  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.
