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

Abstract

The effects of substituting transition metals (TM: Co, Rh, Ni and Pd) on the Ru site with respect to the electrical conductivity and Seebeck coefficient for the binary semiconducting intermetallic compound RuGa 2 have been investigated above room temperature. Only Rh substituted RuGa 2 exhibited a higher electrical conductivity compared with undoped RuGa 2 . The sign of the Seebeck coefficient at 373 K for all doped samples is negative and their magnitudes exhibit rather large values of 150 < «S 373K « < 350 µVK ¹1, indicating that Co, Rh, Ni and Pd work as n-type dopants. However, the sign changes from negative to positive at high temperature. This implies that the effective carrier doping is insufficient to obtain a high efficiency n-type material. To investigate the effect of TM substitution on the electronic density of states, the Korringa-Kohn-Rostoker Green's function method under a coherent potential approximation has been employed. The calculation indicates that the dopant d-states at the conduction band affect the transport properties.

Phase stability and thermoelectric properties of semiconductor-like tetragonal FeAl2

“…Theoretical studies also predicted that t-FeAl 2 exhibits a band-gap near the Fermi level, which was explained by the 14 electrons rule or 18 − n (n = 4) electrons rule, where n is the average number of Fe-Fe bonds [5,6,[8][9][10][11][12]. Indeed, analog compounds RuAl 2 and RuGa 2 have been reported as narrow bandgap semiconductors with a high power factor, S 2 σ [7, [13][14][15][16]. From these theoretical and experimental works, it is expected that t-FeAl 2 also behaves like a semiconductor.…”

Improvement of the Thermoelectric Performance of Pseudogap and Narrow-Gap Compounds via Theoretical Calculations

“…16) Other n-type dopants (Co, Ni, Rh, and Pd) could not produce sufficient carrier numbers, mainly because of the formation of significant impurity bands. 21) These results indicate that determining impurity band formation using theoretical calculations would be a beneficial way to select a suitable dopant for tuning a material's thermoelectric properties.…”

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

“…3) However, experimental carrier doping of RuGa 2 via transition metals substitution on the Ru site (hole doping: Re, electron doping: Ir, Rh, Co, Ni and Pd) [3][4][5] was not able to achieve the theoretically predicated ZT values. Ponnambalam et al 6) reported that carrier doping of RuGa 2 (Cr, Mn, Si and Co) below room temperature resulted in the effective mass of n-type RuGa 2 being larger than that of p-type RuGa 2 , as expected from band structure, leading to a larger absolute value of S for n-type RuGa 2 at the same doping level.…”

“…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…”