Structural and Thermoelectric Properties of Chimney–Ladder Compounds in the Ru-Mn-Si System

Abstract

We have investigated phase relationships of the sesquisilicide alloys in the Ru-Mn-Si system. A series of chimney-ladder phases Ru 1Àx Mn x Si y (0.14 £ x £ 0.97, 1.584 £ y £ 1.741) are formed over a wide compositional range between Ru 2 Si 3 and Mn 4 Si 7 . We also investigated thermoelectric properties of the directionally solidified Ru 1Àx Mn x Si y alloys as a function of Mn content and temperature. The dimensionless figure of merit ZT for alloys with high Mn content (x ‡ 0.75) increases as the Mn content increases. The alloy with x = 0.90 exhibits ZT as high as 0.76 at 874 K.

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.…”

“…NCL structure is described by T m E n , where T and E describe transition metals and group 13-15 elements, respectively, and have complexed unit cells composed of m-step helices of E atoms and n-step helices of T atoms. 17) Many materials with NCL structure show high thermoelectric efficiency due to its low κ, for example higher manganese silicide (MnSi γ ), [18][19][20][21] Ru 2 Si 3 , 18,19,22) and VGe γ . 23) Recently, a new NCL phase compound was reported in an Fe-Ge system.…”

Thermoelectric properties of Fe and Al double substituted MnSi (γ~1.73)

“…A large number of chemical substitutions have been reported for MnSi γ . Most of these focus on the transition metal sublattice and include Mn 1 À x Fe x Si γ (ZT¼0.45 at 800 K) [19,20], Mn 1 À x Cr x Si γ (ZT¼0.45 at 900 K) [20][21][22], co-doping with Cr and Ru (ZT¼0.6 at 850 K) [21], Mn 1 À x Ru x Si γ (ZT¼0.75 at 875 K for x¼ 0.1) [23,24] and Mn 1 À x Re x Si γ (ZT¼ 0.6 at 800 K) [25]. Substitutions into the main group sublattice have also been explored, and in particular hole doping using Al has been found to be a promising route towards obtaining good figures of merit (e.g.…”