SBN60, strontium-barium niobate at 100 K

The title compound, Sr_0.6Ba_0.4Nb₂O₆ (strontium barium niobium oxide), belongs to the group of strontium-barium niobates with varying composition of Sr and Ba. Their general formula can be written as Sr_xBa_{1 - x}Nb₂O₆. Below the Curie temperature, T_c, these materials indicate ferroelectric properties. The Curie temperature for SBN60 is equal to 346±0.5 K so the structure is in the ferroelectric phase at the measurement temperature of 100 K. Characteristic for this family of compounds is the packing along the z-axis. The NbO₆ corner-sharing octa­hedra surround three types of vacancy tunnels with penta­gonal, square and triangular shapes. The Sr²⁺ ions partially occupy two unique sites, the first one located inside the penta­gon and the second one in the square tunnels. Consequently, they are situated on the mirror plane and the inter­section of two glide planes, respectively. The site inside the penta­gonal tunnel is additionally disordered so that the same position is shared by Ba²⁺ and Sr²⁺ ions whereas another part of the Ba²⁺ ion occupies a different position (relative occupancies 0.43:0.41:0.16). One of the Nb^V atoms and three of the O^2- ions occupy general positions. The second Nb^V atom is located on the inter­section of the mirror planes. Two remaining O^2- ions are located on the same mirror plane. Only the Nb^V atom and one of the O^2- ions which is located on the mirror plane are not disordered. Each of the remaining O^2- ions is split between two sites, with relative occupancies of 0.52:0.48 (O^2- ions in general positions) and 0.64:0.36 (O^2- ion on the mirror plane).