%0 Journal Article
%A Ostapchuk, T.
%A Petzelt, J.
%A Zelezny, V.
%A Pashkin, A.
%A Pokorny, J.
%A Drbohlav, I.
%A Kuzel, R.
%A Rafaja, D.
%A Gorshunov, B. P.
%A Dressel, M.
%A Ohly, Ch.
%A Hoffmann-Eifert, S.
%A Waser, R.
%T Origin of soft-mode stiffening and reduced dielectric response in SrTiO3 thin films
%J Physical review / B
%V 66
%N 23
%@ 0163-1829
%C College Park, Md.
%I APS
%M PreJuSER-32287
%P 235406
%D 2002
%Z Record converted from VDB: 12.11.2012
%X 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.
%K J (WoSType)
%F PUB:(DE-HGF)16
%9 Journal Article
%U <Go to ISI:>//WOS:000180279400097
%R 10.1103/PhysRevB.66.235406
%U https://juser.fz-juelich.de/record/32287