Dielectric anomalies in (BaxSr1-x)4Nd2Ti4Nb6O30 ceramics with various radius differences between A1-and A2-site ions

Dielectric response of tetragonal tungsten bronze dielectrics (BaxSr1-x) 4Nd2Ti4Nb6O30 was investigated over a broad temperature and frequency range, and the obvious composition- dependent dielectric anomalies with respect to x value were discussed in detail in association with the radius differences between A1- and A2- site ions. With decreasing the magnitude of radius difference between A1- and A2- site ions, the normal ferroelectric peak above 400 K became weaker, and two relaxor peaks at lower temperatures became obvious. The low- and high-temperature relaxor behaviors, which followed well the Vogel- Fulcher relationship, were associated with the polar clusters caused by the off-center Nb/Ti displacements and the incommensurate tilting modulation, respectively. (C) 2007 American Institute of Physics.