Compositional dependence of disordered structures in Na½Bi½TiO3-BaTiO3 solid solutions

Highlights: • Diffuse X-ray scattering collected from 4 compositions of Na_½Bi_½TiO₃-x%BaTiO₃. • Oxygen octahedral tilts, atomic displacements and modulations existed. • All local disordered structures evolved across the morphotropic phase boundary. - Abstract: Disordered structures contribute to the relaxor ferroelectric properties of the lead-free system Na_½Bi_½TiO₃-(x)%BaTiO₃. Such structures are difficult to characterize with conventional structural analysis techniques. Here, diffuse X-ray scattering was used to analyze the disordered structures from four single-crystals of Na_½Bi_½TiO₃-(x)%BaTiO₃, with compositions of (x)% = 0%, 4%, 9% and 17%. Such a range of compositions allowed a distinction between the structures that occur across the morphotropic phase boundary, where enhanced electro-mechanical properties have been reported. Throughout the compositional range, the resulting diffuse scattering showed the modification of correlated atomic displacements, transformation of planar defects in the oxygen octahedral tilt-systems, and the presence of modulations of approximately 10 unit cells. The results reported here demonstrate an evolution of the short-range structures across the morphotropic phase boundary that may underpin the electro-mechanical properties of Na_½Bi_½TiO₃-(x)%BaTiO₃. This information will ultimately assist in tailoring disordered structures for next-generation piezoelectric materials.