Direct observation of local ferroelectric phase transitions in BaxSr1−xTiO3 thin films

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.