Oxygen vacancy induced strong anisotropy of the thermoelectric properties of strontium barium niobate

Electronic structure and thermoelectric properties of strontium barium niobate were investigated by first principles calculations combined with the semi-classical Boltzmann theory. The band structure corresponding to lattice anisotropy shows higher band dispersion along c axis, but the conducive pathway is mainly along ab plane. As a result, the values of power factor are in the same order of magnitude along different directions. Thus, the lattice anisotropy alone cannot result in the strong anisotropic thermoelectric properties of strontium barium niobate. Oxygen vacancies not only act as charge carrier donors, but also enhance the band dispersion and change the magnetic quantum number of the electrons around the bottom of conduction band. Accordingly, the thermoelectric properties of strontium barium niobate show very strong anisotropy after oxygen reduction.