The HT-S measuring system is used for the temperature-dependent simultaneous measurement of the Seebeck coefficient and the electrical conductivity of material samples from room temperature to 1000 K under inert gas or in a vacuum.
Measured temperature dependence of the Seebeck coefficient of a Ni-Cu sample.
Seebeck coefficient of a Ni-Cu sample. The results of the simultaneous measurement system HT-S (red) agree very well with those of another measurement system at DLR (CTEM; blue) and a comparison measurement at PTB.
Measurement of electrical conductivity and Seebeck coefficient are an integral part of thermoelectric material development. In our department, a measuring system for simultanous determination of electrical conductivity and Seebeck coefficient from room temperature to 1000K was developed and is regularly used in routine characterisation procedures.
The electrical conductivity is determined using the 4-probe measurement method. Metallic probe tips with predefined spacing are pressed onto a sample of known geometry using high-temperature springs.
To measure the Seebeck coefficient, a temperature gradient is imposed onto the sample using miniature heating elements. Two probe tips act as supply lines for the measuring current and, simultaneously, as thermocouples for temperature measurement. Thus, the generated thermovoltages and temperatures can be measured to calculate the Seebeck coefficient.
The accuracy of the measuring system was verified through an internal laboratory comparison and by comparative measurements at the Physikalisch-Technische Bundesanstalt Berlin (PTB). Measurement results on a Cu-Ni alloy from two different DLR systems and a PTB measuring system are shown in the diagram. The measurement system used at DLR is involved in international round-robin comparison measurements.
Based on the in-house developments for hardware and software, precise control of the measurement process is possible and measurement accuracies can be reliably estimated within the framework of internal comparisons, process redundancy and through the use of in-house developed and certified reference materials.
Contact
Prof. Dr. rer. nat. Wolf Eckhard Müller
Head of department Thermoelectric Materials and Systems
