TY  - JOUR
AU  - Ostapchuk, T.
AU  - Petzelt, J.
AU  - Zelezny, V.
AU  - Pashkin, A.
AU  - Pokorny, J.
AU  - Drbohlav, I.
AU  - Kuzel, R.
AU  - Rafaja, D.
AU  - Gorshunov, B. P.
AU  - Dressel, M.
AU  - Ohly, Ch.
AU  - Hoffmann-Eifert, S.
AU  - Waser, R.
TI  - Origin of soft-mode stiffening and reduced dielectric response in SrTiO3 thin films
JO  - Physical review / B
VL  - 66
IS  - 23
SN  - 0163-1829
CY  - College Park, Md.
PB  - APS
M1  - PreJuSER-32287
SP  - 235406
PY  - 2002
N1  - Record converted from VDB: 12.11.2012
AB  - 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.
KW  - J (WoSType)
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000180279400097
DO  - DOI:10.1103/PhysRevB.66.235406
UR  - https://juser.fz-juelich.de/record/32287
ER  -