Zintl phase $Yb1−xCaxCd2Sb2$ with tunable thermoelectric properties induced by cation substitution

It has been shown previously that the thermoelectric properties of the Zintl phase compound $YbCd2Sb2$ can be finely tuned via Zn substitution at the Cd-site in the anionic $(Cd2Sb2)2−$ framework. Here we report the results of the investigation of isoelectronic substitution of Yb by Ca. The $p$-type $Yb1−xCaxCd2Sb2$ $(0.2≤x≤0.8)$ samples have been synthesized via a solid-state reaction followed by suitable cooling, annealing, grinding, and spark plasma sintering densification processes. In samples with $x=0.2$⁠, 0.4, 0.5, 0.6, 0.8, the electrical conductivity, Seebeck coefficient, and thermal conductivity measurements have been carried out in the temperature range from 300 to 650 K. It is found that the Ca substitution effectively lowers the thermal conductivity for all samples at high temperature, while it significantly increases the Seebeck coefficient. As a result, the dimensionless figure of merit $ZT$ of 0.96 has been attained at 650 K for samples with $x=0.4$⁠, while the value is 0.78 for the unsubstituted $YbCd2Sb2$