Ferroelectric phase transitions in BaTiO3/SrTiO3 superlattices studied by ultraviolet Raman spectroscopy

D. A. TENNE; X. X. XI; A. SOUKIASSIAN; W. TIAN; Y. L. LI; L. Q. CHEN; D. G. SCHLOM; A. BRUCHHAUSEN; A. FAINSTEIN; X. Q. PAN; A. CANTARERO; R. S. KATIYAR

Baltimore, MD, USA

Conferencia; Annual March Meeting , American Physical Society (APS); 2006

Ferroelectric (BaTiO3)m/(SrTiO3)n superlattices (SLs) grown by molecular beam epitaxy on SrTiO3 substrates have been investigated by ultraviolet (UV) Raman spectroscopy. Using the UV excitation allowed us to overcome the problem of overwhelming substrate contributions in Raman spectra and made possible the observation of phonons in SLs having the ferroelectric BaTiO3 layers as thin as 2 unit cells. The ferroelectric paraelectric phase transitions have been observed. Depending on the thickness of the BaTiO3 layers and strain, the phase transition temperature varies by hundreds of degrees from »140 K to 630 K, which is over 200 degrees higher than in bulk BaTiO3. Below Tc, the SLs likely remain in the single (tetragonal) ferroelectric phase down to 7 K, i.e. the low-temperature phases characteristic for bulk BaTiO3, are suppressed by strain. The experimental data are in good agreement with the results of the thermodynamic calculations of polarization in SLs as a function of temperature.