Energy conversion is employed to power generation utilizing the Seebeck effect or cooling utilizing the Peltier effect. Herein, we study several Ir3Ge7 typed semiconductor materials for potential thermoelectric energy conversion. Mo3Sb7, crystallizing in Ir3Ge7 type, can be rendered semiconducting by a partial Sb-Te substitution without noticeable structure changes, resulting in Mo3Sb5Te2 with 55 valence electrons per formula unit. Meanwhile, large cubic voids in the Mo3Sb5Te2 crystal structure provide the possibility of filling the voids with small cations to decrease the thermal conductivity by the so-called rattling effect. To verify this idea, the thermal and electrical transport properties of Mo3Sb5.4Te1.6 and Ni0.06Mo3Sb5.4Te1.6 are studied. The material, Nb3Sb2Te5, is isoelectronic with Mo3Sb5Te2 and crystallizes in the Ir3Ge7 type like Mo3Sb5Te2. Its thermoelectric properties are studied. Re3(GeAs)7 also crystallizes in the cubic Ir3Ge7 type and different doping levels can be achieved by adjusting the ratio of Ge and As. Here we study the Re3GeAs6 and Re3Ge0.6As6.4 materials. Like Mo3Sb5Te2, its crystal structure contains large voids, making it also possible to fill in small cations as rattler. Co is attempted to insert in the crystal to get Co0.05Re3Ge0.4As6.6. The resulting thermoelectric properties are discussed in this document
