Structural and magnetic properties of MoO₃-TeO₂ glasses

A series of tellurite glasses containing MoO₃ with the nominal composition x(MoO₃)-(1 - x)(TeO₂), where x = 0.10, 0.20, 0.30, and 0.40, have been investigated using X-ray photoelectron spectroscopy (XPS) and temperature-dependent magnetization techniques. The Te 3d core level spectra for all glass samples show symmetrical peaks at essentially the same binding energies as measured for TeO₂ oxide and with full-widths at half-maximum (FWHM) that do not vary with increasing MoO₃. These features indicate that the chemical environment of the Te atoms in the glasses does not vary significantly with the addition of MoO₃ and that the Te ions exist in a single configuration, namely TeO₄ trigonal bipyramid (tbp). The O 1s spectra, however, show asymmetry for samples with composition x ≤ 0.30 and are subsequently fitted with two peaks. One arises from the presence of oxygen atoms in the Te-O-Te, Mo-O-Mo and Te-O-Mo environments which are termed bridging oxygen (BO) and the other from oxygen atoms in an MoO environment which are termed non-bridging oxygen (NBO). The O 1s peak for x = 0.40 is more narrow and symmetric, and is fitted to a single peak due to the BO atoms. While the analysis of the Mo 3d spectra indicates the presence of Mo ⁶⁺ ions only, the temperature-dependent magnetic susceptibility measurements shows a weak paramagnetic behavior which can be explained by having less than 1 at.% of the Mo ions existing in a magnetic Mo⁵⁺ valence state, a percentage below the detection level of the XPS determinations.