The Seebeck Coefficient

The Seebeck effect, named after Thomas Johann Seebeck who discovered it in the early 1920’s, is the ability of a material to produce a voltage when a temperature gradient is introduced between its two ends. It is the basis for thermocouple physics. The Seebeck coefficient is measured in microvolts per Kelvin.

We use a cryochamber to measure the Seebeck coefficient from temperatures ranging 30-300 K. A thin-film semiconductor is clamped down between two copper blocks within the chamber; to ensure electrical contact between the copper and the sample, small indium strips are laid down between them. A K-type thermocouple (chromel-alumel) connected to the “cold” block, but electrically insulated from it, records the temperature of the chamber. A K-type differential thermocouple attached to both blocks (in thermal contact but not electrical) yields the temperature gradient between the blocks. A 19 Ω resistor resides in the “hot” block, electrically insulated from the copper, and provides a small (3-5 K) temperature gradient across the sample once a current is passed through it.

Once the current is turned off, the voltage produced by the sample and the temperature gradient between the two copper blocks are measured. Measurements are taken until both the potential across the sample and the temperature gradient between the blocks return to 0 mV. The potential is plotted against the temperature gradient and the slope of the line yields the Seebeck coefficient.

• Equipment Used
  • LabView
  • Computer Instrumentation
  • Cryogenics
• Pictures
• Troubleshooting

Omega thermocouple reference

In particular this oneIntroduction to Practical Temperature Measurements