Thermoelectric and Lattice Dynamical Properties of Ge$_{2}$Sb$_{2}$Te$_{5}$

Ge$_{2}$Sb$_{2}$Te$_{5}$ (GST) has been widely used as phase-change materials in optical data storage media and nonvolatile RAM devices. At elevated temperature, GST is known to undergo subsequent structural transitions from a non-conducting amorphous to (metastable) disordered cubic phase and then to a conducting hexagonal phase above 300$^{\circ}$C. Given that hexagonal-GST has already been reported to have promising thermoelectric properties and transport properties critically depend on the bonding information, a direct correlation between its structural- and transport properties needs to be established. In this talk, we will present the evolution of thermoelectric and lattice dynamical properties of GST in different phases via first principles calculations based on density functional theory. A better understanding of the origin of low-thermal conductivity in hexagonal-GST may provide critical information for further improvement of its thermoelectric figure of merit (ZT).