Abstract
Fe2Ge3 with an incommensurate Nowotny chimney-ladder (NCL) structure is a promising material for thermoelectric applications due to its low thermal conductivity. Previous experimental studies on Fe2Ge3 have mainly focused on polycrystalline samples, resulting in a limited understanding of the material's intrinsic thermoelectric properties and the underlying causes of its low thermal conductivity. Here we report the synthesis and thermoelectric properties of single crystalline Fe2Ge3. Millimeter-sized Fe2Ge3 single crystals grown by the chemical vapor transport method enable the study of the intrinsic thermoelectric properties. The Seebeck coefficient of Fe2Ge3 is negative and its magnitude increases linearly with temperature, showing a degenerate n-type semiconductor behavior. Analysis of the electrical resistivity and specific heat data indicates the existence of an Einstein mode with a characteristic temperature of about 60 K, suggesting the presence of low-energy optical phonons. The thermal conductivity of Fe2Ge3 along the c axis is as low as 1.9Wm−1K−1 at 300 K and exhibits a nearly temperature-independent characteristic, which is distinct from the previous theoretical calculations with a stronger temperature dependence. The low thermal conductivity may be attributed to the scattering of acoustic phonons by low-energy optical modes and the presence of non-extended diffuson modes, as reported in another NCL compound, MnSi1.74. This study provides valuable insights into the electrical and thermal properties of Fe2Ge3, which can open up possibilities for future advances in thermoelectric applications.
