Metal-metal bonding in the KSbO3-type oxides La4Ru6O19 and La3U3O11: A mechanism for band gap formation in t(2g) states - art. no. 085111

The electronic structures of La3Ru3O11 and La4Ru6O19 were calculated using a LMTO-ASA-TB method. Although both compounds have similar conduction netwo rks, La3Ru3O11 was found to have a very normal band structure while La4Ru6O 19 showed many striking features. The t(2g) band is split into three portio ns of clearly defined orbital origin. The two highest-energy portions are e xtremely narrow (similar to0.15 eV), and each have a capacity of only 1 ele ctron per Ru atom. The highest portion of the t(2g) band is separated from the remainder of the band by a gap of 0.5 eV. All these features occur in t he absence of Jahn-Teller distortions. The origin of the gap is instead fou nd to lie in metal-metal bonding due to the unusually short Ru-Ru distance in La4Ru6O19 (2.5 Angstrom vs 3.0 Angstrom for La3Ru4O11).