Thermoelectric studies of ${\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{\mathrm{Te}}_2$ ($0\le x\le 0.3$)

We report thermoelectric properties of ${\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{\mathrm{Te}}_2$ ($0\le x\le 0.3$) alloy series where superconductivity at low temperatures emerges as the high-temperature structural transition ($T_s$) is suppressed. The isovalent ionic substitution of Rh into Ir has different effects on physical properties when compared to the anionic substitution of Se into Te, in which the structural transition is more stable with Se substitution. Rh substitution results in a slight reduction of lattice parameters and in an increase of number of carriers per unit cell. Weak-coupled BCS superconductivity in ${\mathrm{Ir}}_{0.8}{\mathrm{Rh}}_{0.2}{\mathrm{Te}}_2$ that emerges at low temperature ($T_c^{\mathrm{zero}}=2.45\mathrm{K}$) is most likely driven by electron-phonon coupling rather than dimer fluctuations mediated pairing.

Figure 1

(a) The Rietveld refinement of the background subtracted ${\mathrm{IrTe}}_2$ synchrotron powder x-ray diffraction up to $\mathrm{Q}\sim 12{\AA }^{-1}$. Plots show the observed (dots) and calculated (red solid line) powder patterns with a difference curve. The vertical tick marks represent Bragg reflections in the $P\overline{3}m1$ space group. Inset shows the evolution of the normalized intensity of (100) Bragg reflection with increasing $x$ in ${\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{\mathrm{Te}}_2$. (b) Unit cell parameters as a function of Rh substitution up to $x=0.3$. Inset shows crystal structure of ${\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{\mathrm{Te}}_2$ with Ir/Rh sites marked in blue and Te sites marked in orange.

Figure 2

Temperature dependence of electrical resistivity for ${\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{\mathrm{Te}}_2$ ($0\le x\le 0.3$). Inset shows the enlarged low temperature part of $2\sim 4$ K (normalized at 4 K).

Figure 3

Temperature dependence of Seebeck coefficient for ${\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{\mathrm{Te}}_2$ ($0\le x\le 0.3$). Inset shows the evolution of $S_{300\text{K}}$ (balls) and $S/T$ (circles) as a function of Rh content $x$.

Figure 4

Temperature dependence of (a) total thermal conductivity $\kappa$, (b) electronic part ${\kappa }_e$, and (c) phonon term ${\kappa }_L$ for ${\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{\mathrm{Te}}_2$ ($0\le x\le 0.3$).

Figure 5

(a) Temperature dependence of specific heat $C_p$ for ${\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{\mathrm{Te}}_2$ ($0\le x\le 0.3$). (b) The low temperature specific heat divided by temperature $C_p/T$ as a function of $T^2$ in zero field. The solid curve represents the fittings using $C_p/T=\gamma +\beta T^2$. Inset shows the evolution of Debye temperature ${\mathrm{\Theta }}_D$ and electronic specific heat coefficient $\gamma$.