Abstract
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 μV K−1 and 2.64 × 104 Ω−1 m−1, respectively. The κ 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.
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