Giant increase of ferroelectric phase transition temperature in highly strained ferroelectric superlattice
1 Laboratoire de Physique de la Matière Condensée, Université de Picardie - 33 rue Saint-Leu, 80039 Amiens Cedex, France
2 Faculty of Physics, Southern Federal University - 5, Zorge str. Rostov-on-Don, 344090, Russia
Received: 18 March 2014
Accepted: 24 March 2014
We report epitaxial strain effects in the lead-free ferroelectric/paraelectric superlattice (SL) for a modulation period Λ of about 100 Å. We have demonstrated that the large strain in SL induces ferroelectricity in BaZrO3 layers, a material that is paraelectric at any temperature in the bulk form. The induced polar axis in BaZrO3 layers is perpendicular to the plane of the substrate while BaTiO3 layers exhibit in-plane polar orientation. Raman spectroscopy revealed a lattice ordering in SL due to the misfit strain generated by the large lattice mismatch between the alternating BaZrO3 and BaTiO3 layers. Such strain induces a huge upward frequency shift of the lowest E(1TO) soft mode from in the BaTiO3 single film to in the SL. The temperature of the ferroelectric phase transition in the SL was found to be upshifted by about with respect to the BaTiO3 single crystal.
PACS: 77.55.fe – BaTiO3-based films / 78.30.-j – Infrared and Raman spectra
© EPLA, 2014