First-principles calculations of carrier-doping effects in SrTiO₃

Carrier-doping effects on the structural phase transitions in SrTiO₃ are investigated by the first-principles calculations. It is found that the instabilities of the cubic phase to both the TiO₆-octahedron rotated phase and the ferroelectric phase are modulated characteristically by the electron doping and the hole doping. The results of the calculations are consistent with a previous experiment in which carrier electrons were introduced by impurity doping, and with another experiment where carriers were doped in SrTi¹⁸O₃ by photo-irradiation. The modulations of the instabilities are explained by a simple and intuitive mechanism.