Theoretical Investigation of the Electronic, Structural, Optical and Thermodynamic Properties of LaxSr1-xTiO3 (x=0, 0.125, 0.25)

To better understand the electronic, optical, and thermodynamic behaviors of lanthanum doped strontium titanate (STO) LaxSr1-xTiO3 (x = 0, 0.125, 0.25) at high temperatures for possible fuel cell and sensor applications, ab initio thermodynamics have been employed by combining the first-principles density functional theory with lattice phonon dynamics to investigate their electronic structures and thermodynamic evolutions versus temperatures. Different from pure STO, our results show that after La-doping into STO, the corresponding LaxSr1-xTiO3 become metallic without a band-gap. Doping La into STO dramatically alters the optical properties of pure STO which have wide applications for sensor technology development. With increasing La-doping level x, the calculated free energy Delta G(T) and enthalpy Delta H(T) of LaxSr1-xTiO3 decrease at given temperature T, while with increasing T, the Delta G(T) decrease, but the Delta H(T) increase for all LaxSr1-xTiO3 studied.