Composition dependence of thermoelectric properties of binary narrow-gap Ga67−xRu33+x compound

Effects of Transition Metal (TM: Co, Rh, Ni and Pd) Substitution for Ru on Thermoelectric Properties for Intermetallic Compound RuGa₂

“…Figure 1 shows the experimental and calculated XRD patterns for Co, Rh, Ni and Pd substituted RuGa 2 . As for the Co substituted sample, there exist very small amounts of the secondary phase RuGa 3 , which is also observed in undoped, 7) Re- 8) and Ir-substituted RuGa 2 .…”

“…S of undoped RuGa 2 exhibits a large positive value of 300 µVK ¹1 at 373 K. In the TM substituted samples, the sign of S changes from positive to negative and S exhibits a large value of 150 < «S« < 350 µVK ¹1 at about 373 K, indicating that the chemical potential, µ, shifts to the conduction band. Figure 4 shows the magnitude of S at 373 K, «S 373K «, as a function of carrier concentration at room temperature n 300K for undoped RuGa 2 , 7) and samples doped with Re, 8) Ir 10) and TM substituted RuGa 2 . Undoped and Re substituted RuGa 2 exhibit a strong correlation between «S« and carrier concentration shown with dotted line.…”

“…7) The nominal composition was selected as (Co, Rh, Ni, Pd) 2 Ru 31.4 Ga 66.6 because the maximum ZT can be obtained for Ru 33.4 Ga 66.6 through non-doping 7) and around 2 at% substitution of single electron dopant for Ru site. 10) Mother ingots were synthesized by an arc-melting technique in a purified argon (6N) atmosphere.…”

“…15) The maximum ZT found among these intermetallic compounds is 0.50 at 773 K for RuGa 2 compound. 7) Although the effects of hole 8) and electron doping 10) on the thermoelectric properties above room temperature have been investigated for RuGa 2 , we have investigated various kinds of electron dopants effects on the electrical conductivity and Seebeck coefficient for RuGa 2 compound: we selected single electron doping elements (Co and Rh) and double electron doping elements (Ni and Pd). Furthermore, to elucidate the effects of TM substitution on the electronic density of states, N(E), the Korringa-Kohn-Rostoker Green's function method under a coherent potential approximation (KKR-CPA) 16,17) has been employed.…”

First-Principles-Based Phonon Calculation and Raman Spectroscopy Measurement of RuGa₂ and RuAl₂ with High Thermoelectric Power Factors

“…Our group has investigated thermoelectric properties of narrow band gap binary intermetallic compounds comprised of group-13 and transition metal elements using electronic structure calculations. [1][2][3][4][5] In the current study, we focus on TiSi 2 -type RuGa 2 and RuAl 2 , which are Nowotny chimney-ladder phases. These compounds have a narrow band gap, approximately 0.3 eV near the Fermi level, which leads to a high power factor, S 2 σ, in a mid-temperature range (RuGa 2 : 2.8 mW m…”