The influence of nickel on the chemistry of nickel-zinc phosphate glasses

Abstract

The glasses of the NiO-ZnO-P₂O₅ system were prepared in two compositional series formally expressed in oxides: metaphosphate series (A), i.e. without changing the anion, xNiO-(50-x)ZnO-50P₂O₅ and the metaphosphate to pyrophosphate series (B), i.e. with changing the anion, xNiO-(50–0.75x)ZnO-(50–0.25x)P₂O₅. Using magnetic susceptibility, Raman spectroscopy and electron absorption spectroscopy it was determined that all glasses containing nickel were paramagnetic with Ni²⁺ tetrahedral coordination. The Ni-O(P) bond was found to have a higher ionicity compare to Zn-O(P) bond. If metaphosphate is changed to pyrophosphate, series (B), glasses can only be prepared up to 20 mol% of NiO and at higher concentration crystalline nickel pyrophosphate appears. It follows that Ni²⁺ ions do not connect pyrophosphate structural units and are therefore unable to form a cationically linked glass network. The glass transition temperature and the coefficient of thermal expansion are related to the concentration of metaphosphates and, in principle, increase with rising nickel content.