Experimental and computational approaches to study the high temperature thermoelectric properties of novel topological semimetal CoSi.
Shamim SkNisha ShahiSudhir Kumar PandeyPublished in: Journal of physics. Condensed matter : an Institute of Physics journal (2022)
Here, we study the thermoelectric properties of topological semimetal CoSi in the temperature range 300-800 K by using combined experimental and density functional theory (DFT) based methods. CoSi is synthesized using arc melting technique and the Rietveld refinement gives the lattice parameters of a = b = c = 4.445 Å. The measured values of Seebeck coefficient ( S ) shows the non-monotonic behaviour in the studied temperature range with the value of ∼-81 μ V K -1 at room temperature. The | S | first increases till 560 K (∼-93 μ V K -1 ) and then decreases up to 800 K (∼-84 μ V K -1 ) indicating the dominating n-type behaviour in the full temperature range. The electrical conductivity, σ (thermal conductivity, κ ) shows the monotonic decreasing (increasing) behaviour with the values of∼5.2×105(12.1 W m -1 K -1 ) and∼3.6×105(14.2 W m -1 K -1 ) Ω -1 m -1 at 300 K and 800 K, respectively. The κ exhibits the temperature dependency as, κ ∝ T 0.16 . The DFT based Boltzmann transport theory is used to understand these behaviour. The multi-band electron and hole pockets appear to be mainly responsible for deciding the temperature dependent transport behaviour. Specifically, the decrease in the | S | above 560 K and change in the slope of σ around 450 K are due to the contribution of thermally generated charge carriers from the hole pockets. The temperature dependent relaxation time ( τ ) is computed by comparing the experimental σ with calculated σ / τ and it shows temperature dependency of 1/ T 0.35 . Further this value of τ is used to calculate the temperature dependent electronic part of thermal conductivity ( κ e ) and it gives a fairly good match with the experiment. Present study suggests that electronic band-structure obtained from DFT provides a reasonably good estimate of the transport coefficients of CoSi in the high temperature region of 300-800 K.