Synthesis and Characterization of Melt-Spun Metastable Al6Ge5

The electronic structure and thermoelectric (TE) properties of metastable Al6Ge5 were investigated. The crystal structure with nominal composition Al6Ge5 is identified as isostructural to the high-performance TE material Zn4Sb3. The calculated density of states (DOS) shows that Al6Ge5 is a semiconductor with small bandgap of E (g) = 0.44 eV. Moreover, as Al6Ge5 has sharp edges in the DOS near the Fermi energy, high Seebeck coefficient (S) values are expected. Ribbon samples of Al6Ge5 were prepared using a single-roll melt-spinning method. We developed a process to prepare Al6Ge5 as the main component using this method under various optimal conditions, mainly cooling rate. Room-temperature values for S and electrical conductivity are -17.5 mu V K-1 and 2.64 x 10(4) Omega(-1) m(-1), respectively. The kappa value of around 0.5 W m(-1) K-1 at room temperature is considerably low. Although Al6Ge5 has potential to be a good TE material, the S value of the prepared samples is low, like metals, mainly due to impurities existing in the samples. High zT is considered obtainable by preparing high-purity single-phase Al6Ge5 with optimized carrier concentration.