Fermi surface complexity, effective mass, and conduction band alignment in n-type thermoelectric Mg3Sb2-xBix from first principles calculations

Abstract

Using first principles calculations, we study the conduction band alignment, effective mass, and Fermi surface complexity factor of n-type Mg3Sb2-xBix (x = 0, 1, and 2) from the full ab initio band structure. We find that with increasing the Bi content the K and M band minima moves away from the conduction band minimum CB1 while the singly-degenerate $\Gamma$ band minimum shifts rapidly downward and approaches the conduction band minimum. But the favorable six-fold degenerate CB1 band minimum keeps dominating the conduction band minimum and there is no band crossing between the $\Gamma$ and CB1 band minima. In addition, we show that the connection of the CB1 carrier pockets with the energy level close to the band minimum M can strongly enhance the carrier pocket anisotropy and Fermi surface complexity factor, which is likely the electronic origin for the local maximum in the theoretical power factor. Our calculations also show that the band gap, density of states effective mass, Seebeck coefficient, and Fermi surface complexity factor decrease with increasing the Bi content, which is unfavorable to the electrical transport. However, reducing the conductivity effective mass with increasing the Bi content is beneficial to the electrical transport by improving carrier mobility and weighted mobility as long as the detrimental bipolar effect is insignificant. As a result, in comparison with n-type Mg3Sb2, n-type Mg3SbBi shows higher power factors and a much lower optimal carrier concentration for the theoretical power factor at 300 K, which can be easily achieved by the experiment.

References in corpus (6)

• BoltzTraP. A code for calculating band-structure dependent quantities
• High three dimensional thermoelectric performance from low dimensional bands
• Relating chemical bonding to physical properties: The origin of unexpected isotropic properties in layered materials
• Mg${}_{3+\delta }$Sb${}_x$Bi${}_{2-x}$ family: A promising substitute for the start-of-art n-type thermoelectric materials near room temperature
• Theory of Band Warping and its Effects on Thermoelectronic Transport Properties
• Theory of thermoelectricity in Mg${}_3$Sb${}_2$ with an energy- and temperature-dependent relaxation time

Cited by in corpus (9)

• Rapid one-step synthesis and compaction of high-performance n-type Mg3Sb2 thermoelectrics
• Probing efficient n-type lanthanide dopants for Mg${}_3$Sb${}_2$ thermoelectrics
• Materials design criteria for ultra-high thermoelectric power factors in metals
• Enhanced thermoelectric performance by van Hove singularities in the density of states of type-II nodal-line semimetals
• First principles study on the thermoelectric performance of CaAl${}_2$Si${}_2$-type Zintl phase compounds
• The role of electronic bandstructure shape in improving the thermoelectric power factor of complex materials
• Sommerfeld-Bethe analysis of ZT in inhomogeneous thermoelectrics
• Possibility of n-type doping in CaAl${}_2$Si${}_2$-type Zintl phase compound CaZn${}_2{X}_2$ ($X$ = As, P)
• First-principles Study of Metallic-atom Diffusion in Thermoelectric Material Mg${}_3$Sb${}_2$