Uniaxial Tensile Strain Induced the Enhancement of Thermoelectric Properties in <i>n</i>-Type BiCuO<i>Ch</i> (<i>Ch</i> = Se, S): A First Principles Study

• Main Authors: Chunpeng Zou, Chihou Lei, Daifeng Zou, Yunya Liu
• Format: Article
• Language: English
• Published: MDPI AG 2020-04-01
• Series: Materials
• Subjects: BiCuOSe; BiCuOS; strain; thermoelectric properties; electronic structure
• Online Access: https://www.mdpi.com/1996-1944/13/7/1755

It is well known that the performance of thermoelectric measured by figure of merit <i>ZT</i> linearly depends on electrical conductivity, while it is quadratic related to the Seebeck coefficient, and the improvement of Seebeck coefficient may reduce electrical conductivity. As a promising thermoelectric material, BiCuO<i>Ch</i> (<i>Ch</i> = Se, S) possesses intrinsically low thermal conductivity, and comparing with its <i>p</i>-type counterpart, <i>n</i>-type BiCuO<i>Ch</i> has superior electrical conductivity. Thus, a strategy for increasing Seebeck coefficient while almost maintaining electrical conductivity for enhancing thermoelectric properties of <i>n</i>-type BiCuO<i>Ch</i> is highly desired. In this work, the effects of uniaxial tensile strain on the electronic structures and thermoelectric properties of <i>n</i>-type BiCuO<i>Ch</i> are examined by using first-principles calculations combined with semiclassical Boltzmann transport theory. The results indicate that the Seebeck coefficient can be enhanced under uniaxial tensile strain, and the reduction of electrical conductivity is negligible. The enhancement is attributed to the increase in the slope of total density of states and the effective mass of electron, accompanied with the conduction band near Fermi level flatter along the Γ to Z direction under strain. Comparing with the unstrained counterpart, the power factor can be improved by 54% for <i>n</i>-type BiCuOSe, and 74% for <i>n</i>-type BiCuOS under a strain of 6% at 800 K with electron concentration 3 × 10²⁰ cm⁻³. Furthermore, the optimal carrier concentrations at different strains are determined. These insights point to an alternative strategy for superior thermoelectric properties.