title: Structural characterization of a new acentric Ruddlesden-Popper layered perovskite compound: LiHSrTa2O7.
abstract: A new n = 2 member acentric Ruddlesden-Popper layered perovskite LiHSrTa(2)O(7) (LiDSrTa(2)O(7)) has been synthesized and structurally characterized from Rietveld treatment of its powder X-ray and high-resolution neutron diffraction data. It can be synthesized by a partial Li(+)/H(+) exchange from the mother phase Li(2)SrTa(2)O(7) either in solid state by NH(4)Cl or in dilute HNO(3) by controlling the amount of H(+). This compound crystallizes in the orthorhombic acentric space group Ama2 (no. 40) with lattice constants a = radical2a(p) approximately 5.5522(1) A, b = radical2a(p) approximately 5.5248(1) A and c approximately 18.7745(4) A. Classically, Ta(5+) ions occupy the octahedral sites of the kinked perovskite blocks and Sr(2+) ions completely fill the perovskite cages while Li(+) and D(+) ions are found in the interlayer spacing. Efficient positive second harmonic generation response, performed at room temperature on a polycrystalline sample, shows unambiguously the acentric character of this new phase. Interestingly, the choice of the acentric Ama2 space group to describe the structure is revealed only by high-resolution neutron diffraction data: in the interlayer spacing, Li(+) and D(+) cations are unequally distributed on different sites (two 4a sites for Li(+) and two 4b sites for D(+) ions).
authors.affiliation: Laboratoire des Oxydes et Fluorures, FR n degrees 2575 IRIM2F, UMR CNRS 6010, Faculté des Sciences et Techniques, Université du Maine, Avenue O. Messiaen, F-72017, Le Mans, France.
authors.forename: Cyrille
authors.initials: C
authors.lastname: Galven
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Fourquet
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Suard
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Crosnier-Lopez
authors.forename: Françoise
authors.initials: F
authors.lastname: Le Berre