Nanoscale polar regions embedded within ferroelectric domains in Na1/2Bi1/2TiO3-BaTiO3

Relaxor ferroelectrics are an eminent group of functional materials, characterized by complex micro- and nanoscale structures, accounting for their enhanced piezoelectric properties. In the (1-x)Na1/2Bi1/2TiO3-xBaTiO3 (NBT-BT) solid solution, the evolution of nanoscale domains and their hierarchical association with ferroelectric domains is investigated using conventional and scanning transmission electron microscopy on compositions with 6, 9, and 12 mol % BT. Short-range fluctuations in the local polar displacement (polar nanoregions, PNRs) account for a heterogeneous nanostructure at the morphotropic phase boundary (6 mol % BT). Platelike nanodomains of tetragonal P4bm symmetry coexist with a minor volume fraction of rhombohedral R3c nanodomains. Their overall population decreases with increasing BT content. However, ferroelectric P4mm domains in the composition with 12 mol % BT still exhibit nanoscale regions, which deviate from the average polarization. Small volume fractions of both P4bm and R3c nanodomains remain embedded within the ferroelectric domains. This hierarchical domain configuration underpins the complex structural characteristics of NBT-based relaxor ferroelectrics.