# Low pressure glass-ceramics for the immobilization of long-lived iodine radioisotopes

Yann Morizet, Gabin Haryouli, Sami Soudani, Hanyu Hu, Michael Paris,
Philippe Deniard, Lionel Campayo, Philippe Navaro

► To cite this version:

Yann Morizet, Gabin Haryouli, Sami Soudani, Hanyu Hu, Michael Paris, et al.. Low pressure glass-ceramics for the immobilization of long-lived iodine radioisotopes. Journal of Nuclear Materials, In press, pp.155999. 10.1016/j.jnucmat.2025.155999. hal-05124971

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Distributed under a Creative Commons Attribution 4.0 International License
1 LOW PRESSURE GLASS-CERAMICS FOR THE IMMOBILIZATION OF LONG-LIVED

2 IODINE RADIOISOTOPES

3

4 Yann Morizetª, Gabin Haryouliª,b, Sami Soudaniª,b, Hanyu Huᵇ, Michael Parisᵇ, Philippe

5 Deniardᵇ, Lionel Campayoᶜ, Philippe Navaroᵃ

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7 ªNantes Université, Université Angers, Le Mans Université, CNRS, UMR 6112, Laboratoire

8 de Planétologie et Géosciences, F-44000 Nantes, France

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10 ᵇNantes Université, CNRS, Institut des Matériaux de Nantes Jean Rouxel, IMN, F-44000

11 Nantes, France

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13 ᶜCEA, DES, ISEC, DE2D, Université de Montpellier, Marcoule, F-30207, Bagnols sur Cèze,

14 France

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17 *Corresponding author: Yann Morizet

18 Postal address:

19 Laboratoire de Planétologie et Géosciences (LPG), UMR 6112, Nantes Université.

20 2 rue de la Houssinière, 44322 Nantes Cedex (FRANCE)

21 phone: +33 (0) 2 5112 5491

22 fax: +33 (0) 2 5112 5268

23 *E-mail: yann.morizet@univ-nantes.fr

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**Abstract**

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There have been substantial scientific works in the past years for finding adequate immobilization matrices for iodine radioisotopes. Lately, iodosodalite glass-ceramics or glass-composites represent a promising material. Under pressure, glass-ceramics represent an even better material. In the present work, we have synthesised I-bearing glass-ceramics under low pressure conditions (0.5 GPa) and using a thermal step from melting (1250°C) to crystallization temperature (813°C). The produced materials show the coexistence between I-rich iodosodalite (>10 mol.% I) and I-poor glass matrix (<1 mol.% I) and without the presence of detrimental crystalline phase such as nepheline. The iodosodalite proportion remains low though (~10%). Raman spectroscopy on the iodosodalite crystals seems to indicate that the β cage could be filled either with I⁻ or IO₃⁻ species. The analyses of the glass structure using <sup>11</sup>B NMR show an increase in the BO₄ proportion that could suggest an increase in the chemical durability. In the end, the produced materials have most of the prerequisite for a relevant matrix for immobilization of iodine radioisotopes.

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**Keywords**

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Low-pressure glass-ceramics, iodine radioisotopes immobilisation, chemical durability.

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**1. Introduction**

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The iodine 129 radioisotope represents a major troublesome element in the management of nuclear waste produced by nuclear plant activity. Despite its relatively low radioactivity (β⁻ emitter), <sup>129</sup>I is considered as an intermediate level nuclear waste. It has a long half-life (15.7 My) and is highly mobile in the environment.<sup>1-5</sup> Finally, <sup>129</sup>I can fix into human organism and induce DNA disorder and thyroid cancers.<sup>6-8</sup> Currently, there is no ideal solution to immobilize those radioisotopes and up to now France and United Kingdom have chosen to release <sup>129</sup>I radioisotope into the Channel Sea with possible environment consequences.<sup>9,10</sup>
In most nuclearized countries the solution that is employed to immobilize the most harmful radioactive waste is a vitrification protocol that produces glass matrices at high-temperature, typically in the range 1000-1250°C; however, this method cannot be adequately applied to <sup>129</sup>I owing to the strong volatilization of iodine under high-temperature conditions. A recent review by Asmussen et al.<sup>11</sup> listed the solutions put forward to immobilize in a durable and safe way the iodine radioisotopes. From all the suggested materials, glass-ceramics represent a serious candidate corresponding to a material in which crystals (of single or multiple crystalline phases) are in equilibrium embedded in a glass matrix.<sup>12-15</sup> Glass-ceramic is formed by the crystallization of a parental glass melted at high temperature and slowly cooled down.<sup>15</sup> The thermal protocol used for the crystallization of the phases can involve several temperature steps.<sup>16</sup> Such assembly offers several advantages: 1) a double barrier protection (crystal + glass) often employed in heavy metal immobilization<sup>17-19</sup>, 2) an increase in the load of nuclear waste in both crystal and glass<sup>20</sup> and 3) a potential improvement of the chemical durability and mechanical resistance<sup>20,21</sup>. Nevertheless, there is always the problem of iodine volatility at high temperature rendering difficult to produce such an immobilization material.

Recent works proposed instead glass-composites as an alternative in which a I-rich crystalline phase, iodosodalite (Na<sub>8</sub>Al<sub>6</sub>Si<sub>6</sub>O<sub>24</sub>I<sub>2</sub>) is produced at ambient pressure and relatively mild temperature conditions using hydrothermal protocol and then embedded with a glass binder.<sup>22-24</sup> It is not clear if a double barrier protection applies with this method considering a possible weakness of crystal/binder interfaces that might eventually constitute preferential pathways for water and decrease the chemical durability.

Recent research conducted by our group proposed the use of high-pressure synthesis to incorporate iodine into different types of matrices: from glass<sup>25-29</sup> to glass-ceramics<sup>30</sup>. The use of high-pressure methods has long been known in Earth Sciences for the study of volatile behaviour in magmatic systems with planetary degassing application<sup>31-33</sup>; applied to the
74 immobilization of volatile radioisotopes is a relatively new topic. For aluminoborosilicate 75 glasses, the use of high-pressure protocol that is industrially feasible (at pressure up to 0.5 76 GPa) improves significantly the iodine incorporation into the glass structure therefore 77 representing a potential solution for the immobilization of iodine radioisotopes²⁹. Regardless 78 of industrial feasibility, increasing pressure enhances the incorporation of halogens into the 79 glass structure for aluminoborosilicate compositions (e.g. chlorine³⁴ and iodine²⁹).

80 The work of Soudani et al.³⁰ represents the most advanced work in producing true glass- 81 ceramics (i.e. obtained from the crystallization of a parental high-temperature liquid) enriched 82 with respect to iodine and made under high-pressure conditions. Although this preliminary 83 work is very promising, it suffers from major drawbacks. First, glass-ceramics samples were 84 synthesised at pressure of 1.0 and 1.5 GPa, which is not achievable from the industrial 85 viewpoint. Second, almost all the produced I-bearing glass-ceramics contained nepheline 86 (NaAlSiO₄) that is a detrimental crystalline phase for nuclear waste consideration as 87 nepheline is quickly altered and will induce porosity in the immobilization matrix³⁵⁻³⁷.
88 Finally, in their work Soudani et al.³⁰ could not determine the ratio between crystalline and 89 glass matrix, hence the incorporation rate was not determined.

90 In the present work, we have pursued the work of Soudani et al.³⁰. High-pressure glass 91 ceramics were synthesised at 0.5 GPa using a single thermal step. Recovered samples were 92 characterized to determine the iodine incorporation and the chemical composition of the 93 coexisting phases. The chemical properties of the glass-ceramics are assessed with 94 spectroscopic methods and compared to the initial starting glass.

## 2. Experimental and analytical methods

### 2.1. *Starting material*
The NH starting material has been prepared from analytical grade reagents (see Table 1). 97

These included silica (SiO₂, 99.4%), orthoboric acid (H₃BO₃, 99.9%, VWR, France), sodium carbonate (Na₂CO₃, 99.95%, Thermo Fisher Scientific, USA), alumina (Al₂O₃, 99%, Thermo Fisher Scientific, USA) and calcium oxide (CaO, 99.9%, Sigma Aldrich, USA). Two hundred grams of a dried batch were heated in a Pt-Au crucible at 1100°C for 3 hours with two intermediate steps at 400 and 800°C for 3 hours each. A heating ramp of 5°C/min was used between each step. The melted material was eventually poured into a graphite crucible pre-heated at 530°C and was allowed to stay at this temperature for one hour to remove mechanical stresses. A translucent homogeneous glass was obtained in this way and does not show evidence of crystalline phase nor unreacted materials. The investigated glass composition is similar to the glass composition investigated in Soudani et al.³⁰ or Jolivet et al.²⁵. It is a Low Activity Waste (LAW) glass composition that could represent a potential matrix for the immobilisation of iodine radioisotopes. 108 109

For the present experiments, we used different sources of iodine: either I₂ (VWR Chemicals) or I₂O₅ (Alfa Aesar); as also described in Soudani et al.³⁰. Glass powder was loaded into Pt tubes along with iodine source and Pt capsule was welded shut by arc-welding. We used Pt tubing with different dimensions: 5.0-5.4 mm, 8.6-9.0 mm or 7.6-8.4 mm inner and outer diameter Pt tubes, respectively; and almost 15 mm in length. We did not observe any change in the experiment depending on the type of tube. We tested also the effect of adding Al₂O₃ onto the crystallization process. The sample GC-NH-5 is prepared with an addition of 5 mol.% Al₂O₃ with the aim of promoting the crystallization of the Al-rich iodosodalite into the experimental charge. 110 111 112 113 114 115 116 117 118

## 2.2. *High-pressure syntheses*

High-pressure experiments were conducted in a solid-media piston-cylinder apparatus at a pressure of 0.5 GPa in order to keep conditions that are accessible from the industrial point of 120 121
view. For such “low-pressure” conditions, we used a 1 inch pressure plate. The sample Pt capsule is placed inside a Magnorite© ceramic, then surrounded by the graphite furnace and followed by the Pyrex and talc sleeves.

The protocol for synthesising high-pressure glass and glass-ceramics is described elsewhere<sup>29,30,34</sup> and details are given in Table 1 for each sample. The solid assembly is placed under pressure at 0.5 GPa and a heating step is performed at 550°C. During the experiment the pressure is constantly monitored by a Stigma© needle pump; the temperature is controlled by a B-type thermocouple located at the top of the Pt capsule. For synthesising I-bearing glass sample (i.e. NH-3 in Table 1), we heated the sample up to 1250°C at a rate of 40°C/min followed by a rapid quenching by cutting off the power. For 1 inch pressure plate, the quench rate is estimated below 100°C/s in the first 500°C. The glass-ceramic syntheses involved three steps for GC-NH-1 or two steps for the other samples. The three steps consist in melting at 1250°C, cooling down to the nucleation temperature (Tn) at 594°C, a 24h dwell at Tn and heating to the crystallization temperature (Tc) at 813°C and a 24h dwell at Tc (i.e. Tn and Tc are the same as in Soudani et al.<sup>30</sup> considering that it is the same starting composition). For the two-step sample syntheses, we did not cool down to Tn and only a 24h dwell at Tc was adopted. In fact, we did not observe any significant change in the proportion or size of crystalline phases in the glass-ceramics. We also tested several cooling rates: 20, 10 and 3°C/min (see Table 1).

Samples were recovered from the high-pressure experiments and either mounted entirely into epoxy resin plug or opened before embedding into the epoxy plug. The embedded Pt capsule was then cut in half using a diamond shear. The yellowish NH-3 glass colour is consistent with the presence of incorporated elemental iodine I<sub>2</sub> and an excess of iodine is also found surrounding the glass sample<sup>25,29</sup>. The glass-ceramics are mostly grey to white in colour.

### 2.3. Scanning Electron Microscopy (SEM) for major element concentration determination
Major elements concentrations have been measured using a SEM Zeiss Merlin equipped with an Energy Dispersive Spectrometer probe and a crystal silicon drift. The acquisition conditions were 15 kV and 0.5 nA for acceleration voltage and probe current, respectively. The glass-ceramics were mounted in epoxy plugs and subsequently polished down to 1 µm.

We used carbon coating for analyses. SEM images were taken at different location of the sample and with different magnification. The recorded images were treated using JMicrovision® for determining the proportion on the surface for crystalline phase and surrounding glass matrix. An average crystal proportion and associated standard deviation was determined from the analysis of several images taken for a given sample. Knowing that pressure is isotropic during the experiment and that we took large scale pictures on the sample, we expect the crystal surface to be also representative of the bulk volume for estimating the crystalline proportion within the experimental charge.

For EDS spectra, the acquisition time was set to 60 s to obtain a reliable definition of the peaks for quantification. We adopted different acquisition protocol to determine the chemical compositions for 1) the glass matrix, 2) the crystalline phases and 3) the entire experimental charge. We should point out that the acquisition on the entire experimental charge implies that the sample is homogeneous. This might not be entirely the case; however, this is an approximation. We performed areas rather than point analyses quantification to avoid alkali loss under the electron beam. At least 5 scans were conducted on the glass matrix, the crystals and the entire experimental charge and the error on each oxide and iodine was determined from the standard deviation of these repeated analyses.

Owing to its low mass, $B_2O_3$ has not been quantified in the high-pressure synthesised sample, however, it has been previously determined in our research group works on the same glass composition³⁸. The standards used for major elements quantification are corundum for $Al_2O_3$, wollastonite for CaO and $SiO_2$, NaCl for $Na_2O$ and RbI for I. The most important standard
deviation obtained on the glass matrix oxide concentration is observed for either SiO₂ or Na₂O and is mostly seen for iodosodalite crystal compositions. We suspect that it is possibly due to the fact that a slight fraction of the glass matrix is also analysed during crystal analysis owing to the small crystal size.

## 2.4. Micro-Raman spectroscopy

We acquired maps of Raman spectra on several glass-ceramics sample: GC-NH-4, GC-NH-5 and GC-NH-11. The acquisitions were carried out on a LabRam© HR800 Evolution spectrometer from Jobin-Yvon. The spectrometer is equipped with a 1800 grooves/mm grating corresponding to a spectral resolution of ~0.5 cm⁻¹. Such a high-resolution is useful for crystalline materials that could exhibit very sharp Raman signals. We used solid laser operating at a 532 nm wavelength with an output power of 100 mW. With this output laser power, we did not observe any damage on the sample surface. The analyses were performed with a X100 Olympus objective. We acquired spectra between 250 and 1750 cm⁻¹ in order to cover the spectral range for silicate network units (800-1200 cm⁻¹) and boron network units (1300-1600 cm⁻¹). The spectrometer was calibrated using Si metal plate at 520.7 cm⁻¹.

We used confocal mode using hole at 50 µm for acquiring the spectra. For each spectrum, spectral autofocus mode implemented in Labspec 6© was used in the 1000 cm⁻¹ spectral region. Map of Raman spectra was obtained on sample embedded in epoxy resin plug. We tried to analyse flat surface as much as possible, however, we had to remove several spectra showing high background or evidence for epoxy resin signal. At least 200 spectra were collected for each sample with a step of ~20 µm vertically in between each spectrum.

Acquisition time was 15 s repeated 10 times, which corresponds to an acquisition duration of ~36h on each sample. The background subtraction was performed with Labspec 6© using a fourth-order polynomial function anchored in areas containing no spectral vibrations: ~250,
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~1200 and ~1650 cm⁻¹. The background subtraction is conducted automatically on the 200

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## 2.5.X-ray Diffraction (XRD)

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Glass-ceramic powders were characterized by XRD for determining the nature of the crystalline phases and their relative proportions. For most of the samples, 0.3 mm capillary were filled with finely ground powders and acquisition was conducted on a Debye-Scherrer geometry INEL CPS120 operating at 40 kV and 20 mA. The CPS 120 detector is a curved detector with an aperture of 120° 2 theta. Hence, no scan of the detector is necessary to cover all the 2 theta range. Acquisition duration was set to 24h. We used the Cu Kα1 wavelength at 1.54098 Å thanks to a quartz monochromator. GC-NH-1 diffractogram was acquired on a Bruker D8 Advance with a Bragg-Brentano geometry and operating with the Cu Kα1 wavelength at 1.540598 Å and with a germanium (111) monochromator. For this sample, we acquired diffractogram between 10 and 90° at a step of 0.01°. The recorded diffractograms were treated using QualX software³⁹ and the implemented PDF-2 database⁴⁰ for determining the coexisting crystalline phases. Rietveld refinement was performed using JANA2020© software⁴¹ for refining the crystallographic structure and determining the proportion of the mineral phases in the glass-ceramics.

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## 2.6.Nuclear Magnetic Resonance (NMR) spectroscopy

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We acquired ¹¹B, ²³Na and ²⁷Al Solid State NMR spectra on a Bruker Avance III 500 MHz using a 2.5 mm Magic Angle Spinning (MAS) probe at the Larmor frequencies of 160.46, 132.29 and 130.32 MHz. The ¹¹B, ²³Na and ²⁷Al spectra were referenced with H₃BO₃ solution at 19.6 ppm, with NaNO₃ solution at 0 ppm and with Al(NO₃)₃ solution at 0 ppm.

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The glass-ceramic powder was loaded into a 2.5 mm ZrO₂ rotor with a Teflon cap. We acquired the ¹¹B and ²⁷Al MAS spectra at a MAS frequency of 20 kHz with a single π/12

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excitation for a radio frequency field strength of 20 kHz. We set the MAS frequency at 30

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kHz for $^{23}$Na spectrum acquisition and we used a single $\pi$/8 excitation at a radio frequency

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field strength of 20 kHz. The recycle delays between consecutive scans were 5 s for $^{11}$B and

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1 s for both $^{27}$Al and $^{23}$Na.

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We followed the protocol described in previous works$^{42,43}$ to remove the probe signal as well

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as the satellite transition spinning sidebands from the central transition of the $^{11}$B NMR

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spectra. The spectra were fitted using the DMFit software$^{44}$. The description of the fit is

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provided in the Results and Discussion section.

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### 3. Results and discussion

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#### 3.1. *Crystalline proportions and major element quantification in glass-ceramics*

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Typical SEM backscattered images are represented in Figure 1 for two glass-ceramic samples:

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GC-NH-6 and GC-NH-11. We observe the coexistence of a crystalline phase in bright and a

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glass matrix in dark. Both samples were prepared with $I_2O_5$ loaded into the Pt capsule but

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with different cooling rate between 1250 and 813°C: 20 and 3°C/min, respectively. For both

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samples the crystalline phase proportion determined using JMicrovision© (based on several

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images for each sample and different magnification) is roughly the same at 10.3 and 11.7%

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for GC-NH-6 and GC-NH-11, respectively; however, on the images, we observe that the

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crystal size is twice as large in GC-NH-11 as in GC-NH-6. We suggest that using different

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cooling rate to attain Tc is a key parameter in the crystals growth. Further experiments are

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required to confirm this aspect. It should be emphasised that the crystalline proportion only

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represents an approximation considering that it is obtained on a single sample surface and it

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does not take into account the distribution of crystals into the entire sample volume.

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We also observe on the images that the crystals have particular orientations. This particular

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orientation could be explained by a possible sample convection due to the temperature
gradient along the Pt capsule (i.e. 15 mm in length with thermocouple located at the top of the capsule). This implies that iodosodalite crystals have probably been formed during the cooling under the liquid state of the sample; otherwise, we would not have observed such orientated pattern under the solid state. Therefore, it would be interesting to conduct intermediate step at temperature higher than Tc for enhancing the crystallization of iodosodalite for future studies.

The fact that we obtain larger crystal size at slower cooling rate is also witnessing that there is a region between 1250 and 813°C at 0.5 GPa that promotes the crystallisation of iodosodalite; however, a dwell seems necessary to increase the crystallization.

Quantification has been obtained from EDS measurements. The results are shown in Table 1 for the crystals, the glass matrix and the entire sample. We assume that the entire sample composition can be approximated to the global SEM EDS analysis (i.e. crystals + glass). The determined crystal composition is somehow close to that of iodosodalite (i.e. Na<sub>8</sub>Al<sub>6</sub>Si<sub>6</sub>O<sub>24</sub>I<sub>2</sub>).

The theoretical composition for iodosodalite is 26.7 Na<sub>2</sub>O, 20.0 Al<sub>2</sub>O<sub>3</sub>, 40.0 SiO<sub>2</sub> and 13.3 mol.% I. The data reported in Table 1 for iodosodalite have lower I content in most of the case, lower Na<sub>2</sub>O, higher SiO<sub>2</sub> and reveals the presence of CaO. Considering the small size of the iodosodalite crystals in most of the samples (~5 µm), the reported compositions in Table 1 may not represent the true crystal composition and slight contribution from the underneath glass matrix (i.e. with lower I, higher SiO<sub>2</sub> and CaO) is expected. On the contrary, for GC-NH-11, which has the largest iodosodalite crystals (>10 µm), we have composition data very close to the theoretical composition with almost no CaO and I content close to 13.3 mol.%.

Alternatively, it is possible that 1) iodosodalite crystals have unfilled cages thus explaining the lower I content (also related to a lower Na<sub>2</sub>O content) and 2) synthesised crystals are in fact a solid solution between several end-members with CaO, for instance.

The glass matrices within the glass-ceramic have a very low I content (<1 mol.%) as compared to the equivalent I-bearing glass NH-3 with 1 mol.%, with iodine loaded as I<sub>2</sub>. As
269 shown in Table 1, it appears that the I content measured in the glass matrix for GC-NH-6 and
270 GC-NH-11 is higher than for the others. This is explained by the fact that those two samples
271 were loaded with I₂O₅ instead of I₂ and it has been demonstrated that I solubility in
272 aluminoborosilicate glasses is higher in the case I₂O₅ is loaded as the iodine source during the
273 experiment. Morizet et al.²⁶ explained this difference by the change in I speciation within the
glass. With I₂, the I speciation within the glass is represented either by only iodide species (I⁻)
274 or a mixture between iodide species and molecular iodine (I⁰) whereas with I₂O₅, the I
275 speciation is a complex mixture between iodide and iodate (IO₃⁻) species. The systematic
distribution in between the iodine species in this later case is not clearly investigated. Owing
276 to the complex chemistry of iodine, we cannot exclude the possibility to have other iodine
277 species with different redox state such as hypoiodite (I⁺), iodite (I³⁺) or periodate (I⁷⁺). So far,
278 except for I⁷⁺ observed in Morizet et al.²⁶, there is no evidence for such species in
279 aluminoborosilicate glasses.
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282 From the structure point of view, IO₃⁻ is likely to have a higher affinity with the glass matrix
283 and therefore higher I incorporation is. In the case of I₂, the higher I content in NH-3 is
284 explained by the higher Na₂O content in the glass composition as compared to the Na₂O
285 content in the glass matrix of the equivalent glass-ceramics: GC-NH-1, GC-NH-4 and GC-
286 NH-8. In the meantime, the iodosodalite crystallization consumes the available iodine from
287 the surrounding glass. Surprisingly, the total incorporated iodine is not higher in glass
288 ceramics than in parental glass. For instance, I²⁺ for GC-NH-1 is 1.2±0.1 mol.% that is, within
289 error, identical to the I²⁺ in NH-3 at 1.0 mol.%. Unfortunately, we did not synthesise the
290 equivalent NH glass loaded with I₂O₅ as we experienced failures to synthesise such sample;
291 however, the I²⁺ measured for GC-NH-6 and GC-NH-11 is on the same order or possibly
292 slightly higher than what is expected for a comparable glass. Soudani et al.³⁰ reported 1.5
293 mol.% I for similar glass composition synthesised at 1.0 GPa. Morizet et al.²⁹ reported 2.6

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294 mol.% I for B15Na30 loaded with I₂O₅ and melted and equilibrated at 1.0 GPa. We might
295 expect ~2 mol.% at 0.5 GPa for B15Na30 that is a pure sodic (Ca-free) glass. The results
296 reported in Table 1 contrast with the common assertion that glass-ceramics can incorporate a
297 larger quantity of nuclear wastes. Nevertheless, except for GC-NH-5 that contains nepheline,
298 the data shown in Table 1 and glass-ceramics in Figure 1 constitute a major breakthrough in
299 the iodine radioisotope immobilization. We expect a higher thermodynamic stability of the
300 shown glass-ceramics considering that I is incorporated in both the glass matrix and the
301 embedded crystals. It represents an efficient double barrier process that could reinforce the
302 material durability.²⁰,²¹

303 The proportion of iodosodalite has also been determined from the bulk using the
304 subsequent fit of the ²⁷Al NMR spectra. The ²⁷Al MAS NMR spectra are shown in Figure 2
305 for the I-bearing glass NH-3, and two glass-ceramics GC-NH-4 and GC-NH-6. There is a
306 clear distinction between the glass spectrum and the glass-ceramic spectra. The NH-3 glass
307 spectrum exhibits an asymmetric line shape consistent with the quadrupolar nature of Al
308 nuclei. We observe no evidence for highly coordinated Al species (i.e. AlO₅ and AlO₆) and Al
309 is only in four-fold coordination. For glass-ceramics, on top of the glass matrix signal there is
310 an additional sharper signal that is attributed to the Al species in the iodosodalite crystals
311 considering that for those samples it is the only crystalline phase that contains Al. The spectra
312 have been simulated with Czjzek lines⁴⁵. The derived parameters are provided in Suppl. Mat..
313 The obtained δᵢₐ ᵢ and Cq for the AlO₄ units in glass are ranging from 62.9 to 66.3 ppm and
314 from 4.7 to 5.0 MHz, respectively; in agreement with reported parameters for AlO₄ in glasses
315 in the literature⁴⁶⁻⁴⁸. For iodosodalite, the obtained δᵢₐ₉ and Cq are 61.4-62.0 ppm and 1.7-2.0
316 MHz, respectively. These results are in agreement with recent reported results for
317 iodosodalite⁴⁹. We totally excluded the GC-NH-5 in the present analysis as this sample
318 contains significant amount of nepheline and it appears difficult to discriminate the signal of
319 iodosodalite and nepheline from the ²⁷Al NMR. For the nepheline-free glass-ceramics, we 320 have determined the proportion of iodosodalite and glass matrix. To derive the proportion of 321 iodosodalite in the bulk material, we have considered a theoretical iodosodalite composition 322 with 20 mol.% Al₂O₃, the measured mol.% Al₂O₃ in the glass matrix (see Table 1) and the 323 derived proportion of the Al species (see Suppl. Mat.) as follows:

$$ \% \text{Iodosodalite} = 100 \times \frac{\frac{Al_{\text{lodo.}}^{\text{NMR}}}{Al_{\text{lodo.}}^{\text{Th.}}} / \frac{Al_{\text{lodo.}}^{\text{NMR}}}{Al_{\text{lodo.}}^{\text{Th.}}} + \frac{Al_{\text{Glass}}^{\text{NMR}}}{Al_{\text{Glass}}^{\text{EDS}}}}{Al_{\text{lodo.}}^{\text{NMR}} / Al_{\text{lodo.}}^{\text{Th.}}} $$

324 The derived iodosodalite proportion for nepheline-free samples ranges from 4.9 to 11.8% in 325 GC-NH-4 and GC-NH-1, respectively. The error reported from the fit using DMFit is on the 326 order of ±0.1%. As seen in Table 1, this result slightly contrasts with the proportion 327 determined using image analysis. We might explain that because the image analysis is only a 328 partial view of the entire sample. Hence, we believe that our approach using ²⁷Al NMR 329 spectrum simulation is much more precise in determining the glass to crystal ratio. The 330 iodosodalite proportion is ~10% in our glass-ceramic sample. We suspect that a more 331 complex thermal treatment should be necessary to potentially increase the proportion in 332 crystalline phases as demonstrated in a previous work.⁵⁰ 333

334 **3.2. Iodosodalite crystal lattice and β-cage filling**

335 The cell parameter of the cubic iodosodalite in the glass-ceramics has been determined from 336 the Rietveld refinement of the XRD data that are shown in Figure 3 for GC-NH-6 and GC- 337 NH-8. In addition, the refinement results for other observed crystalline phases in experimental 338 charges: nepheline, NaI and NaPt₃O₄, are provided in the Suppl. Mat. In Figure 3, the 339 diffractogram is represented along with the simulated diffractogram and the residual. We 340 considered fitting the diffraction pattern between 2.5 and 110° for 2θ. The obtained cell
parameter is also reported and all the results are given in the Table 1. We used standard crystalline structure for iodosodalite (n°1534899 from Beagley et al.⁵¹) taken from the Crystallographic Open Database (COD)⁵² with space group I-43m and cell parameter of 9.008 Å.

The optimization was performed as follow: 1) background function is optimized using a 15-20 terms Legendre polynomial, 2) the peak line shape is set to pseudo-Voigt and parameters of the peak line shape are optimized, 3) concerning the structure, the lattice parameter, the atomic position for Na and O and site occupancy for I have been refined as well as atomic displacement parameters for all of the atoms (Al and Si being constrained). The wRp figures of merit obtained at the end of the refinement are reported in Suppl. Mat.. We analysed the results through Fourier maps of the electronic residue. We observed a positive residue (see Suppl. Mat.) located on the I atoms. Part of this positive residue is possibly ascribed to the quality of the data. For instance, the electronic residue obtained on GC-NH-1 acquired on a Bruker D8 Advance diffractometer is by far lower that electronic residue obtained for the other sample acquired on the INEL CPS120. Nonetheless, there is systematically a positive residue observed on the I atoms in the lattice structure which could be explained by a possible difference in the β cage filling in the iodosodalite structure. By extension, it implies that the used crystallographic model for iodosodalite is not entirely adequate. Two types of iodosodalite are currently known: one with β cage filled with I⁻ units surrounded by Na⁺ cations for charge compensation²²⁻²⁴ and less common one in which the β cage is filled with IO₃⁻ units surrounded also by Na⁺ cations⁵³. For this later case, there is no existing crystallographic structure in the COD. Except for GC-NH-5, we obtained a cell parameter that is very close in between the samples at ~9.005 Å. This is consistent with the identical conditions used: same pressure, comparable temperature history and identical initial composition. With the sole use of XRD we are not able to determine how the β cages are
366

filled with iodine. With the use of I₂ or I₂O₅ as the initial source for iodine and considering that the main I speciation will be I⁻ or I⁵⁺, respectively; we could obtain iodosodalite crystal exhibiting either I⁻ or IO₃⁻ filling in the β cage.

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Micro-Raman mapping has been obtained for a few glass-ceramic samples with the objective to investigate the spectroscopic signature of the coexisting glass matrix and crystalline phases.

The maps are shown in Figure 4 for GC-NH-5, GC-NH-4 and GC-NH-11. The images in Figure 4 correspond to intensity maps obtained by taking the ratio of the spectrum intensity between 300-500 cm⁻¹ and 1350-1600 cm⁻¹. The choice of these regions lies on the fact that it corresponds to an intense signal for crystalline materials (~400 cm⁻¹) and it also corresponds to the signal for the stretching of boron species (ν₁ B-O 1300-1550 cm⁻¹) only present in the glass matrix. Therefore, the areas in blue colour correspond to a low intensity ratio and the absence of crystalline phases. On the contrary, the areas in yellow to red colour correspond to a high intensity for this ratio and therefore the presence of crystal. On each map, we extracted a single spectrum representative of nepheline, iodosodalite and glass matrix.

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In Figure 4A, the spectrum attributed to nepheline is consistent with typical nepheline spectrum taken from the RRUFF⁵⁴ Raman database (nepheline n° R040025) with an asymmetric signal located at 1000 cm⁻¹ and a strong signal at 400 cm⁻¹. On the image in Figure 4A, the signal for nepheline is predominant suggesting that nepheline crystals are large (>100 µm), although we did not observe it by SEM due to the poor chemical contrast in backscattered imaging between the glass matrix and the nepheline crystals. For the three samples, the signal for the glass matrix is in agreement with current knowledge for aluminoborosilicate glasses⁵⁵⁻⁵⁷ with several broad signals at low frequency (~500 cm⁻¹) and high frequency for the silicate units symmetric stretching (~1000 cm⁻¹) and the boron units symmetric stretching (~1450 cm⁻¹). For GC-NH-11, the signal for the glass matrix also exhibits a broad signal located at ~800 cm⁻¹ that could correspond to the symmetric stretch for

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iodine to oxygen bonds ($v_1$ I-O) as mentioned in previous works⁵⁸,⁵⁹. Early work by Durig et al.⁶⁰ and more recent work by Liang et al.⁶¹ reported identical Raman signal for crystalline sodium iodate and iodate species in solution and also on the effect of pressure on the Raman signal of iodate species. The signal at 800 cm⁻¹ observed in GC-NH-11 loaded with $I_2O_5$ is not seen in GC-NH-4 loaded with $I_2$ in agreement with the fact that I speciation is expected to be mostly $IO_3^-$ in GC-NH-11 and $I^-$ in GC-NH-4.²⁶,²⁹

The spectra obtained for iodosodalite are not purely represented by iodosodalite vibrational signals and the glass matrix vibrations are also present in most cases. Although, we used confocal configuration on the spectrometer to reduce the size of the laser spot on the sample, the iodosodalite crystal size is too small for analysing only the crystal itself and the spectrum is contaminated by the surrounding glass matrix. Nonetheless, it is possible to see, regardless of the sample, that iodosodalite crystals are disseminated throughout the surface of the samples. It is less apparent for GC-NH-11 in which the crystal size is much bigger (>10 µm).

In Figure 4C, we also added a chlorosodalite spectrum taken from the RRUFF (sodalite n°R06416) and the spectrum obtained on an iodosodalite synthesised by Soudani et al.³⁰. An interesting feature requires to be further investigated: there is an intense signal located at 800 cm⁻¹ that seems to correspond to the stretching vibration of I-O bonds as mentioned before.

The peak is sharp and could be assigned to $v_1$ I-O for $IO_3^-$ groups in iodosodalite crystals.

Whereas it is expected for GC-NH-11 (i.e. loaded with $I_2O_5$), it is surprising to observe such a signal for GC-NH-4 (i.e. loaded with $I_2$) for which the expected iodosodalite vibrational signal is more like the one obtained for the iodosodalite synthesised by Soudani et al.³⁰. For such an iodosodalite, the $\beta$ cages are expected to be filled with $I^-$ species. Although the intensity ratio 800/400 is less intense for GC-NH-4 than for GC-NH-11, it suggests that the obtained iodosodalite crystals have $\beta$ cages partially filled with $IO_3^-$ species. Currently, we are not able to determine the distribution between $I^-$ and $IO_3^-$ species. Certainly, the quantity of $IO_3^-$ should
416 be much more important for GC-NH-11 than for GC-NH-4. Further investigations are
417 required to determine the β cage occupancy and the I speciation in iodosodalite crystals and if
418 a solid solution exists between two end-members: Na<sub>8</sub>Al<sub>6</sub>Si<sub>6</sub>O<sub>24</sub>(2I<sup>-</sup>) to Na<sub>8</sub>Al<sub>6</sub>Si<sub>6</sub>O<sub>24</sub>(2IO<sub>3</sub><sup>-</sup>).

3.3. *Glass-ceramics improved chemical durability*

420 The ¹¹B NMR spectra are shown in Figure 5 for the initial ambient pressure glass NH-0, the
421 high-pressure I-bearing glass NH-3 and two glass-ceramics loaded with I₂ (GC-NH-4) and
422 I₂O₅ (GC-NH-5). The spectra consist in a symmetric intense line at 0 ppm attributed to BO₄
423 units and a broad asymmetric line ascribed to BO₃.⁶²⁻⁶⁴ We do not observe additional signal
424 that could be attributed to crystalline boron species. It suggests that boron is incompatible and
425 does not incorporate into the produced crystalline phases. Therefore, the analyse of the boron
426 speciation reflects the structure of the glass matrix only.

427 The proportion between both species expressed with the N₄ = [BO₄] / ([BO₃] + [BO₄]) ratio is
428 important to assess as it gives insights into the polymerization of the borosilicate network that
429 could be linked to some extent to its chemical durability of the glass. The higher the N₄ value,
430 the higher chemical durability is expected considering that BO₄ units represent the most
431 polymerized boron species within the glass.⁶² The BO₄ peak is simulated with a single
432 Gaussian line. The BO₃ broad peak is simulated with two asymmetric lines corresponding to
433 ring and non-ring BO₃ units.²⁹ We provide the entire set of parameters in the Suppl. Mat.. The
434 δₗ₀ are ~0, ~14 and ~18 ppm for BO₄, BO₃ ring and BO₃ non-ring, respectively. The Cq for
435 BO₃ ring and non-ring are ~2.4 and ~2.6 MHz, respectively. Those derived values are in
436 agreement with literature data for comparable glass compositions.⁶²⁻⁶⁴

437 Systematically, we observe an increase in the N₄ value from the initial ambient pressure glass
438 NH-0 with N₄ = 0.40 to the high-pressure I-bearing glass-ceramics with N₄ higher than 0.43.
439 We put aside the GC-NH-5 that is peculiar as it contains nepheline, hence, merely comparable
440

with the others. It should be emphasised that the error associated with the determination of the
N₄ is extremely low (on the order of 0.03) and therefore the observed change in N₄ value is
beyond any possible analytical error.²⁸,⁶⁵

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Such increase in the N₄ value indicates that there is a conversion of BO₃ units into BO₄ units
representing the most polymerized boron species in the glass. As a result, we suggest an
increase in the chemical durability of the I-bearing glass-ceramics that is more important than
for the equivalent I-bearing glass. In comparison to ambient pressure I-free glass, both are
expected more durable assuming that the chemical durability of a glass ceramic might be
driven by the chemical durability of the residual glass. This possible increase in the chemical
durability can arise from three conjugated aspects. Previous works⁶⁵⁻⁶⁷ demonstrated that for
aluminoborosilicate glasses, the synthesis under high-pressure conditions induces an increase
in the degree of polymerization of the borosilicate network. For Al-bearing glasses, the
increase in pressure can induce a change in the Al coordination towards higher coordination
with AlO₅ and AlO₆ species, which have an intermediate role in the glass composition.⁶⁵ In
our case, as shown in Figure 2, we do not observe the presence of highly coordinated Al
species indicating that Al behaves as a regular network former with AlO₄ units. The second
aspect is that it has been proven that I incorporation into the glass structure induces an
increase in the glass polymerization due to the fact that Na cations are scavenged by I species
(I⁻ or IO₃⁻) for charge compensation and therefore part of Na cations do not act as network
modifiers anymore²⁹. Although the I amount in the glass is relatively low for the glass-
ceramics (<0.5 mol.%), it has been shown that almost four Na⁺ cations are required for the
charge compensation of I species⁶⁸. Finally, the crystallization of iodosodalite has induced a
decrease in the Na₂O in the glass. For instance, the initial Na₂O is 24.2 mol.% in NH-0
whereas it ranges between 19.8 and 22.1 mol.% in the iodosodalite glass-ceramics. Such
difference could explain the increased polymerization of the glass matrix for the glass-

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ceramics. Based on the ¹¹B and ²⁷Al MAS NMR results we suggest that there is an increase in the glass polymerization that is beneficial for increasing the glass chemical durability. This is a prerequisite for the validation of a nuclear waste bearing matrix to be disposed in geological deposit for thousands of years. The link between these structural evolutions (a first insight) and the assessment of the corresponding chemical durability will be the topic of future works.

We compile the observed chemical properties (i.e. I content and N₄) in a plot as shown in Figure 6. On the left-hand side of the x scale, we placed the glass data: NH-0 and NH-3; on the right-hand side, the data for the glass-ceramics. We did not place the error bars on each point for sake of clarity. We also did not include the GC-NH-5 in this plot. We observe that there is an increase in I content and N₄ value towards GC-NH-11 sample. This sample might represent the most advanced and promising synthesis for I immobilization as it combines higher I content and higher N₄ value that is an indication of the higher chemical durability.

## 4. Summary

In the present work, we have synthesised I-bearing aluminoborosilicate glass and glass-ceramics under high-pressure conditions that are feasible industrially: 0.5 GPa. The glass-ceramics show the coexistence between iodosodalite encapsulated into a I-bearing glass matrix. We suggest that these glass-ceramics could be close to the expected material for iodine radioisotope nuclear waste immobilization with double barrier properties. The glass matrix seems to have a higher degree of polymerization and therefore higher chemical durability.

Nevertheless, additional experimental work is required so as to increase the crystalline proportion that does not exceed ~10% in the present synthesised glass-ceramics. More complex thermal history could be beneficial. Adopting this method could also improve the iodine incorporation that is currently less than 2 mol.% I.
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There is an issue on the crystallographic structure of the high-pressure iodosodalite. We suspect that the iodosodalite cages are filled not only with I⁻ species, as it is commonly thought; but also, with IO₃⁻ species on the basis of the Raman signal obtained. Further investigations are requested to assert this point; however, it requires advanced analytical methods that can probe µm-size crystals.

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### Acknowledgements

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The authors are grateful to the Agence Nationale de la Recherche, which financed the current work through the ANR project "Iodine-CLEAN-UP" (ANR-20-CE08-0018). The authors thank the Région Pays de la Loire for financing the present research through the "Trajectoire nationale de la recherche ligérienne" program. The authors thank the Laboratoire de Planétologie et Géosciences, Nantes Université and the CNRS for providing access to the analytical facilities. SEM-EDS, XRD and NMR measurements were performed using the IMN's characterization platform, PLASSMAT, Nantes, France.

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503

### References

504

505

[1] X. Chen, M. Gong, P. Yi, et al., Distribution of ¹²⁹I in terrestrial surface water environments, Nucl. Instrum. Methods Phys. Res. B 361 (2015) 604–608.

506

507

[2] A. Aldahan, V. Alfimov, G. Possnert G, ¹²⁹I anthropogenic budget: major sources and sinks, Appl. Geochem. 22 (2007) 606–618.

508

509

[3] C. Madic, M. Lecomte, P. Baron, B. Boullis, Separation of long-lived radionuclides from high active nuclear waste, CR Phys. 3 (2002) 797-811.

510

511

[4] Q. Hu, P. Zhao, J.E. Moran, J.C. Seaman, Sorption and transport of iodine species in sediments from the Savannah River and Hanford Sites, J. Cont. Hydr. 78 (2005) 185-205.
512

[5] Y. Wang, T. Guo, Y. Fan, L. Zhang, Z. Guo, P. Cheng, J. Lan, Q. Liu, X. Hou,

513

Anthropocene <sup>129</sup>I record in the Yellow Sea sediments and its indication for river-delivered

514

radioactive pollution to marginal seas, Env. Sci. Tech. 58 (2024) 12633-12642.

515

[6] J.R. Goldsmith, C.M. Grossman, W.E. Morton, R.H. Nussbaum, E.A. Kordysh, M.R.

516

Quastel, R.B. Sobel, F.D. Nussbaum, Juvenile hypothyroidism among two populations

517

exposed to radioiodine, Environ. Health Perspect. 107 (1999) 303-308.

518

[7] C.M. Grossman, R.H. Nussbaum, F.D. Nussbaum, Cancers among residents downwind of

519

the Hanford, Washington, plutonium production site, Arch. Environ. Health 58 (2003) 267-

520

274.

521

[8] V. Drozdovitch, Radiation exposure to the thyroid after the Chernobyl accident, Front.

522

Endocrinol. 994 (2021) 569041.

523

[9] R. Michel, A. Daraoui, M. Gorny, et al., Iodine-129 and iodine-127 in European seawaters

524

and in precipitation from Northern Germany, Sci. Total Environ. 419 (2012) 151-169.

525

[10] E. Englund, A. Aldahan, X.L. Hou, et al., Iodine (<sup>129</sup>I and <sup>127</sup>I) in aerosols from northern

526

Europe, Nucl. Instrum. Methods Phys. Res. B 268 (2010) 1139-1141.

527

[11] R.M. Asmussen, J. Turner, S. Chong, B.J. Riley, Review of recent developments in

528

iodine wasteform production, Front. Chem. 10 (2022) 1043653.

529

[12] H. Li, L. Wu, D. Xu, X. Wang, Y. Teng, Y. Li, Structure and chemical durability of

530

barium borosilicate glass-ceramics containing zirconolite and titanite crystalline phases, J.

531

Nuc. Mat. 466 (2015) 484-490.

532

[13] D. He, H. Zhong, C. Gao, Characteristics and dielectric properties of ZrO<sub>2</sub>-doped

533

calcium borosilicate glass-ceramics, Mat. Res. Bull. 123 (2020) 110703.
534

[14] J. McCloy, S. Schuller, Vitrification of wastes: from unwanted to controlled crystallization, a review, CR Géoscience – Sciences de la planète 354 (2022) 121–160.

535

536

[15] J. Deubener, M. Allix, M.J. Davis, A. Duran, T. Höhe, T. Honma, T. Komatsu, S. Krüger, I. Mitra, R. Müller, S. Nakane, M.J. Pascual, J.W.P. Schmelzer, E.D. Zanotto, S. Zhou, Updated definition of glass-ceramics, J. Non-Cryst. Solids 501 (2018) 3-10.

537

538

539

[16] M. Allix, L. Cormier, Crystallization and glass-ceramics, in: J.D. Musgraves, J. Hu, L. Calvez (Eds.), Springer Handbook of Glass, Springer Handbooks Cham, 2019, pp. 113–167.

540

541

[17] C. Liao, Y. Tang, C. Liu, K. Shih, F. Li, Double-Barrier mechanism for chromium immobilization: A quantitative study of crystallization and leachability, J. Hazard Mat. 311 (2016) 246-253.

542

543

544

[18] P. Loiseau, D. Caurant, N. Baffier, L. Mazerolles, C. Fillet, Glass-ceramics nuclear wastes formes obtained from SiO₂-Al₂O₃-CaO-ZrO₂-TiO₂ glasses containing lanthanides (Ce, Nd, Eu, Gd, Yb) and actinides (Th): study of internal crystallisation. J. Nuc. Mat. 335 (2004) 1432.

545

546

547

548

[19] R.D. Rawlings, J.P. Wu, A.R. Boccaccini, Glass-ceramics: Their production from wastes – A Review, J. Mater. Sci. 41 (2006) 733-761.

549

550

[20] D. Caurant, P. Loiseau, O. Majerus, V. Aubin-Chevaldonnet, I. Bardez, A. Quintas, Glasses, Glass-Ceramics and Ceramics for Immobilization of Highly Radioactive Nuclear Wastes, Nova Science Publishers, Inc., New York, 2009.

551

552

553

[21] P. Loiseau, D. Caurant, Glass-ceramic nuclear waste forms obtained by crystallization of SiO₂–Al₂O₃–CaO–ZrO₂–TiO₂ glasses containing lanthanides (Ce, Nd, Eu, Gd, Yb) and actinides (Th): Study of the crystallization from the surface, J. Nuc. Mat. 402 (2010) 38-54.

554

555
556

557

[22] M. Hassan, S. Venkatesan, H.J. Ryu, Non-volatile immobilization of iodine by the cold sintering of iodosodalite, J. Hazard Mater. 386 (2020) 121646.

558

559

[23] S. Chong, J.A. Peterson, B.J. Riley, et al., Glass-bonded iodosodalite waste form for immobilization of ¹²⁹I, J. Nuc. Mater. 504 (2018) 109–121.

560

561

[24] S. Chong, B.J. Riley, R.M. Asmussen, et al., Iodosodalite synthesis with hot isostatic pressing of precursors produced from aqueous and hydrothermal processes, J. Nuc. Mater. 538 (2020) 152222.

562

563

564

[25] V. Jolivet, Y. Morizet, M. Paris, T. Suzuki-Muresan, High pressure experimental study on iodine solution mechanisms in nuclear waste glasses, J. Nuc. Mater. 533 (2020) 152112.

565

566

[26] Y. Morizet, J. Hamon, C. La, et al., Immobilization of ¹²⁹I in nuclear waste glass matrixes synthesized under high-pressure conditions: an experimental study, J. Mater. Chem. 9 (2021) 23902–23915.

567

568

569

[27] Y. Morizet, M. Paris, J. Hamon, C. La, S. Grolleau, T. Suzuki-Muresan, Predicting iodine solubility at high pressure in borosilicate nuclear waste glasses using optical basicity: an experimental study, J. Mat. Sci. 57 (2022) 16600–16618.

570

571

572

[28] S. Soudani, M. Paris, Y. Morizet, The effect of iodine on the local environment of network-forming elements in aluminoborosilicate glasses: an NMR study, J. Am. Ceram. Soc. 107 (2024) 4557–4571.

573

574

575

[29] Y. Morizet, S. Soudani, J. Hamon, M. Paris, C. La, E. Gautron, Iodine dissolution mechanisms in high-pressure aluminoborosilicate glasses and their relationship to oxygen, J. Mat. Chem. A 11 (2023) 22891.

576
577

[30] S. Soudani, L. Le Gars, Y. Morizet, Deniard P., Gautron E., Grolleau S. (2023) High-pressure glass-ceramics for iodine nuclear waste immobilization: Preliminary experimental results. Cer. Int. 49, 30029-30038.

578

579

580

[31] B.O. Mysen, R.J. Arculus, D.H. Eggler, Solubility of carbon dioxide in melts of andesite, tholeiite, and olivine nephelinite composition to 30 kbar pressure, Contrib. Mineral. Petrol. 53 (1975) 227-239.

581

582

583

[32] G. Iacono-Marziano, Y. Morizet, E. Le Trong, F. Gaillard, New experimental data and semi-empirical parameterization of H₂O–CO₂ solubility in mafic melts, Geochim. Cosmochim. Acta 97 (2012) 1-23.

584

585

586

[33] E.M. Stolper, The speciation of water in silicate melts, Geochim. Cosmochim. Acta 46 (1982) 2609-2620.

587

588

[34] V. Jolivet, Y. Morizet, N. Trcera, V. Fernandez, T. Suzuki-Muresan, Incorporation of chlorine in nuclear waste glasses using high-pressure vitrification: Solubility, speciation, and local environment of chlorine, Am. Mineral. 108 (2023) 1032-1042.

589

590

591

[35] C.P. Rodriguez, J.S. McCloy, M.J. Schweiger, et al., Optical basicity and nepheline crystallization in high alumina glasses. US Department of Energy, Pacific Northwest National Laboratory (2011) 20184.

592

593

594

[36] J.H. Christian, K.M. Fox, E.N. Hoffman, C.C. Herman, Examining the Role of Canister Cooling Conditions on the Formation of Nepheline from Nuclear Waste Glasses. US Department of Energy, Savannah River National Laboratory (2015) 22470.

595

596

597

[37] J.S. McCloy, M.J. Schweiger, C.P. Rodriguez, J.D. Vienna, Nepheline crystallization in nuclear waste glasses: Progress toward acceptance of high-alumina formulations, Int. J. App. Gl. Sci. 2 (2011) 201-214.

598

599
600 [38] V. Jolivet, L. Jossé, M. Rivoal, M. Paris, Y. Morizet, L. Carole, T. Suzuki-Muresan, 601 Quantification of boron in aluminoborosilicate glasses using Raman and ¹¹B NMR, J. Non- 602 Cryst. Solids 511 (2019) 50-61.

603 [39] A. Altomare, C. Cuocci, C. Giacovazzo, A. Moliterni, R. Rizzi, QUALX: A computer 604 program for qualitative analysis using powder diffraction data, J. Appl. Cryst., 41 (2008) 815- 605 817.

606 [40] S. Kabekkodu, A. Dosen, T. Blanton, PDF-5+: a comprehensive Powder Diffraction 607 File™ for materials characterization, Pow. Diff. 39 (2024) 47-59.

608 [41] V. Petricek, M. Dusek, L. Palatinus, Crystallographic computing system JANA2006: 609 general features, Z. Kristallogr. 229 (2014) 345–352.

610 [42] F. Angeli, T. Charpentier, D. De Ligny, C. Cailleteau, Boron speciation in sodalime 611 borosilicate glasses containing zirconium, J. Am. Ceram. Soc. 93 (2010) 2693e2704.

612 [43] T. Charpentier, L. Martel, A.H. Mir, J. Somers, C. Jegou, S. Peuget, Self-healing 613 capacity of nuclear glass observed by NMR spectroscopy, Sci. Rep. 6 (2016) 25499.

614 [44] D. Massiot, F. Fayon, M. Capron, I. King, S. Le Calv e, B. Alonso, J.O. Durand, B. 615 Bujoli, Z. Gan, G. Hoatson, Modelling one and two-dimensional solid-state NMR spectra, 616 Magn. Reson. Chem. 40 (2002) 70-76.

617 [45] G. Czjzek, J. Fink, F. Götz, H. Schmidt, J. Coey, J.-P. Rebouillat, A. Liénard, Atomic 618 coordination and the distribution of electric field gradients in amorphous solids, Phys. Rev. B 619 23 (1981) 2513.

620 [46] J.R. Allwardt, J.F. Stebbins, B.C. Schmidt, D.J. Frost, A.C. Withers, and M.M. 621 Hirschmann, Aluminum coordination and the densification of high-pressure aluminosilicate 622 glasses. Am. Mineral. 90 (2005) 1218–1222.
623

[47] J.F. Stebbins, S. Kroeker, S.K. Lee, T. Kiczenski, Quantification of five-and six-

624

coordinated aluminum ions in aluminosilicate and fluoride containing glasses by high-field,

625

high-resolution <sup>27</sup>Al NMR. J. Non-Cryst. Solids 275 (2000) 1–6.

626

[48] D.R. Neuville, L. Cormier, V. Montouillout, P. Florian, F. Millot, J.-C. Rifflet, D.

627

Massiot, Amorphous materials: Properties, structure, and durability: Structure of Mg- and

628

Mg/Ca aluminosilicate glasses: <sup>27</sup>Al NMR and Raman spectroscopy investigations. Am.

629

Mineral. 93 (2008) 1721–1731.

630

[49] H. Trill, H. Eckert, V.I. Srdanov, Mixed halide sodalite solid solution systems.

631

Hydrothermal synthesis of an amorphous structural characterization by Solid State NMR (2003).

632

[50] H. Zhu, F. Wang, Q. Liao, Y. Zhu, Synthesis and characterization of zirconolite-sodium

633

borosilicate glass-ceramics for nuclear waste immobilization, J. Nuc. Mat. 532 (2020)

634

152026.

635

[51] B. Beagley, C. Henderson, D. Taylor, The crystal structures of aluminosilicate-sodalites:

636

X-ray diffraction studies and computer modelling. Mineral. Mag 46 (1982) 459–464.

637

[52] A. Vaitkus, A. Merkys, T. Sander, M. Quirós, P.A. Thiessen, E.E. Bolton, S. Gražulis, A

638

workflow for deriving chemical entities from crystallographic data and its application to the

639

Crystallography Open Database, J. Cheminf. 15 (2023).

640

[53] J.-C. Buhl, The properties of salt-filled sodalities. Part 4; Synthesis and heterogeneous

641

reactions of iodate-enchlathrated sodalite Na<sub>8</sub>[AlSiO<sub>4</sub>]<sub>6</sub>(IO<sub>3</sub>)<sub>2-x</sub>(OH·H<sub>2</sub>O)<sub>x</sub>; 0.7 < x < 1.3,

642

Thermochim. Acta 286 (1996) 251–262.

643

[54] B. Lafuente, R.T. Downs, H. Yang, N. Stone, The power of databases: the RRUFF

644

project. In: Highlights in Mineralogical Crystallography, T. Armbruster and R.M. Danisi, eds.

645

Berlin, Germany, W. De Gruyter, (2015) pp 1-30.
646

[55] H. Hu, S. Soudani, J. Hamon, N. Trcera, M. Paris, Y. Morizet, Multi-spectroscopic investigations for comprehensive structural analysis of aluminoborosilicate glasses: I. Integrating Raman, XPS, XAS and NMR techniques. Glass Europe (in press).

647

648

649

[56] D. Manara, A. Grandjean, O. Pinet, J. Dussossoy, D. Neuville, Sulfur behavior in silicate glasses and melts: Implications for sulfate incorporation in nuclear waste glasses as a function of alkali cation and V₂O₅ content. J. Non-Cryst. Solids 353 (2007) 12–23.

650

651

652

[57] U. Bauer, H. Behrens, M. Fechtelkord, S. Reinsch, J. Deubener, Water-and boron speciation in hydrous soda–lime–borate glasses. J. Non-Cryst. Solids 423 (2015) 58–67.

653

654

[58] M.R. Cicconi, E. Pili, L. Grousset, D.R. Neuville, The influence of glass composition on iodine solubility, MRS Adv. 4 (2019) 971–979.

655

656

[59] M.R. Cicconi, E. Pili, L. Grousset, P. Florian, J.C. Bouillard, D. Vantelon, et al., Iodine solubility and speciation in glasses, Sci. Rep. 9 (2019) 7758.

657

658

[60] J.R. Durig, O.D. Bonner, W.H. Breazeale, Raman studies of iodic acid and sodium iodate, J. Phys. Chem. 69 (1965) 3886–3892.

659

660

[61] A. Liang, R. Turnbull, D. Errandonea, A review on the advancements in the characterization of the high-pressure properties of iodates, Prog. Mater. Sci. 136 (2023) 101092.

661

662

663

[62] L.S. Du, J.F. Stebbins, Network connectivity in aluminoborosilicate glasses: a high-resolution ¹¹B, ²⁷Al and ¹⁷O NMR study, J. Non-Cryst. Solids 351 (2005) 3508–3520.

664

665

[63] L.S. Du, J.F. Stebbins, Nature of silicon-boron mixing in sodium borosilicate glasses: a high-resolution ¹¹B and ¹⁷O NMR study, J. Phys. Chem. B 107 (2003) 10063–10076.

666
[64] M.M. Smedskjaer, J.C. Mauro, R.E. Youngman, C.L. Hogue, M. Potuzak, Y. Yue, Topological principles of borosilicate glass chemistry. J. Phys. Chem. B 115 (2011) 12930–12946.

[65] S. Soudani, M. Paris, Y. Morizet, Influence of high-pressure on the short-range structure of Ca or Na aluminoborosilicate glasses from ¹¹B and ²⁷Al solid-state NMR. J. Non-Cryst. Solids 638 (2024) 123085.

[66] S. Bista, J.F. Stebbins, J. Wu, T.M. Gross, Structural changes in calcium aluminoborosilicate glasses recovered from pressures of 1.5 to 3 GPa: Interactions of two network species with coordination number increases, J. Non-Cryst. Solid. 478 (2017) 50–57.

[67] A.C. Lee, E.J. Kim, S.K. Lee, Pressure-induced structural evolution in boron bearing model rhyolitic glasses under compression: Implications for boron isotope compositions and properties of deep melts in Earth’s interior, Geochim. Cosmochim. Acta 332 (2022) 220–238.

[68] Y. Morizet, N. Trcera, T. Suzuki-Muresan, S. Soudani, E. Fonda, and M. Paris. Local environment of iodine dissolved as iodate in high-pressure aluminoborosilicate glasses: A I K-edge x-ray absorption spectroscopic study. J. Chem. Phys. 156 (2022) 154508.

Figure caption

Figure 1: SEM EDS images obtained for GC-NH-6 and GC-NH-11 at two different magnifications. There is coexistence between a glass matrix and crystals assigned to iodosodalite. Owing to the temperature gradient during the experiment, the crystals appear orientated due to possible convection during crystallization.

Figure 2: ²⁷Al MAS NMR spectra for initial starting glass NH-0, I-bearing glass NH-3 and two glass-ceramics GC-NH-4 and GC-NH-6. Whereas the glass spectra have been simulated using a single asymmetric Czjzek line corresponding to Al species in four-fold coordination;
690 the glass-ceramic spectra are simulated using two asymmetric lines to account for the
691 presence of iodosodalite crystals. The proportion of iodosodalite is indicated.

692 Figure 3: X-ray diffractogram obtained on several glass-ceramics powders. The Rietveld
693 refinement of the structure is shown in black and the residual from the difference in blue. The
694 derived lattice parameter of the cubic iodosodalite is also indicated.

695 Figure 4: Raman mapping obtained for GC-NH-5 (A), GC-NH-4 (B) and GC-NH-11 (C). The
696 map has been obtained using the ratio between peak intensities. We choose to represent the
697 ratio between 300-500 cm⁻¹ and 1350-1600 cm⁻¹. Individual spectra have been selected to
698 represent the glass matrix, the iodosodalite and also the nepheline in GC-NH-5. We also tried
699 to compare the obtained spectra with available spectra from the RRUFF database for
700 nepheline (R040025), sodalite (R06416) and also with a iodosodalite spectrum taken from
701 Soudani et al.³⁰. It should be pointed out that the iodosodalite spectra are different in between
702 GC-NH-4 and GC-NH-11.

703 Figure 5: ¹¹B MAS NMR spectra obtained on initial glass NH-0, I-bearing glass NH-3 and
704 two glass-ceramics GC-NH-4 and GC-NH-6 loaded with I₂ and I₂O₅, respectively. The
705 different spectra have been fitted with one Gaussian line for BO₄ units at ~0 ppm and two
706 asymmetric lines for BO₃ units at ~18 and ~12 ppm. The N₄ corresponds to the proportion of
707 BO₄ units over total boron species and is reported next to each spectrum.

708 Figure 6: I content in mol.% and N₄ obtained for the investigated glass and glass-ceramics.
709 The error bars are not represented for clarity.

710
<table><caption>712 Table 1: Experimental conditions, major element concentrations, analytical results.</caption><thead><tr><th rowspan="2">Samp<br>le</th><th rowspan="2">Initial I<br>(mol.%)</th><th rowspan="2">Cooling<br>rate<br>(°C/min)</th><th colspan="6">Glass matrix composition (mol.%)</th><th colspan="6">Iodosodalite composition</th><th rowspan="2">I<sup>tot</sup></th><th rowspan="2">Cryst.<br>Phases<sup>e</sup></th><th rowspan="2">Latt.<br>Par.<br>(Å)<sup>f</sup></th><th colspan="2">SEM<br>EDS</th><th colspan="2">NMR</th></tr><tr><th>SiO<sub>2</sub></th><th>Al<sub>2</sub>O<sub>3</sub></th><th>B<sub>2</sub>O<sub>3</sub></th><th>CaO</th><th>Na<sub>2</sub>O</th><th>I</th><th>SiO<sub>2</sub></th><th>Al<sub>2</sub>O<sub>3</sub></th><th>CaO</th><th>Na<sub>2</sub>O</th><th>I</th><th>%Gl<br>ass</th><th>N<br>4</th><th>%<br>Gla<br>ss</th></tr></thead><tbody><tr><td>NH<br>-0<sup>a</sup></td><td>0</td><td></td><td>43.<br>1</td><td>9.5</td><td>15.<br>1</td><td>8.<br>0</td><td>24.<br>2</td><td></td><td></td><td></td><td></td><td></td><td>0</td><td>Gl.</td><td></td><td>100</td><td>4<br>0<br>0</td><td>100</td></tr><tr><td>NH<br>-3<sup>b</sup></td><td>5<br>4</td><td>I<sub>2</sub></td><td>45.<br>0(3)</td><td>10.<br>2(2)</td><td>13.<br>7(1)</td><td>7.<br>8(2)</td><td>22.<br>3(2)</td><td>1.<br>0(1)</td><td></td><td></td><td></td><td>1.<br>0(1)</td><td>Gl.</td><td></td><td>100</td><td>3<br>9</td><td>100</td></tr><tr><td>GC</td><td>7</td><td></td><td>47.<br>3(2)</td><td>8.4<br>(4)</td><td>15.<br>1</td><td>8.<br>5(3)</td><td>20.<br>8(2)</td><td>0.<br>1(0)</td><td>45.<br>4(1)</td><td>15.<br>4(5)</td><td>3.<br>4(7)</td><td>27.<br>3(1)</td><td>8.6<br>(10)</td><td>1.<br>2(1)</td><td>Gl.+IS+<br>NaI</td><td>9.0<br>06(1)</td><td>86.8<br>(1.3)</td><td>0.<br>4<br>3</td></tr><tr><td>NH<br>-1<sup>c</sup></td><td>6</td><td>I<sub>2</sub></td><td>20</td><td>2(2)</td><td>1</td><td>3(3)</td><td>8(8)</td><td>0(0)</td><td>4(4)</td><td>7(1)<br>7(2)</td><td>6(5)<br>6(3)</td><td>8(8)</td><td>3(2)<br>6(0)</td><td>1.<br>0(1)</td><td>Gl.+IS</td><td>9.0<br>06(1)</td><td>85.7<br>(0.9)</td><td>0.<br>4<br>8</td></tr><tr><td>GC</td><td>8</td><td></td><td>47.<br>3(4)</td><td>8.5<br>(1)</td><td>15.<br>1</td><td>8.<br>7(1)</td><td>20.<br>2(3)</td><td>0.<br>2(0)</td><td>51.<br>7(7)</td><td>14.<br>7(1)</td><td>4.<br>7(2)</td><td>20.<br>6(6)</td><td>8.7<br>(4)</td><td>1.<br>0(1)</td><td>Gl.+IS+<br>Neph.</td><td>9.0<br>14(1)</td><td>81.8<br>(1.3)</td><td>0.<br>3<br>1</td></tr><tr><td>NH<br>-4</td><td>9</td><td>I<sub>2</sub></td><td>20</td><td>20</td><td>1</td><td>2(2)</td><td>19.<br>2(2)</td><td>0(1)</td><td>49.<br>1(2)</td><td>18.<br>1(2)</td><td>5.<br>4(1)</td><td>21.<br>2(2)</td><td>6.3<br>4(6)</td><td>1.<br>4(6)</td><td>Gl.+IS+<br>Neph.</td><td>9.0<br>07(2)</td><td>89.7<br>(0.6)</td><td>0.<br>4<br>8</td></tr><tr><td>GC</td><td>3</td><td>I<sub>2</sub>+<br>Al<sub>2</sub>O<sub>3</sub></td><td>20</td><td>44.<br>0(1)</td><td>13.<br>9(1)</td><td>15.<br>1</td><td>7.<br>8(0)</td><td>19.<br>2(2)</td><td>0.<br>1(1)</td><td>48.<br>1(2)</td><td>18.<br>4(1)</td><td>19.<br>2(2)</td><td>13.<br>5(1)</td><td>1.<br>5(1)</td><td>Gl.+IS</td><td>9.0<br>06(1)</td><td>83.2<br>(10.5)</td><td>0.<br>4<br>7</td></tr><tr><td>NH<br>-5<sup>d</sup></td><td>7</td><td>I<sub>2</sub>O<sub>5</sub></td><td>20</td><td>7(1)</td><td>8.5<br>(1)</td><td>15.<br>1</td><td>8.<br>6(1)</td><td>19.<br>8(1)</td><td>0.<br>4(1)</td><td>48.<br>1(2)</td><td>18.<br>0(0)</td><td>1.<br>8(8)</td><td>13.<br>5(1)</td><td>1.<br>1(1)</td><td>Gl.+IS</td><td>9.0<br>06(1)</td><td>83.2<br>(10.5)</td><td>0.<br>4<br>7</td></tr><tr><td>GC</td><td>5</td><td></td><td>46.<br>9(1)</td><td>8.3<br>(1)</td><td>15.<br>1</td><td>8.<br>5(1)</td><td>21.<br>1(2)</td><td>0.<br>1(1)</td><td>45.<br>9(8)</td><td>17.<br>2(4)</td><td>1.<br>5(5)</td><td>23.<br>3(4)</td><td>12.<br>1(7)</td><td>1.<br>1(1)</td><td>Gl.+IS+<br>NaPt<sub>3</sub>O<sub>4</sub></td><td>9.0<br>03(1)</td><td>88.3<br>(0.7)</td><td>0.<br>5<br>3</td></tr><tr><td>NH<br>-6</td><td>7</td><td>I<sub>2</sub>O<sub>5</sub></td><td>20</td><td>7(1)</td><td>8.5<br>(1)</td><td>15.<br>1</td><td>8.<br>6(1)</td><td>19.<br>8(1)</td><td>0.<br>4(1)</td><td>48.<br>1(2)</td><td>18.<br>0(0)</td><td>0.<br>8(8)</td><td>23.<br>9(1)</td><td>12.<br>9(5)</td><td>1.<br>8(1)</td><td>Gl.+IS+<br>NaPt<sub>3</sub>O<sub>4</sub></td><td>9.0<br>03(1)</td><td>88.3<br>(0.7)</td><td>0.<br>5<br>3</td></tr><tr><td>GC</td><td>4</td><td></td><td>46.<br>9(1)</td><td>8.3<br>(1)</td><td>15.<br>1</td><td>8.<br>5(1)</td><td>21.<br>1(2)</td><td>0.<br>1(1)</td><td>45.<br>9(8)</td><td>17.<br>2(4)</td><td>1.<br>5(5)</td><td>23.<br>3(4)</td><td>12.<br>1(7)</td><td>1.<br>1(1)</td><td>Gl.+IS+<br>NaPt<sub>3</sub>O<sub>4</sub></td><td>9.0<br>03(1)</td><td>88.3<br>(0.7)</td><td>0.<br>5<br>3</td></tr><tr><td>NH<br>-8</td><td>5</td><td>I<sub>2</sub></td><td>10</td><td>9(1)</td><td>8.0<br>(1)</td><td>15.<br>1</td><td>8.<br>4(1)</td><td>22.<br>1(1)</td><td>0.<br>5(1)</td><td>44.<br>7(1)</td><td>18.<br>2(5)</td><td>0.<br>4(4)</td><td>23.<br>9(1)</td><td>12.<br>9(5)</td><td>1.<br>8(1)</td><td>Gl.+IS+<br>NaPt<sub>3</sub>O<sub>4</sub></td><td>9.0<br>03(1)</td><td>88.3<br>(0.7)</td><td>0.<br>5<br>3</td></tr><tr><td>GC</td><td>3</td><td></td><td>45.<br>9(3)</td><td>8.0<br>(1)</td><td>15.<br>1</td><td>8.<br>4(1)</td><td>22.<br>1(1)</td><td>0.<br>5(1)</td><td>44.<br>7(1)</td><td>18.<br>2(5)</td><td>0.<br>4(4)</td><td>23.<br>9(1)</td><td>12.<br>9(5)</td><td>1.<br>8(1)</td><td>Gl.+IS+<br>NaPt<sub>3</sub>O<sub>4</sub></td><td>9.0<br>03(1)</td><td>88.3<br>(0.7)</td><td>0.<br>5<br>3</td></tr><tr><td>NH<br>-11</td><td>5</td><td>I<sub>2</sub>O<sub>5</sub></td><td>3</td><td>9(3)</td><td>8.0<br>(1)</td><td>15.<br>1</td><td>8.<br>4(1)</td><td>22.<br>1(1)</td><td>0.<br>5(1)</td><td>44.<br>7(1)</td><td>18.<br>2(5)</td><td>0.<br>4(4)</td><td>23.<br>9(1)</td><td>12.<br>9(5)</td><td>1.<br>8(1)</td><td>Gl.+IS+<br>NaPt<sub>3</sub>O<sub>4</sub></td><td>9.0<br>03(1)</td><td>88.3<br>(0.7)</td><td>0.<br>5<br>3</td></tr></tbody></table>

713 a The initial glass composition has not been analysed considering that volatilization of elements was not expected with the adopted experimental protocol. The reported mol.% B₂O₃ has been used for all glass-ceramics samples.

716 b The NH-3 is a pure I-bearing glass synthesised at 1250°C. The mol.% B₂O₃ has been determined from Laser Ablation Inductively Coupled Plasma Mass Spectrometry.

718 c The GC-NH-1 is the only sample in the present study for which a thermal dwell at nucleation temperature has been used: Tn = 594°C.

720 d A small amount of Al₂O₃ (+5 mol.%) has been added.

721 e Crystalline phases determined from XRD analysis: Gl., glass; IS, iodosodalite; Neph., nepheline; NaI and NaPt₃O₄.

723 f The crystal lattice parameter in Å is the one determined for iodosodalite crystalline phase and obtained from Rietveld refinement of the diffractograms.
<figure><img src="image_2.png" /></figure>

727

728 Figure 1

729
<figure><img src="image_3.png" /><figcaption>Figure 2</figcaption></figure>
<figure><img src="image_4.png" /></figure>

734

<figure><img src="image_5.png" /></figure>

735

736 Figure 3
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /><figcaption>Figure 4</figcaption></figure>
<figure><img src="image_9.png" /></figure>

745

746 Figure 5

747
<figure><img src="image_10.png" /><figcaption>Figure 6</figcaption></figure>

749

750

751

752

753