Synthesis and structure of Bi2LaO4Cl: a novel variant of the sillen phases

Abstract

A new series of layered oxyhalides, Bi₂MO₄Cl(M = La, Nd, Y), has been synthesized. Bi₂LaO₄Cl has been characterised by a combination of X-ray and neutron powder diffraction: space group P4/mmm, a= 3.9547(1), c= 9.1 275(3)Å. The structure consists of alternating layers of ‘triple fluorite’, [M₃O₄]⁺ and halide, Cl^–. Within the fluorite layers there is perfect ordering of the cations, –Bi–O₂–La–O₂–Bi, such that La is coordinated only by oxide layers and Bi by both oxide and chloride layers. This phase represents the simplest example of an intergrowth structure containing the [M₃O₄] block layer, which is found in several of the copper oxide superconductors. The structure also suggests the existence of a new family of layered oxyhalides parallel with the well known Sillen phases, [M₂O₂]X_n, with triple [M₃O₄] fluorite layers replacing the normal double [M₂O₂] layers.