Structural investigation of nickel polyphosphate coacervate glass–ceramics

Abstract

Nickel polyphosphate coacervates have been prepared through the coacervation process of sodium polyphosphate and Ni²⁺ chloride solutions by the addition of different solvents with low molecular weight. The great potential of nickel polyphosphate coacervates as a material precursor was demonstrated by preparation of nickel polyphosphate glass–ceramics. Structural and spectroscopic properties were analyzed by thermal analysis, X-ray powder diffraction, Raman spectroscopic and UV-VIS techniques. Raman spectra for the nickel polyphosphate coacervates and nickel polyphosphate coacervates glass–ceramics samples shows that the addition of solvents leads to a depolymerization of the polyphosphate chains, resulting in an increase of shorter chains species based on pyrophosphates. The identification and quantification of Ni₂P₄0₁₂, β-Ni₂P₂O₇ and δ-Ni₂P₂O₇ crystalline phases present in the nickel polyphosphate glass–ceramics were carried out by X-ray powder diffraction using the Rietveld method. Quantitative phase analyses of the three polymorph forms were also evaluated. Based on interpretation of reflectance spectroscopy and Rietveld refinement, Ni²⁺ ions may occupy distorted octahedral and tetrahedral sites.