Influence of niobium oxide content on the structural features of silver phosphate glasses and their corresponding glass-ceramics

Silver phosphate glasses in the Ag2O-Nb2O5-P2O5 ternary system were prepared using the conventional quenching method. The glasses were defined by the 50Ag2O-xNb2O5-(50-x)P2O5 composition with 0 ≤ x ≤ 25 mol %. They were found coloured. Their density and molar volume values are examined. The X-ray diffraction analysis was confirmed their amorphous state. The glass-ceramics were achieved by performing heat treatments of the elaborated glasses. To highlighting the impact of replacing P2O5 by Nb2O5 on the structural properties of the elaborated glasses and glass-ceramics, Raman analysis was carried out. This technique permitted the identification of various structural units of phosphate, mainly metaphosphates and pyrophosphate, and revealed that niobium adopts an octahedral oxygen environment. The controlled crystallization of the glasses leads to the formation of an orthorhombic silver niobate phase AgNbO3 mixed with a secondary phase Ag4P2O7 for glasses with high niobium content (x ≥ 15 mol%) and AgPO3 for glasses with low niobium concentration (x ≤ 15 mol%).