1.2 Historical development of thermoelectric materials and devices

Thermoelectric materials have a rich history dating back to the 1800s. From Seebeck's voltage discovery to Peltier's cooling effect, these early findings laid the groundwork for modern thermoelectric devices.

Semiconductors revolutionized the field in the 1950s, with bismuth telluride emerging as a game-changer. Today, thermoelectrics power space missions and find use in everyday applications, showcasing their versatility and importance.

Early Pioneers

Seebeck and Peltier Effects

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• Thomas Johann Seebeck discovered the Seebeck effect in 1821
  • Observed voltage generation when two dissimilar metals were joined and subjected to a temperature gradient
  • Led to the development of thermocouples for temperature measurement
• Jean Charles Athanase Peltier discovered the Peltier effect in 1834
  • Found that passing an electric current through a junction of two different metals caused heating or cooling
  • Peltier effect forms the basis for thermoelectric cooling devices

Thomson Effect and Theoretical Foundations

• William Thomson (Lord Kelvin) established the relationship between Seebeck and Peltier effects in 1851
  • Predicted and later experimentally verified the Thomson effect
  • Thomson effect describes heat absorption or generation when current flows through a material with a temperature gradient
• Altenkirch's theory in early 1900s laid groundwork for thermoelectric efficiency
  • Developed mathematical model for thermoelectric generators and refrigerators
  • Identified key material properties for efficient thermoelectric devices (high electrical conductivity, low thermal conductivity)

Semiconductor Thermoelements

Ioffe's Contributions and Bismuth Telluride

• Abram Ioffe introduced semiconductor thermoelements in the 1950s
  • Recognized semiconductors as superior thermoelectric materials compared to metals
  • Developed doped semiconductors for improved thermoelectric performance
• Bismuth telluride emerged as a breakthrough thermoelectric material
  • Discovered to have excellent thermoelectric properties at room temperature
  • Became the primary material for commercial thermoelectric coolers and generators
  • Alloys of bismuth telluride (Bi2Te3) with antimony and selenium further improved performance

Figure of Merit and Material Optimization

• Figure of merit (ZT) introduced as a measure of thermoelectric material efficiency
  • Dimensionless parameter combining Seebeck coefficient, electrical conductivity, and thermal conductivity
  • ZT = (S^2σ / κ)T, where S is Seebeck coefficient, σ is electrical conductivity, κ is thermal conductivity, and T is absolute temperature
• Optimization of ZT became a central focus of thermoelectric research
  • Efforts to increase Seebeck coefficient and electrical conductivity while decreasing thermal conductivity
  • Development of new materials and nanostructuring techniques to enhance ZT

Applications

Space Exploration and Terrestrial Use

• Radioisotope thermoelectric generators (RTGs) developed for space exploration
  • Provided long-lasting power source for deep space missions (Voyager, Cassini, New Horizons)
  • Utilized heat from radioactive decay of plutonium-238 to generate electricity
• Terrestrial applications of thermoelectric devices expanded
  • Thermoelectric coolers used in portable refrigerators and electronic cooling
  • Waste heat recovery systems in automotive and industrial sectors
  • Wearable thermoelectric generators for powering small electronic devices