Seebeck coefficient measurement setup

All Rights Reserved. The setup can measure the value of S in the said temperature range for small samples. The auxiliary heaters maintain the temperature gradient. The set overall sample temperature and temperature gradient is maintained by controller circuit and other ancillary circuits.

Keywords: Differential temperature controller, Seebeck coefficient, Semiconductors. Cite this paper: Ravindrapal M. Ravindrapal M. Joshi Department of Electronics, M. Article Outline 1. Introduction 2. Operating Technique 3. Results and Conclusions 4. Future Scope for Improvements. Introduction The measurement of Seebeck coefficient as a function of temperature is one of the most significant methods for investigating electronics properties of solids.

The quantity S can be used to determine the mobility ratio, the concentration of majority carriers, the position of Fermi level, scattering mechanism, etc, and it has been used for the study of electrical transport properties of samples by many investigators []. The polarity of S indicates the types of dominant carriers or the type of dominant electric conduction. The instrument is very compact, low power and easy to operate.

Operating Technique The sketch of the experimental setup is shown in Figure 1. It consists of two blocks. Block — 1: Sample holder with heaters and pick up probes and Block — 2: electronic circuits controlling temperature and temperature gradient across the sample.

The sample holder consists of two low power heaters A and B 15W each. Both the thermocouples are of K type. The sample under investigation is mounted directly on the heaters and is held by two pick up probes which are of copper or stainless steel.

The probes are made of copper or stainless steel so that they are a good conductor of electricity and measures the developed electrical signals at the sample surface where the junction if formed between the probe and the sample. Thus these probes measures the Seebeck voltage developed across the two ends of the sample.

Figure 1. Experimental system The Figure 2 shows the details of the Block 2 of the setup. The Block 2 consists of temperature indicator, proportional controller and two heater control circuits which drives the two heaters A and B. Error amplifier A generates a signal corresponding to the temperature difference between T and set T.

The sample holder was designed to have a compact structure and can be directly mounted in a standard cryostat system for temperature-dependent measurements. For the Seebeck coefficient measurement, a thin bar-shaped sample is mounted bridging two copper bases; and two ceramic heaters are used to generate a temperature gradient along the sample.

Two type T thermocouples are used to determine both temperature and voltage differences between two widely separated points on the sample. The thermocouple junction is flattened into a disk and pressed onto the sample surface by using a spring load. The flexible fixation method we adopted not only simplifies the sample mounting process but also prevents thermal contact deterioration due to the mismatch of thermal expansion coefficients between the sample and other parts.