Lead-free piezoelectrics; Raman delineation of phase boundaries

There is a need to identify ferroelectrics with strong temperature-independent piezoelectric responses to replace the ubiquitous PbZr$_{x}$Ti$_{1-x}$O$_{3}$ (PZT). It is central in this search to establish the phase diagram of candidate materials, especially the existence of a temperature-independent phase boundary similar to that in PZT. We will report Raman investigations of a number of target materials, and report clear evidence of such a boundary in one of them and weaker, as yet incomplete evidence in another.