Ferroelectric Phase Transition and Acoustic Properties of Nanoscale Oxide Heterostructures Probed by UV Raman Spectroscopy

A. BRUCHHAUSEN; N. D. LANZILLOTTI-KIMURA; A. FAINSTEIN; A. SOUKIASSIAN; D. A. TENNE; D. G. SCHLOM; X. X. XI; A. CANTARERO

Paris, Francia

Conferencia; 12th International Conference on Phonon Scattering in Condensed Matter (Phonons 2007); 2007

Institut des NanoSciences de Paris, y otros

The ferroelectric properties of nanoscale materials are strongly influenced by finite size and by the misfit strain imposed by an underlying substrate. Challenging questions are how thin a ferroelectric can be and still be ferroelectric, and what is the phase transition temperature of a nanoscale ferroelectric. In this presentation, the application of ultraviolet (UV) Raman spectroscopy for studies of lattice dynamics and ferroelectric phase transitions in nanoscale ferroelectrics will be presented. Temperature-dependent high-resolution UV Raman experiments demonstrate that BaTiO3/SrTiO3 superlattices with BaTiO3 layers as thin as one-unit-cell are ferroelectric with the Tc as high as 250 K. Furthermore, due to the interplay between size, boundary conditions, and strain, the Tc in BaTiO3/SrTiO3 superlattices can be tuned by hundreds of degrees from ~ 170 to 650 K by varying the substrate and the thickness of the BaTiO3 and SrTiO3 layers[1]. Furthermore, the high quality of epitaxial growth, the large acoustic impedance mismatch, and the strong coupling between charge and lattice vibrations in these multifunctional materials, make them attractive candidates for the conception of novel phonon devices at THz frequencies[2].We describe the design of acoustic Bragg mirrors and cavities, and we present the first study of acoustic phonons in these oxide epitaxial multilayers. The coupling between acoustic modes and the ferroelectric phase transitions is investigated. [1] Probing Nanoscale ferroelectricity by ultraviolet Raman spectroscopy, D. A. Tenne et al., Science 313, 1614 (2006). [2] Piezoelectric oxide acoustic mirrors and cavities, A. Soukiassian et al., Appl. Phys. Lett. 90, 42909 (2007).