Electronic structure and thermoelectric properties of narrow-band-gap intermetallic compound Al2Fe3Si3

We investigated the electronic structure and thermoelectric properties of a ternary intermetallic compound Al2Fe3Si3 composed only of abundant elements. First-principles band structure calculations implied that the target compound Al2Fe3Si3 forms a narrow band gap of a few hundred meV near the Fermi level, indicating that both p- and n-type thermoelectric properties can be obtained by shifting the chemical potential. We present the thermoelectric properties of the narrow-band-gap intermetallic compound Al2Fe3Si3, which was synthesized by arc melting and spark plasma sintering. The conduction type could be controlled through changing the Al/Si ratio. The measured Seebeck coefficients were +55 and -90 mu V K-1 for p- and n-type materials, respectively. The obtained power factor was 370-400 mu W m(-1) K-2 in a mid-temperature region for both p- and n-type materials. Because of the low crystal symmetry of Al2Fe3Si3, the phonon thermal conductivity at 300 K exhibited a relatively low value of 4.5-5.5 W m(-1) K-1, despite being composed of relatively light elements. The estimated dimensionless figure of merit was found to be less than 0.04, which should be largely enhanced for practical applications.