Giant phonon softening and avoided crossing in aliovalence-doped heavy-band thermoelectrics

Abstract

Aliovalent doping has been adopted to optimize the electrical properties of semiconductors, while its impact on the phonon structure and propagation is seldom paid proper attention to. This work reveals that aliovalent doping can be much more effective in reducing the lattice thermal conductivity of thermoelectric semiconductors than the commonly employed isoelectronic alloying strategy. As demonstrated in the heavy-band NbFeSb system, a large reduction of 65% in the lattice thermal conductivity is achieved through only 10% aliovalent Hf-doping, compared to the 4 times higher isoelectronic Ta-alloying. It is elucidated that aliovalent doping introduces free charge carriers and enhances the screening, leading to the giant softening and deceleration of optical phonons. Moreover, the heavy dopant can induce the avoided-crossing of acoustic and optical phonon branches, further decelerating the acoustic phonons. These results highlight the significant role of aliovalent dopants in regulating the phonon structure and suppressing the phonon propagation of semiconductors.

References in corpus (6)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• EPW: A program for calculating the electron-phonon coupling using maximally localized Wannier functions
• Covalent bonding and the nature of band gaps in some half-Heusler compounds
• Ultralow Thermal Conductivity in Full-Heusler Semiconductors
• Ultrasensitive barocaloric material for room-temperature solid-state refrigeration
• Electron-phonon interaction and spectral weight transfer in Fe${}_{1-x}$Co${}_x$Si

Cited by in corpus (4)

• When is the Four-phonon Effect in Half-Heusler Materials more Pronounced?
• Neutron scattering studies of complex lattice dynamics in energy materials
• Carrier scattering considerations and thermoelectric power factors of half-Heuslers
• Dopant-modulated lattice softening drives drastic thermal conductivity reduction in β-FeSi2 thermoelectrics