Dielectric response of temperature-graded ferroelectric films

The dielectric susceptibility and dielectric tunability of the temperature-graded BaTiO3 thin films are investigated by using a modified transverse Ising model, taking the four-spin interaction and quantum fluctuation into account. There is a broad and smooth peak of the dielectric susceptibility at low temperature except for the sharp dielectric peak corresponding to the phase-transition temperature, irrespective of the sign of the temperature gradient. This behavior is different from the homogeneous bulk materials. Although the temperature gradient reduces the dielectric susceptibility, the temperature stability of the dielectric susceptibility can be effectively improved between the two dielectric peaks. The quantum fluctuation not only can enhance the temperature stability of the dielectric susceptibility but also has a significant influence on the dielectric tunability. Furthermore, a high dielectric tunability can be achieved by adjusting an appropriate positive temperature gradient, the quantum fluctuation strength, and the four-spin interaction strength.