Center for Functional Nanomaterials Seminar

Oriented nanocomposite film consisting of ferroelectric and low-K dielectric phases is a potential candidate as a tunable material used in microwave devices. Here, the orientation control of the composite is a key issue for achieving the desired properties. In this presentation, the oblique growth of BaTiO3(BTO)-CeO2 nanostructures is demonstrated by self-assembly approach. The obtained oblique nanostructures show over an order of magnitude larger coefficient of dielectric nonlinearity in comparison with pure ferroelectrics. BTO-CeO2 films were grown on Pt(111) electrodes by pulsed laser deposition. It was found that the composite orientation is strongly influenced by the growth direction of the columnar major component; therefore, it depends on the volume fraction of two components. As a particular example, a 15mol%BTO-85mol%CeO2 film has elongated BTO crystals of 2-8nm widths lying in between "obliquely-grown" CeO2 columns. This film showed a very low relative permittivity of 50 due to the presence of CeO2, but still showed appreciable tunability. As a result, the coefficient of dielectric nonlinearity increases up to 25 times that of conventional BTO-based ferroelectrics. It also shows a low dielectric loss below 1% at 10GHz and excellent temperature stability of the dielectric properties. The obtained results are discussed in comparison with the theoretical model.