Structure and viscosity of phase‐separated BaO–SiO₂ glasses

Abstract

Barium silicate glasses with 0‐40 mol% BaO were synthesized either by aerodynamical levitation and laser heating (at low barium content) or by conventional melting and quenching process. Characterization by means of Raman scattering spectroscopy and scanning transmission electron microscopy reveals a structural transition between glasses with low BaO content (<10 mol%) showing an atomic network resembling the one of amorphous silica, and glasses with a BaO content larger than 10 mol%, which exhibit the typical signature of a binary silicate glass with Q2 and Q3 units. Viscosity curves show a marked increase of the viscosity as the BaO content decreases below 20 mol%. Barium is found to easily diffuse and promote phase separation while silicon remains homogeneously distributed. A dramatic increase in the viscosity is observed as phase separation proceeds, resulting in the formation of Ba‐rich nodules in a percolating SiO2‐rich matrix at low barium content, or in Ba‐poor nodules in a BaO‐rich matrix at large barium content.

Novel Er3+/Ho3+‐codoped glass‐ceramic fibers for broadband tunable mid‐infrared fiber lasers

“…For the precursor fiber core, the Raman spectrum exhibits some broad bands without any crystal peak indicative of an amorphous material. The bands located at 476 and 995 cm −1 are responsible for the Si–O–Si stretching or bending vibration . The bands situated at 774 and 1450 cm −1 are related to the stretching vibration of BO 4 and BO 3 units, separately .…”

“…The bands located at 476 and 995 cm À1 are responsible for the Si-O-Si stretching or bending vibration. 26,27 The bands situated at 774 and 1450 cm À1 are related to the stretching vibration of BO 4 and BO 3 units, separately. 28,29 However, the Raman spectra of GC fiber cores show intensive peaks (173, 208, and 262 cm À1 ) that are consistent with the vibrational modes of NaYF 4 crystal, indicating the precipitation of NaYF 4 nanocrystals in the fiber core.…”

Dissolution and Diffusion-Based Reactions within YBa2Cu3O7−x Glass Fibers

“…The formation of silica-rich precipitations has been observed previously in glass-forming systems and is explained in terms of the existence of a miscibility gap [19][20][21][22][23][24]. The literature shows that the formation of silica-rich precipitations is attributed to a liquid-liquid phase separation mechanism in silicate melts as the temperature cools.…”

“…The literature shows that the formation of silica-rich precipitations is attributed to a liquid-liquid phase separation mechanism in silicate melts as the temperature cools. However, the dominant phase separation mechanism (spinodal phase separation versus nucleation and growth) can be difficult to identify [19][20][21][22][23][24]. Miscibility gaps are reported for the CuO-SiO 2 system [25], the BaO-SiO 2 [20][21][22] and the Y 2 O 3 -SiO 2 [26,27] system, but no in-depth phase and morphology studies were performed for the CuO-SiO 2 and Y 2 O 3 -SiO 2 system.…”

Nucleation and crystallization of Ba2Si3O8 spherulites in a barium aluminum silicate glass, and mechanical properties of the obtained glass-ceramics

“…Let us note that at 700 °C,  is less than 2.10 12 Pa.s, and G is about 0.92xG (20 °C) and is thus about 25 GPa [30], so that the Maxwell relaxation time ( = ) is about 1.3 min. This rough estimation supports the fact that creep adopts a pure viscous regime at times larger than several hours, which validates the use of Eq.…”