Investigation of the unoccupied states in Sr₂YRuO₆ single crystals doped with Cu

The electronic structure single crystals of the new double perovskite Sr₂YRu_1-xCu_xO₆ (x = 0-0.05) has been investigated by x-ray absorption nearedge structure (XANES) spectroscopy. The Cu K-edge spectra show that Cu is incorporated as Cu¹⁺ and Cu ²⁺ in the crystals grown in air and in an oxygen atmosphere and Ru⁵⁺ is seen in the Ru K-edge spectra. The O K-edge and the Ru L ₃-edge spectra indicate an increase in the unoccupied states (hole concentration) as x is increased, accompanied by a lattice distortion from an increased O-Ru-O bond angle. These changes observed even with a small Cu addition are interpreted to result from the Cu 3d-O 2p hybridization as Cu replaces Ru in the octahedral sites.