Abstract
We have recently evidenced the existence of a complex path of polarisation rotation via two monoclinic phases in the giant-piezoelectric materials PSN PT that is similar to the PMN-PT system. In this article we have presented the state of knowledge on the PSN-PT system and have given new results showing the close connection between the local inhomogeneous chemical order of Sc/Nb/Ti cations and the stability of different ferroelectric phases. The notion of morphotropic phase boundaries is discussed in relation with the gradual appearance of long-range polar order with increasing Ti content in PSN-PT. Comparison with the films and nanopowders/ceramics has also been made.