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The temperature dependent band edge energy of the novel tungsten bronze type calcium barium niobate (CBN) is measured over a temperature range from 80 K to 573 K. CBN has been under investigation for serveral years and is believed to be a promising material for future applications.Czochralski-grown, colorless single crystals from the congruently melting composition with a calcium content of 0.281 were used. A numerical fit has been applied, comparing the results of CBN to those of the well known relaxor ferroelectric strontium barium niobate (SBN). The band edge energy of CBN was found to be higher than in SBN over the whole temperature range.

We present investigations of the domain dynamics and of the evolution of the critical exponent β 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 β 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.