PACS 77.80.Bh; 77.55.+fThe temperature-dependent polarization of SrTiO 3 thin films is investigated using confocal scanning optical microscopy. A homogeneous out-of-plane and inhomogeneous in-plane ferroelectric phase are identified from images of the linear electrooptic response.Both hysteretic and non-hysteretic behavior are observed under a dc bias field. Unlike classical transitions in bulk ferroelectrics, local ferroelectricity is observed at temperatures far above the dielectric permittivity maximum. The results demonstrate the utility of local probe experiments in understanding inhomogeneous ferroelectrics.

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The temperature dependence of the local ferroelectric polarization of BaxSr1−xTiO3 thin films is measured with submicrometer resolution using confocal scanning optical microscopy. The local ferroelectric hysteresis loop changes shape and disappears as the temperature is increased over a narrow range of temperatures (ΔT∼10 K). The local Curie temperature TC(x,y) varies significantly with position, and the distribution of TC is consistent with the broad temperature dependence of the dielectric permittivity measured through conventional methods. These results directly confirm the hypothesis that the ferroelectric phase transition in these materials is inhomogeneously broadened.

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