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Research Article

Amorphous boron oxide at megabar pressures via inelastic X-ray scattering

View ORCID ProfileSung Keun Lee, Yong-Hyun Kim, Paul Chow, Yunming Xiao, Cheng Ji, and Guoyin Shen
PNAS June 5, 2018 115 (23) 5855-5860; first published May 21, 2018; https://doi.org/10.1073/pnas.1800777115
Sung Keun Lee
aSchool of Earth and Environmental Sciences, Seoul National University, 08826 Seoul, Korea;
bInstitute of Applied Physics, Seoul National University, 08826 Seoul, Korea;
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  • ORCID record for Sung Keun Lee
  • For correspondence: sungklee@snu.ac.kr
Yong-Hyun Kim
aSchool of Earth and Environmental Sciences, Seoul National University, 08826 Seoul, Korea;
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Paul Chow
cHigh Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439
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Yunming Xiao
cHigh Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439
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Cheng Ji
cHigh Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439
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Guoyin Shen
cHigh Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439
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  1. Edited by David Walker, Columbia University, Palisades, NY, and approved April 30, 2018 (received for review January 16, 2018)

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Significance

When compressed above megabar pressures (100 GPa), glasses may undergo structural transitions into more densely packed networks that differ from those at ambient pressure. While inelastic X-ray scattering (IXS) provides a rare opportunity to probe the pressure-induced bonding transitions, a decade of efforts to collect an IXS signal from any matters beyond 100 GPa have not been successful. Here, IXS spectra for B2O3 glasses up to ∼120 GPa revealed its unique densification paths characterized with the unexpected stability of four-coordinated boron ([4]B). This is in contrast to other prototypical glasses where highly coordinated cations ([4,5,6]Si and [4,5,6]Ge) form at much lower pressure, confirming that the cation with a smaller atomic radius undergoes coordination transformation at higher pressure.

Abstract

Structural transition in amorphous oxides, including glasses, under extreme compression above megabar pressures (>1 million atmospheric pressure, 100 GPa) results in unique densification paths that differ from those in crystals. Experimentally verifying the atomistic origins of such densifications beyond 100 GPa remains unknown. Progress in inelastic X-ray scattering (IXS) provided insights into the pressure-induced bonding changes in oxide glasses; however, IXS has a signal intensity several orders of magnitude smaller than that of elastic X-rays, posing challenges for probing glass structures above 100 GPa near the Earth’s core–mantle boundary. Here, we report megabar IXS spectra for prototypical B2O3 glasses at high pressure up to ∼120 GPa, where it is found that only four-coordinated boron ([4]B) is prevalent. The reduction in the [4]B–O length up to 120 GPa is minor, indicating the extended stability of sp3-bonded [4]B. In contrast, a substantial decrease in the average O–O distance upon compression is revealed, suggesting that the densification in B2O3 glasses is primarily due to O–O distance reduction without the formation of [5]B. Together with earlier results with other archetypal oxide glasses, such as SiO2 and GeO2, the current results confirm that the transition pressure of the formation of highly coordinated framework cations systematically increases with the decreasing atomic radius of the cations. These observations highlight a new opportunity to study the structure of oxide glass above megabar pressures, yielding the atomistic origins of densification in melts at the Earth’s core–mantle boundary.

  • amorphous boron oxide
  • extreme compression
  • megabar pressures
  • inelastic X-ray scattering

When under extreme compression, amorphous oxides undergo structural transitions into more densely packed glassy networks that are significantly different from those at ambient pressure (e.g., refs. 1⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓–16). The detailed structures of the glasses at high pressure are among the remaining fundamental mysteries in modern physical sciences. Particularly, information about the structure of oxide glasses under megabar pressure conditions is important to identify the inherent yet unknown densification mechanisms upon extreme compression and to clarify the evolution of Earth’s lower mantle up to the boundary between the core and the mantle at ∼134 GPa, where formation of dense oxide melts has been suggested (17, 18). Despite the fundamental importance and geophysical implications, the in situ probing of bonding environments in glasses beyond megabar pressure conditions has not been successful, primarily because of the lack of suitable experimental probes.

While elastic X-ray scattering can be used to study oxide glasses at high pressure, the direct coordination environments of framework cations including B in low-z glasses above 100 GPa are unknown because of the small atomic scattering factors of the low-z elements and the extensive overlap among multiple pair correlation functions that accompany the formation of multiple coordination states (e.g., [4,5,6,7]Si and [3,4]B) (3, 19). The limited scattering vector range under high-pressure conditions adds ambiguity in the pair distribution function of the first coordination environments. Although NMR spectroscopy has revealed novel structural transitions in low-z glasses under extreme environments, its application has been limited to the maximum quench pressure of ∼12 GPa because of the necessity of a large amount of glass sample (∼3–10 mg) and the lack of in situ high-pressure solid-state NMR techniques (1, 4, 8, 20⇓⇓–23). Similar pressure limits of ∼17 GPa have been documented for neutron scattering (9, 11, 16, 24).

Nonresonant inelastic X-ray scattering (NIXS, or X-ray Raman scattering), which can probe core electron excitation from glasses in a diamond anvil cell (DAC), has enabled exploration of the pressure-induced changes in atomic configurations around boron and oxygen in oxide glasses under extreme compression (25⇓⇓⇓⇓⇓–31). For example, boron K-edge NIXS showed the transition from [3]B to [4]B in diverse borate glasses up to ∼30 GPa (e.g., refs. 5, 25, 32, and 33). The evolution of oxygen configurations (oxygen K-edge) in SiO2, GeO2, and B2O3 glasses (v-B2O3) as well as other more complex glasses up to ∼40 GPa has been reported (25, 29, 34⇓–36). Furthermore, a silicon L-edge spectrum was obtained for v-SiO2 up to ∼74 GPa (37). Nevertheless, NIXS has not been performed beyond 100 GPa because of the inherent challenges of inelastic X-ray techniques (with a signal intensity several orders of magnitude smaller than that of elastic X-rays). The collection of a high-quality single-oxygen K-edge NIXS spectrum of oxide glasses at high pressure can take 1–2 d of beam time in the third-generation synchrotron sources (25). With increasing pressure, the gap between the diamond anvils decreases, increasing the background signals from the gaskets and anvils. These inherent difficulties pose a major challenge for probing structural changes in glasses with NIXS above 100 GPa. While the signal reduction of incident and scattered photons is inevitable, a polycapillary postsample collimator with improved X-ray optics provides a new opportunity to collect the signal primarily from the sample, with significantly reduced background signals (see Materials and Methods and SI Appendix, section S1 and Fig. S1 for comparison of NIXS spectrum with and without the polycapillary postsample collimator). This provides the potential to explore details of structural transitions in glasses at megabar pressure conditions (38, 39).

Like GeO2, and SiO2 glasses, B2O3 is an archetypal glass former with a peculiar metastability toward crystallization (19, 40, 41). The addition of boron into oxide melts reduces the viscosity and melting temperatures (42). The pressure-induced bonding changes in framework cations, including boron, account for the anomalous pressure dependence of its viscosity and elastic properties (20, 43, 44). While pioneering experimental efforts have been devoted to studying the structure of v-B2O3 at high pressure up to ∼30 GPa (5, 9, 33), the post-[4]B transition into [5]B has not been experimentally identified. Ab initio calculations suggested the prevalence of only [3]B and [4]B in v-B2O3 up to ∼1.5 megabars (45, 46). This is in contrast to Si and Ge in SiO2 and GeO2 glasses, respectively, where successive coordination transformation into multiple coordination states (e.g., [4,5,6]Si and [4,5,6,7]Ge) is expected at relatively low pressure up to ∼5–30 GPa (e.g., refs. 10, 13⇓–15, and 47⇓⇓⇓–51). Although this difference indicates the effects of the nature of the cations and their electronic structures on the transition pressures of the corresponding cations, a systematic relationship between the types of cations and the transition pressure in the glasses has not been established. Experimentally verifying the bonding environments around boron in v-B2O3 at pressures above 100 GPa has thus been anticipated. Along with the cation environments, changes in oxygen coordination beyond megabar pressures may reveal the densification mechanisms of boron coordination transformation. The formation of [4]B in v-B2O3 accompanies the formation of [3]O. Most of the suggested densification mechanisms in oxide glasses involve oxygen coordination transformation from [1]O (i.e., nonbridging oxygen) to [2]O (i.e., bridging oxygen) at a relatively low pressure and the subsequent transition to [3]O (4, 8, 20, 22, 52). However, the densification involving [3]O itself and its effect on the densification in glasses under extreme compression remain unexplored. In this study, we report boron and oxygen K-edge NIXS spectra for v-B2O3 in the megabar pressure range close to that at the Earth’s core–mantle boundary.

The boron K-edge NIXS spectra for v-B2O3 up to 119.4 GPa [with a beam size of ∼8 × 5 μm2 (h × v)] unveil the evolution of boron coordination states upon extreme compression (Fig. 1). The spectra for v-B2O3 at 1 atm and 15.0 GPa have been reported previously, where a much larger beam (80 × 20 μm2) with a culet size of 500 μm was used (5). These spectra are consistent with the current measurements at 1 atm and 16.7 GPa, respectively. The features at 194 eV and 203 eV stem from the transition of a 1s electron to an unoccupied B–O π* antibonding orbital and to an σ* antibonding orbital, respectively. These features are characteristic of [3]B. The additional feature at 198–200 eV is due to [4]B, corresponding to a transition to its 2p/2s σ* antibonding orbital (53). The intensity of the [4]B peak increases with pressure, confirming the coordination transformation from [3]B to [4]B. Most boron is [4]B above ∼30 GPa, as evidenced by the disappearance of the π* peak. With a further increase in pressure up to megabar levels, the gradual shift in the main [4]B peak is observed, indicating densification within amorphous tetrahedral borate networks. The observed peak shift is not significant, suggesting the extended stability of [4]B in v-B2O3 up to ∼120 GPa. The NIXS data do not show any signs of coordination transformation to [5]B, which is consistent with ab initio calculations (45, 54). The minor features at ∼201 eV and ∼205 eV and an emergence of the pre-edge feature (at 194 eV) are identified at high pressure (e.g., 119.4 GPa), reflecting the possibility of structural changes. While these features cannot be fully disregarded based solely on the statistical variation in the spectrum, consideration of the current signal-to-noise ratio and the statistical uncertainty of the B K-edge spectra at high pressure suggests that these minor features are likely to be spectral noises (SI Appendix, section S2 and Fig. S2).

Fig. 1.
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Fig. 1.

Boron K-edge NIXS spectra for B2O3 glass at pressures up to ∼119.4 GPa, as labeled. The spectra are plotted as normalized scattered intensity vs. energy loss (incident energy – elastic energy). Those for 1 atm and 15 GPa have been previously reported (5). The spectra in black were collected with a 0.7-eV scan. See SI Appendix, Fig. S2 for the NIXS spectra without smoothing with spectral uncertainty.

Fig. 2 shows the oxygen K-edge NIXS spectra for v-B2O3 at low pressure range (5) and at 101.6 GPa (SI Appendix, section S2 and Fig. S3). The spectrum at 1 atm shows a sharp peak at 536 eV and a broad feature at 544 eV, both stemming from the bridging [3]B–[2]O–[3]B (5). The major portion (∼75%) of [3]B in bridging oxygen constitutes a trimembered planar ring (i.e., boroxol ring) (41, 55, 56). Only a broad σ* feature at 543 eV is observed at 8.4 GPa and 22.5 GPa, while the peak at 536 eV decreases, suggesting a collapse of the boroxol ring. The oxygen K-edge NIXS spectrum for v-B2O3 at 101.6 GPa shows a shift in the main σ* feature and an increase in the intensity of feature at ∼547 eV (Fig. 2). The observed changes can stem from multiple structural changes upon extreme compression and are similar to those observed for MgSiO3 and SiO2 glasses at high pressure (29, 36, 57). Recent ab initio calculations of oxygen K-edge NIXS spectra for crystalline MgSiO3 and SiO2 phases up to ∼120 GPa indicated that the shift can be primarily correlated with a decrease in the average O–O distance (34, 36, 58). The main oxygen K-edge feature is further broadened at 101.6 GPa, indicating a much wider O–O distribution and, thus, an enhanced topological disorder that is due to an increase in bond angle ([2]O–[4]B–[2]O and [3]O–[4]B–[3]O) and B–O length distribution.

Fig. 2.
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Fig. 2.

Oxygen K-edge NIXS spectra for B2O3 glass at pressures ranging from 1 bar to 100 GPa, as labeled. Those for 1 atm and 8 GPa were previously reported (5) but are shown here for comparison. The shaded box shows the shift in the feature and peak broadening with increasing pressure (only to the guide for eyes). See SI Appendix, Fig. S3 for the NIXS spectra without smoothing with spectral uncertainty.

With increasing pressure, formation of 3[4]B–[3]O is expected at the expense of [2]O and [3]B (i.e., [3]B–[2]O–[3]B + [3]B → 3[4]B–[3]O). Because the boron coordination number in v-B2O3 is 4 above ∼30 GPa and up to ∼120 GPa, the fraction of [3]O for this pressure range is invariant and is two-thirds of all oxygen in the glass (SI Appendix, section S3). Therefore, the oxygen K-edge feature of [3]O at megabar pressures consists of contributions from the two-thirds of [3]O (i.e., 3[4]B–[3]O) and one-third of [2]O that are linked to [4]B (i.e., [4]B–[2]O–[4]B). The observed shift in the edge feature at 101.6 GPa is due to the topological contraction of networks mainly around [3]O. More extensive NIXS studies of model compounds above 100 GPa are required to establish the quantitative effect of pressure on their local structures and NIXS features. Nonetheless, our results confirm that the reduction in the O–O distance in [3]O is the major densification mechanism in v-B2O3 above ∼30 GPa.

Theoretical calculations of the NIXS spectrum can provide useful constraints on the atomistic origin of the pressure-induced NIXS feature changes (Figs. 1 and 2) (36, 58). Fig. 3, Left shows the calculated boron K-edge NIXS spectra for crystalline B2O3–I and B2O3–II with increasing pressure. Detailed calculation conditions and information about crystal structures are presented in SI Appendix, section S4, Fig. S4, and Table S1. The stability of B2O3–II at high pressure has been explored up to ∼46 GPa (59, 60), but the post-B2O3–II phase transition at higher pressure has not been observed. Therefore, we extended the existing equation of state (EOS) of B2O3–II to 120 GPa to explore the evolution of the edge features with a variation in the B–O bond length [d(B-O)] up to the megabar pressure range (SI Appendix, section S4). The d(B-O) in the extrapolated EOS can also be underestimated if distortion of [4]B polyhedra is not considered. Therefore, we calculated the metastable EOS for the B2O3–II beyond megabar by relaxing the atomic positions in the unit cell with a fixed space-group symmetry (SI Appendix, section S4). Note that the current ab initio simulations do not allow us identify the new, high-pressure B2O3–II above 46 GPa, which is beyond the scope of the current study. Further experimental and theoretical studies are necessary to confirm the stability of B2O3–II beyond 46 GPa. Therefore, the current theoretical calculation provides a qualitative guide to the effect of pressure on the σ* peak shift. The edge features shift to higher energy with increasing pressure: While the change in the NIXS peak maxima (Peakmax) for the optimized cell (red dotted curve) is smaller than that obtained from the extrapolated EOS (gray dotted curve), the calculated Peakmax for both cases shifts with increasing pressure mainly because of a reduction in d(B-O) (Fig. 3, Right and SI Appendix, section S4). Based on the calculated trends, an observed minor shift in the σ* peak in v-B2O3 (Fig. 1) corresponds to a decrease in d(B-O) of ∼0.05–0.08 Å upon compression up to 120 GPa. This change is somewhat smaller than that estimated from the compression of B2O3–II to 120 GPa [∼0.08 (estimated from the red curve)–0.2 Å (from the extended EOS)] (Fig. 3). These results indicate that densification of v-B2O3 is mostly due to the reduction in the average O–O distance without the formation of highly coordinated boron (e.g., [5]B), at least up to ∼120 GPa, confirming the stability of sp3-bonded [4]B in v-B2O3. Once the fraction of [3]O reaches a threshold value of two-thirds, the flexibility of the network is expected to decrease. However, the current observation shows that the reduction in the average O–O distance is prevalent without involving further coordination transformation in [4]B. Therefore, the structural densification in v-B2O3 is largely topological (without forming [5]B). A decrease in O–O distance at a given coordination number has been known for the other covalent oxide glasses, such as v-GeO2 below the threshold pressure at which the coordination transformation does not occur (e.g., ref. 61 and references therein). This decrease in B2O3 is also likely to be associated with the increase in packing density that stems from a decrease in [2]O–[4]B–[2]O and [3]O–[4]B–[3]O bond angle and formation of smaller ring networks (i.e., puckering of the networks). While ab initio simulations of the NIXS feature for v-B2O3 at high pressure remain to be calculated, the current simulations of crystalline polymorphs provide a systematic relationship between bond length and its effect on edge features (SI Appendix, section S4). Further experimental exploration of the glasses above several megabars is required to observe evidence of post-[4]B transition (SI Appendix, section S5).

Fig. 3.
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Fig. 3.

(Left) Calculated boron K-edge NIXS spectra for crystalline B2O3–I and B2O3–II, with varying unit cell volumes and pressures, as labeled. The gray and red dotted curves show the calculated peak maximum (Peakmax) for σ* based on extended EOS and optimized metastable EOS. See SI Appendix, section S4 for the detailed calculation methods and crystal structures of B2O3–I and B2O3–II with varying pressures. The calculated NIXS spectra for B2O3–I with varying unit cell volumes with respect to that at 1 atm, as labeled, are added to demonstrate the effect of pressure on the position of the π* peak ([3]B). While the exact pressure value may not be fully known, the estimated pressures of the contracted cell of B2O3–I are ∼4.5 (with a normalized unit cell volume of 0.94) and 10.3 GPa (with a normalized volume of 0.88). See SI Appendix, section S4 for additional details. (Right) Calculated peak maximum [Peakmax, red rhomboids (with geometry optimization) and black rhomboids (based on extended EOS)] of [4]B in B2O3–II with varying pressures (Top) and B-O bond lengths [d(B-O), Bottom]. The latter can be roughly described by the following linear equation: Peakmax = −15.8 × d(B-O) + 220.

The current results provide a prospect for the study of densifications in archetypal oxide glasses, including v-B2O3, v-SiO2, and v-GeO2. For v-SiO2 and v-GeO2, successive transformation of [4]Si (and [4]Ge) into highly coordinated [5,6,7]Si (and [5,6,7]Ge) contributes to the overall densification of the glasses (SI Appendix, section S6). The transition pressure for these highly coordinated Ge in v-GeO2 (∼12 GPa for [5]Ge) is much lower than that in v-SiO2 (∼25 GPa for [5]Si) obtained from in situ high-pressure experiments (10, 11, 47, 48, 50, 51, 61), which is due to the significantly more contracted electron distribution in the latter [Si (with an atomic radius of 1.1 Å at ambient pressure): [Ne] 3s2 3p2] than that in the former [Ge (1.25 Å): [Ar] 3d10 4s2 4p2]. While a similar trend was predicted by the theoretical simulations of v-Al2O3 under compression (62), experimental results at high pressure are not available because of difficulty in synthesis of Al2O3 glass. Rather, direct Al [1.25 Å: [Ne] 3s2 3p1] coordination states for aluminosilicate glasses are well-documented experimentally: [5,6]Al is observed at 3–10 GPa, depending on the glass composition, similar to the threshold pressure for [5,6]Ge (1, 8, 20, 63⇓⇓–66). The systematics suggest that the atomic radii of framework cations play a major role in the nature of the pressure-induced coordination transformation.

In borate glasses, [3]B begins to transform to [4]B under low-pressure conditions (3–5 GPa), reaching the average coordination number of ∼3.5 at ∼8–15 GPa (5, 9) (SI Appendix, section S6). However, in contrast to the successive coordination transformation in Al (and Si and Ge) in glasses, once the sp3 bond in [4]B forms [B (0.85 Å): 1s2 2s2 2p1] (Figs. 1 and 3), the boron coordination transformation into [5]B is hindered at least up to ∼120 GPa. With the new [4]B results, the predominance diagram of distinct coordination states (labeled with Roman numerals) of framework cations (B, Si, and Ge) in archetypal covalent oxide glasses can be constructed as functions of the pressures and atomic radii of the framework cations (Fig. 4). Because the diagram is the predominance diagram, not a stability field diagram, it labels the most abundant species among the diverse and mixed coordination states in a given pressure and atomic radius. The dotted lines represent the hypothetical boundaries where the fractions of two coordination numbers of the cations are expected to be similar (SI Appendix, section S6). For example, along the line crossing III and IV, the average coordination number of the cation is 3.5, and the fractions of [3]B and [4]B are close to identical. The shaded areas between the boundaries show the most dominant coordination state (III, IV, V, and VI) of these cations. For instance, in the region marked with VI, the 6-coordinated species are expected to be dominant, although multiple coordination environments (e.g., 4, 5, 7, and other coordinated species) are possible (SI Appendix, section S6). Considering the predicted (and/or confirmed) coordination transformation in other framework cations in oxide glasses (SI Appendix, section S6), the current results account for the effect of the chemical nature of framework cations on the transition pressure. Note again that the boundaries and areas are to visually distinguish the states and are based on a limited number of data points. Therefore, the figure is a conceptual model because the atomic radii at high pressure and the quantitative transition pressures for these oxide glasses are not fully known. More experimental data to quantify the boundaries and additional theoretical confirmations of the proposed predominance are needed. An earlier empirical approach based on the hard-sphere model used the concept of pressure-dependent oxygen-packing density for revealing quantitative coordination number of cations and the threshold packing fraction for coordination transformation (67). In contrast, the current model uses the atomic radii obtained at 1 atm as a controlling indicator independent of pressure to provide a guideline for predicting the transition pressure. Because an increase in cation–oxygen bond length (that is partly dependent on the cation radius) is one of the important controls of oxygen radius in the earlier packing-density model, from which the packing density is estimated, the current model provides a complementary view of the model on oxygen packing fraction.

Fig. 4.
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Fig. 4.

Predominance diagram, where the most dominant coordination states (labeled with Roman numerals) of framework cations (B, Si, and Ge) in B2O3, SiO2, and GeO2 glasses with varying pressure and atomic radius of the framework cations are shown. While single coordination states are labeled, cations with multiple coordination environments coexist. The effect of pressure on the atomic radius of the cations in these glasses is not taken into consideration. Further exploration of this effect remains to be done. The red, black, dark blue, green, and light blue squares denote the average coordination numbers of the cations of 3.5, 4, 4.5, 5.5, and 6.5, respectively (SI Appendix, section S6). The dotted lines indicate the hypothetical boundaries among the dominant coordination states.

The structural information provided in the current study is qualitative because of the insufficient number of IXS pressure scans (particularly the O K-edge data) and uncertainty in the spectra at high pressure. In addition, the lack of structural information about crystalline B2O3 phases beyond the megabar pressure range makes it difficult to establish the robust relationships between the internal structural variables, including the B–O length and edge feature at the extended pressure condition (SI Appendix, section S4). We, thus, use the ab initio calculations only to provide a guide to the observed transition. The need for extensive effort remains before the nature of structural transformation in oxide glasses is fully explained. Furthermore, whether the [4]B is quenchable is of central importance. [4]B is not quenchable to 1 atm upon decompression from ∼22.5 GPa (5). As the NIXS spectrum for the decompressed glass from ∼120 GPa is not currently available, a B K-edge NIXS experiment for the decompressed glass above megabar remains to be performed.

The current study highlights the utility of in situ NIXS as a unique probe for the electronic structures of soft and/or condensed matter (both crystalline and amorphous) under extreme compression above megabar pressure conditions. The in situ NIXS for prototypical v-B2O3 revealed the novel densification paths characterized with the extended stability of sp3-bonded [4]B beyond 100 GPa. Major densification is associated with the contraction of [3]O and the average O–O distance reduction. The results allow us to conclude the effect of the atomic radius (and/or the nature of electron distribution) on the threshold pressure in the highly coordinated states, confirming that the framework cation with a smaller atomic radius will undergo coordination transformation at higher pressure. While the effect of atomic radius of cation on the pressure for coordination transformation in crystalline materials has been demonstrated, development of a similar proposal for noncrystalline oxides has not been available. The current result confirms that a similar conceptual framework can be used to reveal the nature of noncrystalline materials under extreme compression. This simple relationship may provide a useful guide to study the structural transformation in complex, multicomponent glasses where the structural transformation can be more complicated by the presence of diverse nonnetwork forming cations. The densification model can be applied to account for the stability, oxygen configurations, and solubility of elements and isotopes into the dense melts at the core–mantle boundary. Particularly, dense oxide melts with predominant [3]O can result in enhanced contraction at the basement of the lower mantle, increasing melt density, which suggests the stable presence of the dense melts in contact with crystalline Mg-silicate polymorphs. Potential prevalence of [4]B in the compressed melts and magmas may account for the enrichment of 10B (instead of 11B) in Earth’s mantle, as the lighter B can be preferentially partitioned into the highly coordinated boron in oxides.

Materials and Methods

v-B2O3 was synthesized by melting H3BO3 crystal in a Pt crucible above the melting temperature for ∼5 min followed by quenching. This melting–quenching procedure was repeated five times, forming a bubble-free v-B2O3. The glass was loaded into a modified panoramic DAC with a Be gasket inside a glove box under an Ar atmosphere, which minimizes the hydration of the glasses. No pressure medium was used. The diamond culet and gasket hole diameter are ∼150 and 60 μm, respectively. Boron and oxygen K-edge NIXS spectra were collected at the High Pressure Collaborative Access Team (HPCAT) beamline 16-ID-D at the Advanced Photon Source. The DAC was mounted on a multiaxis goniometer, where the NIXS spectra were collected by scanning the incident beam energy relative to the fixed analyzer energy of 9.908 keV with a resolution of ∼1.4 eV FWHM. The monochromatic X-rays produced by a cryogenically cooled double-crystal Si(111) monochromator were focused to 8 × 5 μm2 (h × v, FWHM) with a KB mirror pair and an additional pinhole upstream of the sample. Inelastic X-rays were collected at a scattering angle of 25° using polycapillary optics with a single spherical Si(555) analyzer operating in a backscattering geometry (see SI Appendix, section S1 for the details of polycapillary setup). The pressure measurement is based on the Raman signal from the diamond culet (68). The difference in pressure between the center and edge of the sample above 63.5 GPa varies from ∼6.0–6.9 GPa. Here, we report the average pressure [(maximum pressure + minimum pressure)/2)]. The difference in pressure between the center and the edge of the sample above 63.5 GPa varies from ∼6.0–6.9 GPa. Here, we report the average pressure [(maximum pressure + minimum pressure)/2)]. Because of the pressure gradient and the radial beam path geometry of the current experiment (i.e., the X-ray beam passes through gasket), we note that NIXS signals with varying pressure ranges can be collected. Therefore, the current signals at high pressure may contain spectral information of oxide glasses with varying pressure conditions, potentially contributing to a broadening in the spectrum. The boron K-edge spectra were collected with varying pressures from 1 atm to 119.4 GPa. The oxygen K-edge spectrum was collected at 101.6 GPa. The spectrum at 22.5 GPa was collected with the experimental conditions described in the previous study where a beam size of ∼80 × 20 μm2 (h × v) was used (5). The background was subtracted from the spectra, which were normalized to the continuum energy tail. The step size varied from 0.25 to 0.7 eV, which could affect position of the NIXS features (∼0.3 eV) (SI Appendix, section S7).

Acknowledgments

We thank P. Eng for helpful discussion, Y. Yi for help with the calculations, and four anonymous reviewers and the editor for careful and constructive suggestions which greatly improved the manuscript’s quality and clarity. This work was supported by Samsung Science and Technology Foundation Grant BA1401-07, National Research Foundation of Korea Grant 2017R1A2A1A17069511) (to S.K.L.), and Department of Energy (DOE), Basic Energy Sciences, Division of Materials Sciences and Engineering Award DE-FG02-99ER45775 (to Y.X., P.C., C.J., and G.S.). HPCAT operations are supported by DOE National Nuclear Security Administration under Award DE-NA0001974, with partial instrumentation funding by NSF. The Advanced Photon Source is a User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357.

Footnotes

  • ↵1To whom correspondence should be addressed. Email: sungklee{at}snu.ac.kr.
  • Author contributions: S.K.L. and G.S. designed research; S.K.L., Y.-H.K., P.C., Y.X., C.J., and G.S. performed research; S.K.L., Y.-H.K., P.C., Y.X., C.J., and G.S. contributed new reagents/analytic tools; S.K.L., Y.-H.K., P.C., Y.X., and G.S. analyzed data; and S.K.L. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1800777115/-/DCSupplemental.

Published under the PNAS license.

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References

  1. ↵
    1. Allwardt JR
    (2005) Aluminum coordination and the densification of high-pressure aluminosilicate glasses. Am Mineral 90:1218–1222.
    OpenUrlAbstract/FREE Full Text
  2. ↵
    1. Ghosh DB,
    2. Karki BB,
    3. Stixrude L
    (2014) First-principles molecular dynamics simulations of MgSiO3 glass: Structure, density, and elasticity at high pressure. Am Mineral 99:1304–1314.
    OpenUrlAbstract/FREE Full Text
  3. ↵
    1. Schubert G
    1. Hemley RJ,
    2. Struzhkin VV,
    3. Cohen RE,
    4. Shen G
    (2015) Measuring high-pressure electronic and magnetic properties. Treatise on Geophysics, ed Schubert G (Elsevier, Oxford), 2nd Ed, pp 313–349.
  4. ↵
    1. Lee SK
    (2010) Effect of pressure on structure of oxide glasses at high pressure: Insights from solid-state NMR of quadrupolar nuclides. Solid State Nucl Magn Reson 38:45–57.
    OpenUrlCrossRefPubMed
  5. ↵
    1. Lee SK, et al.
    (2005) Probing of bonding changes in B2O3 glasses at high pressure with inelastic X-ray scattering. Nat Mater 4:851–854.
    OpenUrlCrossRef
  6. ↵
    1. Van Hoang V
    (2004) Molecular dynamics study on structure and properties of liquid and amorphous Al2O3. Phys Rev B 70:134204.
    OpenUrl
  7. ↵
    1. Stebbins JF,
    2. McMillan PF,
    3. Dingwell DB
    1. Wolf GH,
    2. McMillan PF
    (1995) Pressure effects on silicate melt structure and properties. Structure, Dynamics, and Properties of Silicate Melts, eds Stebbins JF, McMillan PF, Dingwell DB (Mineralogical Society of America, Washington, DC), Vol 32, pp 505–562.
    OpenUrl
  8. ↵
    1. Yarger JL, et al.
    (1995) Al coordination changes in high-pressure aluminosilicate liquids. Science 270:1964–1967.
    OpenUrlAbstract/FREE Full Text
  9. ↵
    1. Zeidler A, et al.
    (2014) High-pressure transformation of SiO2 glass from a tetrahedral to an octahedral network: A joint approach using neutron diffraction and molecular dynamics. Phys Rev Lett 113:135501.
    OpenUrl
  10. ↵
    1. Benmore CJ, et al.
    (2010) Structural and topological changes in silica glass at pressure. Phys Rev B 81:054105.
    OpenUrl
  11. ↵
    1. Salmon PS, et al.
    (2012) Density-driven structural transformations in network forming glasses: A high-pressure neutron diffraction study of GeO2 glass up to 17.5 GPa. J Phys Condens Matter 24:415102.
    OpenUrlCrossRefPubMed
  12. ↵
    1. Takada A,
    2. Bell RG,
    3. Catlow CRA
    (2016) Molecular dynamics study of liquid silica under high pressure. J Non-Cryst Solids 451:124–130.
    OpenUrl
  13. ↵
    1. Tse JS,
    2. Klug DD,
    3. Le Page Y
    (1992) High-pressure densification of amorphous silica. Phys Rev B Condens Matter 46:5933–5938.
    OpenUrlPubMed
  14. ↵
    1. Wang Y, et al.
    (2014) Atomistic insight into viscosity and density of silicate melts under pressure. Nat Commun 5:3241.
    OpenUrlPubMed
  15. ↵
    1. Wang Y,
    2. Shen G
    (2014) High-pressure experimental studies on geo-liquids using synchrotron radiation at the advanced photon source. J Earth Sci 25:939–958.
    OpenUrl
  16. ↵
    1. Zeidler A, et al.
    (2014) Density-driven structural transformations in B2O3 glass. Phys Rev B 90:024206.
    OpenUrl
  17. ↵
    1. Lay T
    (2015) Deep Earth structure: Lower mantle and D′′. Treatise on Geophysics (Elsevier, Oxford), 2nd Ed, pp 683–723.
  18. ↵
    1. Stixrude L,
    2. Karki B
    (2005) Structure and freezing of MgSiO3 liquid in Earth’s lower mantle. Science 310:297–299.
    OpenUrlAbstract/FREE Full Text
  19. ↵
    1. Elliot SR
    (1988) Physics of Amorphous Materials (Wiley, New York).
  20. ↵
    1. Lee SK
    (2011) Simplicity in melt densification in multicomponent magmatic reservoris in Earth’s interior revealed by multinuclear magnetic resonance. Proc Natl Acad Sci USA 108:6847–6852.
    OpenUrlAbstract/FREE Full Text
  21. ↵
    1. Lee SK,
    2. Fei YW,
    3. Cody GD,
    4. Mysen BO
    (2003) Order and disorder in sodium silicate glasses and melts at 10 GPa. Geophys Res Lett 30:1845.
    OpenUrlCrossRef
  22. ↵
    1. Xue X,
    2. Stebbins JF,
    3. Kanzaki M
    (1994) Correlations between O-17 NMR parameters and local structure around oxygen in high-pressure silicates and the structure of silicate melts at high pressure. Am Mineral 79:31–42.
    OpenUrlAbstract
  23. ↵
    1. Lee SK, et al.
    (2017) Quasi-equilibrium melting of quartzite upon extreme friction. Nat Geosci 10:4336–4441.
    OpenUrl
  24. ↵
    1. Salmon PS,
    2. Zeidler A
    (2015) Networks under pressure: The development of in situ high-pressure neutron diffraction for glassy and liquid materials. J Phys Condens Matter 27:133201.
    OpenUrl
  25. ↵
    1. Lee SK,
    2. Eng PJ,
    3. Mao HK
    (2014) Probing of pressure-Induced bonding transitions in crystalline and amorphous Earth materials: Insights from x-ray Raman scattering at high pressure. Spectroscopic Methods in Mineralology and Materials Sciences, Reviews in Mineralogy & Geochemistry, eds Henderson GS, Neuville DR, Downs RT (Mineralogical Soc of America, Chantilly, VA), Vol 78, pp 139–174.
  26. ↵
    1. Schulke W
    (2007) Non-resonant inelastic X-ray scattering: Regime of core-electron excitation (X-ray Raman scattering). Electron Dynamics by Inelastic X-Ray Scattering (Oxford Univ Press, Oxford), Vol 7, p 186.
    OpenUrl
  27. ↵
    1. Sternemann C,
    2. Wilke M
    (2016) Spectroscopy of low and intermediate Z elements at extreme conditions: In situ studies of Earth materials at pressure and temperature via X-ray Raman scattering. High Press Res 36:275–292.
    OpenUrl
  28. ↵
    1. Lelong G, et al.
    (2012) Evidence of fivefold-coordinated Ge atoms in amorphous GeO2 under pressure using inelastic x-ray scattering. Phys Rev B 85:134202.
    OpenUrl
  29. ↵
    1. Lin JF, et al.
    (2007) Electronic bonding transition in compressed SiO2 glass. Phys Rev B 75:012201.
    OpenUrl
  30. ↵
    1. Meng Y, et al.
    (2008) Inelastic x-ray scattering of dense solid oxygen: Evidence for intermolecular bonding. Proc Natl Acad Sci USA 105:11640–11644.
    OpenUrlAbstract/FREE Full Text
  31. ↵
    1. Mao WL, et al.
    (2006) X-ray-induced dissociation of H2O and formation of an O2-H2 alloy at high pressure. Science 314:636–638.
    OpenUrlAbstract/FREE Full Text
  32. ↵
    1. Lee SK,
    2. Eng PJ,
    3. Mao HK,
    4. Meng Y,
    5. Shu J
    (2007) Structure of alkali borate glasses at high pressure: B and Li K-edge inelastic X-ray scattering study. Phys Rev Lett 98:105502.
    OpenUrlCrossRefPubMed
  33. ↵
    1. Lee SK,
    2. Eng PJ,
    3. Mao HK,
    4. Shu JF
    (2008) Probing and modeling of pressure-induced coordination transformation in borate glasses: Inelastic x-ray scattering study at high pressure. Phys Rev B 78:214203.
    OpenUrl
  34. ↵
    1. Yi YS,
    2. Lee SK
    (2012) Pressure-induced changes in local electronic structures of SiO2 and MgSiO3 polymorphs: Insights from ab initio calculations of O K-edge energy-loss near-edge structure spectroscopy. Am Mineral 97:897–909.
    OpenUrlAbstract/FREE Full Text
  35. ↵
    1. Moulton BJA, et al.
    (2016) In situ structural changes of amorphous diopside (CaMgSi2O6) up to 20 GPa: A Raman and O K-edge X-ray Raman spectroscopic study. Geochim Cosmochim Acta 178:41–61.
    OpenUrl
  36. ↵
    1. Yi YS,
    2. Lee SK
    (2016) Atomistic origins of pressure-induced changes in the O K-edge x-ray Raman scattering features of SiO2 and MgSiO3 polymorphs: Insights from ab initio calculations. Phys Rev B 94:094110.
    OpenUrl
  37. ↵
    1. Fukui H,
    2. Kanzaki M,
    3. Hiraoka N,
    4. Cai YQ
    (2008) Coordination environment of silicon in silica glass up to 74 GPa: An x-ray Raman scattering study at the silicon L edge. Phys Rev B 78:012203.
    OpenUrl
  38. ↵
    1. Chow P, et al.
    (2015) Focusing polycapillary to reduce parasitic scattering for inelastic x-ray measurements at high pressure. Rev Sci Instrum 86:072203.
    OpenUrl
  39. ↵
    1. Shen G,
    2. Mao HK
    (2017) High-pressure studies with x-rays using diamond anvil cells. Rep Prog Phys 80:016101.
    OpenUrl
  40. ↵
    1. Ferlat G,
    2. Seitsonen AP,
    3. Lazzeri M,
    4. Mauri F
    (2012) Hidden polymorphs drive vitrification in B2O3. Nat Mater 11:925–929.
    OpenUrlPubMed
  41. ↵
    1. Youngman RE,
    2. Haubrich ST,
    3. Zwanziger JW,
    4. Janicke MT,
    5. Chmelka BF
    (1995) Short- and intermediate-range structural ordering in glassy boron oxide. Science 269:1416–1420.
    OpenUrlAbstract/FREE Full Text
  42. ↵
    1. Gerald S
    1. Dingwell DB
    (2007) Properties of rocks and minerals - Diffusion, viscosity, and flow of melts. Treatise on Geophysics, ed Gerald S (Elsevier, Amsterdam), pp 419–436.
  43. ↵
    1. Lee SK
    (2005) Microscopic origins of macroscopic properties of silicate melts and glasses at ambient and high pressure: Implications for melt generation and dynamics. Geochim Cosmochim Acta 69:3695–3710.
    OpenUrlCrossRef
  44. ↵
    1. Clark AN,
    2. Lesher CE,
    3. Jacobsen SD,
    4. Wang Y
    (2016) Anomalous density and elastic properties of basalt at high pressure: Reevaluating of the effect of melt fraction on seismic velocity in the Earth’s crust and upper mantle. J Geophys Res 121:4232–4248.
    OpenUrl
  45. ↵
    1. Ohmura S,
    2. Shimojo F
    (2010) Ab initio molecular-dynamics study of structural, bonding, and dynamic properties of liquid B2O3 under pressure. Phys Rev B 81:014208.
    OpenUrl
  46. ↵
    1. Trachenko K,
    2. Brazhkin VV,
    3. Ferlat G,
    4. Dove MT,
    5. Artacho E
    (2008) First-principles calculations of structural changes in B2O3 glass under pressure. Phys Rev B 78:172102.
    OpenUrl
  47. ↵
    1. Hong XG, et al.
    (2007) Intermediate states of GeO2 glass under pressures up to 35 GPa. Phys Rev B 75:104201.
    OpenUrl
  48. ↵
    1. Kono Y, et al.
    (2016) Ultrahigh-pressure polyamorphism in GeO2 glass with coordination number >6. Proc Natl Acad Sci USA 113:3436–3441.
    OpenUrlAbstract/FREE Full Text
  49. ↵
    1. Kono Y,
    2. Park C,
    3. Kenney-Benson C,
    4. Shen G,
    5. Wang Y
    (2014) Toward comprehensive studies of liquids at high pressures and high temperatures: Combined structure, elastic wave velocity, and viscosity measurements in the Paris–Edinburgh cell. Phys Earth Planet Inter 228:269–280.
    OpenUrlCrossRef
  50. ↵
    1. Mei Q, et al.
    (2010) High-pressure x-ray diffraction measurements on vitreous GeO2 under hydrostatic conditions. Phys Rev B 81:174113.
    OpenUrl
  51. ↵
    1. Sato T,
    2. Funamori N
    (2010) High-pressure structural transformation of SiO2 glass up to 100 GPa. Phys Rev B 82:184102.
    OpenUrl
  52. ↵
    1. Lee SK,
    2. Kim HI,
    3. Kim EJ,
    4. Mun KY,
    5. Ryu S
    (2016) Extent of disorder in magnesium aluminosilicate glasses: Insights from Al-27 and O-17 NMR. J Phys Chem C 120:737–749.
    OpenUrl
  53. ↵
    1. Garvie IAJ,
    2. Craven AJ,
    3. Brydson R
    (1995) Parallel electron energy-loss spectroscopy (PEELS) study of B in minerals: The electron energy-loss near edge structure (ELNES) of the B K-edge. Am Mineral 80:1132–1144.
    OpenUrlAbstract
  54. ↵
    1. Brazhkin VV, et al.
    (2008) Nature of the structural transformations in B2O3 glass under high pressure. Phys Rev Lett 101:035702.
    OpenUrlCrossRefPubMed
  55. ↵
    1. Lee SK,
    2. Mibe K,
    3. Fei Y,
    4. Cody GD,
    5. Mysen BO
    (2005) Structure of B2O3 glass at high pressure: A 11B solid-state NMR study. Phys Rev Lett 94:165507.
    OpenUrlCrossRefPubMed
  56. ↵
    1. Bray PJ
    (1985) Nuclear magnetic resonance studies of glass structure. J Non-Cryst Solids 73:19–45.
    OpenUrlCrossRef
  57. ↵
    1. Lee SK, et al.
    (2008) X-ray Raman scattering study of MgSiO3 glass at high pressure: Implication for triclustered MgSiO3 melt in Earth’s mantle. Proc Natl Acad Sci USA 105:7925–7929.
    OpenUrlAbstract/FREE Full Text
  58. ↵
    1. Wu M,
    2. Liang Y,
    3. Jiang JZ,
    4. Tse JS
    (2012) Structure and properties of dense silica glass. Sci Rep 2:398.
    OpenUrlPubMed
  59. ↵
    1. Cherednichenko KA,
    2. Godec YL,
    3. Kalinko A,
    4. Mezouar M,
    5. Solozhenko VL
    (2016) Orthorhombic boron oxide under pressure: In situ study by X-ray diffraction and Raman scattering. J Appl Phys 120:175901.
    OpenUrl
  60. ↵
    1. Solozhenko VL,
    2. Kurakevych OO,
    3. Le Godec Y,
    4. Brazhkin VV
    (2015) Thermodynamically consistent p–T phase diagram of boron oxide B2O3 by in situ probing and thermodynamic analysis. J Phys Chem C 119:20600–20605.
    OpenUrl
  61. ↵
    1. Guthrie M, et al.
    (2004) Formation and structure of a dense octahedral glass. Phys Rev Lett 93:115502.
    OpenUrlCrossRefPubMed
  62. ↵
    1. Hoang VV,
    2. Oh SK
    (2005) Simulation of pressure-induced phase transition in liquid and amorphous Al2O3. Phys Rev B 72:054209.
    OpenUrl
  63. ↵
    1. Lee SK
    (2004) Structure of silicate glasses and melts at high pressure: Quantum chemical calculations and solid-state NMR. J Phys Chem B 108:5889–5900.
    OpenUrl
  64. ↵
    1. Lee SK,
    2. Cody GD,
    3. Fei YW,
    4. Mysen BO
    (2004) Nature of polymerization and properties of silicate melts and glasses at high pressure. Geochim Cosmochim Acta 68:4189–4200.
    OpenUrlCrossRef
  65. ↵
    1. Kelsey KE, et al.
    (2009) Cation field strength effects on high pressure aluminosilicate glass structure: Multinuclear NMR and La XAFS results. Geochim Cosmochim Acta 73:3914–3933.
    OpenUrlCrossRef
  66. ↵
    1. Lee SK, et al.
    (2012) Structure of shock compressed model basaltic glass: Insights from O K-edge X-ray Raman scattering and high-resolution 27Al NMR spectroscopy. Geophys Res Lett 39:L05306.
    OpenUrl
  67. ↵
    1. Zeidler A,
    2. Salmon PS,
    3. Skinner LB
    (2014) Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions. Proc Natl Acad Sci USA 111:10045–10048.
    OpenUrlAbstract/FREE Full Text
  68. ↵
    1. Akahama Y,
    2. Kawamura H
    (2007) Diamond anvil Raman gauge in multimegabar pressure range. High Press Res 27:473–482.
    OpenUrl
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Amorphous boron oxide at megabar pressures via inelastic X-ray scattering
Sung Keun Lee, Yong-Hyun Kim, Paul Chow, Yunming Xiao, Cheng Ji, Guoyin Shen
Proceedings of the National Academy of Sciences Jun 2018, 115 (23) 5855-5860; DOI: 10.1073/pnas.1800777115

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Amorphous boron oxide at megabar pressures via inelastic X-ray scattering
Sung Keun Lee, Yong-Hyun Kim, Paul Chow, Yunming Xiao, Cheng Ji, Guoyin Shen
Proceedings of the National Academy of Sciences Jun 2018, 115 (23) 5855-5860; DOI: 10.1073/pnas.1800777115
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