K3NB3TI2O11F4

Zn the crystal structure of the tetragonal bronze K3Nb3Ti2F4O11 (potas sium niobium titanium fluoride oxide), the asymmetric unit contains tw o STX(6) octahedra, where X = O, F or OF (= 1/4 F + 3/4 O), and ST = ( 3/5 Nb + 2/5 Ti). The average ST-X distance is 1.966 Angstrom and the valency angles vary from 173.7 (2) to 180 degrees. The K-atom environm ent is similar to that in ferroelectric phases, but the weak distortio n of the octahedra and the occupation of their centres by Nb5+ and Ti4 + cations result in paraelectric behaviour.