Origin of soft-mode stiffening and reduced dielectric response in SrTiO3 thin films

Ostapchuk, T.; Pashkin, A.; Rafaja, D.; Waser, R.; Dressel, M.; Gorshunov, B. P.; Zelezny, V.; Kuzel, R.; Hoffmann-Eifert, S.; Drbohlav, I.; Ohly, Ch.; Petzelt, J.; Pokorny, J.

doi:10.1103/PhysRevB.66.235406

Journal Article

Origin of soft-mode stiffening and reduced dielectric response in SrTiO3 thin films

Ostapchuk, T. ; Petzelt, J. ; Zelezny, V. ; Pashkin, A. ; Pokorny, J. ; Drbohlav, I. ; Kuzel, R. ; Rafaja, D. ; Gorshunov, B. P. ; Dressel, M. ; Ohly, C.FZJ* ; Hoffmann-Eifert, S.FZJ* ; Waser, R.FZJ*

2002
APS College Park, Md.

Physical review / B 66(23), 235406 (2002) [10.1103/PhysRevB.66.235406]

This record in other databases:

Please use a persistent id in citations: http://hdl.handle.net/2128/1244 doi:10.1103/PhysRevB.66.235406

Abstract: The problem of the reduced dielectric response in thin films of high-permittivity materials is analyzed by studying the soft-mode response in several SrTiO3 thin films by means of Fourier transform far infrared, monochromatic submillimeter, and micro-Raman spectroscopies. A 300-nm-thick metalorganic chemical vapor deposition film, quasiepitaxially grown on a (0001) sapphire substrate with a perfect <111> orientation, displays a ferroelectric transition near 125 K induced by a tensile residual stress, appearing apparently simultaneously with the antiferrodistortive transition. On the other hand, polycrystalline chemical solution deposition films grown on (0001) sapphire, and also tensile stressed, show a harder soft mode response without the appearance of macroscopic ferroelectricity. This effect, which increases with the film thickness, is explained by a strong depolarizing field induced by the percolated porosity and cracks (in the 10-nm scale) along the boundaries of columnar grains (normal to the probe field direction). Brick-wall model calculations showed that 0.2 vol. % of such a porosity type reduces the permittivity from 30000 to less than 1000. The activation of the forbidden IR modes in the Raman spectra in the whole 80-300-K temperature range studied is explained by the effect of polar grain boundaries, in analogy with the bulk ceramics.

Keyword(s): J

Classification: