Thermoelectric properties of (In, Cr)2Ge2Te6 layered compounds

Abstract

Ternary layered compounds belonging to the M₂N₂Q₆ family have recently garnered considerable attention owing to their compositional diversity and intrinsically low thermal conductivity. In this work, we systematically investigate the crystal structures and thermoelectric properties of layered (In, Cr)₂Ge₂Te₆ compounds by combining experimental characterization with first-principles calculations. The Cr₂Ge₂Te₆ compound exhibits stronger structural anisotropy, a narrower band gap, and higher thermoelectric performance than In₂Ge₂Te₆. Both materials show ultralow lattice thermal conductivity, originating from their low sound velocities and pronounced atom vibration coupling. Moreover, alloying In₂Ge₂Te₆ with Cr₂Ge₂Te₆ effectively strengthens point-defect phonon scattering, leading to further reduced lattice thermal conductivity and improved thermoelectric performance. Notably, InCrGe₂Te₆ exhibits a lattice thermal conductivity as low as 0.85 W m⁻¹ K⁻¹ near room temperature and drops to 0.43 W m⁻¹ K⁻¹ at 750 K, leading to a maximum zT value of 0.38. Further optimization of the carrier concentration is expected to yield higher thermoelectric performance.