X-ray absorption in relation to valency of iridium in sputtered iridium oxide films

摘要

Electronic and structural changes induced by the charge storage reaction due to proton insertion in sputtered iridium oxide films (SIROFs) have been invstigated by in situ X-ray absorption spectroscopy at the L_3 edge of iridium atoms in 1 M H_2SO_4. The iridium valency is shown to increase from 3 to 3.85 when the potential varies from -0.2 to +1 V(SCE). In XANES spectra, the white line peak height and energy position decrease with insertion. The fine structures of the spectra have been analyzed and simulated in view of structural parameter extraction. A correspondence curve is established between the interatomic Ir-O distance in the first shell and the iridium valency. A strong decrease of this distance is observed with the oxidation state of iridium accompanied by a conspicuous decrease of the Debye-Waller factor.