Recrystallization induced in situ nanostructures in bulk bismuth antimony tellurides: a simple top down route and improved thermoelectric properties

Recrystallization induced in situ nanostructure formation was used as a new means to obtain high performance polycrystalline thermoelectric materials, which was realized by a simple hot forging process to the coarse-grained Bi0.5Sb1.5Te3 alloys. The pole figure measurement showed that the oriented textures were weakened or eliminated after hot forging of the alloys with a quasi-layered crystal structure, implying the presence of deformation recrystallization. Transmission electron microscopy observation revealed the recrystallization induced in situ nanostructures and high density of defects in the hot forged samples. Transport property measurements indicated that the hot forged samples had both increased electrical power factor and reduced thermal conductivity, compare to the initial alloys without hot forging. The maximum ZT values of >1.3 at room temperature were reproducibly obtained for the hot forged samples, suggesting that the simple new method can be applied for large scale production of high performance polycrystalline thermoelectric materials with in situ nanostructures.