Microscopic insight into temperature-graded ferroelectrics

A microscopic approach based on the first-principles effective Hamiltonian is developed to study the polarization response in temperature-graded ferroelectrics. This approach has been applied to the case of (Ba(0.75)Sr(0.25))TiO? alloy. A comparison of the computational results with available experimental data attests to the remarkable accuracy of the present approach. Our computations reveal a strong anisotropy in the response of polarization to the temperature gradient (TG). In particular, the polarization offset along the direction of TG is an order of magnitude lower than in the perpendicular direction. The large as well as the small TGs are considered and found to yield qualitatively different polarization field responses. Among other striking findings are (i) the coexistence of different phases in chemically homogeneous regions, (ii) formation of low-symmetry phases, and (iii) thermally controlled polarization rotation.