This title appears in the Scientific Report : 2002 

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, Ch. / Hoffmann-Eifert, S. / Waser, R.
Elektrokeramische Materialien; IFF-EKM
Physical review / B, 66 (2002) S. 235406
College Park, Md. APS 2002
Journal Article
Materialien, Prozesse und Bauelemente für die Mikro- und Nanoelektronik
Physical Review B 66
Please use the identifier: in citations.
Please use the identifier: in citations.
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.