Probing thermopower on the microscale

Abstract

Thermoelectric (TE) generators provide electrical energy from direct conversion of heat by means of the Seebeck effect; without moving parts, completely silent, and with negligible maintenance. As any other heat engine this conversion exploits only a fraction of the Carnot efficiency (Rowe (ed.), CRC Handbook of Thermoelectrics (CRC Press Inc., 1995), p. 19 [1]). The TE efficiency is linked to the thermoelectric figure of merit Z, which itself is given by basic material properties: Z ¼ S 2 s/k. These are the electrical conductivity s, the thermal conductivity k and the Seebeck coefficient or thermopower S, which is known as the factor of proportionality between voltage output and applied temperature difference in a given TE sample. A distinct sensitivity to the carrier concentration and structural variations make the control and stabilisation of thermopower very challenging in complex material structures since degradation by diffusion, decomposition or evaporation can be observed in many cases during synthesis, operation and even in the process of characterisation of TE semiconductors; particularly at elevated temperatures. Investigating structural and compositional properties, stability, and performance of TE materials, and consequently aiming to understand their interaction, mainly methods like X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) or integral temperature dependent measurements of particular transport properties are used. Although TE materials research satisfies highest requirements on accuracy, the above mentioned techniques are not perfectly qualified to investigate promising material classes thoroughly. Against the background of usually complex material structures this article aims to show, that an efficient characterisation of TE materials becomes accessible for several questions by use of a spatially resolved determination of the thermopower.

Fabrication and characterization of nickel contacts for magnesium silicide based thermoelectric generators

“…The Seebeck coefficient mapping allows for an easy identification of the Mg 2 Si region (S Mg2Si -% À60 lV/K) and the Ni region (S Ni % À13 lV/K). The magnitude of both values is smaller but comparable to the bulk integral values [18,25], which is due to the working principle of the PSM [20]. The potential mappings show a gradual and linear decrease from left to right.…”

“…Spatially resolved measurements of electrical potential, contact resistances, and Seebeck coefficient were performed using a Potential-Seebeck-Microprobe (PSM) [19,20]. The setup consists of a sample stage and a moveable tip that can contact the sample at various positions.…”

Thermoelectric properties of the unfilled skutteruditeFeSb3from first principles and Seebeck local probes

“…2. The Seebeck coefficient of a FeSb 3 film with a thickness of 1.5 µm was determined at room temperature using a Seebeck Microprobe 25,26 . The spatial resolution of the microprobe is of the order of tens of micrometers.…”

Unraveling Self‐Doping Effects in Thermoelectric TiNiSn Half‐Heusler Compounds by Combined Theory and High‐Throughput Experiments

“…[ 42 ] The Seebeck coeffi cients of the materials library were measured using the Potential-Seebeck Microprobe. [ 43 ] This scanning setup consists of a heated probe tip, an X -Y -Z stage and two type-T thermocouples and electronics for data acquisition. While one thermocouple is connected to the heated tip, the other is fi xed to the top surface of the materials library with the use of silver paste.…”

“…However, due to weak variations of thermal properties along the ML samples, which show a signifi cant impact on the accuracy and spatial resolution of determined Seebeck coeffi cients of thin fi lms, contrasts of thermopower in terms of relative Seebeck coeffi cient differences can be revealed with much higher accuracy and a resulting relative error of 1%-2%. [ 43 ] Consequently, the setup is able to map combinatorial libraries in a high-throughput manner offering the effi cient detection of HHCs with promising thermoelectric properties. Figure 1 a shows an optical image of the Ni-Ti-Sn thin fi lm ML in its state after annealing at 873 K for 4 h in vacuum.…”