Mechanism of Rare Earth Incorporation and Crystal Growth of Rare Earth Containing Type‑I Clathrates

Type-I clathrates possess extremely low thermal conductivities, a property that makes them promising materials for thermoelectric applications. The incorporation of cerium into one such clathrate has recently been shown to lead to a drastic enhancement of the thermopower, another property determining the thermoelectric efficiency. Here we explore the mechanism of the incorporation of rare earth elements into type-I clathrates. Our investigation of the crystal growth and the composition of the phase Ba_8–<i>x</i>RE_<i>x</i>TM_<i>y</i>Si_{46–<i>y</i>} (RE = rare earth element; TM = Au, Pd, Pt) reveals that the RE content <i>x</i> is mainly governed by two factors, the free cage space and the electron balance