The orthorhombic to tetragonal phase transition in Bi1.75Te0.25SrNb1.75Hf0.25O9

The necessity to produce materials with better performances than those observed in ferroelectric perovskites has generated the creation of new oxides, especially those belonging to the Aurivillius family. In the last few years much attention has been paid to the study of these materials, and this has opened up new fields due to their basic and applied properties. In this contribution a Raman analysis and a hyperfine study by perturbed angular correlations spectroscopy of Bi1.75Te0.25SrNb1.75Hf0.25O9 were carried out to reveal information about the lattice and the electronic structure. By the use of these techniques, it was observed that the ferroelectric to paraelectric phase transition at about 570 K is driven by a soft mode, and the broadening of the dielectric constant as a function of temperature previously observed at T-C is connected to disorder in the Bi/Te-O layer.