Tuned electronic band structure and intensified phonon scattering of Ge2Sb2Te5 by strain engineering for thermoelectric performance

Abstract

The strain engineering effect on the thermoelectric properties of Ge2Sb2Te5 has been investigated using first-principles calculations combined with Boltzmann transport theory. The results show that 3% strain tunes the band gap to a desirable value and leads to a band convergence of conduction bands. The multiband transport and more localized density of state in the conduction bands significantly increase the power factor of n-type Ge2Sb2Te5. The strain-induced phonon vibration spectrum convergence enhances the phonon scattering rate. The low-frequency acoustic-optical branch coupling and the unique high-frequency optical branch scattering at 3% strain together contribute to the reduction of the lattice thermal conductivity. At 700 K, 3% strain results in the maximum enhancement of the thermoelectric properties of Ge2Sb2Te5, enhanced by 30% and 424% for p- and n-type Ge2Sb2Te5 compared with no strain one, respectively.