Nanoscale phase quantification in lead-free (Bi1/2Na1/2)TiO₃-BaTiO₃ relaxor ferroelectrics by means of ²³Na NMR

We address the unsolved question on the structure of relaxor ferroelectrics at the atomic level by characterizing lead-free piezoceramic solid solutions (100−x)(Bi1/2Na1/2)TiO₃−xBaTiO₃ (BNT−xBT) (for x=1,4,6, and 15). Based on the relative intensity between spectral components in quadrupolar perturbed ²³Na nuclear magnetic resonance, we present direct evidence of the coexistence of cubic and polar local symmetries in these relaxor ferroelectrics. In addition, we demonstrate how the cubic phase vanishes whenever a ferroelectric state is induced, either by field cooling or changing the dopant amount, supporting the relation between this cubic phase and the relaxor state.