Materials by design for energy applications through theory and experiment

Resume : Recently, the silicate olivine family (Li2MSiO4, where M = Fe, Mn, and Co) has been extensively studied as cathode materials for lithium ion batteries because of its high theoretical capacity ~ 300 mA g-1. Despite this promising feature, a major bottleneck in these materials is their low electronic conductivity. In the present work Li2CoSiO4 was synthesized by the sol-gel method using Polyacrylic acid as the chelating agent and nanocomposite was prepared by adding MWCNT as conductive additive. MWCNTs were refluxed in concentrated H2SO4/HNO3 (3/1 v/v) at 50º C for 5 hrs to prepare carboxylic acid functionalized MWCNTs and then washed with ultrapure water. After the treatment, the functionalization yield of the oxygen-containing groups such as carboxylic group on the surface of the MWCNTS was quantified by EDX analysis. The composite electrode was prepared by ball-milling Li2CoSiO4 with functionalized MWCNTs in NMP to enhance homogeneous mixing. BMPyTFSI solutions of LiTFSI having a concentration of 0.2 mol kg-1 was used as electrolyte. Electrochemical performance of the cathode material was evaluated by fabricating CR2032 lithium coin cell with lithium foil as the anode and 0.2M LiTFSI-BMPyTFSI solution as the electrolyte. The reversible electrochemical reaction of the composite electrode material studied by cyclic voltammetry and the results of galvanostatic charge/discharge studies at 0.01C rate are also discussed. Keyword: MWCNT, Li2CoSiO4, BMPyTFSI

Resume : Metal oxides offer a rich family of materials that are abundant, cheap, easy to produce and stable. They hence attract high research interest with applications for catalysis, sensors, photovoltaics and many others. The number of possible combinations of binary and ternary oxides is enormous and only small fraction of them is known. While many photovoltaics cells include metal oxides as part of the system, producing a cell that is made of just oxides is still a very difficult task. This is because the material needs to fulfill specific demands for the band gap, conductivity, excited states life time, band alignment and more. In this talk I will describe how a high throughput experimental setup is connected to theoretical calculations, traditional and high throughput, for the task of finding novel oxide materials that would enable better oxide based photovoltaic cells.

Resume : Inorganic-organic perovskite (CH3NH3PbI3) solid state solar cells have received immense interest due to their high photovoltaic conversion efficiencies of close to 15 %. Generally, spiro-OMeTAD, an organic molecule is used in these devices as the hole transporting material. Copper thiocyanate (CuSCN) which has higher hole mobility than spiro has not been explored as a suitable replacement. Apart from the high hole mobility, CuSCN is also cheaper and more robust to degradation in ambient conditions. In this report, we demonstrate both normal and inverted CuSCN based perovskite solar cells processed by solution based methods. We study the correlation of nanostructuring in CuSCN on the device performance. We also investigate the advantages and limitations of both normal and inverted configurations. This study also opens new windows for further exploration of CuSCN as a hole transporter in perovskite based solar cells.

Resume : Metal nanoparticles (NPs) exhibit extraordinary optical resonances: when excited by electromagnetic radiation they can show localized-surface-plasmon-resonance (LSPR) due to the collective oscillations of their conduction electrons. The possibility of tuning the LSPR wavelength through the visible to near infrared region makes metal NPs promising for technological applications. Also light scattering is another optical property of metal NPs that is of interest and it is used as a powerful tool in biological and molecular recognition and to increase the light trapping in thin-film Si and organic solar cells for achieving a higher photocurrent. In addition to pure metal NPs, also, metal/dielectric core/shell NPs are studied in this sense. In fact, for core–shell NPs, the position of the LSPR and the angular-dependent scattered light intensity can be tuned by varying the ratio between the core radius and the shell thicknes. In this work, we focus our attention, in particular, on the light scattering properties of Ag/Ag2O, Al/Al2O3, Cu/Cu2O, Pd/PdO, and Ti/TiO2 core/shell NPs as a function of the core radius/shell thickness ratio and on a relative comparison. We report theoretical results about the angle-dependent light scattering properties of spherical NPs on the basis of a generalized Mie approach. The results can be of help in the design of tunable efficiency light scattering devices (biological and molecular sensors, solar cells).

Resume : Rapid decline of fossil fuels and increasing environmental pollution as well as increasing the amount of waste and lack of appropriate methods of collection and the elimination of waste and increasing co, co2 and sulfur in the air from the consequences of burning garbage and fossil fuels that increase the temperature of the atmosphere and many problems for society has created.This article tries to overcome these problems with thermal energy recycle waste using plasma arc methods have in some way to go high temperature bonds between the molecular material and power breakdown is not resistance The decomposition process must be very high temperatures (thermal plasma), and without the presence of oxygen (Pyrolisis) will be done. Move in this article how to break down without oxygen and process waste elimination system by the plasma arc, forming arc plasma reactor and gas-forming major components of the waste elimination system and economic and environmental results we have discussed that Saving fossil fuels and fuel conservation for future generations and environmental pollution to a considerable size and reduces the remains of recyclable materials can be used as raw materials in the industry that makes its economy Efficiency of industrial raw materials are. This way, as a significant waste volume reduction has found hazardous waste disposal will be followed

Resume : Productivity growth of wind energy as a clean source needed to achieve improved strategy in production and transmission and management of wind resources in order to increase quality of power and reduce costs. New technologies based on power converters that cause changing turbine speed to suit the wind speed blowing turbine, improve extraction efficiency power from wind. This article introduces variable speed wind turbines and optimization of power, and is presented methods to use superconducting inductor in the composition of power converter and is proposed the dc measurement for the wind farm and especially is considered techniques available to them. In fact, this article reviews mechanisms and function, changes of wind speed turbine according to speed control strategies of various types of wind turbines and examines power possible transmission and ac from producing location to suitable location for a strong connection Integrating wind farm generators, without additional cost or equipment. Also covers main objectives of the dynamic control of wind turbines, and the methods of exploitation and the ways of using it that including the unique process these components. Effective algorithm is presented for power control in order to extracting maximum the active power and maintains power factor at the desired value.

Resume : Rechargeable lithium-oxygen batteries with high theoretical energy density are an attractive energy storage technology that could realize long-range electric vehicles. In general, a lithium-oxygen battery consists of a Li metal anode, a Li+-conducting electrolyte, and a porous cathode. In addition to providing chemical and mechanical protection of Li metal, the battery design presents many challenges associated with electrolytes, including non-volatility, moisture insensitivity, and air stability. In this work, we report quasi-solid-state lithium-oxygen batteries constructed using polymer gel electrolytes with ionic liquids. Dimensionally stable, elastic, non-volatile, hydrophobic polymer gel electrolytes are synthesized using LiTFSI, ionic liquid, and PVdF-co-HFP. Quasi-solid-state lithium-oxygen batteries are constructed with the prepared polymer gel electrolyte, and their discharge-charge performances are analyzed. The electrolyte stability, which is of potential concern, is discussed.

Resume : The rechargeable Li-air battery is a promising candidate for next-generation energy storage devices. One of the technical challenges that must be achieved for the use of the Li-air in practical applications is its operation in ambient air environment. Currently, most of the research work comprises either the use of pure oxygen to feed the cell or tests performed in a controlled, dried atmosphere. In this way, the cell is not subjected to the presence of moisture responsible for the unwanted corrosion of the lithium anode. Traces of carbon dioxide can also penetrate into the cell and generate carbonate species that may accumulate at the cathode surface. We developed protective membranes to optimize the performance of the cathode. Polyvinylidene difluoride, PVDF membranes were prepared via non-solvent induced phase separation. Such membranes were already in themselves hydrophobic and porous. Incorporation of sacrificial silica nanoparticles (SiO2NPs) into the precursor solution, followed by their removal, resulted in a more careful control of the porosity. The hydrophobic character of the membranes was not affected by the SiO2NPs removal, which resulted in alveolar-like structures responsible of the homogeneous porosity of the membrane. These features make such membranes promising for their use as moisture-preventing agents and the results obtained by cycling the Li-air cell along with their benefits will be presented.

Resume : In the present study we show the results of theoretical studies of the thermoelectric phenomena in the granulated semiconductors. Recently, solar and thermal energy conversion technologies based on solid-state electronics tend to employ rather low-dimensional systems. To describe properly thermoelectric effects in low-dimensional semiconductors, we propose an effective medium model (EMM) of heterogeneous semiconductor medium comprising biphasic granules – semiconductor crystal grains covered by insulator nanofilms. The phase of a granule is characterized by its electric and heat conductivities, σi and χi respectively, Seebeck factor αi, typical size di, and efficiency of thermoelectric transformation Zi (i=1,2). We write expressions for estimation of effective parameters σeff, χeff, αeff and Zeff based on the linear Onsager thermodynamic considerations and analyze their values depending on degree of asymmetry of the granule components. In the framework of this method the more complicated ternary medium is considered as well. The studies show that a narrow necking path for electric and thermal currents is the tunneling contacts at the boundaries, and thus we consider in particular details the role of the resonance levels due to the tunneling contacts. We also study the possibility for optimization of the studied medium properties under various technological conditions, applying electron beams and -irradiation. The developed model has been tested on the samples of microgranular silicon with various sizes of the grains. We show that irradiation is a perfect tool to control the effective medium properties. A satisfactory agreement of EMM with our previous experiments has been obtained.

Resume : Nowadays, solar cell technology attracts much attention in reliable and high efficiency photovoltaic applications. Thin-film SiGe solar cells have important advantages such as high photocurrent and their compatibility with the process developed for pure Si cells. In order to improve the electrical efficiency performances of the conventional SiGe solar cell, we have introduced a new multi-trench technique. In the proposed method, the multi-trench is created in the silicon layer and filled with n-type doped SiGe. The p-type trenches under the SiGe layer improve the electrical performance of the proposed design. By 2-D numerical simulation, we have investigated the electrical performances of the proposed design and compared with it a conventional thin-film SiGe solar cell. The proposed accurate numerical models have been used as objective function to optimize the electrical performance of the SiGe-based solar cell. The obtained results show that the proposed design can be considered as a potential candidate for high performance photovoltaic applications.

Resume : Density functional theory is an ideal method for the study of a large range of systems due to its balance between accuracy and computational efficiency, however the applicability of standard implementations is limited to systems of around 1000 atoms or smaller due to their cubic scaling with respect to the number of atoms. In order to overcome these limitations, a number of methods have been developed which use localized orbitals to take advantage of the nearsightedness principle and reformulate the problem in a manner which can be made to scale linearly with the number of atoms, paving the way for calculations on systems of 10,000 atoms or more. We have recently implemented such a method in the BigDFT code (http://bigdft.org), which uses an underlying wavelet basis set that is ideal for linear-scaling calculations due to it exhibiting both orthogonality and compact support. This use of wavelets also has the distinct advantage that calculations can be performed in a choice of boundary conditions - either free, wire, surface or periodic. This distinguishes it from other linear-scaling codes, which are generally restricted to periodic boundary conditions, and thus allows calculations on charged systems using open boundary conditions without the need for adding a compensating background charge. We will first outline the method and implementation within BigDFT, after which we will present results showing both the accuracy and the flexibility of the approach.

Resume : In this work, we investigated the physico-chemical properties of Cd-free CuIn7S11 and CuIn11S17 thin films in order to propose an alternative to the Cadmium Sulphide (CdS) as buffer layer for CuInS2 based solar cells. CuIn7S11 and CuIn11S17 thin films were deposited by single source vacuum thermal evaporation on glass substrates heated at different temperature. The structural, morphological, optical and electrical properties of thin films were studied using X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Vis spectroscopy and Hall-effect measurements. XRD results revealed that the samples deposited at room temperature were amorphous in nature while those deposited on heated substrates were polycrystalline with a preferred orientation along (311) plane of the spinel phase. The optical properties of the films were obtained from the analysis of the transmittance and reflectance data. All films exhibit a high optical transmission in the visible region. The band gap energy values of the CuIn7S11 and CuIn11S17 films decreases from 2.30 to 1.68 and from 2.54 to 1.95 eV, respectively, by increasing the substrate temperature. We exploited the models of Wemple-DiDomenico and Spitzer-Fan for the analysis of the dispersion of the refractive index and the determination of the optical constants of the films. Hall-effect measurements revealed that all films are p-type conductivity.

Resume : In this work, the effect of the substrate temperature on the structural and optical properties of the new sulfosalt Sn3Sb2S6 films deposited by thermal vacuum evaporation was studied. Sn3Sb2S6 thin films have been deposited onto glass substrates at various substrate temperatures in the range 30-160°C. The layers were analyzed by X-ray diffraction (XRD) and spectrophotometric measurements. They have a good crystallinity, homogeneity and adhesion. The optical constants were obtained from the analysis of the experimental recorded transmission and reflectance spectral data over the wavelength range 300-1800 nm. We found that by increasing the substrate temperature from 30 to 160°C, the optical band gap decreased from 1.47 to 1.18 eV. The absorption coefficients of the thin films are in the range of 105-106 cm-1. It was found that the refractive index dispersion data obeyed the single oscillator of the Wemple–DiDomenico model, from which the dispersion parameters and the high-frequency dielectric constant were determined. The electric free carrier susceptibility and the carrier concentration on the effective mass ratio versus the substrate temperature were estimated according to the model of Spitzer and Fan.. So, the new sulfosalt Sn3Sb2S6 material is a good candidate for photovoltaic applications as an absorber material.

Resume : One dimensional nanostructures nanotubes, nanowires, nanorods are expected to be ideal active components for nanometer-scale electronic and optoelectrontronic devices. Complex nanostructured materials such as heterostructured semiconductor nanowires are being extensively studied due to their promising properties for the development of novel nanoscale devices. These structures, together with extremely high quantum efficiency, exhibit increased possibility of manipulation of carrier localization in them by means of band-offsets and size variations. These facts imply high importance of core-multy-shell nanowires (CMS-NW) for optical application. A significant advantages in controlled growth of CMS-NW make their theoretical investigation relevant. In this paper the method for defining electronic structure of carriers in CMS-NW of cylindrical shape is presented. The method allows one to calculate single particle states of electrons and holes for arbitrary number of shells. The method is applied for ZnO/ZnMgO heretostructure. The choice of materials is condition by properties of ZnO (a direct wide band-gap -3.37 eV, high exciton binding energy – 60 meV) and I-type band-offst it forms with ZnMgO alloy.

Resume : Abstract We built a new microscale device based on the modulation of a cw laser beam for heating thin film thermoelectric samples. This compact micro ZT-meter allows a simultaneous measurement of the basic thermoelectric parameters: thermal conductivity (λ), electrical resistivity (ρ) and Seebeck coefficient (S). Our experiments could be conducted typically from room temperature up to 250 ?C. The samples are ZnO and TiOx thin films (close to 500 nm thick) grown by pulsed-laser deposition on Si substrates. The laser heating induces two main thermal gradients that could give also simultaneously the in-plane and transverse thermoelectric parameters. Those first results will be discussed in this first part. On the other hand, we can find several techniques in literature that make it possible to improve the figure of merit ZT ( ). The nano-structuring by femto and nanosecond laser beam is a new way to improve the figure of merit ZT by the interface scattering of phonons leading to lower thermal conductivity., We will also study directly with the new micro ZT-meter the effect of the nanostructuration on the Seebeck coefficient and more globally on the enhancement of the figure of merit.

Resume : Silicon−germanium alloying is emerging as one of the most promising strategies to engineer heat transport at the nanoscale. The significant difference in the mass between Si and Ge atoms together with the similar electronic structure allows expecting an increase of the figure of merit ZT. Here, we perform first-principles electron transport calculations to assess at what extent such approach can be followed without worsening the electrical conduction properties of the system, providing then a path toward high-efficiency thermoelectric materials. On the basis of single-impurity scattering the assumption that Ge alloying does not affect significantly the conductance seems sound: (i) only interstitial defects act as efficient scattering centers, but their concentration is expected to be negligible; (ii) substitutional defects are easily incorporated in the Si lattice and the transport channels of the pristine wire are only marginally affected. Yet, in SiGe alloy NWs, Ge concentrations of up to 70% can be reached, thus we addressed explicitly the study of Si1−xGex, with x ranging from 0.1 to 0.7. The calculated conductances show that in all the cases alloyed SiGe NWs scatter carriers like abrupt inclusion of an all-Ge NW segment, with scattering concentrated at the interface. This is an important result, because abrupt junctions are difficult to obtain, while (random) concentration gradients can be obtained in an easier way. [1] M. Amato, et al., Nano Lett. 12, 2717 (2012).

Resume : Thermoelectric devices convert heat into energy and vice versa. For the better performance, good electrical conductivity and Seebeck coefficient are necessary with low thermal conductivity. The bulk silicon is a poor thermoelectric material due to the high thermal conductivity, ~150 W∙m-1∙K-1, at room temperature, giving ZT= 0.01 value. But, silicon is being on test for thermoelectric applications due to its well-developed semiconductor process technology and material abundance. Especially, silicon is still a valuable thermoelectric material in the low dimensional structures, such as nanowires because the thermal conductivity is expected to decrease by phonon scattering. In this study, we evaluated the thermoelectric properties of silicon nanowires (SiNWs) with different doping types, length (10 um, 40 um) and number of wires (1, 6 wires). For the measurement of Seebeck coefficients and power factors, we fabricated test structure including micro-heaters, temperature sensors and SiNWs. It takes advantages of using the semiconductor device manufacturing process. SiNWs have 50 nm widths which are smaller than the mean free path of the phonons (~ 100 nm) and yet larger than that of electrons (~ 5 nm). The optimized doping levels of SiNWs are ~1.2×10^20 cm-3 and ~3.5×10^20 cm-3 for n- and p- type, respectively. In the results, the best Seebeck coefficients and power factors are 113.83 μV/K, 0.67 mW∙m-1∙K-2 and -113.25 μV/K, 0.59 mW∙m-1∙K-2 for n- and p-type SiNWs, respectively.

Resume : We have investigated the broad class of half Heusler compounds. Our search through 79,057 different compositions has yielded 77 thermodynamically stable ternary compounds. We have calculated the bulk thermal conductivity for these compounds, employing a fully ab-initio approach [1]. For a large fraction of them the bulk thermal conductivities are much lower than those of known half Heuslers. We have developed several machine learning techniques that permit us to considerably reduce the computation time, while still being accurate enough for efficient screening. We have also estimated the thermoelectric figure of merit (ZT) of the compounds within the small grain approximation [2]. When compared with common semiconductors like Si, Ge, or the III-V compounds, half-Heuslers stand out due to having higher power factors. Estimated ZT’s suggest that for some of the nanograined half-Heuslers the figure of merit might reach values above 2. [1] J. Carrete et al., PRX (accepted). [2] J. Carrete et al., submitted.

Resume : Magnetic materials underpin a vast and diverse range of modern technologies, going from data storage to energy production and use. However, the choice of magnets for mainstream applications is limited to a few dozens and the development of a new high-performance magnetic compound is a long and often unpredictable process. Here we describe a systematic pathway to the discovery of novel magnetic materials for multiple applications, which demonstrates an unprecedented throughput and speed up in the discovery process. We have constructed a massive electronic structures library for Heusler alloys containing 236,856 materials. We have then extracted those magnetic compounds with specific electronic properties, such as half-metallicity and large magnetization density, and finally established whether these can be fabricated at thermodynamical equilibrium. Based on our analysis we have identified 249 stable new intermetallic Heuslers, including 21 new magnets. Our work paves the way for large scale design of novel magnetic materials at unprecedented speed.

Resume : In this presentation, we show how to use on-line resources to search for novel thermo- electrics, topological-insulators, magnets, and binary/ternary phase diagrams.

Resume : We found [1] that a CuO/CeO2 catalyst where the CeO2 carrier is nanocube-shaped, exposing the less stable (001) surface, has better selectivity than others where CeO2 exposes different surfaces in the purification of H2 from CO via preferential oxidation of the latter. Thus we have attempted to understand this phenomenon, which may help to better design the catalyst, using DFT simulations at the PBE+U theory level and periodic CeO2 slab models with CuOx wires lying on them to model the supported catalyst. We find that on CeO2(001) the Cu oxide wires adhere better and deform the CuOx structure more than on CeO2(111) due to the lower stability and higher reactivity of CeO2(001). The deformation and higher wetting effect in the latter case explains that no CuO peaks are seen in XRD for the CeO2 nanocubes-based sample, while they are seen when using a nanosphere-type CeO2 for similar surface Cu coverage. Besides, the progressive reduction of CuO to Cu2O and of the latter to Cu(0) is found to be less favourable on CeO2(001); this agrees with the higher selectivity to CO2 found for the nanocube-supported sample, since H2 activation and oxidation is assumed to require the Cu(0) redox state. In addition, upon anion vacancy formation the fraction of electrons released which goes to form Ce(3+) instead of reducing Cu is larger on CeO2(001) than on CeO2(111), which may have additional consequences for reactivity. [1] D. Gamarra et al., Appl. Catal. B: Environmental 130-131, 224 (2013).

Resume : High-throughput electronic structure calculations are more and more popular in materials science and in the design of new compounds. Electronic structure theory, like Density Functional Theory, can be efficiently used to calculate stabilities and electronic properties as bandgaps of new compounds. However, in practice, the methods are often limited to rather small atomic-scale systems or periodic crystals with only a limited number of atoms in the unit cell. It is therefore of interest to be able to derive generally useful information from simple systems to be applied in other, more complex, crystals. Here, we consider a large database of calculated stabilities and bandgaps of oxides and oxynitrides in the cubic perovskite structure previously studied as new materials for photoelectrocatalytic water splitting [1,2]. We use the database as a testing ground for existing ideas about the behavior of these types of compounds and we derive some new simple chemical-based rules which combine structural information, like the ionic radii of the chemical elements, with electronic data, like the number of electrons and the valences of the pure elements. The rules extracted from the ABO3 cubic perovskite are then tested using the ABO2N and A2BO4 stoichiometry in the cubic and layered perovskite structure, respectively. These rules allow a saving in computer time of around 80 %. [1] Energy Environ. Sci., 5, 5814 (2012). [2] Energy Environ. Sci., 5, 9034 (2012).

Resume : The ideal ferroic refrigerant is one that has a composition- and field-dependent phase transition with a large entropy change [1]. I will show how the search for suitable magnetic refrigerants leads to: a survey of novel critical and tricritical material systems [2,3], the development of characterisation tools to study first order phase transitions, and the use of hi-resolution neutron diffraction data as an ideal test of ab initio theories of finite temperature magnetism [4]. I will highlight the importance of tuning magneto-elastic coupling so as to: (a) exploit the full potential of magnetic cooling and (b) minimise the use of rare earth elements in the life cycle of a future magnetic refrigerator. [1] S. Fähler et al., Adv. Eng. Mater. 14 10-19 (2012). [2] K.G. Sandeman, Scr. Mater. 67 566-571 (2012) [3] A. Barcza et al., Phys. Rev. Lett. 104 247202 (2010) [4] J.B. Staunton et al., Phys. Rev. B 87 060404 (2013) The research leading to these results has received funding from the European Community's 7th Framework Programme under grant agreement Nos. 214864 (SSEEC) and 310748 (DRREAM).

Resume : First principles calculations of the vibrational, thermodynamic and mechanical properties of the Ni-Ti-Sn Heusler and half-Heusler compounds have been performed (RSC Advances, 3(44) , 2013, 22176-22184). First, we have calculated the Raman and infrared spectra of NiTiSn, providing benchmark theoretical data directly useful for the assignments of its experimental spectra and clarifying the debate reported in the literature on the assignment of itsmodes. Then, we have discussed the significant vibrational density-of-states of Ni2TiSn at low-frequencies. These states are at the origin of (i) its smaller free energy, (ii) its higher entropy, and (iii) its lower Debye temperature, with respect to NiTiSn. Then, we have reported the mechanical properties of the two compounds. In particular, we have found that the half-Heusler compound has the largest stiffness. Paradoxically, its bulk modulus is also the smallest. This unusual behavior has been related to the Ni-vacancies that weaken the structure under isostatic compression. Both compounds show a ductile behavior. We have then in a second study, combined first principles calculations and experiments (X-Ray diffraction and dilatometry measurements) to  determine the thermal properties of NiTiSn (half-Heusler) and Ni2TiSn (Heusler) compounds. These properties are important especially if these materials are to be used in thermoelectric applications. First, we have obtained the mode Gruneisen parameter for both compounds along the high symmetry directions of the first Brillouin zone and show that it never takes negative values. Then the thermal expansion has been calculated for Ni2TiSn up to 1500K and the agreement is excellent with our high energy X-Ray diffraction measurements (ESRF) and dilatometry experiments. In contrast, the agreement is less satisfactory for NiTiSn due to the difficulty of making high-quality samples. Finally we have calculated the heat capacity (at constant volume and at constant pressure) of both compounds and have also obtained a remarkable agreement with existing experimental data. In particular the heat capacity of Ni2TiSn has been decomposed into a purely electronic contribution and a phonon-mediated response. Both contributions are discussed.

Resume : The recently synthesized n-type copolymer poly(N,N'-bis-2-octyldodecylnaphtalene-1,4,5,8-bis-dicarboximide-2,6-diyl-alt-5,5-2,2-bithiophene) (P(NDI2OD-T2)) has attracted much interest since it is highly soluble, air-stable and it provides high electron field-effect mobility (exceeding 1 cm2 /Vs)[1,2]. It has been observed that P(NDI2OD-T2) chains can preaggregate in solution depending on the specific solvent used for film casting.In particular,toluene (TOL) promotes preaggregation while chloronaphthalene (CN) solutions present nonaggregated chains.Organic solar cells obtained from nonaggregated chains have shown highly increased power conversion efficiency with respect to those built from preaggregated ones[3], while the mobility in field-effect transistors can be controlled over two orders of magnitude by controlling the degree of preaggregation in solution[2].The aggregation of polymer chains in solvent is strongly correlated to the solubility,but despite the above experimental facts,only few theoretical studies exist on the solubility of semiconducting polymers in solvents[4].We have studied at the atomic scale the P(NDI2OD-T2) solubility in TOL and CN,showing that the aggregated configurations are favored in TOL, while isolated chains are more probable in CN[5]. [1]Yan et al. Nature 2009, 457, 679-686 [2]Caironi et al. Sci. Rep. 2013, 3, 3425 [3]Steyrleuthner et al, JACS 2012, 134, 18303-18317. [4]Caddeo et al. Macromol. 2013, 46 (19), 8003-8008 [5]Caddeo et al. in prepar.

Resume : Sn2Sb2S5 thin films were deposited on no heated glass substrates by single source vacuum evaporation method. The as-deposited films were annealed in air for one hour in the temperature range 70- 350°C in order to investigate the influence of annealing on the structural, optical and electrical properties. XRD study shows that annealed films are crystallized with the preferential orientation (602). High absorption coefficients in the range 105-106 cm-1 were reached in the energy range 2-3.25 eV and two optical direct transitions were found. Oscillator energy E0 and dispersion energy Ed of the films after annealing were estimated according to the model of Wemple-DiDomenico single oscillator. Spitzer Fan model was applied to determine the electric free carrier susceptibility and the ratio of carrier concentration to the effective mass. The layers annealed at temperatures greater than 150°C exhibit a resistive hysteresis behavior .These properties offer perspective to Sn2Sb2S5 for its application in many advanced technologies such as photovoltaic applications and optical storage.

Resume : The modeling of the thermoelectric transport properties in highly doped silicon is of key importance in the field of the thermoelectric properties of silicon nanostructures. Recently, a significant power factor enhancement has been observed in highly doped polycrystalline silicon. This has been attributed to the combined effects of energy filtering and inhomogeneous dopants distribution under high doping conditions. Towards further understanding the thermoelectric transport properties of highly doped Si nanostructures with an inhomogeneous impurity distribution, we have performed Monte Carlo simulations taking into account the Pauli Exclusion Principle and assuming different impurity distributions. The potential profile is determined by self-consistently solving the Poisson Equation in 1-d at each simulation step. We present here and discuss our preliminary results on the electron thermoelectric properties in terms of the mobility, conductivity and heat generation of the studied devices. It is shown that including the electron degeneracy in the simulations is of crucial importance in properly determining the magnitude of the electrical conductivity and of the energy filtering along the device. Furthermore, the mobility is found sensitive to the actual impurity distribution.

Resume : Thermal energy harvesting has become of great interest nowadays to moderate the rising energy demand with autonomous sensors and devices (e.g. wireless sensor networks). In most of the compact devices/sensors, the dissipated thermal energy is lost. Pyroelectric materials can provide thermal energy harvesting for electrical generation in compact systems with temporal variations of the temperature (without necessity of thermal gradients as thermoelectric materials). According to recent reports, single-crystalline pyroelectric films should provide an enhanced conversion energy efficiency, and integration on silicon platforms would boost its potential applications. Here, we will show the example of pyroelectric BaTiO3 thin films integrated on silicon by molecular beam epitaxy (MBE) via a thin SrTiO3 buffer layer and SrRuO3 bottom electrode. The heterostructures are (micro)structurally characterized by RHEED, XRD and AFM. They are epitaxial and flat, and present ferroelectricity depending on growing conditions and post-deposition annealing. Challenges and strategies for ultimate conversion energy efficiency based on structural and electrical properties will be discussed.

Resume : Olivine (LiFePO4) is known as a suitable and safe cathode material for lithium-ion batteries and is therefore increasingly used in multiple applications. However, compared to other commercial cathode materials it suffers from poor conductivity and a slightly diminished energy density due to its comparably low redox potential of 3.4 V. Intimate mixing with carbon and substitution of iron with manganese (4.1 V redox potential) can increase the conductivity and energy density of olivine, respectively. Nanostructured LiFe0,5Mn0,5PO4/C composite was synthesized from amorphous, Fe0,5Mn0,5PO4 prepared by spray-flame synthesis using a solution of iron and manganese acetylacetonate and tributylphosphate in toluene. A subsequent solid-state reaction of the high-surface area product (with Li2CO3 and glucose) was used to synthesize the final composite with a mean particle size of about 45 nm. Characterization with X-ray diffraction, electron microscopy, M??bauer spectroscopy and electron paramagnetic resonance spectroscopy confirmed a successful synthesis of the desired material. Electrochemical investigations showed very good electrical conductivity and a discharge capacity of 148 mAh/g. The energy density could be increased by about 10% compared to manganese free olivine reaching 522 mWh/g. A surprisingly high discharge capacity was observed at high discharge rates exceeding 80 mAh/g at 16C.

Resume : In the present work, sulfonation of poly ether ether ketone (PEEK) was carried out by dissolving it in con.H2SO4 at different time intervals and temperatures to have various degrees of sulfonation (DS). Based on the thermal and mechanical analysis the sample with DS ~ 54 % was selected for preparing lithium ion conducting polymer electrolytes. Polymer electrolytes based on SPEEK and lithium bis(trifluoromethanesulfonic acid) (LiTFSI) were prepared by solvent-casting technique by varying the weight ratio of the lithium salt with DMSO as solvent. Thermogram of polymer electrolytes show a weight loss (~20%) in the temperature range 220 - 280 °C indicating the decomposition of sulfonic acid group (-SO3H) attached to the polymer backbone. Compared to pure SPEEK membranes, lithium doped samples start to decompose earlier due to the interaction of Li+ to the sulfonic acid group. The glass transition temperature of the polymer electrolytes observed in DSC curve decreases with increase in salt concentration revealing the plasticizing effect of the ion association as the salt is added. 7Li NMR results show a single central transition line around -1.1 ppm and its intensity increases with increase in salt concentration indicating the presence of free mobile lithium ions. Mechanical stability of both hydrophobic and hydrophilic domains of the SPEEK membranes was investigated in terms of salt concentration by Dynamic Mechanical Analysis (DMA). Keywords: SPEEK, Sulfonation, NMR

Resume : Thermoelectric (TE) materials show great promise for converting wasted heat into useful electricity. TE systems have many unique advantages such as silent operation, time reliability, and dimensional scalability. Although MnO2 powders have been used in the last 60 years as positive electrodes in dry-cell alkaline batteries, recently Song et al. [1] found that this material show a giant Seebeck coefficient of S = 20 mV/K, which is 100 times higher than bismuth telluride, one of the best TE materials. In this experimental project, we present preliminary results of Seebeck coefficient and Electrical Conductivity as a function of particle electrical resistance (R ~ 10-80 Ω) and packing density (δP = 2.4 – 3.5 g/cm3). These thermoelectric properties were also measured as a function of MnO2 particle size ( d ~ 5 nm-150 µm). Preliminary results show that the Seebeck coefficients for the 10-80 Ω resistance values are consistent with the bulk MnO2 values. Exponential behavior observed in electrical conductivity and thermoelectric power factor is induced by the exponential correlation between electrical resistance and tube length. The packing density reaches an upper plateau for sample S6 (d ~ 79 µm) and the highest power factor is measured for sample S4 (i.e., PF = 5.7 * 10-7 W/(m K2) at a packing density value of dP ~ 2.7 g/cm3. [1] F. F. Song, L. Wu and S. Liang, Nanotech. 23, 085401, (2012).

Resume : One of the biggest challenges in the field of manufacturing wind turbines is lack of a cloning method available and affordable and similar to those for a wind turbine during the actual performance falls in wind farms. However, today, using software such as FLUENT fluid flow passing on blades to simulate or more precisely the turbines, the first small-scale laboratory and wind tunnel tests made,that has highly accurate but somewhat since their wind tunnel in many places academic and scientific research, technology is considered expensive and many of these places without access to the wind tunnel are on it, so we had to considered invent a new method for testing small turbines and laboratory like what the photos in the wind tunnel happens, In this study, in fact wind tunnel using a torque producing device simulations are then compared this new technique with conventional test methods in the wind tunnel explains the results of a laboratory example of the type of wind turbines in two state Savonious shows The above state. The output in two cases with good approximations are very close together and can test this method for laboratory samples in small farthermost before making the giant turbines could be used.