Redetermination of Nd2Ti2O7: a non-centrosymmetric structure with perovskite-type slabs

Single crystals of dineodymium(III) dititanium(IV) heptaoxide, Nd2Ti2O7, were synthesized by the flux method and found to belong to the family of compounds with perovskite-type structural motifs. The asymmetric unit contains four Nd, four Ti and 14 O-atom sites. The perovskite-type slabs are stacked parallel to (010) with a thickness corresponding to four corner-sharing TiO6 octahedra. The Nd and Ti ions are displaced from the geometrical centres of respective coordination polyhedra so that the net polarization occurs along the c axis. The investigated crystals were all twinned and have a halved monoclinic unit cell in comparison with the first structure determination of this compound.