Preparation and properties of binary oxide glasses containing rare earth oxides.

Abstract

Thermal image furnace melting and twin-roller quenching were used to prepare glasses containing large amounts of rare earth oxides in Ln2O3-MXOY systems (Ln2O3=La2O3, Nd2O3, Y2O3; MXOY=SiO2, Al2O3, TiO2, Nb2O5).The glass-forming regions were found at the following compositions close to the eutectic points of the phase diagrams: (20-30)Ln2O3-(70-80)SiO2, 60Ln2O3-40SiO2, 20Ln2O3-80Al2O3, 20Ln2O3-80 TiO2, (20-30)Ln2O3-(70-80)Nb2O5 and 60Ln2O3-40Nb2O5. The glass transition temperature Tg was determined by DTA. All the glasses showed high glass transition temperatures over 700°C. Although Tg increased or decreased with Ln2O3 content depending upon the system, the change was linear with Ln2O3 content around the eutectic compositions. This seems to indicate that there is no peculiar behavior of viscosity itself at the eutectic compositions. The liquidus viscosity becomes the maximum at the eutectic compositions due to low liquidus temperatures, which makes glass-formation easier at the eutectic compositions.A glass model consisting of four-coordinated aluminum units was proposed for Ln2O3-Al2O3 glasses based on the results of IR spectra and observed AlKα chemical shifts. On the other hand IR spectra of Ln2O3-TiO2 glasses showed a mixture of six- and four-coordinated titanium units.Visible and ultraviolet absoption spectra of Nd3+ were studied on Nd2O3-MXOY glasses. The peak positions of these absorption bands moved towards lower wave numbers linearly with increasing compositional basicity of the glasses. Their color changed from purple-like blue to green-like blue, as the absorption bands shifted towards lower wave numbers.