Chaotic states observed in strontium barium niobate

Abstract

High-resolution dark-field images of strontium barium niobate (BaSrNb₄O₁₂) reveal a hierarchy of chaotic states imposed upon the essentially tetragonal-tungsten-bronze framework structure. Thus, 180° ferroelectric domains were observed, at room temperature, having spatial extent < 500 Å. Within these, 90° ferroelastic domain textures were discovered, revealing orthorhombic symmetry for strontium barium niobate. Within each domain an incommensurate superlattice was found, which contains intergrowth of two different orthorhombic structures. Finally, high-resolution dark-field images show fluctuations in the occupancy of Ba and Sr sites along [001] tunnels of strontium barium niobate, since their average occupancy is 5/6. The contributions these various chaotic states may make to the thermodynamic stability and singular optical properties of strontium barium niobate are discussed.