Formation of metastable ferroelectric clusters in at the paraelectric phase

We present experimental evidence indicating that in potassium lithium tantalate niobate at the paraelectric phase, ferroelectric clusters are formed to compensate the space charge induced field created in a photorefractive process. These clusters are distributed in a slow spontaneous process and form a dipolar grating which is spatially correlated with the photorefractive space charge grating. By investigating the Gibbs free energy, we show that the compensating gratings are formed only in the temperature region where a metastable ferroelectric state is allowed to exist at the paraelectric phase. The compensation process, as well as its temperature and electric field dependence are interpreted in terms of the Gibbs free energy.