Investigation of Cul-Containing Molybdophosphate Glasses by Infrared Reflectance Spectroscopy

Superionic glasses xCuI―(1 ― x)[Cu2MoO4―CuPO3] were prepared and studied by infrared reflectance spectroscopy to investigate the structure of the oxyanion matrix and the type of sites occupied by copper ions. The study was complemented by the consideration of glasses 0.67CuI―0.33[Cu2MoO4―Cu3PO4] and xCuI-(1 ― x)[Cu2O-nP2O5] with n = 0.33, 0.50, 1.0. The oxyanion structure of glasses xCuI―[1 - x)[Cu2MoO4―CuPO3] was found to involve discrete PO43-, P2O74- and MoO42- units, where P and Mo are 4-fold coordinated to oxygen, and molybdate octahedral species which have the MoO3 stoichiometry and are linked by Mo-O-Mo bridging bonds. Despite the nominal metaphosphate composition (CuPO3) of these glasses the spectra gave no signature for metaphosphate structures based on the PO3― unit. Also, increasing amounts of Cul were found to favor the creation of PO43- and MoO3 species at the expense of P2O74- and MoO42-. These findings were explained by the acidity order P2O5 > MoO3 and the need to accommodate the bulky Cul in the glassy matrix, a process facilitated by condensed MoO3 octahedral species. Cu ions were found to be present as monovalent cations and to occupy oxide and iodide sites. The latter sites organize into Cul-like pseudophases at high Cul contents, in agreement with the conduction pathway model for superionic glasses.