Thermal and structural analysis of 40La2O3-10Nb2O5-(50-x)Al2O3-xBaO glasses

Abstract Aluminate glasses have excellent optical and mechanical properties, in addition to high thermal and chemical stability. However, aluminate glasses require high melting temperatures and exhibit poor glass forming ability, causing difficulties while preparation by the melt-quench method. Therefore, it is necessary to establish novel methods to improve melting conditions and glass forming tendencies for aluminate glasses. 40La2O3-10Nb2O5-(50-x)Al2O3-xBaO (x = 0, 2.5, 5, 7.5, 10) glasses were prepared by the aerodynamic levitation method. XRD, DTA, and Raman and NMR spectroscopic techniques were used to investigate the effects of BaO on the structure and thermal properties—including crystallization behavior—of lanthanum aluminate glass. The results show that the addition of BaO increases the glass transition temperature (Tg) and stability ΔT of the baseline glass, as Al-Ba-7.5 (40Al2O3-10Nb2O5–42.5Al2O3–7.5BaO) glass has the highest ΔT value (151 °C). The 27Al MAS NMR spectrum of a high BaO-content glass (Al-Ba-10) shows that about 80% of [IV]Al and 15% of [V]Al are present in the glass network. Raman scattering spectra indicate that a peak shown around 790 cm−1canbe assigned to the internal stretching vibrations of the Al-non-bridging oxygen (NBO) bonds in depolymerized [AlO4/2] tetrahedrons. The crystallization activation energies were calculated to be 1157.1 kJ/mol and 891.7 kJ/mol (Kissinger method) for Al-Ba-x (x = 0, 7.5) glasses, respectively, which progresses as a diffusion-controlled three-dimensional growth process. The nucleation rate of Al-Ba-0 decreases continuously, while Al-Ba-7.5 increases.