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Shino HAYAFUNE, Tatsuya SAKAMAKI, Haruki ICHIKAWA, [Yohei ONODERA](https://orcid.org/0000-0002-3080-6991), [Shinji KOHARA](https://orcid.org/0000-0001-9596-2680), Ken-ichi FUNAKOSHI, Akio SUZUKI

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[Effects of CO<sub>2</sub> on the structure of silicate melts considering the degree of polymerization under pressure](https://mdr.nims.go.jp/datasets/ffef3d66-1128-4403-bee1-25ae043f3c49)

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Microsoft Word - manuscript_JMPS_mark_rev2.docx1 Effects of CO2 on the structure of silicate melts considering the degree of 1 polymerization under pressure 2  3 Shino HAYAFUNE *,**, Tatsuya SAKAMAKI *, Haruki ICHIKAWA *, Yohei ONODERA **, 4 Shinji KOHARA **, Ken-ichi FUNAKOSHI ***, and Akio SUZUKI * 5  6 * Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, 7 980-8578, Japan 8 ** Center for Basic Research on Materials, National Institute for Materials Science 9 (NIMS), Ibaraki, 305-0047, Japan 10 *** Neutron Science and Technology Center, Comprehensive Research Organization for 11 Science and Society (CROSS), Ibaraki, 319-1106, Japan 12  13 Corresponding author: 14 Name: Shino Hayafune 15 E-mail address: shino.hayafune.t1@dc.tohoku.ac.jp 16  17 ABSTRACT 18 Carbon dioxide (CO2) is a prevalent volatile in Earth’s interior, but its effects on the structural 19 properties of magmas or silicate melts remain insufficiently understood. Previous studies 20 have indicated that the addition of CO2 can decrease the viscosity of silicate melts, but only 21 if they are fully polymerized. In this study, we explored the effects of CO2 considering the 22 degree of polymerization on the structure of silicate melts at high pressures of up to ~5 GPa 23 using in situ synchrotron X-ray diffraction (XRD) and classical molecular dynamics (MD) 24 simulations. The first sharp diffraction peak (FSDP) position of the X-ray structural factor 25 S(Q), which shows the periodicity of an intermediate-range structure, was not affected by 26 the addition of CO2 for partially depolymerized sodium silicate melt (Na2Si3O7). On the other 27 hand, the height of the FSDP for fully polymerized silicate melt (SiO2) slightly decreased, 28 indicating that the Si–O network structure was disordered by the addition of CO2. This 29 difference in the behavior of the FSDP may be attributed to the type of carbon species.  30  31 Keywords: silicate melt structure, CO2, carbonate ion, high pressure  32 2 INTRODUCTION 33  34 Carbon dioxide (CO2) is an important volatile in Earth’s interior. CO2-bearing (i.e., 35 carbonated) magmas such as kimberlite are known to be generated deep in Earth’s interior 36 (e.g., Keshav et al., 2005). To uncover the migration behavior of carbonated magma in deep 37 Earth, the transport properties of analogs such as silicate melts have been studied, including 38 density and viscosity. Measurements at high pressures have revealed that the addition of CO2 39 decreases the density of silicate melts (e.g., Sakamaki et al., 2011). Although measurements 40 of the viscosity are more limited, they indicate that the effect of CO2 on the viscosity is 41 affected by the degree of polymerization of silicate melts. The degree of polymerization is 42 often expressed in terms of the parameter NBO/T, which is defined as the ratio between the 43 number of nonbridging oxygen (NBO) atoms and the number of tetrahedrally coordinated 44 (i.e., network-forming) cations (T) (Mysen and Richet, 2019). Adding CO2 has been shown 45 to decrease the viscosity of fully polymerized silicate melts (i.e., NBO/T = 0). For example, 46 Suzuki (2018) reported that adding 0.5 wt% CO2 reduced the viscosity of molten jadeite 47 (NaAlSi2O6, NBO/T = 0) by one to two orders of magnitude. In contrast, Brearley and 48 Montana (1989) reported that adding 0.5 wt% CO2 had no effect on the viscosity of molten 49 sodium melilite (NaCaAlSi2O7), which is partially depolymerized (NBO/T = 0.67) under the 50 assumption that Al is entirely tetrahedrally coordinated. The physical properties of magmas 51 are known to be sensitive to the atomic structure (e.g., Sakamaki, 2018). Thus, understanding 52 the effects of CO2 on the structures of silicate melts at high pressures and temperatures is 53 important for clarifying the migration behavior of carbonated magmas. 54 In this study, we conducted in situ X-ray diffraction (XRD) measurements complemented 55 by molecular dynamics (MD) simulations to investigate the effects of CO2 on the structure 56 of a sodium silicate melt (Na2Si3O7, NBO/T = 0.67) at high pressures. MD simulations were 57 further conducted to investigate the effects of CO2 on the structures of silicate melts 58 considering the degree of polymerization. 59  60 METHODS 61  62 Experiment 63 Dry Na2Si3O7 was prepared in powder form from reagent-grade SiO2 and Na2SiO3, and 64 3 carbonated Na2Si3O7 (0.5 wt% CO2) was prepared in powder form by adding Na2CO3 as the 65 CO2 source. The amount of CO2 was kept below the solubility of Na2Si3O7 melt under the 66 experimental conditions to avoid the liquid immiscibility of the silicate and carbonate melts 67 (Dasgupta et al., 2006; Brooker and Kjarsgaard, 2011). Figure 1 shows a cross section of the 68 high-pressure cell assembly for the experiment. A boron–epoxy cube was used as a pressure-69 transmitting medium, and the pressure marker was a mixture of MgO and h–BN (3:2 weight 70 ratio). The temperature T was estimated by calibration against the electric power (Fig. S1), 71 which was performed in a preliminary experiment using a cell assembly with a W97Re3–72 W75Re25 thermocouple (Fig. S2). The pressure P was calculated using the third-order Birch–73 Murnaghan equations of state of MgO (Tange et al., 2009). XRD measurements were 74 conducted in situ using MAX80 (Shimomura, 1984), which is a cubic multi-anvil apparatus 75 installed at the AR-NE5C beamline of the Photon Factory Advanced Ring (PF-AR) in 76 Tsukuba, Japan. Measurements were conducted over a P range of 2–5 GPa, and T was kept 77 at just above the melting point of the silicates. White X-rays in the energy range of 20–140 78 keV were used as incident X-rays, and scattered X-rays from the melt were detected with a 79 germanium detector. The detailed experimental procedure is summarized in Ohashi et al. 80 (2018). 81 We derived two different functions to analyze the structure of the silicate melts. The total 82 structure factor S(Q) was determined by correcting diffraction profiles using the MCEDX 83 code (Funakoshi, 1997), and it is defined as 84  S(Q) = Icoh(Q)/N  − %∑ 'cifi(Q)(2 −i '∑ cifi(Q)i (2)'∑ cifi(Q)i (2,   (Eq. 1), where N, Icoh(Q), ci, and fi(Q) are the number of atoms in the scattering system, coherent 85 scattering intensity, the concentration of atoms i, and atomic scattering factor, respectively. 86 The reduced pair distribution function G(r) was used to analyze the local structure and short-87 range order of the silicate melts, and it is derived as 88  G(r) = 2π/ Q{S(Q)  −  1}M(Q)sin(Qr)dQQmaxQmin,  (Eq. 2), where r is the atomic distance. M(Q) is the Lorch modification function, which was 89 introduced to suppress the termination ripples of G(r) (Lorch, 1969). 90  91 Simulation 92 Classical MD simulations of dry and carbonated (0.5 and 5.0 wt% CO2) Na2Si3O7 and SiO2 93 4 melts were performed using the Large-scale Atomic/Molecular Massively Parallel Simulator 94 code (Thompson et al., 2022). The Na2Si3O7 melt was partially depolymerized (NBO/T = 95 0.67), whereas the SiO2 melt was fully polymerized (NBO/T = 0). Table 1 gives the 96 specifications of the simulated systems, where each contained approximately 30,000 97 particles. We employed the empirical force field developed by Guillot and Sator (2011), 98 which can be used to treat the chemical reaction of CO2 + O2– ↔ CO32−, in which CO2 99 molecules react with O2– in a silicate melt to form CO32− and vice versa. P was kept at 2 or 100 5 GPa, and T was kept at 2000 K. Ewald summations were applied to evaluate long-range 101 Coulombic interactions. Periodic boundary conditions were imposed in the simulations, and 102 the time step was 1 fs. The simulation was started with atoms assigned random 103 configurations and velocities. We first ran calculations for 50 ps at 2 or 5 GPa and at 3000 104 K. Then, the systems were cooled to 2000 K for 10 ps and relaxed for 50 ps. All simulations 105 were carried out in the NPT (isothermal isobaric) ensemble.  106 The three-dimensional structure was analyzed to obtain Qn species (Stebbins, 1995; Mysen 107 and Richet, 2019), carbon species, and ring statistics. The primitive (Si–O)n ring size 108 distributions for melts were calculated using the SOVA package (Shiga et al., 2023). 109  110 RESULTS AND DISCUSSION 111 Figure 2 shows the total structure factors S(Q) and reduced pair distribution functions G(r) 112 for dry and carbonated (0.5 wt% CO2) Na2Si3O7 melts at high pressures, obtained by XRD 113 measurements. In previous studies, the first sharp diffraction peak (FSDP) of S(Q) for silicate 114 melts has been assigned to a succession of SiO4 polyhedra with corner-sharing oxygen atoms 115 manifested by the periodicity given by 2π/QFSDP (Funamori, 2004; Shuseki et al., 2024, 116 Onodera et al., 2019a). Figure 3 shows S(Q) for dry and carbonated (5.0 wt% CO2) Na2Si3O7 117 and SiO2 melts at high pressures, obtained by MD simulations. For the Na2Si3O7 melt, the 118 overall features of S(Q) and the FSDP obtained by XRD measurements (Fig. 2a) and MD 119 simulations (Fig. 3a) changed negligibly with the addition of 0.5 wt% CO2. Neither did the 120 overall features of G(r) change significantly (Fig. 2b). Note that as carbon capsules were 121 used as sample containers, there is some concern as to whether CO2 is fully retained during 122 the XRD experiments. The MD simulations confirmed that S(Q) remained the same for both 123 melts with the addition of only 0.5 wt% CO2 (Fig. S3). However, a different behavior was 124 observed when 5.0 wt% CO2 was added to the SiO2 melt, which resulted in a slight decrease 125 in the height of the FSDP (Fig. 3b), indicating that the Si–O network structure became 126 5 disordered. Slight pressure-dependent changes in S(Q) and G(r) are observed, which are 127 discussed in more detail in the supplementary (see Figs. S4 and S5). 128 It is also revealed that the degree of polymerization of these melts changed negligibly with 129 the addition of CO2. Figure 4 shows the distributions of Qn species for dry and carbonated 130 (5.0 wt% CO2) Na2Si3O7 and SiO2 melts obtained by MD simulations. It is found that some  131 of the oxygen atoms (several mol%) of Q4 SiO4 tetrahedra occupy the center of the OSi3 132 triclusters (Fig. S6). The distributions of Qn species for these melts are almost identical 133 between CO2-free and CO2-bearing conditions, indicating that the degree of polymerization 134 of these melts is almost unchanged. This result is consistent with that reported by Morizet et 135 al. (2015), who used first-principles MD simulations of basaltic melts containing CO2, and 136 showed that CO2 may have a limited effect on the degree of polymerization of basaltic melt. 137 Therefore, a slight decrease in the height of the FSDP observed in CO2-bearing SiO2 melts 138 (Fig. 3b) may not be caused by a change in the degree of polymerization of the melt structure. 139 Figure 5 shows the fractions of carbon species in the Na2Si3O7 and SiO2 melts at 5 GPa, 140 obtained by MD simulations. The pressure dependence of CO2/(CO2+CO32−) for CO2-141 bearing melts is summarized in Fig. S7. The MD simulations confirmed the formation of 142 two types of carbon species: CO2 and carbonate ions (CO32−). Previous investigations of 143 carbonated quenched glasses by infrared (IR) spectroscopy (Mysen, 1976; Fine and Stolper, 144 1986) have revealed that CO32− is dominant in depolymerized (basic and ultrabasic) melts, 145 but the depolymerized melt in our study (i.e., Na2Si3O7) contained approximately 20% CO2 146 (Fig. 5a). This discrepancy may be because the previous studies using IR spectroscopy 147 underestimated the abundance of CO2 species of the glasses because the following reaction 148 occurs upon quenching: CO2 + O2– → CO32− (Morizet et al., 2001; Guillot and Sator, 2011; 149 Konschak and Keppler, 2014; Vuilleumier et al., 2015). In our MD simulations, we found 150 three types of CO32−: isolated carbonate ions that were not connected to Si (CO32−, Fig. 6a), 151 nonbridging carbonate ions connected to one Si atom (Si–CO32−, Fig. 6b), and network 152 carbonate ions connected to two Si atoms (Si–CO32−–Si, Fig. 6c). We recognized two 153 structural types of network carbonate ions that connect to two Si atoms in SiO2 melt (Fig. 154 6c), but it was difficult to qualify their fraction using our program code. The charge neutrality 155 of nonbridging and network carbonate ions in SiO2 melt should be carefully considered. In 156 general, these carbonate ions are considered to interact with network modifier cations such 157 as Na+ and Ca+ (Guillot and Sator, 2011; Ni and Keppler, 2013). Although SiO2 melt does 158 not have such network modifier cations, a considerable amount of carbonate ions exists, 159 6 probably owing to a structure in the melt where a local charge compensation is not 160 maintained. Indeed, in addition to the bridging oxygen and Q4, we find the presence of OSi3 161 triclusters (Fig. S6) and Q3 (Fig. 4b) which is the signature of a structure in which a charge 162 compensation is not maintained locally. 163 The behaviors of FSDP upon the addition of CO2 can be explained by the carbon species 164 in the melts. For Na2Si3O7 melt, molecular CO2 and nonbridging carbonate ions 165 predominantly exist (Fig. 5a). Previous results suggest that molecular CO2 is only loosely 166 associated with the melt structure (Ni and Keppler, 2013), and nonbridging carbonate ions 167 are mainly formed by displacement from NBO atoms (Guillot and Sator, 2011). A similar 168 behavior is observed in the FSDP of S(Q) where carbonate ions do not greatly change the 169 intermediate-range structure of melt (Figs. 2a, 3a). On the other hand, SiO2 melt has 170 molecular CO2 and carbonate ions as nonbridging and network carbonate ions (Fig. 5b). The 171 Si–O network of the SiO2 melt has a relatively ordered structure in which SiO4 tetrahedra 172 are fully bonded via bridging oxygen atoms. However, the inclusion of nonbridging and 173 network carbonate ions disrupts the order of this network, which causes the reduction in the 174 correlation estimated by the FSDP full width at half maximum (FWHM) (Onodera et al., 175 2019a) associated with the height decrease of the FSDP (Fig. 3b). 176 To obtain deep insight into the intermediate-range structure, the (Si–O)n ring size 177 distribution between dry and CO2-bearing melts is compared. The primitive (Si–O)n ring size 178 distributions for dry and carbonated (5.0 wt% CO2) Na2Si3O7 and SiO2 melts are plotted in 179 Fig. 7. It is found that there is little difference between dry and carbonated melts for Na2Si3O7 180 melt, but a distinct difference was observed for SiO2 melt. As can be seen in Fig. 7b, the 181 large (Si–O)n rings are transformed into smaller (Si–O)n rings by nonbridging and network 182 carbonate ions; this is associated with bond interchange under high P-T conditions. This 183 behavior is different from that caused by alkali ions (network modifier cations) in silicate 184 glass at ambient pressure (Onodera et al., 2019b). 185 Our results suggest that the addition of CO2 changes the network structure of the fully 186 polymerized SiO2 melt (NBO/T = 0) to some extent, whereas it negligibly changes the 187 network structure of the depolymerized Na2Si3O7 melt (NBO/T = 0.67). This behavior can 188 be explained by the structural effect of carbonate species on the network structure of melts. 189  190  191 ACKNOWLEDGMENTS 192 7 We thank K. Obata for assistance with the experimental preparations. This research was 193 performed with the support of JSPS KAKENHI Grant Numbers 20H05878, 20H05881, 194 JP21K18641, and JP23K22588. Synchrotron experiments were conducted at the AR-NE5C 195 beamline with the approval of the High Energy Accelerator Research Organization (KEK) 196 (Proposal Nos. 2021G512 and 2023G519), and the calculations in this study were performed  197 using the Numerical Materials Simulator at the National Institute for Materials Science 198 (NIMS).  199 8 REFERENCES 200 Brearley M. and Montana A. (1989) The effect of CO2 on the viscosity of silicate liquids at 201 high pressure. Geochim. Cosmochim. Acta 53, 2609–2616. 202 Brooker R. A. and Kjarsgaard B. A. (2011) Silicate–Carbonate Liquid Immiscibility and 203 Phase Relations in the System SiO2–Na2O–Al2O3–CaO–CO2 at 0.1–2.5 GPa with 204 Applications to Carbonatite Genesis. J. Petrol. 52, 1281–1305. 205 Dasgupta R., Hirschmann M. M. and Stalker K. (2006) Immiscible Transition from 206 Carbonate-rich to Silicate-rich Melts in the 3 GPa Melting Interval of Eclogite + CO2 207 and Genesis of Silica-undersaturated Ocean Island Lavas. J. Petrol. 47, 647–671. 208 Fine G. and Stolper E. (1986) Dissolved carbon dioxide in basaltic glasses: concentrations 209 and speciation. Earth Planet. Sci. Lett. 76, 263–278. 210 Funakoshi K. (1997) Energy-dispersive x-ray diffraction study for alkali silicate melts using 211 synchrotron radiation under high pressure and temperature. Ph. D. thesis, Tokyo 212 Institute of Technology. 213 Funamori N. (2004) Exploratory studies of silicate melt structure at high pressures and 214 temperatures by in situ X-ray diffraction. J. Geophys. Res. 109, B03203. 215 Ghosh S., Ohtani E., Litasov K., Suzuki A. and Sakamaki T. (2007) Stability of carbonated 216 magmas at the base of the Earth’s upper mantle. Geophys. Res. Lett. 34, L22312. 217 Guillot B. and Sator N. (2011) Carbon dioxide in silicate melts: A molecular dynamics 218 simulation study. Geochim. Cosmochim. Acta 75, 1829–1857. 219 Keshav S., Corgne A., Gudfinnsson G. H., Bizimis M., McDonough W. F. and Fei Y. (2005) 220 Kimberlite petrogenesis: Insights from clinopyroxene-melt partitioning experiments 221 at 6 GPa in the CaO–MgO–Al2O3–SiO2–CO2 system. Geochim. Cosmochim. Acta 222 69, 2829–2845. 223 Konschak A. and Keppler H. (2014) The speciation of carbon dioxide in silicate melts. 224 Contrib. Mineral. Petrol. 167, 998. 225 Lorch E. (1969) Neutron diffraction by germania, silica and radiation-damaged silica glasses. 226 J. Phys. C Solid State Phys. 2, 229–237. 227 Morizet Y., Kohn S. C. and Brooker R. A. (2001) Annealing experiments on CO2-bearing 228 jadeite glass: an insight into the true temperature dependence of CO2 speciation in 229 9 silicate melts. Mineral. Mag. 65, 701–707. 230 Morizet Y., Vuilleumier R. and Paris M. (2015) A NMR and molecular dynamics study of 231 CO2-bearing basaltic melts and glasses. Chem. Geol. 418, 89–103. 232 Mysen B. O. (1976) The role of volatiles in silicate melts: Solubility of carbon dioxide and 233 water in feldspar, pyroxene, and feldspathoid melts to 30 kb and 1625 °C. Am. J. Sci. 234 276, 969–996. 235 Mysen B. and Richet P. (2019) Structure and Property Concepts. In Silicate Glasses and 236 Melts (Second Edition) Elsevier Science, Amsterdam. pp. 109–141. 237 Ni H. and Keppler H. (2013) Carbon in Silicate Melts. Rev. Mineral. Geochem. 75, 251–287. 238 Ohashi T., Sakamaki T., Funakoshi K. and Suzuki A. (2018) Pressure–induced structural 239 changes of basaltic glass. J. Mineral. Petrol. Sci. 113, 286–292. 240 Onodera Y., Kohara S., Tahara S., Masuno A., Inoue H., Shiga M., Hirata A., Tsuchiya K., 241 Hiraoka Y., Obayashi I., Ohara K., Mizuno A. and Sakata O. (2019a) Understanding 242 diffraction patterns of glassy, liquid and amorphous materials via persistent 243 homology analyses. J. Ceram. Soc. Jpn. 127, 853–863. 244 Onodera Y., Takimoto Y., Hijiya H., Taniguchi T., Urata S., Inaba S., Fujita S., Obayashi I., 245 Hiraoka Y. and Kohara S. (2019b) Origin of the mixed alkali effect in silicate glass. 246 NPG Asia Mater. 11, 75. 247 Sakamaki T. (2018) Structure and Properties of Silicate Magmas. In Magmas Under 248 Pressure: Advances in High-Pressure Experiments on Structure and Properties of 249 Melts (eds. Y. Kono and C. Sanloup). Elsevier, Amsterdam. pp. 323–341. 250 Sakamaki T., Ohtani E., Urakawa S., Terasaki H. and Katayama Y. (2011) Density of 251 carbonated peridotite magma at high pressure using an X-ray absorption method. Am. 252 Mineral. 96, 553–557. 253 Shiga M., Hirata A., Onodera Y. and Masai H. (2023) Ring-originated anisotropy of local 254 structural ordering in amorphous and crystalline silicon dioxide. Commun. Mater. 4, 255 91. 256 Shimomura O. (1984) Multi-anvil type X-ray apparatus for synchrotron radiation. Mater. 257 Res. Soc. Symp. Proceesdings 22, 17–20. 258 Shuseki Y., Kohara S., Kaneko T., Sodeyama K., Onodera Y., Koyama C., Masuno A., Sasaki 259 10 S., Hatano S., Shiga M., Obayashi I., Hiraoka Y., Okada J. T., Mizuno A., Watanabe 260 Y., Nakata Y., Ohara K., Murakami M., Tucker M. G., McDonnell M. T., Oda H. and 261 Ishikawa T. (2024) Atomic and Electronic Structure in MgO–SiO2. J. Phys. Chem. A 262 128, 716–726. 263 Stebbins J. F. ed. (1995) Dynamics and structure of silicate and oxide melts: Nuclear 264 Magnetic Resonance studies. In Reviews in Mineralogy Mineralogical Society of 265 America, Geochemical Society, Washington. pp. 190–246. 266 Suzuki A. (2018) Effect of carbon dioxide on the viscosity of a melt of jadeite composition 267 at high pressure. J. Mineral. Petrol. Sci. 113, 47–50. 268 Tange Y., Nishihara Y. and Tsuchiya T. (2009) Unified analyses for P-V-T equation of state 269 of MgO: A solution for pressure-scale problems in high P-T experiments. J. Geophys. 270 Res. 114, B03208. 271 Thompson A. P., Aktulga H. M., Berger R., Bolintineanu D. S., Brown W. M., Crozier P. S., 272 In ’T Veld P. J., Kohlmeyer A., Moore S. G., Nguyen T. D., Shan R., Stevens M. J., 273 Tranchida J., Trott C. and Plimpton S. J. (2022) LAMMPS - a flexible simulation 274 tool for particle-based materials modeling at the atomic, meso, and continuum scales. 275 Comput. Phys. Commun. 271, 108171. 276 Vuilleumier R., Seitsonen A. P., Sator N. and Guillot B. (2015) Carbon dioxide in silicate 277 melts at upper mantle conditions: Insights from atomistic simulations. Chem. Geol. 278 418, 77–88. 279  280 TABLE CAPTION 281  282 Table 1. Number of atoms i (Ni) of each species in the simulated systems of silicate melts. 283  284 FIGURE CAPTIONS 285  286 Figure 1. Schematic illustration for the high-P cell assemblies used in XRD measurements. 287 Figure 2. Total structure factors S(Q) and reduced pair distribution functions G(r) for dry 288 and carbonated (0.5 wt% CO2) Na2Si3O7 melts at high pressures obtained by XRD 289 measurements. Successive curves are displaced upward by 1 (left) and 5 (right) for clarity, 290 11 respectively. 291 Figure 3. Total structure factors S(Q) for dry and carbonated (5.0 wt% CO2) melts at high 292 pressures obtained by MD simulations: (a) Na2Si3O7 and (b) SiO2. Successive curves are 293 displaced upward by 1 for clarity. 294 Figure 4. Distributions of Qn species for dry and carbonated (5.0 wt% CO2) melts obtained 295 by MD simulations at 5 GPa and 2000 K: (a) Na2Si3O7 and (b) SiO2. 296 Figure 5. Fractions of carbon species in carbonated (5.0 wt% CO2) melts at 5 GPa and 2000 297 K: (a) Na2Si3O7 and (b) SiO2. 298 Figure 6. Characterization of carbonate ions in the silicate melts (snapshots) under high 299 pressure. For clarity, only bonds between atoms are shown. (a) Free carbonate ion, (b) 300 Nonbridging carbonate ion, and (c) Network carbonate ions. 301 Figure 7. Primitive ring size statistics for dry and carbonated (5.0 wt% CO2) (a) Na2Si3O7 302 and (b) SiO2 melts at high pressures obtained by MD simulations. 303 Figure S1. Temperature calibration for the electric power. 304 Figure S2. Schematic illustration for the high-P cell assemblies with a thermocouple. 305 Figure S3. Total structure factors S(Q) for dry and carbonated (0.5 wt% CO2) Na2Si3O7 melts 306 at high pressures obtained by MD simulations. Successive curves are displaced upward by 307 1 for clarity. 308 Figure S4. FSDP position for Na2Si3O7 melt at high pressures obtained by XRD 309 measurements at 1350 K and MD simulations at 2000 K. 310 Figure S5. Partial pair-correlation functions gSiSi(r) for Na2Si3O7 melt at high pressures and 311 2000 K obtained by MD simulations. 312 Figure S6. Typical atomic configuration formed by the combination of SiO4 tetrahedron and 313 OSi3 tricluster.Figure S7. Pressure dependence of CO2/(CO2+CO32−) for carbonated (5.0 314 wt% CO2) SiO2 and Na2Si3O7 melts obtained by MD simulations at 2000 K. 315 3.0 mmAmorphous B + epoxyZrO2MgOGraphiteMoh-BNMgO＋h-BNSampleFigure 1. Schematic illustration for the high-P cell assemblies used in XRD measurements. (S. Hayafune)Figure 2. Total structure factors S(Q) and reduced pair distribution functions G(r) for dry and carbonated (0.5 wt% CO2)Na2Si3O7 melts at high pressures obtained by XRD measurements. Successive curves are displaced upward by 1 (left) and 5(right) for clarity, respectively. (S.Hayafune)G(r)r (Å)(b)S(Q)FSDP(a)Q (Å–1)ｄFigure 3. Total structure factors S(Q) for dry and carbonated (5.0 wt% CO2) melts at high pressures obtained by MDsimulations: (a) Na2Si3O7 and (b) SiO2. Successive curves are displaced upward by 1 for clarity. (S. Hayafune)Q (Å–1)FSDPS(Q)Q (Å–1)FSDP(a) (b)S(Q)(a) (b)Q0 Q1 Q2 Q3 Q4Fraction (arb. unit)Fraction (arb. unit)Figure 4. Distributions of Qn species for dry and carbonated (5.0 wt% CO2) melts obtained by MD simulations at 5 GPa and 2000 K : (a) Na2Si3O7 and (b) SiO2. (S. Hayafune)Q0 Q1 Q2 Q3 Q4(a) (b)00.20.40.60.800.20.40.60.8CO2 CO32− Si–CO32− Si–CO32−–Si CO2 CO32− Si–CO32– Si–CO32−–SiFraction (arb. unit)Fraction (arb. unit)Figure 5. Fractions of carbon species in carbonated (5.0 wt% CO2) melts at 5 GPa and 2000 K: (a) Na2Si3O7 and (b) SiO2. (S. Hayafune)(c) Network carbonate ions(b) Nonbridging carbonate ion(a) Fee carbonate ionFigure 6. Characterization of carbonate ions in the silicate melts (snapshots) under high pressure. For clarity, only bonds between atoms are shown. (a) Free carbonate ion, (b) Nonbridging carbonate ion, and (c) Network carbonate ions. (S. Hayafune)(a) (b)Fraction (arb. unit)Fraction (arb. unit)n-foldn-foldFigure 7. Primitive ring size statistics for dry and carbonated (5.0 wt% CO2) (a) Na2Si3O7 and (b) SiO2 melts at high pressures obtained by MD simulations. (S. Hayafune)W97Re3–W75Re25 thermocoupleTemperature(℃)Power (W)Figure S1. Temperature calibration for the electric power.(S. Hayafune)W97Re3–W75Re25 thermocouple3.0 mmAmorphous B + epoxyZrO2MgOGraphiteMoh-BNMgO＋h-BNAl2O3 tubeW97Re3–W75Re25Figure S2. Schematic illustration for the high-P cell assemblies with a thermocouple. (S. Hayafune)W97Re3–W75Re25 thermocoupleS(Q)Q (Å–1)5 GPa, 2000 K5 GPa, 2000 KFigure S3. Total structure factors S(Q) for dry and carbonated (0.5 wt% CO2) Na2Si3O7 melts at high pressures obtained by MD simulations. Successive curves are displaced upward by 1 for clarity. (S. Hayafune)W97Re3–W75Re25 thermocouplePosition of FSDP (Å–1)Pressure (GPa)Figure S4. FSDP position for Na2Si3O7 melt at high pressures obtained by XRD measurements at 1350 K and MD simulations at 2000 K. (S. Hayafune)W97Re3–W75Re25 thermocoupler (Å)gSi–Si(r)Figure S5. Partial pair-correlation functions gSiSi(r) for Na2Si3O7 melt at high pressures and 2000 K obtained by MD simulations. (S. Hayafune)SiO4tetrahedra OSi3 triclusterFigure S6. Typical atomic configuration formed by the combination of SiO4 tetrahedron and OSi3 tricluster. (S. Hayafune)W97Re3–W75Re25 thermocoupleSiO2Na2Si3O7CO2/(CO2+CO32–)Pressure (GPa)Figure S7. Pressure dependence of CO2/(CO2+CO32−) for carbonated (5.0 wt% CO2) SiO2 and Na2Si3O7 melts obtained by MD simulations at 2000 K. (S. Hayafune) figures_JMPS_rev2.pdf スライド 1 スライド 2 スライド 3 スライド 4 スライド 5 スライド 6 スライド 7 スライド 8 スライド 9 スライド 10 スライド 11 スライド 12 スライド 13 スライド 14