Glass-like Lattice Thermal Conductivity and Thermoelectric Properties of Incommensurate Chimney-Ladder Compound FeGe_γ

Abstract

We have characterized the thermoelectric properties of FeGeγ, which is one of the promising Nowotny chimney-ladder compounds. A glass-like low lattice thermal conductivity below 1.0 W m–1 K–1 is observed around 373 K because of its complex structural nature, i.e., incommensurate structure. A first-principles band structure calculation implies that a narrow band gap of ∼0.2 eV is formed near the Fermi level for a hypothetical composition of Fe2Ge3 with a Ru2Sn3-type structure, leading to a large power factor of 1.90 mW m–1 K–2 near 600 K. The maximum dimensionless figure-of-merit of 0.57 is attractive as a starting point; calculation using the Boltzmann transport equation under a constant relaxation time approximation predicts that a further enhancement of ZT exceeding unity at 600–700 K can be achieved by optimizing the valence electron count per transition metal and further reduction of the lattice thermal conductivity.

Investigation of the bipolar effect in the thermoelectric material CaMg2Bi2 using a first-principles study

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The TE conversion efficiency and performance-price ratios of TE devices developed so far and those under development are insufficient to compete with fossil fuel based energy resources. Some intrinsic issues need to be solved for TE materials design and synthesis, and some of them have been lasting for decades.…”

Structural, Magnetic and Thermoelectric Properties of hp‐Mn3Ge5

“…The Seebeck coefficient is positive in the measured range (Figure , bottom left) with rather high values ( S 300K = 93 μV · K –1 ) and it increases linearly above 100 K. The total thermal conductivity (Figure , top right) increases with increasing temperature but remains overall low ( κ 300K = 1.85 W · K –1 · m –1 ), which may be attributed to the complex crystal structure of hp ‐Mn 3 Ge 5 . However, previous studies reveal both lower, and much higher values , . Therefore, additional studies are required to get a clear picture of the role of the crystal structure.…”

Growth of epitaxial FeGeγ nanocrystals with incommensurate Nowotny chimney-ladder phase on Si substrate

“…26) Furthermore, the compound had incommensurate NCL structure, where lattice parameter of crystal structures along c-axis is changed by shrinking the helix period of the E (= Ge) atoms due to compositional modulation. [26][27][28] The 29,30) which is lower than some NCL phase compounds such as MnSi γ [18][19][20][21] and VGe γ . 23) Moreover, electronic structure of the composition Fe 2 Ge 3 was calculated.…”

“…Fe 2 Ge 3 has a narrow band gap of ∼0.2 eV and the steep density of states near band edges, which leads to large Seebeck coefficient. 29,30) These features brought the high ZT value of 0.57 in FeGe γ . 29) As mentioned above, we are proposing the new approach: the shortening of both v g and τ by nanostructuring of material with complex crystal structure.…”