Despite the difficulty of experimentally studying polyamorphic transitions in high-Tg glasses, it is well known that silica glass has two high-density phases: the cold-compressed and hot-compressed high-density amorphous phases (c-HDA and h-HDA). By means of vibrational spectroscopy techniques under pressure, we first evidence that the yield strength under hydrostatic pressure is identical for glasses of similar density, whatever the thermo-mechanical history, showing that the elastic limit of a silica glass depends solely of its density. Our results also reveal the changes in the energy landscape of amorphous silica under high pressure. Above a certain threshold pressure, the energy barriers between the different amorphous phases vanish and the glass is automatically driven toward the c-HDA phase, whatever the initial structure and the temperature of compression. Very high pressures can therefore erase all traces of a glass’s thermodynamic history.

In this study, we investigated the effect of different compression routes on the lead metasilicate (PbSiO3) composition. Glass samples were compressed in a Belt press up to 5 GPa at room temperature (cold compression) and high temperatures (hot compression) up to 673 K, both at comparable experimental conditions concerning pressure and temperature gradients and times. The set of densified glasses was analyzed ex-situ by Brillouin, Raman and infrared spectroscopies, providing a multiscale structural probe. The dataset revealed a progressive decrease in the refractive index-weighted longitudinal sound velocities for the cold-compression and a minimum at about 450 K for hot-compression. Raman and infrared analyses indicate increasing depolymerization of the silicate network as an effect of densification, which is more pronounced at higher temperatures. Moreover, distinct mechanical properties are discussed regarding the inherent structural modifications resulting from the compression treatments.

The present study focuses on synthesizing and investigating the structure of Eu3+-doped sodium calcium silicate and calcium alumino silicate glasses under extreme high-pressure conditions. For a thorough understanding of glassy systems in extreme conditions, we conducted in-situ micro-luminescence experiments using a diamond anvil cell, reaching pressures up to 16 GPa. Hydrostatic pressure demonstrated a notable impact on luminescence, attributed to the nephelauxetic effect causing the contraction of central-ion-ligand distances. The band transitions of Eu3+ from the D-5(0) to F-7(1,2) states revealed pronounced pressure-induced splitting, highlighting the pressure influence on crystal-field properties. The energy shifts for the D-5(0) -> F-7(1) transitions were determined to be 0.14 nmGPa(-1) and 0.20 nmGPa(-1) for sodium calcium silicate and calcium alumino silicate, respectively. These distinct slope differences indicated a lower structural adaptability of the former glass, resulting in reduced deformability under high-pressure conditions. Furthermore, as pressure increased, the asymmetry ratio of the D-5(0) -> F-7(2/1) transitions decreased, though it consistently maintains levels higher than unity, reflecting the highly asymmetric environment surrounding Eu3+ ions. The estimated elastic limit for both samples was approximately 7 GPa. To assess pressure-induced changes in the local environment, Judd-Ofelt intensity parameters were employed for the calcium alumino silicate glass. The trends observed throughout compression revealed that Omega(2) > Omega(4) up to 6.8 GPa, while Omega(2) < Omega(4) for higher pressures, indicating higher covalency between Eu3+ ions and ligands in the elastic domain compared to the plastic domain. The observed increase in Si and Al coordination in the plastic domain was found to play a role in these parameters.

High pressure may pave the way towards atypical phenomena and properties in glass science. Through compression, vitreous silica presents a well-established elastic anomaly (EA) and the scarcely investigated elastic modulus anomaly (EMA). In this paper, we present a study of the EMA for the densified lead metasilicate (PbSiO3) glass, despite its low silica content and lack of the classical EA. PbSiO3 glass was densified in diamond anvil cell and Belt press apparatus and analyzed by Brillouin spectroscopy and, when applicable, spectroscopic ellipsometry. The elastic modulus anomaly is characterized by a decrease in the longitudinal sound velocity of the densified glass compared to the uncompressed glass and attributed to the low glass ability to undergo significant densification. Densification pathways in PbSiO3 glass are discussed in light of in-situ Brillouin and Raman probes.

Memory effects are a classic feature of disordered materials. With Raman-microspectroscopy we evidence a memory effect in the deformation of densified soda-lime silicate glasses, and with molecular dynamics simulations we identify the network reconfigurations it originates from. These results pave the way toward a better understanding of plastic instability, damage, and rupture properties in iono-covalent glassy materials.

In this study, lead metasilicate glasses (PbSiO3) were densified at different maximum pressures in a diamond anvil cell (DAC) at room temperature. The densified glass samples were investigated ex-situ by Raman spectroscopy to probe their pressure-induced plastic deformation limit and permanent structural modifications on the Q(n) distribution. With a high Pb content, this glass exhibits a low elastic limit at similar to 4 GPa, which is linked to an initial compact structure. Spectral curve fitting of the high-frequency region of the Raman spectra, consisting of symmetric Si-O stretching modes, exhibit subtle Q(n) population modifications with maximum pressure. This reveals silica network depolymerization where the proportion of non-bridging oxygens (NBO) increases at the expense of bridging oxygens (BO). Possible densification mechanisms are discussed in contrast to those known in other silicate glasses.

SiO2 glass structure has been permanently modified by uniaxial compression. Within such a loading, the structure is supposed to be affected both by densification and shear flow. We propose to compare recovered silica samples with similar densities, initially deformed plastically under a hydrostatic compression or under a uniaxial compression. From micro-Raman spectroscopy experiments, the shear strain effects have been highlighted on the structural modifications of the glass and have been confirmed from molecular dynamic simulations. In particular, medium range order depends on the mechanical history in plastically deformed glasses. Indeed, both experiments and simulations demonstrate that small rings are favored when permanent shear strain acts with densification, thus allowing a structural signature identification of the densification process.

Macroscopic Suprasil F300 type silica glasses densified under high pressure and high temperature were irradiated with 2.5 MeV electrons. This paper focuses on the point defects generation in those densified silica glasses. We demonstrated that the unattributed 540 nm emission band was clearly enhanced when the irradiated glasses exhibit a higher density either initially generated by high pressure cycle or by irradiation at high dose ( > 3 GGy). The spectral shape of the emission band related to Non Bridging Oxygen Hole Center (NBOHC) is also modified with a broader FWHM due to an additional contribution near 610 nm indicating a larger distribution of NBOHC species in these densified glasses.

From initial calcium aluminosilicate glass, transparent glass-ceramics have been successfully synthesized under simultaneous high pressure and temperature (SHPT). Possible homogeneous volumetric crystallization of this glassy system, which was not achieved previously by means of conventional heat treatment, has been put in evidence with a SHPT procedure. Structural, mechanical, and optical properties of glass and glass-ceramic obtained were investigated. Raman spectroscopy and X-ray diffraction allowed to identify two main crystalline phases: merwinite [Ca3Mg(SiO4)2] and diopside [CaMgSi2O6]. A Raman scanning profile showed that the formation of merwinite is quite homogeneous over the bulk sample. However, the sample surface also contains significant diopside crystals. Instrumented Berkovich nanoindentation was applied to determine the effect of SHPT on hardness from glass to glass-ceramic. For Eu-doped samples, the broadband emission due to 4f65d1 → 4f7 transition of Eu2+ was studied in both host systems. Additionally, the 5D0 → 7FJ transition of Eu3+ was used as an environment probe in the pristine glass and the glass-ceramic.

In situ micro-Raman spectroscopy was used to investigate the structural evolution of OH(-)-free calcium aluminosilicate glasses, under high pressure and at room temperature. Evaluation was made of the role of the SiO2 concentration in percalcic join systems, for Al/(Al  +  Si) in the approximate range from 0.9 to 0.2. Under high pressure, the intensity of the main band related to the bending mode of bridging oxygen ([Formula: see text][T-O-T], where T  =  Si or Al) decreased gradually, suggesting that the bonds were severely altered or even destroyed. In Si-rich glasses, compression induced a transformation of Q (n) species to Q (n-1). In the case of Al-rich glass, the Al in the smallest Q (n) units evolved from tetrahedral to higher-coordinated Al (([5])Al and ([6])Al). Permanent structural changes were observed in samples recovered from the highest pressure of around 15 GPa and, particularly for Si-rich samples, the recovered structure showed an increase of three-membered rings in the Si/Al tetrahedral network.

Densified silica can be obtained by different pressure and temperature paths and for different stress conditions, hydrostatic or including shear. The density is usually the macroscopic parameter used to characterize the different compressed silica samples. The aim of our present study is to compare structural modifications for silica glass, densified from several routes. For this, densified silica glasses are prepared from cold and high temperature (up to 1020 °C) compressions. The different densified glasses obtained in our study are characterized by micro-Raman spectroscopy. Intertetrahedral angles from the main band relative to the bending mode decrease and their values are larger for densified samples from high temperature compression than those samples from cold compression. The relative amount of 3-membered rings deduced from the D2 line area increases as a function of density for cold compression. The temperature increase during the compression process induces a decrease of the 3 fold ring population. Moreover, 3 fold rings are more deformed and stressed for densified samples at room temperature at the expense of those densified at high temperature. Temperature plays a main role in the reorganization structure during the densification and leads to obtaining a more relaxed structure with lower stresses than glasses densified from cold compression. The role of hydrostatic or non-hydrostatic applied stresses on the glass structure is discussed. From the Sen and Thorpe central force model, intertetrahedral angle average value and their distribution are estimated.

Modelling the mechanical response of silica glass is still challenging, due to the lack of knowledge concerning the elastic properties of intermediate states of densification. An extensive Brillouin Light Scattering study on permanently densified silica glasses after cold compression in diamond anvil cell has been carried out, in order to deduce the elastic properties of such glasses and to provide new insights concerning the densification process. From sound velocity measurements, we derive phenomenological laws linking the elastic moduli of silica glass as a function of its densification ratio. The found elastic moduli are in excellent agreement with the sparse data extracted from literature, and we show that they do not depend on the thermodynamic path taken during densification (room temperature or heating). We also demonstrate that the longitudinal sound velocity exhibits an anomalous behavior, displaying a minimum for a densification ratio of 5%, and highlight the fact that this anomaly has to be distinguished from the compressibility anomaly of a-SiO2 in the elastic domain.

Fiber Optic Sensors (FOSs) based on Brillouin scattering are widely used in large infrastructures to detect modifications over large distances. In doped silica fibers the Brillouin Frequency Shift (BFS) is proportional both to temperature and strains. In this work we establish that the sensitivity of FOSs to hydrostatic pressure can be forecast from the behavior of the glass under hydrostatic compressions in a diamond anvil cell. It is shown that the BFS under a hydrostatic pressure is a manifestation of the elastic anomaly observed in silica glass. This anomaly vanishes in GeO2 glass and accounts for the decrease of the sensor sensitivity when the GeO2 doping concentration increases in a silica fiber. The progressive vanishing of the anomaly in sodium aluminosilicate glasses which contain the same amount of silicon dioxide (75%) but differ in the Na2O and Al2O3 ratio allows to determine the composition of a glass with a BFS independent of the pressure. Such a glass composition will provide a pressure-independent temperature FOSs.

The in situ elastic and plastic behaviors of sodium aluminosilicate glasses with different degrees of depolymerization were analyzed using Brillouin spectroscopy. The observed elastic anomaly progressively vanished with depolymerization. The densification process appears to be different from that observed in pure silica glass. In the plastic regime of densified glasses hysteresis loops were observed and related to modification of the local silicon environment facilitated by the addition of sodium.

Raman scattering experiments have been carried out to study persistent densification in SiO2 glass following hydrostatic compression at room temperature. A new relationship linking selective Raman parameters to the degree of densification in the glass has been developed here. This approach will allow quantification of the residual densification in silica following microindentation experiments, with the goal being the development of a constitutive law for amorphous silica.

Low frequency vibrations, a universal feature of amorphous solids which is responsible for thermodynamical anomalies at low temperature, are complicated to record in high pressure device, notably because of the closeness of the elastic line. We first present an experimental protocol allowing to record the in situ low-frequency Raman scattering of samples under high pressure in the diamond anvil cell apparatus with a high quality. This protocol is particularly adapted to study the evolution of the boson peak of glassy materials. The second part is dedicated to the study of the boson peak of a-GeO2, a typical strong glass. The results, which clearly show the non-Debye behaviour of this material at the beginning of the compression where an anomalous compression takes place, are compared to previous measurements on a-SiO2. Interpretation in terms of local structural transitions and discussions about the elastic nanoheterogeneities of the amorphous state are addressed. (C) 2012 Elsevier B.V. All rights reserved.

The elastic and plastic behaviors of silica glasses densified at various maximum pressure reached (12 GPa, 15 GPa, 19 GPa, and 22 GPa), were analyzed using in situ Raman and Brillouin spectroscopies. The elastic anomaly was observed to progressively vanish up to a maximum pressure reached of 12 GPa, beyond which it is completely suppressed. Above the elastic anomaly the mechanical behavior of silica glass, as derived from Brillouin measurements, is interpreted in terms of pressure induced transformation of low density amorphous silica into high density amorphous silica.

The deposition of a thin layer of a quantum-cutter material on top of silicon-based solar cells seems to be a promising solution to reduce the thermalization losses. This mechanism has been reported in materials codoped with Pr3+-Yb3+, where Pr3+ can sensitize two Yb3+ ions for one absorbed blue photon. In the present Letter, we analyze precisely energy transfers between Pr3+ and Yb3+ in CaYAlO4, and we measure a quantum-cutting rate of 145%. We show that a very efficient back transfer from Yb3+ toward the (1)G4 level of Pr3+ ion leads to a strong reduction of the quantum yield.

Pressure induced densification in a molecular arsenic sulfide glass is studied at ambient temperature using x-ray scattering, absorption and Raman spectroscopic techniques in situ in a diamond anvil cell. The relatively abrupt changes in the position of the first sharp diffraction peak, FSDP, and the pressure-volume equation of state near ∼2 GPa suggest a phase transition between low- and high-density amorphous phases characterized by different densification mechanisms and rates. Raman spectroscopic results provide clear evidence that the phase transition corresponds to a topological transformation between a low-density molecular structure and a high-density network structure via opening of the constituent As4S3 cage molecules and bond switching. Pressure induced mode softening of the high density phase suggests a low dimensional nature of the network. The phase transformation is hysteretically reversible, and therefore, reminiscent of a first-order phase transition.