Issue 12, 1974

Structural theory for non-stoicheiometry. Part I. Defect fluorite-type structures: lanthanoid oxides MOx with 1·7 ⩽x⩽ 2·0

Abstract

The concept of an octahedrally co-ordinated anion vacancy □O6 is introduced to develop a rational structural theory for the known series of ordered non-stoicheiometric lanthanoid oxides of formula MnO2n–2(n= 7–∞). The resulting co-ordination defect (c.d.) has the composition M7//2□O, and it is suggested that this retains its structural integrity in all the homologues. Topological analysis has been employed to establish the fundamental superstructures of the fluorite lattice which characterize these oxide phases. It emerges that the anion deficiency is accommodated by point defects gathered in oblique {213} planes each being separated by (n– 1) oxide-intact {213} planes. Effectively, all these phases are based on regularly spaced intergrowths of the progenitors ι-Pr7O12 and PrO2. It is shown that the homologues are structurally coherent and that irregularity in spacing of intergrown phases provides a logical description for the grossly non-stoicheiometric α-phase which overlays the region MO1·7–MO2·0 at higher temperatures. The extended {213} sheets of defects can be circumscribed coherently by PrO2 to generate finite discs of Pr7//2□O6. Order–disorder transformations are considered in terms of the interchangeability of Pr7//2□O6 and Pr7//2□O7 structural sub-units which are topologically identical. The non-existence of the homologue Pr8O14 and a possible structure for the β′-Pr12O22 phase are examined in terms of the cubic pyrochlore (E81) structure.

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1974, 1335-1350

Structural theory for non-stoicheiometry. Part I. Defect fluorite-type structures: lanthanoid oxides MOx with 1·7 ⩽x⩽ 2·0

R. L. Martin, J. Chem. Soc., Dalton Trans., 1974, 1335 DOI: 10.1039/DT9740001335

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Spotlight

Advertisements