Local structure and redox state of copper in tellurite glasses

Abstract

The local glass structure of tellurite glasses containing CuO with the nominal composition x(CuO) · (1− x)(TeO 2), where x=0.10, 0.20, 0.30, 0.40, and 0.50, as well as the valence state of the copper ions have been investigated by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. The Te 3d core level spectra for all glass samples show symmetrical peaks (Te 3d 5/2 and Te 3d 3/2) at essentially the same binding energies as measured for TeO 2 indicating that the chemical environment of the Te atoms in the glasses does not vary significantly with the addition of CuO. The O 1s spectra, however, show slight asymmetry for all glass samples which results from two contributions, one from the presence of oxygen atoms in the Te–O–Te environment (bridging oxygen BO) and the other from oxygen atoms in an Te–O–Cu environment (non-bridging oxygen NBO). The ratio of NBO to total oxygen was found to increase with CuO content and to be in good agreement with calculated values for the TeO 4 trigonal bipyramid structure. Moreover, the appearance of a satellite peak in the Cu 2p spectra provides definitive evidence for the presence of Cu 2+ ions in these glass samples where the asymmetry and broadening of the Cu 2p 3/2 and Cu 2p 1/2 peaks are indicative of the presence of both Cu 2+ and Cu + ions. The relative concentration Cu 2+ determined from XPS is in good qualitative agreement with the determinations of Cu 2+ from magnetic susceptibility measurements on the same glass samples. Furthermore the susceptibility data follow a Curie–Weiss temperature-dependent behavior ( χ= C/( T− θ)) with negative Curie temperatures indicating that the predominant magnetic interactions between the Cu 2+–Cu 2+ exchange pairs are antiferromagnetic in nature.