Synthesis, crystal structure and ferroelectric properties of Ba2NdFeNb4O15/Si(001) films

Using the method of HF cathode sputtering in an oxygen atmosphere, Ba2NdFeNb4O15/Si(001) heterostructures with layer thicknesses from 75 to 1000 nm were manufactured. Their crystal structure, surface morphology, dielectric characteristics and features of the formation of the ferroelectric state were investigated. It has been established that the films are polycrystalline textured with a predominant orientation of the axes [001] in the direction normal to the substrate surface, in which a significant deformation of the unit cell was observed. It was found that as the thickness of the films increases, the roughness of their surface increases and follows the scaling law. From the volt-farad characteristics (in terms of displacement and hysteresis width), it was found that with a decrease in thickness, the coercive field increases and the internal field increases. This was also confirmed by measuring local residual hysteresis loops using piezoelectric force microscopy. In addition, by the local application of positive and negative external fields, it is possible to form polarized regions in which, in one case, the polarization vector is directed from the substrate to the surface of the film, and in the other, on the contrary, from the film to the substrate. Also, the effective piezoelectric coefficient was determined for all the studied heterostructures. The reasons for the revealed patterns are discussed.