Simulation of current-activated pressure-assisted densification

Angst, Sebastian; Schierning, Gabi; Wolf, Dietrich E.

doi:10.1063/1.4812001

Cited by 3 publications

(3 citation statements)

References 11 publications

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“…In the original version of the CAPAD model heat conduction and Seebeck, respectively Peltier, effect were not taken into account (the corresponding model extensions (Model B) will be discussed below). Instead, the temperatures

T_{i}

were calculated from a simplified energy balance: per time step

Δ t

, particle

i

receives the heat

Δ Q_{i} = \frac{1}{2} \sum_{j} I_{i j} \frac{(μ_{i} - μ_{j})}{e} normalΔ t,

where the summation runs over the nearest neighbors of particle

i

.…”

Section: Processing To Nanocrystalline Bulk and Laser‐sintered Thin Fmentioning

confidence: 99%

“…In order to treat the temperatures

T_{i}

more accurately as a thermodynamic field like the electrochemical potentials

μ_{i}

, the model has been extended to represent a complete Onsager formulation of the problem (Model B) . The electrical currents, in Eq.…”

Section: Processing To Nanocrystalline Bulk and Laser‐sintered Thin Fmentioning

confidence: 99%

“…Our experimental realizations of the PNG were created in a bottom‐up approach from highly doped silicon . In a first step the raw material, highly porous nanopowder from the gas phase synthesis, is densified by CAPAD . It is worth mentioning that processing under air allows oxygen to react with the silicon before densification.…”

Section: Devicesmentioning

confidence: 99%

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Silicon‐based nanocomposites for thermoelectric application

Schierning

Stoetzel

Chavez

et al. 2016

Physica Status Solidi (a)

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Here we present the realization of efficient and sustainable silicon‐based thermoelectric materials from nanoparticles. We employ a gas phase synthesis for the nanoparticles which is capable of producing doped silicon (Si) nanoparticles, doped alloy nanoparticles of silicon and germanium (Ge), SixGe1–x, and doped composites of Si nanoparticles with embedded metal silicide precipitation phases. Hence, the so‐called “nanoparticle in alloy” approach, theoretically proposed in the literature, forms a guideline for the material development. For bulk samples, a current‐activated pressure‐assisted densification process of the nanoparticles was optimized in order to obtain the desired microstructure. For thin films, a laser annealing process was developed. Thermoelectric transport properties were characterized on nanocrystalline bulk samples and laser‐sintered‐thin films. Devices were produced from nanocrystalline bulk silicon in the form of p–n junction thermoelectric generators, and their electrical output data were measured up to hot side temperatures of 750 °C. In order to get a deeper insight into thermoelectric properties and structure forming processes, a 3D‐Onsager network model was developed. This model was extended further to study the p–n junction thermoelectric generator and understand the fundamental working principle of this novel device architecture. Gas phase synthesis of composite nanoparticles; nanocrystalline bulk with optimized composite microstructure; laser‐annealed thin film.

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T_{i}

were calculated from a simplified energy balance: per time step

Δ t

, particle

i

receives the heat

Δ Q_{i} = \frac{1}{2} \sum_{j} I_{i j} \frac{(μ_{i} - μ_{j})}{e} normalΔ t,

where the summation runs over the nearest neighbors of particle

i

.…”

Section: Processing To Nanocrystalline Bulk and Laser‐sintered Thin Fmentioning

confidence: 99%

“…In order to treat the temperatures

T_{i}

more accurately as a thermodynamic field like the electrochemical potentials

μ_{i}

, the model has been extended to represent a complete Onsager formulation of the problem (Model B) . The electrical currents, in Eq.…”

Section: Processing To Nanocrystalline Bulk and Laser‐sintered Thin Fmentioning

confidence: 99%

See 1 more Smart Citation

Silicon‐based nanocomposites for thermoelectric application

Schierning

Stoetzel

Chavez

et al. 2016

Physica Status Solidi (a)

Self Cite

View full text Add to dashboard Cite

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Network theory for inhomogeneous thermoelectrics

Angst

Wolf

2016

New J. Phys.

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The Onsager-de Groot-Callen transport theory, implemented as a network model, is used to simulate the transient Harman method, which is widely used experimentally to determine all thermoelectric transport coefficients in a single measurement setup. It is shown that this method systematically overestimates the Seebeck coefficient for samples composed of two different materials. As a consequence, the figure of merit is also overestimated, if the thermal coupling of the measurement setup to the environment is weak. For a mixture of metal and semiconductor particles near metal percolation the figure of merit obtained by the Harman method is more than 100% too large. For a correct interpretation of the experimental data, information on composition and microstructure of the sample are indispensable. IntroductionThermoelectric materials are important for energy harvesting, especially from waste heat [1,2]. In order to optimize the conversion into electricity, it is desirable to predict device properties by efficient computer simulations. This is one goal of the present paper. More fundamentally, we are going to point out that memory effects render the global response of composite materials, which are common among modern nanostructured thermoelectrics [3], highly complex.The theoretical description of transport processes goes back to Onsager [4,5]. Applied to thermoelectrics, this became known as the Onsager-de Groot-Callen theory [6]. A special case is the so-called constant property model (CPM), where the electric and heat conductivity, σ and κ, and the Seebeck coefficient α are assumed to be constant. This model has been studied in detail analytically in one-dimension [7,8] and will serve as a reference system for validation in this paper.Since analytic calculations are restricted to simple compounds, numerical models have been developed in order to describe inhomogeneous materials. Although these models are also based on the Onsager-de Groot-Callen theory, most of them do not fully describe the thermoelectric effects, since they do not include Joule heat and/or Peltier heat [9,10]. They were used to calculate either the heat and electrical conductances or the Seebeck coefficient [11][12][13]. More complex models [14] exist in the framework of drift-diffusion models, and they are applied e.g. for the simulation of generators in complex geometries [15].In this paper a simple and coherent way to discretize the Onsager transport theory for thermoelectric materials will be used, which includes all relevant effects and time-dependencies. It can be seen as a version of the finite difference method reviewed in [16]. Originally it was designed for the investigation of transport processes in nano-particle configurations [13,17,18], which were mapped to a network model. In this paper it will be applied to disordered bulk systems rather than particle agglomerates.The model, derived in section 2, enables us to study thermoelectric effects in geometries, which can not be solved analytically. It is validated by comparing simulation...

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