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

T. Ostapchuk, J. Petzelt, V. Železný, A. Pashkin, J. Pokorný, I. Drbohlav, R. Kužel, D. Rafaja, B. P. Gorshunov, M. Dressel, Ch. Ohly, S. Hoffmann-Eifert, and R. Waser
Phys. Rev. B 66, 235406 – Published 13 December 2002
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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.

  • Received 17 July 2002

DOI:https://doi.org/10.1103/PhysRevB.66.235406

©2002 American Physical Society

Authors & Affiliations

T. Ostapchuk, J. Petzelt, V. Železný, A. Pashkin, J. Pokorný, and I. Drbohlav

  • Institute of Physics, Academy of Sciences of the Czech Republic Na Slovance 2, 182 21 Prague 8, Czech Republic

R. Kužel and D. Rafaja

  • Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 12116 Prague 2, Czech Republic

B. P. Gorshunov* and M. Dressel

  • Physikalisches Institut, Universität Stuttgart, D-70550 Stuttgart, Germany

Ch. Ohly, S. Hoffmann-Eifert, and R. Waser

  • Institut f. Festkörperforschung Jülich, D-52425 Jülich, Germany

  • *Permanent address: Institut of General Physics, RAS, 119991 Moscow, Russian Federation.

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Issue

Vol. 66, Iss. 23 — 15 December 2002

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