The 1D A7B7O30 crystal lattice : an extreme case of oxygenation/slicing of 3D ABO3 perovskite

Philippe Lacorre (1) , Gwenaël Corbel (1)

1 IMMM - Institut des Molécules et Matériaux du Mans

The A7B7O30 structural type had been first discovered with La7Mo7O30 [1], an intermediate reduction product of oxide-ion conductor La2Mo2O9 [2]. Later on it was extended to substituted tungstates with La7W4M3O30 (M=Nb5+, Ta5+) [3]. A new extension of this structural series to tungsten transition metal substitutes with lower oxidation states [4], namely M=Ti4+, Fe3+ and Zn2+ in La7W7 xMm+xO30 with x=3/(6-m), is now presented. In the A7B7O30 arrangement, isolated perovskite-type columns built up from trans-connected perovskite cages are surrounded by rare earth pseudo-cubes, as in the original perovskite structure. Cations with the lowest oxidation state occupy predominantly (although not exclusively) the shared octahedra between two consecutive perovskite cages in a column. La7W6FeO30 is to date the only compound of this series to be fully ordered, with isolated [FeO6] octahedra (see figure). Important oxygen excess in perovskite-type arrangements have been known for a while in layered frameworks such as AnBnO3n+2 [5], in which each 2D, n octahedral layer thick block, is shifted relative to its neighbour (see figure). The thinner the block, the more oxygen excess. It will be shown that the A7B7O30 columnar structure can be seen as a further oxygenation step of n=3 perovskite layer blocks implying their 1D slicing (see figure). Atomic shifts due to relaxation, as well as charge distribution of cations are comparable in both 2D and 1D structures. Several interesting properties have been evidenced in some 2D AnBnO3n+2 compounds, such as metal-insulator transition, ferroelectricity, or multiferroism. It is expected that the A7B7O30 perovskite arrangement holds promise for further possibilities on the 1D side, provided appropriate formulations (although substitutional constraints are probably stronger than in 3D and 2D perovskites). A prerequisite to proper property measurement is the sample purity, as will be shown with MPr2W2O10, previously confused with impure Pr7W6.25M0.75O30 [6].

Domaines: Cristallographie; Chimie inorganique; Science des matériaux [cond-mat.mtrl-sci]; Matériaux

Philippe Lacorre, Gwenaël Corbel. The 1D A7B7O30 crystal lattice : an extreme case of oxygenation/slicing of 3D ABO3 perovskite. 17th European Conference on Solid State Chemistry - ECSSC17, Sep 2019, Lille, France. ⟨hal-02412668⟩