Tetragonal plus displacive ferroelectric distortion in thin SrTiO-3 films grown on Si(001)

摘要

A ferroelectric crystal is one that possesses a net dipole moment even in the absence of an external electric field. In order for this spontaneous polarization to arise, the center of negative charge of the crystal must displace from the center of positive charge. Accompanying this net displacement of charge there is typically a macroscopic distortion of the unit cell dimensions. Consequently, there exists an intrinsic relationship between strain and ferroelectricity that may be exploited in thin-film growth. Here we combine x-ray absorption fine-structure spectroscopy with x-ray diffraction to study the local structure of thin SrTiO-3 films grown pseudomorphically on Si(001). Our data indicate that below a critical thickness of ~ 80 A, the in-plane compressive strain imposed on the SrTiO-3 layers by the Si substrate results in a tetragonal plus displacive ferroelectric distortion in the films at room temperature. This study therefore suggests the existence of a Curie "thickness" for strained-layer perovskite growth.