Probing polar nanoregions in Sr0.61Ba0.39Nb2O6 via second-harmonic dielectric response -: art. no. 092105

The dielectric susceptibility of pure and chromium-doped Sr0.61Ba0.39Nb2O6 single crystals reveals an appreciable second-harmonic component chi(2) along with the usual first- and third-order ones, chi(1) and chi(3). It is attributed to irreversible prepoling due to trapping of mobile charge carriers in the first half-cycle of the ac probing field. In agreement with predictions for a biased ferroelectric phase transition, the second- and third-order nonlinearity coefficients are observed to minimize at the transition temperature T-c.