Seebeck Coefficient and Resistivity Test System

The Seebeck effect, also known as the first thermoelectric effect, refers to the thermoelectric phenomenon in which the voltage difference between two substances is caused by the temperature difference between two different electrical conductors or semiconductors. It is generally stipulated that the direction of thermoelectric potential is: electrons flow from negative to positive at the hot end.

Principle:

Semiconductor Effect:

The main reason for the Seebeck effect is the result of the diffusion of carriers from the hot end to the cold end. For example, in a p-type semiconductor, due to the high concentration of holes at the hot end, the holes diffuse from the high temperature end to the low temperature end. In the case of an open circuit, a space charge is formed at both ends of the p-type semiconductor (the hot end has a negative charge, and the cold end has a positive charge), and an electric field appears inside the semiconductor. When the diffusion effect and the drift effect of the electric field cancel each other out, a steady state is reached, and an electromotive force caused by a temperature gradient appears at both ends of the semiconductor - thermoelectromotive force. Naturally, the direction of the thermoelectric potential of n-type semiconductors is from the low temperature end to the high temperature end (the Seebeck coefficient is negative). On the contrary, the direction of the thermoelectromotive force of the p-type semiconductor is from the high temperature end to the low temperature end (the Seebeck coefficient is positive), so the conductivity type of the semiconductor can be judged by the direction of the thermoelectromotive force.

Metal Effect:

Diffusion of electrons from the hot end to the cold end. However, the diffusion here is not caused by the concentration gradient (because the electron concentration in the metal is independent of temperature), but by the higher energy and velocity of the electrons at the hot end. Obviously, if this effect is dominant, the coefficient of the Seebeck effect thus produced should be negative.

Although there are many free electrons in the metal, the so-called conduction electrons in the 2kT range near the Fermi energy level mainly contribute to the conduction. The mean free path of these electrons is related to the state of being scattered (phonon scattering, impurity and defect scattering) and the change of energy state density with energy.

Sample Requirements

• Film: 4 mm (can be slightly larger) × 12 mm (try to be around 12 mm)
• Block: the length and width shall not exceed 2 - 4 mm, and the height shall not be less than 8 mm
• During the heating process, the sample is stable, no gas can be released, and there can be no obvious volume expansion. The test is to contact the probe to avoid damage to the instrument.

Application

• Measure the Seebeck coefficient and resistivity of materials

Instrument and Result Display

FAQ

Q1. Can the film sample continue to be tested after being coated with silver paste for a long time?

A. No, the thin film sample cannot be tested after being coated with silver paste for a long time, and it needs to be re-sampled, and there will be problems in contact with the silver paste for a long time.

Q2. When measuring variable temperature, why does the data have multiple data at one temperature point?

A. Because when there are multiple temperature points, each air temperature point is not necessarily measured only once, and each point has a corresponding measured air temperature.

Q3. When testing Seebeck, can it be tested together with resistivity?

A. Yes, they are measured together.

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