First-principles study of electronic structures and elasticity of Al2Fe3Si3

Al2Fe3Si3 intermetallic compound shows promising application in low-cost and non-toxic thermoelectric device because of its relatively high power factor of similar to 700 mu W m(-1) K-2 at 400 K. Herein we performed the first-principles calculations with the projector augmented-wave (PAW) method to study the formation energies, elastic constants, electronic structures, and electronic transport properties of Al2Fe3Si3. We discussed the thermodynamical stability of Al2Fe3Si3 against other ternary crystalline compounds in Al-Fe-Si phase. The band gap of Al2Fe3Si3 was particularly examined using the semilocal and hybrid functionals and the on-site Hubbard correction, which were also applied to beta-FeSi2 to calibrate the prediction reliability of our employed computational methods. Our calculations show that Al2Fe3Si3 is a narrow-gap semiconductor. The semilocal functional within generalized gradient approximation (GGA) shows an exceptional agreement between the predicted band gap of Al2Fe3Si3 and the available experiment data, which is in contrast to the typical trend and rationally understood through a comprehensive comparison. We found that both HSE06 and PBE0 hybrid functionals with a standard setup overestimated the band gaps of Al2Fe3Si3 and beta-FeSi2 too much. The underlying reasons may be ascribed to a large electronic screening, which arises from the unique characteristics of Fe 3d states appearing in both sides of band gaps of Al2Fe3Si3 and beta-FeSi2, and to a reduced delocalization error thanks to the covalent Fe-Si and Si-Si bonding nature. The chemical bonding and elasticity of Al2Fe3Si3 were compared with those of beta-FeSi2 and FeAl2. In Al2Fe3Si3 the Fe-Al bonding is more ionic and the Fe-Si bonding is more covalent. The elastic moduli of Al2Fe3Si3 are comparable to those of beta-FeSi2 and larger than those of FeAl2. Our calculation results indicate that the mechanical strength of Al2Fe3Si3 could be strong enough for the practical application in thermoelectric device.