Ferroelectric thermal phase transition and polarization precursor dynamics in CaxBa1-xNb2O6(CBN) tungsten bronze type oxides

Polycrystals of CaxBa1-xNb2O6(CBN) tungsten bronze type oxides have been prepared and their structural, dielectric, and thermal properties have been investigated. It was found that CBN alloys with ferroelectric tetragonal tungsten bronze structure were only available in a composition range of 0.19 <= x <= 0.32. It was also showed that CBN can be classified as a ferroelectric with a first-order thermal phase transition showing polarization precursor dynamics before transition into the ferroelectric phase, in sharp contrast to an isostructural alloy SrxBa1-xNb2O6(SBN) that shows typical relaxor behaviors. The local polarizations were found to grow exponentially within the paraelectric mother phase in a large temperature range of Tc<T<Tc+ 88~140 K on cooling. Furthermore, a phase diagram was established for CBN ferroelectric alloys. These findings may get an insight into the true nature of ferroelectric phase transition in this potential electro-optic material.