Thermoelectric Materials: What They Are and How They Work

 

Introduction

Thermoelectric materials are materials that have a property called Seebeck coefficient. This property causes the material to generate thermoelectricity when it is subject to a temperature gradient. Thermoelectricity is the ability of certain materials to generate electricity from a temperature difference. The generation of electricity from heat is known as thermal power; this is what makes thermoelectricity useful in energy-efficiency and renewable energy applications. These properties also make them attractive for use in electronics, sensors, and other technologies. This article will explain what thermoeelectrics are and how they work. It will also provide examples of how these properties are used in real-world applications, such as in refrigeration systems, car engines, and semiconductor manufacturing machinery.

Figure: Schematic of Thermoelectric Generators (TEGs)

What is Thermoelectricity?

Thermoelectricity is the ability of certain materials to generate a voltage when subjected to a temperature gradient. This ability is produced by the Seebeck effect. The Seebeck effect is produced by a difference in the Seebeck coefficient between two different materials placed in either side of a “thermoelectric couple”. The thermoelectric couple acts as a diode, allowing the flow of current only in one direction. Thermoelectricity is used in a variety of ways, including in refrigeration systems, car engines, and semiconductor manufacturing machinery. It is also used in spacecraft to convert heat into electricity. Another important use of thermoelectricity is in generating power from waste heat, such as in solar thermal power plants, seawater-based thermoelectric plants, and industrial waste heat recovery systems. In these cases, thermoelectric materials are used to convert the thermal energy from the exhaust of a process into electricity.

How Thermoelectric Materials Work

Thermoelectric materials generate a voltage when subjected to a temperature difference. The voltage is in the direction that opposes the temperature gradient. For example, if a copper bar is placed on one side of a thermoelectric couple and a zinc bar is placed on the other side, the copper bar will get hotter and the zinc bar will get cooler. The thermoelectric couple is made up of the two different materials to create this effect. To explain the concept, let’s take a look at a simplified example with a bar made of copper and a bar made of zinc. The copper bar has a higher Seebeck coefficient than the zinc bar. The thermoelectric couple consists of the two bars arranged in a T-shape. When there is no temperature difference between the two bars, there is no voltage. When there is a temperature difference between the two bars, electrons flow from the copper bar to the zinc bar, creating a voltage across the bars. The voltage is proportional to the temperature difference between the two bars.

Uses of Thermoelectric Materials

Thermoelectric materials can be used in a wide variety of applications. They are especially useful in situations where there is a temperature difference between two parts of a system, such as in refrigeration, car engines, and solar energy systems.

Bismuth-Based Thermoelectric Material

Bismuth is a chemical element that is commonly used as a thermoelectric material. Bismuth-based thermoelectrics are commonly used in refrigeration systems. A bismuth-based thermoelectric material has good thermal conductivity and high Seebeck coefficient. Bismuth-based thermoelectric materials are usually made by either sintering or liquid-phase sintering. Sintering is a method of forming ceramic materials by putting powders together and pressing them under high temperatures. Liquid-phase sintering involves a liquid bismuth compound being poured into a mould, where it crystallizes into a solid bismuth material.

Lead-Based Thermoelectric Material

Lead-based thermoelectrics are commonly used in high-efficiency systems that require a high temperature difference to generate significant power. Lead-based thermoelectric materials are generally made from a lead compound. They have a high Seebeck coefficient and low thermal conductivity, meaning that they are effective in generating electricity from high temperature differences.

Tungsten-Based Thermoelectric Material

Tungsten-based thermoelectrics are commonly used in heating and cooling systems that use electricity to drive the process. Tungsten-based thermoelectrics have high thermal conductivity and a high Seebeck coefficient.

Ceramics and Composites Based on Thermoelectrics

Ceramic materials are usually used as electrodes with intrinsic thermoelectric properties. For example, single-phase ceramics, such as strontium titanate, have good Seebeck coefficients and thermal conductivities, while single-phase ceramics, such as lead zirconate titanate, have high thermal capacitances. Other materials with intrinsic thermoelectric properties are composites, such as silicon carbide with germanium.

Summary

Thermoelectric materials generate a voltage when subjected to a temperature difference. The voltage is in the direction that opposes the temperature gradient. The bismuth-based thermoelectric material is commonly used in refrigeration systems. The lead-based thermoelectric material is commonly used in high-efficiency systems. The tungsten-based thermoelectric material is commonly used in heating and cooling systems. The ceramics and composites based on thermoelectrics are commonly used in single-phase ceramics and other materials with intrinsic thermoelectric properties.