A Raman investigation of the structural evolution of supercooled liquid barium disilicate during crystallization

Abstract

The homogeneous and stoichiometric crystallization of the barium disilicate (BaSi2O5) glass makes it possible to follow the structural evolution of Raman bands from the supercooled liquid to the crystalline phase. We monitored the crystallization of supercooled liquid BaSi2O5 at 790°C over 440 minutes revealing a three‐stage crystallization process: stage 1 involves changes in the barium sites toward a bonding environment that is similar to that in orthorhombic low barium disilicate. The end of stage 1 is marked by the loss of the Q4 species vibration at 1170 cm−1 and the creation of a crystalline band at 490 cm−1. Stage 2 is marked by the transition of the Q3 peak (1060 cm−1) from a Gaussian‐like to a Lorentzian curve, indicating the formation of well‐developed sheet structures. These observations lead us to conclude that the Raman spectra are resolving both the crystalline L‐BS2 phase and the BS2 melt. The final stage involves a rapid decrease in the remaining Qn species to form Q3. This crystallization process involves structural modifications that occur on the tens of microns scale. The barium cations drive the initial stages of crystallization, providing direct evidence that the short‐range order, around network modifiers, is a critical factor involved in homogeneous crystallization.

A theoretical and experimental investigation of hetero- vs. homo-connectivity in barium silicates

“…Assuming that the vibrational modes in the crystalline phase have similar origins to those in the glass (c.f. Brawer and White 1975), as has been demonstrated in the case of BaSi O 5 (Moulton et al 2018), we offer several critical comments. First, the spectra of barium silicates show that the intense stretching modes may originate from the bonds between Si and either BO or NBO atoms, or both.…”

“…We conclude by emphasizing some of the implications for the interpretation of Raman spectra of silicate liquids and glasses (e.g. Moulton et al 2018), where hetero-connectivity is the rule rather than the exception.…”

Identifying and explaining vibrational modes of sanbornite (low-BaSi2O5) and Ba5Si8O21: A joint experimental and theoretical study

“…When doped with rare-earth elements, these materials can be used as light emitting diode materials [23,24]. Although interesting behaviors have been shown, there is a lack of clarity regarding the origin and significance of the vibrational modes and their transitions during crystallization processes [21,[25][26][27][28].…”

“…In such cases it is impossible to make an unambiguous assignment if the calculated intensities are so model-dependent that they cannot be used as an aid. Quantum-chemical computations predicting frequencies and spectral intensities are essential to complement the interpretation of experimental spectra, particularly for complex materials where the high density of states results in spectral complexity [26].…”

Point defects in BaSi2 thin films for photovoltaic applications studied by positron annihilation spectroscopy

“…The MBE and TE samples, as well as some of the RF-sputter deposited samples, show the presence of two additional but low intensity peaks at ∼560 cm −1 and ∼580 cm −1 that could stem from Ba-Si-O phases such as Ba 3 Si 5 O 13 , Ba 2 Si 3 O 8 , or BaO-SiO 2 15,16 that can also be discerned in some of the collected XRD patterns. The Raman spectra of the TE sample show two additional peaks at around 260 cm −1 and 315 cm −1 that may arise from BaO-SiO 2 and/or Ba 2 Si 3 O 8 15,16 indicating a higher degree of oxidation than the MBE sample. In turn, RF-sputter deposited samples reveal the presence of a sharp 250 cm −1 peak that diminishes with increased thickness of the a-Si cap layer and that can be attributed to the presence of oxides in the sub-surface layer, namely, BaO (242 cm −1 ), 17 SiO 2 (245 cm −1 ), 18 and/or BaSiO 3 (247 cm −1 ).…”