Structural and Electronic Factors Governing the Metallic and Nonmetallic Properties of the PyrochloresA2Ru2O7−y☆

Abstract The metal-versus-semiconductor behavior of ruthenium pyrochlores A 2 Ru 2 O 7− y was examined by calculating their electronic band structures. This behavior is explained in terms of the Mott–Hubbard mechanism of electron localization. The width of the t 2 g -block bands of A 2 Ru 2 O 7− y increases with increasing Ru–O–Ru bond angle, and the Ru–O–Ru angle increases with increasing size of the A cation. There is a good linear relationship between the ionic radius of the A cation and the Ru–O–Ru bond angle. This relationship makes it possible to calculate the amount of the O′ atom vacancy based on the observed Ru–O–Ru angle in Tl 2 Ru 2 O 7− y .