Effective mass calculations of SrTiO3-based superlattices for thermoelectric applications lead to new layer design

TL;DR

This study investigates how superlattice structures of SrTiO3 influence the effective mass and bandstructure, aiming to optimize thermoelectric properties by designing new layered configurations.

Contribution

It provides new insights into how superlattice layer design affects effective mass and electronic properties in SrTiO3-based thermoelectric materials.

Findings

Superlattice structure alters effective mass anisotropy.

Finer nanostructures increase effective mass.

Coarser structures reduce effective mass.

Abstract

The effective mass is one of the main factors for enlarging the Seebeck coefficient and electronic conductivity of SrTiO3-based thermoelectric materials [1,2]. The goal of this paper is to clarify, how superlattices can change the effective mass and other features of the bandstructure. The natural Ruddlesden-Popper phase (SrTiO3)n(SrO)m with n=2, m=1 the situation changes, because the TiO6-octahedrons are slightly extended, due to diluted density of the SrO layer. Another effect is the deformed electron density, which leads to reduced effective mass perpendicular to the layer, but enlarged parallel to the plane [3]. The average value of the effective mass over this anisotropy of the 2-dimensional electron gas (2DEG) for pure Ruddlesden-Popper phases is smaller, but can increase beyond the value of pure Pervoskite for certain doping elements. In the same way, artificial superlattices (SrTiO3)x/(SrTi1-z(Nb)zO3)y were examined. When fine nanostructures (n=2, m=3 or n=3, m=2) are present the effective mass increases, when the structure becomes coarser (n=4, m=1) smaller values are determined.