Carriers concentration tailoring and phonon scattering from n-type zinc oxide (ZnO) nanoinclusion in p- and n-type bismuth telluride (Bi2Te3): Leading to ultra low thermal conductivity and excellent thermoelectric properties

Abstract

ZnO/Bi2Te3 (p- and n-type) nanocomposites with 5 vol% nanosized ZnO content are fabricated via ball milling mixing and spark plasma sintering. Herein, ZnO is an intrinsic n-type semiconductor with low thermal conductivity. In ZnO/Bi2Te3 (p- and n-type) composites, ZnO exits as nanoinculsions to more effectively inhabit the phonon transporting, and simultaneously tailor the carrier concentration of composite materials. Ultra low lattice thermal conductivity (0.22–0.3 W/mK2) is obtained in both materials. ZnO nanoinclusions can lead to higher carriers and high electronic conductivity of n-type Bi2Te2.7Se0.3 composite material. Since electronic thermal conductivity is dominant (75%) in thermal conductivity, more phonon scattering from defects and nanoinclusions does not effectively improve ZT values of n-type materials. In contrast, while ZnO addition can obviously reduce the carrier concentration and lead to the resistivity's large increase, ZnO nanoinclusions in p-type Bi1.5Sb0.5Te3 composite material would significantly decrease the lattice and total thermal conductivity. As a result, an enhancement (30%) of ZT values (∼1.3) can be achieved in composite material compared with p-type ingot.