SBN60, strontium-barium niobate at 100 K.

The title compound, Sr0.6Ba0.4Nb2O6 (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 x Ba1 - 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 octa-hedra surround three types of vacancy tunnels with penta-gonal, square and triangular shapes. The Sr(2+) ions partially occupy two unique sites, the first one located inside the penta-gon and the second one in the square tunnels. Consequently, they are situated on the mirror plane and the inter-section of two glide planes, respectively. The site inside the penta-gonal tunnel is additionally disordered so that the same position is shared by Ba(2+) and Sr(2+) ions whereas another part of the Ba(2+) 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 inter-section 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).