Poster:Designing Thermopower Measurement Probe

Thermoelectric effect is a phenomenon in which an electrical voltage difference is induced by a temperature difference across a material. It can commonly be observed in semiconductors and semimetals, and it can be characterized by Seebeck coefficient (thermopower), which is the ratio of negative voltage difference to temperature difference when the heat is applied at one end of a sample. The thermopower values can be positive or negative depending on the type of charge carriers: holes or electrons. This effect has many applications, such as power generation from waste heat, thermocouples for temperature sensing and control, thermocouple vacuum gauge, and thermoelectric refrigerators. Many strongly correlated electron materials in our laboratory exhibit this thermoelectric property, therefore, we need to develop a probe for thermopower measurement that can be used in a cryocooler. In the previous design and data analysis, we used the two well-known materials, Nickel 201 alloy and Platinum 99.9%, to test the accuracy of the probe. We found that the type T differential thermocouple that we used could not sense accurate temperature differences below 100K and only one sample holder cannot subtract the background contribution from wiring efficiently. In the new probe design, we plan to install two Cernox thermometers on the either side of a sample holder (i.e., hot side and cold side) because Cernox has a wide range of sensitivity down to 0.3K. We will also install two sample holders to set up a reference material such as a thin Pt wire for the purpose background subtraction. In addition, to reduce the measurement time, we plan to adopt a slope method over steady state method, as long as each measurement-maintained temperature difference within 3% of the regulating temperature.