Effect of transition element substitution on thermoelectric properties of semiconductor clathrate compounds

Semiconductor clathrate compounds are energetically being studied as a new class of thermoelectric material based on the concept of Phonon Glass and Electron Crystal, since the materials combine glasslike low thermal conductivity and relatively good carrier mobility. These fascinating properties of clathrate compounds depend strongly on the details of their crystal structures. We will review our attempts to improve the thermoelectric properties of clathrate compounds by the modification of the electronic properties through the elemental substitution as well as by the optimization of doping level. We have revealed that the substitution of transition metal platinum, which causes the local ordering at the particular site of the framework, brings about a significant effect on the thermoelectric properties. The result indicates a new way for developing novel clathrate compounds with high thermoelectric performance.