The structural phase diagram of the Pb-free ferroelectric ${\left({\text{Na}}_{1/2}{\text{Bi}}_{1/2}\right)}_{1-x}{\text{Ba}}_x{\text{TiO}}_3$, $x<0.1$, has been explored by Raman spectroscopy at temperatures from 10 to 470 K. The data provide clear evidence for a proposed temperature-independent morphotropic phase boundary at $x\approx 0.055$. However, there is no evidence for a structural phase transition across $T\approx 370\text{K}$ for $x>0.055$, where bulk-property anomalies appear to signal a transition to a nonpolar or antiferroelectric phase. The results identify that the phase above 370 K shows short-range ionic displacements that are identical to those in the long-range-ordered phase below 370 K. These conclusions provide a natural interpretation of the weak piezoelectric response in this system and have important implications for the search for Pb-free piezoelectrics.

• Received 16 February 2010

DOI:https://doi.org/10.1103/PhysRevB.82.104112