Effect of Ti substitution on the thermoelectric properties of the pentatelluride materials M1−xTixTe5 (M=Hf, Zr)

The thermoelectric properties (resistivity and thermopower) of single crystals of the low dimensional pentatelluride materials, ${\mathrm{HfTe}}_{\mathrm{5\hspace{0.17em}}}$ and ${\mathrm{ZrTe}}_{\mathrm{5}},$ have been measured as a function of temperature from 10 $\mathrm{K}\text{<T<320}$ K. The effect of small amounts of Ti substitutional doping ${\mathrm{(M}}_{\text{1−x}}{\mathrm{Ti}}_x{\mathrm{Te}}_5,$ where $\mathrm{M=}\mathrm{Hf}\mathrm{,\hspace{0.5em}}\mathrm{Zr}$ ) on the thermoelectric properties is reported here. A resistive transition occurs in the pentatellurides, as evidenced by a peak in the resistivity, $T_P\text{≈80}$ K for ${\mathrm{HfTe}}_5$ and $T_P\text{≈145}$ K for ${\mathrm{ZrTe}}_5.$ Both parent materials exhibit a large positive ($p$ -type) thermopower near room temperature which undergoes a change to negative ($n$ -type) below the peak temperature. The thermal conductivity is relatively low (≈5 W/m K) for the $M{\mathrm{Te}}_5$ materials. The Ti substitution affects the electronic properties strongly, producing a substantial shift in the peak temperature while the large values of thermopower remain essentially unaffected. These results warrant further investigation of these materials as candidates for low temperature thermoelectric applications.