Structure‐Property Relations in Lanthanide Borate Glasses

Abstract

Glass formation in the system Ln 2 O 3 ‐B 2 O 3 (Ln = Nd, Sm) was studied. Glasses could be formed in the range from 0 to ‐28 mol% rare‐earth oxide (Ln 2 O 3 ), but liquid immiscibility in these systems limits the range of homogeneous glasses to 0 to 1.5 and 25 to 28 mol% Ln 2 O 3 . The infrared spectra indicate that the rare‐earth‐rich glasses are structurally similar to rare‐earth metaborates (LnB 3 O 6 ) which contain (B 3 O 6 )‐ chains. The variation in density, transformation temperature, thermal expansion coefficient, and transformation‐range viscosity of these glasses with the size of the rare‐earth ion is discussed. Glasses near the metaborate composition have a transformation temperature of =700°C, which is high for binary borate glasses. Glasses could not be formed in the systems EU 2 O 3 ‐, Gd 2 O 3 ‐, HO 2 O 3 ‐, and Er 2 O 3 ‐B 2 O 3 , even by quenching at =1300°C/s. The sudden lack of glass formation in the system Ln 2 O 3 ‐B 2 O 3 with Ln 3+ ions smaller than Sm 3+ is explained on the basis of the size effect of the Ln 3+ ion on the stability of (B 3 O 6 )‐ chains in these metaborates.