Oxides of the 3d Transition Metals

The transition metals combine with other elements to form a host of compounds which are electronic conductors and which range in chemical bonding from ionic (oxides), through covalent (sulfides, arsenides) to metallic (carbides, nitrides). This range in valence character promises a great variety of energy band structures and transport processes and offers a rich field for theoretical and experimental investigation. No detailed determination of band structure or transport has been made for any of these compounds, and so they constitute an enormous gap in our knowledge of the solid state. Indeed, except for the 3d oxides, the semiconductor properties of transition metal compounds are largely unknown. In recent years the use of these oxides in electric1 and magnetic2 circuit elements and in heterogeneous catalysis,3 as well as their importance in corrosion4 have emphasized the necessity for a fundamental understanding of their properties. Now, from our point of view, the most fundamental aspect of a solid is its energy band structure. Therefore, it will * This article is a c h a p t e r from Semiconductors, edited by N. B. H a n n a y , to be published by Reinhold Publishing Corp., New York, as p a r t of t h e American Chemical Societ y M o n o g r a p h Series. 1047