Influence of CeO2 on glass formation, structural and thermal properties of sodium niobium phosphate glass.

Cerium is a well-known surrogate to trivalent and tetravalent actinides and has been investigated to explore the structural and thermal characteristics of simulated radwaste-loaded material systems. The solubility and distribution of CeO 2 into a sodium niobium phosphate glass have been explored with the objective of developing a host matrix for radioactive waste immobilization. Niobium phosphate glasses of (100-x) (40Na 2 O–20Nb 2 O 5 –40P 2 O 5)-xCeO 2 (x = 0, 1, 3, 5, 8, and 10 mol%) compositions are prepared by melt-quenching method and are characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and scanning electron microscopy (SEM). This study summarises the influence of cerium ion incorporation on the structure, thermal stability, and formation of crystalline phases of the niobium phosphate glass. The various glass stability parameters, such as Hruby (K H), Weinberg (K W), and Lu–Liu (K LL) parameters are estimated to assess the stability of the glass melt against devitrification in the supercooled region. The spectroscopic analysis ascertains the presence of metaphosphate and pyrophosphate networks as primary structural building units in the glass. However, the Raman analysis demonstrates the influence of CeO 2 on the network linkages arising from the corner-sharing of NbO 6 octahedrons and Nb–O–P bonding in the glass. The CeO 2 loading is optimized up to 8 mol% into the base 40Na 2 O–20Nb 2 O 5 –40P 2 O 5 glass matrix without precipitation of any crystalline phase. The glasses are heat treated to obtain glass-ceramics embedded with the crystalline phases, namely, monazite CePO 4 , NbOPO 4 , NaNbO 3 , and niobium phosphate bronze Na 6 Nb 8 (PO 4) 5 O 15. The microanalysis of these glass ceramics shows that the CeO 2 is more aggregated inside the niobium phosphate bronze framework than in the bulk at a higher temperature. It is also observed that the surface crystallization process is a prevalent mechanism for the crystallization of glasses on heating at crystallization onset temperature. [ABSTRACT FROM AUTHOR]