Structures, thermal expansion, chemical stability and crystallization behavior of phosphate-based glasses by influence of rare earth

The effect of rare earth elements (Y, La, Nd, Sm, and Gd) on the structures, thermal expansion, chemical stability and crystallization behavior of phosphate-based glasses were characterized by using powder X-ray diffraction (PXRD), Scanning Electron Microscope (SEM), X-Ray Fluorescence (XRF), Diffuse reflectance UV–Visible spectra, thermal expansion coefficient, inductively coupled plasma mass spectrometry (ICP-MS) and Differential scanning calorimetry (DSC). UV–Vis spectra not only exhibit the absorption peaks of rare earth cations but also reveal the reduction of band gap (Eg) with increasing the cationic field strength (CFS) of rare earth elements, further establishing the change of non-bridging oxygen (NBOs) density in the glass structures. It is found that there is a decrease in thermal expansion coefficient (α) with increasing the CFS of rare earth, and the study shows a strong correlation between α values and NBOs in the rare earth phosphate glass systems. The chemical durability tests of glass blocks demonstrate that the normalized leach rates (NRRE) increase with decreasing the radius of rare earth elements, and La-doped phosphate glass with high thermal expansion coefficient has good chemical durability. By a two-stage thermal treatment, a preliminary study of the crystallization mechanism for the rare earth phosphate glasses is carried out, and the major crystalline phases are identified.