Domain size effects in a uniaxial ferroelectric relaxor system: The case of SrxBa1−xNb2O6

We present investigations of the domain dynamics and of the evolution of the critical exponent $\beta$ in a ferroelectric relaxor system, exemplarily in the up-to-date controversial strontium barium niobate (SBN). $k$ -space spectroscopy at the phase-transition and when applying an electric field reveals a size-dependent response of the domains. This is supported by pyroelectric measurements that show, by analysis in terms of criticality, the critical exponent $\beta$ is not only dependent on the level of poling but also on the manner in which the poling was achieved. It must be concluded that the crystals undergo a phase transition not—as commonly assumed—in a uniform way with homogeneous polarization throughout the crystal. Instead they behave as a set of more or less independent domains with size-dependent stability. Therefore, one should be very careful with critical exponents—especially those derived from experiments that explicitly or implicitly—assume a uniform polarization behavior.