Dielectric properties and switching processes of ferroelectric superlattices

Abstract

We review dielectric properties of BaZrO3/BaTiO3 (BZ/BT) superlattices deposited on a single-crystal MgO substrate, and having a period of 13.32 nm. These superlattices have specific properties distinguishing them from BZ or BT bulk materials, and from thin films, with a ferroelectric phase transition around 393-395 °?, significantly higher than in bulk samples and thin films of BT, and appearing of second order. The polarization switching occurs in two stages and the precise analysis of experimental data demonstrates that the motion of the domain walls causes the switching processes. We conclude that the mobility of the domain walls decreases on heating. The presence of an internal bias field has been demonstrated and shown to be directed from the superlattice to the substrate, in agreement with an analysis based on the flexoelectric effect. The switching current has been shown to vary in weak fields as 1/E? with the exponent ? much smaller than in thin ferroelectric films. The appearance of the power index ?, which is significantly different from unity, may be due to a decrease in the average value of the switched polarization due to the boundaries between layers of different materials.