Defects-Engineered Bismuth Telluride Alloys Towards Waste Heat Recovery

Among various types of thermoelectric materials, bismuth telluride (Bi₂Te₃) based alloys have been considered as a key material for waste heat recovery as well as active control in temperature. Recently, Intensive effort to engineer the microstructures of bismuth telluride have been made to overcome the current limitation on its thermoelectric energy conversion performance levels (ZT) in viewpoint of defects. In this presentation, we report two plausible powder metallurgy routes to achieve microstructures which exhibit defect-engineered interfaces in p-and n-type bismuth telluride alloys, respectively. For designing favorable defects of p- and n-BiSbTe alloys, the defect formation energy has thermodynamically been calcaulated by First-principle calcuation based on density functional theory under a certain sintering condition. First, considering the wavelengths of carriers and phonons, we introduce geometrical point defect assembly structures in a nano-scale of about 5-10nm are created and dispersed in the p-type BiSbTe crystalline grain. This nanostructure contributes to a reduction in the lattice thermal conductivity and increase in carrier density. Second, novel synthetic process of n-type BiSbTe alloys with antisite defect such as Te@Sb or Te@Bi rather than BiTeSe has been developed by at the same time utilizing the concept of creating dislocation network arrays. As results of these, the fabricated bismuth telluride alloys show peak ZT values of 1.3 for p-type and 1.2 for n-type, respectively which are 1.6 times higher than those of both pristine BiSbTe alloys fabricated by the same method without defect engineering. And characteristically, the defect-engineered bismuth tellurides show simultaneous control which lowers thermal conductivity despite significantly increased electrical conductivity. We think this defect engineering-based fabrication process using conventional powder metallurgy provide a new avenue for improving and modulating the efficiency of thermal-to-electrical conversion in bismuth telluride. Thus, the newly developed materials can be utilized for waste heat recovery of shipbuilding but also can be applied for thermal energy harvester in ICT field.