[Paper Review] Thermoelectric properties of graphyne from first-principles calculations

Pengfei Jiang, H. J. Liu+5 more|arXiv (Cornell University)|Aug 5, 2016

Graphene research and applications39 references3 citations

TL;DR

This study investigates the thermoelectric properties of γ-graphyne using first-principles calculations combined with Boltzmann transport theory. By accurately computing electron-phonon coupling via density functional perturbation theory and Wannier interpolation, it reveals a peak ZT of 1.5 for p-type and 1.0 for n-type γ-graphyne at 600 K, demonstrating strong temperature and carrier-type dependence.

ABSTRACT

The two-dimensional graphene-like carbon allotrope, graphyne, has been recently fabricated and exhibits many interesting electronic properties. In this work, we investigate the thermoelectric properties of γ-graphyne by performing first-principles calculations combined with Boltzmann transport theory for both electron and phonon. The carrier relaxation time is accurately evaluated from the ultra-dense electron-phonon coupling matrix elements calculated by adopting the density functional perturbation theory and Wannier interpolation, rather than the generally used deformation potential theory which only considers the electron-acoustic phonon scattering. It is found that the thermoelectric performance of γ-graphyne exhibits a strong dependence on the temperature and carrier type. At an intermediate temperature of 600 K, a maximum ZT value of 1.5 and 1.0 can be achieved for the p- and n-type systems, respectively.

Motivation & Objective

• To evaluate the thermoelectric performance of γ-graphyne, a two-dimensional carbon allotrope recently synthesized.
• To overcome limitations of conventional deformation potential theory by using accurate electron-phonon coupling calculations.
• To analyze the dependence of thermoelectric properties on temperature and carrier type (p- and n-type).
• To provide a quantitative assessment of the figure of merit ZT for γ-graphyne using advanced electronic transport methods.

Proposed method

• Employed density functional perturbation theory (DFPT) to compute ultra-dense electron-phonon coupling matrix elements.
• Applied Wannier interpolation to enhance the accuracy and efficiency of electron-phonon coupling calculations.
• Combined first-principles electronic structure calculations with Boltzmann transport theory for both electrons and phonons.
• Used the calculated electron-phonon coupling to determine carrier relaxation time, avoiding the simplifications of deformation potential theory.
• Evaluated the thermoelectric figure of merit ZT using the standard formula ZT = (S²σT)/κ, where S is the Seebeck coefficient, σ is electrical conductivity, T is temperature, and κ is total thermal conductivity.
• Performed calculations across a range of temperatures to assess ZT dependence on thermal conditions.

Experimental results

Research questions

• RQ1 What is the thermoelectric performance of γ-graphyne, as quantified by the figure of merit ZT?
• RQ2 How does the ZT of γ-graphyne vary with temperature and carrier type (p- or n-doped)?
• RQ3 To what extent does using accurate electron-phonon coupling improve the prediction of thermoelectric properties compared to deformation potential theory?
• RQ4 What is the role of electron-phonon scattering in determining carrier relaxation time and overall thermoelectric efficiency in γ-graphyne?

Key findings

• At 600 K, γ-graphyne achieves a maximum ZT of 1.5 for p-type doping, indicating strong thermoelectric potential.
• For n-type doping at the same temperature, the maximum ZT reaches 1.0, showing a significant but lower performance compared to p-type.
• The thermoelectric performance of γ-graphyne is strongly dependent on both temperature and carrier type, with optimal performance near 600 K.
• The use of Wannier-interpolated, ultra-dense electron-phonon coupling matrix elements provides a more accurate carrier relaxation time than conventional deformation potential theory.
• The calculated ZT values demonstrate that γ-graphyne is a promising candidate for thermoelectric applications in the intermediate temperature range.
• The study confirms that accurate electron-phonon coupling is essential for reliable prediction of thermoelectric properties in two-dimensional carbon allotropes.