Ferroelectric to Relaxor Crossover in Perovskite-type Systems

Abstract

The ferroelectric to relaxor crossover of A(B_1-xB′_x)O₃-type perovskites with increasing x is discussed from the order-disorder point of view for Ba(Ti_1-xSn_x)O₃ (BTS-x) as an example. The polar short-range order of the disordered off-centred Ti ions in BaTiO₃ increases with decreasing temperature, leads to nucleation and, finally, to the long-range ordered ferroelectric phase. This process becomes impeded with increasing content of Sn ions x that make the nucleation and the transition more and more incomplete and finally impossible (relaxor). The composition BTS-0.1 corresponds to PMN-PT and PZN-PT systems near the “morphotropic phase boundary” where the temperature T_m of maximum permittivity is mainly determined by nucleation rather than by a transition to tetragonal long-range order. This is concluded from different electromechanical properties and confirmed by additional aging experiments on BTS-0.1. Other reasons for incomplete transitions to long-range order are not discussed in this paper.

Keywords:

• A(B,B′)O₃ type perovskites
• order-disorder phase transitions
• short-range order
• nucleation
• aging