficiency, often leads to a strong dependence of the material properties on the different spatial direction considered. This aspect, lately subject of increasing interest, has been often neglected in the study of polycrystalline samples, because of their randomly oriented grain structure. Recently, looking for further improvements in thermoelectric efficiency, techniques for the sintering of polycrystalline samples able to preserve the natural anisotropy of the compounds have been studied and developed. The common target is to produce bulk samples easier to deal with as respect to single crystals, with improved thermal and mechanical properties, preserving the optimal electrical characteristics. In some cases, the latter depending on the crystallographic direction considered. The present work offers a short review of the results obtained for material texture induction using different techniques, focusing on solutions involving a mechanical processing. Large space is given to the open die pressing sintering technique. The technique results to be effective in material texturing and allows to produce polycrystalline large bulks preserving the anisotropy of electrical properties. Both structural analyses and microscopy display strong orientation of the material after sintering. In case of anisotropic materials, thermoelectric analyses performed on processed samples cut in the appropriate direction produced results comparable to the best one reported in literature.

MgB2 tapes have been synthesized through the ex-situ Powder-In-Tube (PIT) method. This technique involves the cold working of tubes of various metals-in this case Ni-previously filled by suitably reacted MgB2 powders, followed by proper heat treatments. In particular, it allows the use of different starting powders and the control over their properties. We studied the influence of the starting powders on the superconducting properties of the final conductors, and we tried to improve their behavior in magnetic field by mastering their grain size and by inserting appropriate doping. In order to improve the pinning properties of the tapes, the granulometry has been varied through ball-milling of MgB2, and different dopants-such as carbon or SiC nanoparticles-, have been introduced either on the precursors or on MgB2. Critical current measurements on the tapes are presented, both magnetic from the SQUID and transport in high magnetic field. In particular, TV characteristics have been measured up to 13 Tesla at GHMFL (Grenoble) in order to extract the critical current in two directions, i.e. with the field perpendicular and parallel to the tape surface.

A nonmagnetic sheath, namely a Ni/Cr alloy (Ni80/Cr20), was used to fabricate MgB/sub 2/ tapes through the powder-in-tube (PIT) ex-situ technique. A series of samples sintered at different temperatures between 200/spl deg/C and 950/spl deg/C were prepared in order to correlate all the superconducting properties between them and with the sintering temperature. The possibility of using a nonmagnetic but at the same time hard sheath chemically compatible with the MgB/sub 2/ phase made possible a simpler interpretation of transport and magnetic measurements in magnetic field. With the chosen cold working parameters, we found that the amount of MgB/sub 2/ lattice strain was not sufficient to produce any enhancement of the upper critical field. The effect of the heat treatment temperature was on one hand to increase the grain connectivity but also to reduce the pinning properties of the superconductor.

In this work, sintering of Zn4Sb3 was performed by open die pressing at 558 K, investigating the role of different starting materials (powders obtained from slowly cooled master alloy ingots or rapidly solidified ribbons) on microstructure, phase stability, thermoelectric properties and mechanical properties. With respect to the master alloy, sintered samples show lower porosity, a slight decrease in Zn content and a partial decomposition of Zn4Sb3 into ZnSb and Zn. Sintering of ground rapidly solidified ribbons further reduces porosity and partially inhibits the decomposition of Zn4Sb3. As sintered samples show a temperature behaviour of the Seebeck coefficient that is intermediate between those of Zn4Sb3 and ZnSb. Thermal cycling between 300 K and 700 K favours the homogenization of the microstructure, due to the recombination of ZnSb and Zn into Zn4Sb3, leading to a Seebeck coefficient typical of Zn4Sb3 single phase. The phase evolution observed upon sintering and thermal cycling is described in terms of competing reactions ruled by thermodynamics and kinetics, and the different behaviour of the samples is explained by the different free energy level of the starting materials. All samples show a brittle behaviour upon stress-strain compressive test and microindentation measurements. A remarkable increase of the fracture strength is observed as the porosity decreases, whereas microhardness values are similar for all samples (220–240 HVN). For the sintered samples, values of the indentation fracture toughness (0.8–0.9 MPa m1/2) are estimated from the length of Palmqvist-type radial cracks.

A current challenge in the thermoelectric field is the discovery of new materials which are inexpensive, easy to synthesize, and comprised of earth-abundant elements. Recently natural mineral tetrahedrites received great interest from thermoelectric community because of their non-toxicity, environmental friendliness and relatively high abundance. Natural "tetrahedrite" exists as a solid solution of tetrahedrite (Cu12Sb4S13) and tennantite (Cu12As4S13), where the Cu atoms are partially replaced by transition metal elements such as Zn, Fe, Mn, Hg or Ni [1-3]. The tetrahedrite/tennantite mineral family is the most widespread sulfosalt on Earth. The ZT values obtained for pure synthetic tetrahedrite Cu12Sb4S13 is 0.56 at 673 K [4]. Synthetic tetrahedrites were variously doped, with interesting results for Ni doped samples with a maximum ZT of 0.7 at 665 K for Cu10.5Ni1.5Sb4S13 [5]. All the synthesis reported in thermoelectric literature are based on a direct melting method starting from pure constituent elements and are characterized by high pressures, high temperatures and long time (up to 2-3 week) [4-6]. In this work, we developed a new fast synthesis and sintering method to obtain Ni-Zn substituted tetrahedrite pellets by means of the combination of ball milling and open die pressing sintering (ODP) methods [7]. X-Ray diffraction (with a profile Rietveld refinements) and Scanning Electron Microscope (equipped with energy dispersive X-Ray spectroscopy) were employed for a structural, morphological and compositional characterization of the obtained samples. Furthermore, the samples were thermoelectric characterized by electrical conductivity and Seebeck coefficient measurements, and Laser Flash Analysis for the thermal conductivity

Nowadays, the real challenge in the thermoelectric field seems to be the identification of efficient thermoelectric materials which should be inexpensive, easy to synthesize, and comprised of Earth-abundant elements. On this basis, tetrahedrite mineral family (Cu12-xTrxSb4S13 where Tr= Cu, Mn, Fe, Co, Ni, Zn), one of the most widespread sulfosalts on Earth's crust, seems to meet the right features for an attractive p-Type Pb-free thermoelectric material, showing a relatively high conversion efficiency [1, 2]. Working on the synthetic geomimetic tetrahedrites is useful to improve the knowledge about this peculiar material, leading to understand how enhance it and how to exploit the natural tetrahedrite mineral more effectively. In this work, both Zn and Ni cations were employed as substituents, according to the stoichiometry Cu10Zn2-xNixSb4S13, by means of ball milling treatment of sulphide precursor powders and one step simultaneous synthesis and sintering by Open Die Pressing [3]. This process is a scalable simple and fast route that lasted few hours, a very short time if compared with those reported in literature so far. The influence of the stoichiometry, the synthesis conditions and the reactive consolidation process parameters on the tetrahedrite phase content and density of the samples were investigated by X-ray diffraction (with a profile Rietveld refinements) and scanning electron microscope (equipped with energy dispersive X-ray spectroscopy). Furthermore, the thermoelectric functional properties of the samples were investigated by electrical conductivity and Seebeck oefficient measurements and Laser Flash Analysis for the thermal conductivity.

Nowadays, the real challenge in the thermoelectric field seems to be the identification of efficient thermoelectric materials which should be inexpensive, easy to synthesize, and comprised of Earth-abundant elements. On this basis, tetrahedrite mineral family (Cu12-xTrxSb4S13 where Tr= Mn, Fe, Co, Ni, Zn), one of the most widespread sulfosalts on Earth's crust, seems to meet the right features for an attractive p-Type Pb-free thermoelectric material, showing a relatively high conversion efficiency [1-2]. Both solid state reaction and solvothermal synthesis approaches were employed for a fast and easy way for Ni-Zn substituted tetrahedrite development. Reactive open die pressing was employed for consolidation of the material [3]. The influence of the stoichiometry, the synthesis conditions and the reactive consolidation process parameters on the tetrahedrite phase content and density of the samples were investigated by X-ray diffraction (with a profile Rietveld refinements) and scanning electron microscope (equipped with energy dispersive X-ray spectroscopy). The thermoelectric properties of the samples (electrical conductivity and Seebeck coefficient measurements, and laser flash analysis) were also performed. Furthermore, the thermal stability of the material was investigated by thermal analyses. References: [1] X. Lu, D.T. Morelli, Physical Chemistry Chemical Physics, 15 (2013) 5762-5766. [2] [1] X. Lu, D.T. Morelli, Y. Xia, V. Ozolins, Chemistry of Materials, 27 (2015) 408-413.. [3] Ceresara, S., C. Fanciulli, F. Passaretti, D. Vasilevskiy. Journal of Electronic Materials 42(7) (2013) 1529-1534.

The Zn4Sb3 phase is considered one of the most interesting compounds for thermoelectric applications in the intermediate temperature range (400-600 K) because of its very low thermal conductivity. Typical processing routes of this mate- rial for technological applications require several steps, in order to obtain a homogeneous single phase with fine microstructure. In this work, melt spinning was used as an intermediate processing step for improving the structural homogenization and microstructure refinement of Zn4Sb3. The effect of rapid solidification on the phase stability and microstructure was investigated. Melt-spun samples show, on the one hand, other crystalline phases in addition to the expected Zn4Sb3-type phase, probably because the high cooling rate did not allow the system to reach the thermodynamic equilibrium. On the other hand, rapid solidification induced a remarkable decrease of crystallite size down to the nanoscale, as estimated by the peak broadening in the X-ray diffraction patterns and shown by scanning electron micrographs. Additionally, the presence of an irreversible exothermic peak in the differential scanning calorimetry (DSC) trace can be likely related to the crystallization of a small amount of amorphous phase, formed as a result of the high cooling rate that could not be detected by XRD.

Research directed to innovative solutions for the national electric system are carried out in many CNR Institutes. In this project, many CNR research groups collaborated to develop a small cogeneration system, environmentally and economically sustainable, which could be integrated into the National grid. For the CHP cogenerator, we have opted for the internal combustion engine that is one solution with highest possibilities of success, thanks to the maturity and reliability of these systems. A prototype engine (15-25 kWe) has been designed deriving from an automotive engine of the latest generation, fuelled by very robust but low cost industrial natural gas. The CHP generator has been improved with unconventional technology and plant solutions that allow increasing the life service, heat and electrical performance, reducing noise and size. More in detail, the studies have been devoted to the w ear reduction through the development of special nanolubricants and of protective hard coatings; to the heat recover by means of innovative metallic foam heat exchangers; to improve the heat and acoustic insulation by means of low-cost geopolymers. The work is funded by the Project MATEC in the framework of a Research Program for the National Electric System.

A current challenge in the thermoelectric field is the discovery of new materials which are inexpensive, easy to synthesize, and comprised of earth-abundant elements. First works regarding Tetrahedrite mineral family (Cu12-xTrxSb4S13 where Tr= Mn, Fe, Co, Ni, Zn), the most widespread sulfosalts on Earth, showed as they could be attractive for thermoelectric application, possessing considerably high values of figure of merit ZT (nearly 1 at 445 °C) among p-Type Pb-free sulphides, mainly due to the intrinsic low lattice thermal conductivity [1-3]. For these reasons, the direct use of natural tetrahedrite mineral could be very appealing way for purchasing an inexpensive and earth-abundant TE material with high conversion efficiency. [1, 4] In this work a solvothermal synthesis was developed for tetrahedrite materials optimizing the synthesis procedures in order to obtain single phase tetrahedrites. Moreover, a preliminary sintering process was performed by means of Open Die Pressing. Structural, morphological, compositional, and functional properties of the material were carried out by X-Ray Diffraction, Field Emission Scanning Electron Microscopy (coupled with Energy Dispersion Spectroscopy), Laser Flash Analysis and electrical conductivity and Seebeck coefficient measurements, respectively. Further thermal analyses were carried out in order to understand the behaviour of the synthesized powders up to 500 °C. References: [1] X. Lu, D.T. Morelli, Physical Chemistry Chemical Physics, 15 (2013) 5762-5766. [2] X. Lu, D.T. Morelli, Y. Xia, F. Zhou, V. Ozolins, H. Chi, X. Zhou, C. Uher, Advanced Energy Materials, 3 (2013) 342-348. [3] K. Suekuni, K. Tsuruta, M. Kunii, H. Nishiate, E. Nishibori, S. Maki, M. Ohta, A. Yamamoto, M. Koyano, Journal of Applied Physics, 113 (2013). [4] X. Fan, E.D. Case, X. Lu, D.T. Morelli, Journal of Materials Science, (2013) 1-11.

Magnesium diboride (MgB/sub 2/) pancake coils and solenoids have been constructed and tested. The magnets have been wound using the react and winding technique. The magnets have been tested in liquid helium bath up to the quench currency. In this paper the coils and their behavior is discussed.

We present a study concerning the partial substitution of yttrium at the lanthanum site of the undoped LaFeAsO and superconducting ${\text{LaFeAsO}}_{0.85}{\text{F}}_{0.15}$ compounds. We prepared samples with a nominal yttrium content up to 70% producing simultaneous shrinkage of both the $a$- and $c$-lattice parameters by 1.8% and 1.7%, respectively. The chemical pressure provided by the partial substitution with this smaller ion size causes a lowering of the spin density wave temperature in the undoped compounds, as well as an increase in the superconducting transition temperatures in the doped ones. The 15% fluorine-doped samples reach a maximum critical temperature of 40.2 K for the 50% yttrium substitution. Comparison with literature data indicates that chemical pressure cannot be the only mechanism which tunes drastically both ${T}_{\text{SDW}}$ and ${T}_{c}$ in 1111 compounds. Our data suggest that the structural disorder induced by the partial substitution in the La site or by doping could play an important role as well.

We measure magnetotransport of F doped SmFeAsO samples up to 28T and we extract the upper critical fields, using different criteria. In order to circumvent the problem of criterion-dependence Hc2 values, we suggest a thermodynamic estimation of the upper critical field slope dHc2/dT based on the analysis of conductivity fluctuations in the critical regime. A high field slope as large as -12T/K is thus extracted for the optimally doped sample. We find evidence of a two-dimensional lowest Landau level (LLL) scaling for applied fields larger than mu_0H_LLL=8T. Finally, we estimate the coherence length values and we observe that they progressively increase with decreasing Tc. In all cases, the coherence length values along the c axis are smaller than the interplanar distance, confirming the two-dimensional nature of superconductivity in this compound., 14 pages, 4 figures, 3 tables Submitted to Phys.Rev.B

We report measurements of resistivity, magnetoresistivity, Hall effect, Seebeck coefficient, infrared reflectivity of undoped SmFeAsO and lightly doped SmFeAs(O0.93F0.07) oxypnictides. All the properties measured on SmFeAsO are characterized by clear signatures of the magnetic instability. A self-consistent picture emerges in which below the magnetic transition carrier condensation occurs due to the opening of spin density wave (SDW) gap. This is accompanied by the mobility increase of not gapped carriers due to the suppression of electron-electron scattering. SmFeAs(O0.93F0.07) exhibits an increase of the metallic character on cooling consistent with electron doping, even though at room temperature values of all the properties nearly overlaps with those of SmFeAsO. However, with temperature decrease all anomalies related to the SDW instability are missed and the superconducting transition occurs. This suggests that doping breaks abruptly the symmetries of the Fermi surface inhibiting the SDW formation in favor of the superconducting transition, with no substantial changes in the density of states or in the effective mass., Comment: Submitted to SUST

The grain size and the grain boundaries play an important role in determining the pinning properties and the current carrying capability of MgB2. Here we present an experimental study on the effect of grain oxidation on the superconducting properties of MgB2 ex-situ Powder-in-Tube (PIT) tapes. We fabricated Fe-sheathed monofilamentary tapes using a variety of powders synthesized in inert (IA) or oxidizing (OA) atmosphere. In order to understand the role of magnesium oxide (MgO) we studied the effect of the presence of the oxidation layer on the field dependence of the critical current density. To this purpose, we developed a process for the powder synthesis and tube filling and sealing in controlled atmosphere to reduce the oxygen contamination; with this process the connectivity of the grains in the final tapes proved to be increased. Then, we introduced a controlled oxidation step. We will show how the presence of the MgO layer enhances the critical current field dependence. High energy X-ray diffraction measurements were performed on the samples, and the grain size of the unsintered and sintered powders in the tapes was measured by means of Scanning Electron Microscopy (SEM). The pinning force was studied, and different mechanisms were found for the samples prepared in IA and OA. The different behavior shown by the two different typologies of tapes was correlated with the presence or absence of the MgO layer.

Ex-situ Powder-In-Tube MgB2 tapes prepared with ball-milled, undoped powders showed a strong enhancement of the irreversibility field H*, the upper critical field Hc2 and the critical current density Jc(H) together with the suppression of the anisotropy of all of these quantities. Jc reached 104 A/cm2 at 4.2 K and 10 T, with an irreversibility field of about 14 T at 4.2 K, and Hc2 of 9 T at 25 K, high values for not-doped MgB2. The enhanced Jc and H* values are associated with significant grain refinement produced by milling of the MgB2 powder, which enhances grain boundary pinning, although at the same time also reducing the connectivity from about 12% to 8%. Although enhanced pinning and diminished connectivity are in opposition, the overall influence of ball milling on Jc is positive because the increased density of grains with a size comparable with the mean free path produces strong electron scattering that substantially increases Hc2, especially Hc2 perpendicular to the Mg and B planes., Comment: 26 pages, 9 figures, submitted to J. Appl. Phys

Equal Channel Angular Extrusion (ECAE) was tested on as-cast Bi0.85 Sb0.15 alloys of different purity (4N and 5N), with the aim of eliminating microstructure inhomogeneities (Sb segregation on dendrite arms). The homogeneity degree promoted by hot plastic deformation was monitored by optical microscopy, SEM, X-ray diffraction, differential thermal analysis and electron microprobe analysis. After 6 ECAE passes at 523 K no trace of dendrites was observable at optical microscope; the micro-homogeneity, however, improved with further increasing the number of passes. High density material was obtained, with an average grain size of about 20 ?m. In the temperature range of 90 to 300 K, the variation of the Seebeck coefficient of the ECAE processed alloys, prepared from 5N purity starting elements, approaches the behaviour of single crystals of similar composition; at temperatures above 150 K, the figure of merit is higher than in single crystals.

We report the synthesis and the physical characterization of p- and n-type thermoelectric oxides, i.e. respectively NaxCoO2 with x nominally close to 0.75 and LaNi1-xCoxO3 with x nominally equal to 0.3, materials that can be used to build unicouples and therefore thermoelectric modules. In order to take advantage of the anisotropy of the NaxCoO2 crystal structure and of the resistivity, the Powder- In-Tube method usually used to fabricate superconducting tapes has been employed for the first time to produce thermoelectric wires and tapes, also based on the similarity between the thermoelectric Cobalt Oxides and the superconducting cuprates. Connectivity was improved through drawing, while texturing was induced in tapes through flat-rolling. This made it possible to significantly reduce the resistivity value, thus enhancing the power factor and the figure of merit of such oxides. Various cold working procedures have been exploited: this method is a fast, reliable way to produce TE legs on a large scale and it has been applied also to the production of the n-type LaNi1-xCoxO3.

We study the effect of neutron irradiation on the critical current density Jc of isotopically pure polycrystalline Mg11B2 samples. For fluences in the range 1017-1018 cm-2, Jc is enhanced and its dependence on magnetic field is significantly improved: we demonstrate that, in this regime, point-like pinning centers are effectively introduced in the system proportionally to the neutron fluence. Instead, for larger fluences, a strong suppression of the critical temperature accompanied by a decrease of both the upper critical field Bc2 and Jc is found., 13 pages, 3 igures

In order to use MgB2 conductors for AC applications, research and development efforts have to be carried out on their architecture and sheath material to minimize the AC losses. This paper will present the fabrication and characterization of two types of ex situ powder-in-tube processed pure MgB2 conductors with properties making them good candidates for AC industrial applications: a multifilamentary tape with 12 filaments with a twisting pitch down to 17 mm and a 361-filament wire with an average single-filament size of about 30 µm. Concerning the twisted tapes we will present values of critical current density of about 105 A cm−2 at 4.2 K and 2 T and we will show that it is possible to achieve a proper compromise between the tape size, the twisting pitch length and the critical current density to face a reduction of the critical current density as a consequence of the strain on the filaments. Concerning the 361-multifilamentary wire we will show appreciable values of critical current density of about 5 × 104 A cm−2 at 4.2 K and 2.5 T which, together with the advantages given by the high number of very thin filaments and the non-magnetic matrix, could justify their employment.