High dielectric tunability of (100) oriented PbxSr1-xTiO3 thin film coordinately controlled by dipole activation and phase anisotropy

Why the dielectric tunability is maximal in dielectrics near the cubic-tetragonal phase transformation point is still unknown, although it is well accepted for tunable dielectrics till now. Here, we report dielectric tunability following a typical (100) oriented PbxSr1-xTiO3 (PST) thin film with different Pb/Sr ratio. The (100) PST thin films were prepared by sol-gel method on the terbium doped lead titanate (2% Tb-PbTiO3) inducing layer. They are tensile strained and the spontaneous polarizations (dipoles) are along the in-plain direction. Driven by the vertical DC bias, the dipoles in the (100) PST will be possibly rotated to the direction along DC bias and thus tunable permittivity appears. All these thin films show high dielectric tunability over 50%, in which the PST45(Pb0.45Sr0.55TiO3) exhibits the highest one. In this paper, the tunability is found controlled coordinately by both the anisotropy of the perovskite phase and the activation of dipole rotation. It increases with increasing the anisotropy when Pb increases based on the enlarging difference in permittivity along a and c directions, while it decreases with increasing the activation energy based on uneasy rotation of dipoles under DC bias. That is why, high dielectric tunability always exists near the cubic-tetragonal phase transformation; at this point, the activation energy is not so high and the permittivity difference keeps still a little significant. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3671645]