Abstract
Knowledge of the thermal conductivity (κ) of solids is crucial for all thermoelectric devices. A new approach in transient measurement to determine this value as well as electric conductivity (σ) and the Seebeck coefficient (S) is presented here. This approach can be combined with current steady-state methods. A cylindrical sample is mounted between two heat-flux sensors that can be heated or cooled at their outer ends. The input signals defining the heat fluxes at the sensors can be any arbitrary function of time, although some waveforms yield more valid results. The method is evaluated by employing a one-dimensional numerical model and finding the best fit to extract the thermal conductivity (κ) of the sample as well as its volumetric heat capacity (cρ) . Trial measurements on an insulating (σ = 1 × 1013 Sm-1) and a conducting sample (σ = 1 × 105 Sm-1) are presented and the results are in good agreement with the literature and data obtained by a commercial laser-flash analysis system. Improvements in comparison to present measurement methods are the direct determination of κ compared to other transient methods like laser-flash analysis, shorter measurement times by acquiring κ(T) data in a single temperature approach, and simultaneous S and σ measurements.
Highlights
Maximizing or minimizing heat transport plays a major role in many applications ranging from thermal isolation of buildings to microelectronics
Thermal conductivity ( κ) is an important material parameter, since, combined with the Seebeck coefficient ( S) and electric conductivity ( σ), it determines the thermoelectric figure of merit, ZT = ( S2σ) / κ, of materials [1,2,3,4,5,6,7,8]
It is possible to use a dynamic or transient mode, which is a transient method based on periodic heat inputs at the ends of the sample. The idea of this transient approach is to combine the advantages of steady-state methods, in particular the direct determination of thermal conductivity ( κ), with those of dynamic methods, which have faster measurement times and the possibility of obtaining additional information on the product of specific heat capacity and mass density corresponding to a volumetric heat capacity
Summary
Maximizing or minimizing heat transport plays a major role in many applications ranging from thermal isolation of buildings to microelectronics. While most current measurement systems support the simultaneous determination of S and σ , κ needs to be measured in a separate setup or a steady-state method, which slows down the whole procedure. Steady-state measurement techniques are usually based on the determination and analysis of a temperature profile across the sample [11,12]. New heat sources like laser or xenon flashes as well as lock-in techniques and new data logging methods are the basis for the more sophisticated transient measurement approaches used to date. The approach proposed here allows one to perform temperature runs, which speeds up the measurement time for acquiring κ(T ) data and is, in principle, compatible with Seebeck coefficient and electrical conductivity measurements, yielding a determination of temperature-dependent ZT data in one approach. This holds for almost all state-of-the-art approaches in which κ is extracted directly from the measurement data [18,19,23]
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