2.4 Coupled transport phenomena in thermoelectrics

Thermoelectric materials exhibit fascinating coupled transport phenomena. These materials can convert temperature differences into electricity and vice versa, thanks to the interplay of various coefficients like Seebeck, Peltier, and Thomson.

Understanding the relationships between these coefficients is crucial for optimizing thermoelectric performance. The Onsager and Kelvin relations provide a framework for analyzing these connections, helping us design better materials for energy harvesting and cooling applications.

Thermoelectric Transport Coefficients

Fundamental Coefficients and Their Significance

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• Thermopower measures voltage generated per unit temperature difference across a material
• Thomson coefficient quantifies heat absorbed or released when current flows through a temperature gradient
• Peltier coefficient describes heat transfer at junction of two different materials when current flows
• Power factor combines electrical conductivity and Seebeck coefficient to evaluate material's thermoelectric performance

Interrelationships and Applications

• Thermopower (Seebeck coefficient) relates to material's ability to convert temperature differences into electricity
• Thomson coefficient links to reversible heating or cooling in a conductor with current and temperature gradient
• Peltier coefficient determines cooling or heating effect at thermoelectric junctions
• Power factor helps optimize thermoelectric materials for maximum power output in generators

Coupled Transport Relations

Onsager and Kelvin Relations

• Onsager relations describe symmetry in transport coefficients for reversible processes
• Kelvin relations connect thermoelectric coefficients (Seebeck, Peltier, Thomson)
• Interdependence of transport coefficients stems from fundamental thermodynamic principles
• Thermoelectric tensors represent anisotropic transport properties in crystalline materials

Applications and Implications

• Onsager relations simplify analysis of complex transport phenomena in thermoelectric systems
• Kelvin relations enable calculation of one coefficient from another (Peltier from Seebeck)
• Interdependence of coefficients allows prediction of overall thermoelectric performance
• Thermoelectric tensors guide material design for optimized directional transport properties