Reaction of nonaqueous halogen solutions with YBa2Cu3O7−x

Abstract

X-ray photoelectron spectroscopy (XPS) has been used to investigate the reaction of YBa2Cu3O7−x films with solutions of HF, HCl, Br2, HBr, I2, and HI in absolute ethanol (EtOH). The XPS core level and x-ray excited Auger spectra from untreated and halogen-treated surfaces are used to identify surface species by comparison with XPS data from the literature and with XPS spectra from more than 20 Y, Ba, and Cu halides, oxides, hydroxides, and carbonates measured in this work. XPS measurements on a number of these materials are being reported for the first time. Treatment of films with HF/EtOH results in the formation of an oxyfluoride with Y:Ba:Cu relative concentrations of 1:4:3. Additional features in the XPS spectra from HF-treated films are also consistent with the formation of CuF, a compound which does not exist in bulk form. Treatment of films with HCl/EtOH results primarily in the formation of BaCl2 (∼75%), with smaller amounts of YCl3, CuCl, and CuCl2. Treatment of films with Br2/EtOH or HBr/EtOH results in the formation of YBr3, BaBr2, and CuBr with relative concentrations 1:4:3. YBa2Cu3O7−x films were found to have no discernible reaction with I2/EtOH solutions, but treatment of films with HI/EtOH results in the formation of CuI on the surface.