Solid-State Synthesis and Thermoelectric Properties of CuFeSe₂-CuFeS₂ Solid Solutions

Area of Science:

• Materials Science
• Solid-state Chemistry
• Energy Conversion

Background:

• Thermoelectric technology offers efficient energy utilization by converting heat to electricity.
• Eco-friendly and cost-effective copper-based thermoelectric materials are actively researched.
• Solid solutions are a key strategy for enhancing thermoelectric properties.

Purpose of the Study:

• To investigate the formation and thermoelectric properties of Cu-chalcogenide solid solutions (CuFeSe2-ySy).
• To explore the relationship between composition, crystal structure, and thermoelectric performance.
• To assess the potential of these materials for efficient energy conversion.

Main Methods:

• Solid-state synthesis of CuFeSe2-ySy compounds (y = 0-2).
• X-ray diffraction (XRD) for structural analysis and phase identification.
• Thermoelectric property measurements (electrical conductivity, Seebeck coefficient, thermal conductivity).

Main Results:

• Single-phase solid solutions formed for 0 ≤ y ≤ 0.4 and 1.6 ≤ y ≤ 2; intermediate compositions formed composite phases.
• Lattice parameters decreased with increasing sulfur content due to its smaller ionic radius.
• Electrical conductivity increased with sulfur content, and the Seebeck coefficient transitioned from p-type to n-type.
• Thermal conductivity significantly decreased, reaching a minimum of 0.97 Wm⁻¹K⁻¹ for CuFeSe0.4S1.6 at 623 K, due to enhanced phonon scattering.
• The power factor did not improve significantly due to the inverse relationship between conductivity and Seebeck coefficient.

Conclusions:

• Solid solution formation in CuFeSe2-ySy impacts crystal structure and thermoelectric properties.
• Enhanced phonon scattering in solid solutions effectively reduces thermal conductivity.
• Despite reduced thermal conductivity, the thermoelectric figure of merit did not show substantial improvement in the studied composition range.