Raymond Leslie Martin

20: Coordination, Topology and Structure in Transition Metal Oxides (1976)

Introduction

20: coordination, topology and structure in transition metal oxides (1976). Explore the real structure of transition metal oxides, focusing on defect organization, coordination, and topological analysis. This 1976 lecture challenges classical defect notions.

Abstract

The Liversidge Research Lecture, delivered before the Royal Society of New South Wales, 15th July 1976. Reproduced by permission of the Royal Society of New South Wales from J. Proc. Roy. Soc. N.S.W., 1976, 109, 137-150."The role of defects in the real structure of transition metal oxides which exhibit gross departures from simple stoicheiometries† is reviewed. The classical notion of a randomized distribution of non-interacting point defects is no longer tenable being replaced by the emerging recognition that a high level of organization into discrete clusters or more extended assemblies of defects is an inherent feature of the real structure of defect solids. The concept of octahedral coordination of vacant oxygen sites, taken in conjunction with topological analysis, is shown to contribute considerable insight into the transformational and structural relationships between defect oxides of the fluorite type."†Now usually spelled 'stoichiometries'.

Review

This paper, originating from the 1976 Liversidge Research Lecture, presents a foundational review on the intricate real structure of transition metal oxides, particularly those exhibiting significant departures from simple stoichiometries. At its core, the lecture challenges the prevailing classical understanding of defects as randomized, non-interacting point entities. Instead, it forcefully advocates for an emerging paradigm where defects are recognized as highly organized features, forming discrete clusters or more extended assemblies within the crystal lattice. This shift in perspective marks a critical advancement in comprehending the fundamental nature of defect solids. The review's substantive contribution lies in demonstrating how the concept of octahedral coordination of vacant oxygen sites, when coupled with rigorous topological analysis, offers profound insights. This methodology is specifically applied to illuminate the complex transformational and structural relationships inherent in fluorite-type defect oxides. By moving beyond simplistic models, the work highlights the sophisticated interplay between local coordination environments and broader structural topology, providing a powerful framework for deciphering the structural evolution and stability of these technologically important materials. The authors underscore that this integrated approach contributes "considerable insight" into phenomena that were previously difficult to rationalize. Published in 1976, this lecture represents a landmark contribution to solid-state chemistry, effectively ushering in a new era of defect chemistry research. Its insistence on organized defect structures laid the groundwork for subsequent detailed studies on crystallographic shear, defect clusters, and modulated structures, profoundly influencing the field's trajectory. The insights presented regarding fluorite-type oxides, leveraging novel analytical tools, would have been particularly impactful, guiding both experimentalists and theorists in their exploration of complex oxides. This work remains a critical reference for understanding the historical development and conceptual shifts in the study of non-stoichiometric materials.

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