Structure and properties of alkali and alkali lead oxynitride phosphate glasses

Abstract

The development ofmicroelectronics towards lower processing temperatures needs a parallel development of lower temperatures sealing materials. Due to particular thermal properties, such as high thermal expansion coefficient, A ,and low glass transition and dilatometric softening temperatures, Tg and Ts, phosphate glasses are of interest for application as low-temperature sealing glasses. An efficient method to significantly improve the accompanying poor chemical durability of these glasses is a partial anionic Substitution of nitrogen(Ν³¯)for oxygen (O²¯), which induces crosslinking between chains through covalent P-N bonds. New Li_(0.25)Na_(0.25)Pb_(0.25)PO_(3-3x/2)N_x phosphorus oxynitride glass compositions (0 < X ≤ 0.69) have been elaborated by thermal treatment of corresponding oxide base glasses in an hydrous ammonia atmosphere, at temperatures ranging from 600 to 750°C and for times up to 30h. The introduction of nitrogenin the glass network induces also a linear decrease in α, and a linear increase in Tg andTs, however without changing them too much. A structural study has been carried out using nuclearmagnetic resonance and x-ray photoelectron spectroscopies. ³¹P MAS NMR shows that the glass network is built up of PO₄, PO₃N and PO₂N₂ tetrahedral units. PO₄-PO₄, PO₄-PO₃N and PO₃N-PO₂N₂ connections, evidenced by ³¹P-MAS NMR, are homogeneously distributed within the glass network. XPS at the Nis core level indicates that nitrogen atoms substitute for both bridging and non-bridging oxygen atoms, as two-coordinated -N= (Nd) or three-coordinated -N< (Nt) species. A higher amount of Nd-type than Nt-type atoms is found for the highest nitrogen contents. ²³Na and ²⁰⁷Pb NMR results show that the nitrogen-oxygen substitution does not affect oxygen atoms coordinating modifier cations. The role played by lead in these "LINaPbPON" glasses is deduced from a comparison with the nitridation study in "LINaPON" and "NaPON" systems. The presence of Pb²⁺ cations has clearly an influence on the nitridation mechanism. They behave essentially as modifier cations, however they show with the nitrogen enrichment an increased network forming character.