Density functional theory and experimental study of the electronic structure and transport properties of La, V, Nb, and Ta doped SrTiO3.

The electronic structure and transport properties of donor doped SrTiO3 are studied using density functional theory with spin-orbit coupling and conductivity, Hall, and Seebeck effect measurements over a wide temperature range (100 K to 600 K). Split-off energies ΔSO are tunable through the dopant SO interaction strength and concentration varying from 28.1 meV for pure STO to 70.93 meV for SrTi0.5Nb0.5O3. At lower carrier concentrations and temperatures, SO coupling has a marked effect on both the filling dependence of the density-of-states mass as well as the temperature dependence of the Seebeck coefficient, with quantitative theoretical predictions based on DFT calculations that include the SO interaction in closer agreement to the experimental data. Moreover, the results suggest that the predictive power of the current theory is not unlimited, with less accuracy for the calculated S predicting the magnitude of the experimental S data at lower dopant concentrations than for degenerately doped systems. A concentration dependent mass enhancement of ∼2-5, relative to the density-of-states mass in the local density approximation, possibly due to the influence of electronic screening of the electron-phonon interaction, would bring the theoretical S in accord with the experimental S data. This additional carrier-dependent enhancement mechanism for S may give an additional degree of freedom in terms of designing new higher efficiency thermoelectric energy materials. [ABSTRACT FROM AUTHOR]