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Hirokazu Masai, [Shinji Kohara](https://orcid.org/0000-0001-9596-2680), Toru Wakihara, Yuki Shibazaki, [Yohei Onodera](https://orcid.org/0000-0002-3080-6991), Atsunobu Masuno, Sohei Sukenaga, Koji Ohara, Yuki Sakai, Julien Haines, Claire Levelut, Philippe Hébert, Aude Isambert, David A. Keen, Masaki Azuma

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[Siliceous zeolite-derived topology of amorphous silica](https://mdr.nims.go.jp/datasets/e2ecd098-24aa-4099-b335-16e3eaa44316)

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Siliceous zeolite-derived topology of amorphous silicaARTICLESiliceous zeolite-derived topology ofamorphous silicaHirokazu Masai 1✉, Shinji Kohara 2✉, Toru Wakihara3, Yuki Shibazaki4, Yohei Onodera 5,15,Atsunobu Masuno 6, Sohei Sukenaga7, Koji Ohara 8,16, Yuki Sakai 9,10, Julien Haines 11, Claire Levelut12,Philippe Hébert13, Aude Isambert 13,17, David A. Keen 14 & Masaki Azuma 9,10The topology of amorphous materials can be affected by mechanical forces during com-pression or milling, which can induce material densification. Here, we show that densifiedamorphous silica (SiO2) fabricated by cold compression of siliceous zeolite (SZ) is perma-nently densified, unlike densified glassy SiO2 (GS) fabricated by cold compression althoughthe X-ray diffraction data and density of the former are identical to those of the latter.Moreover, the topology of the densified amorphous SiO2 fabricated from SZ retains that ofcrystalline SZ, whereas the densified GS relaxes to pristine GS after thermal annealing. Theseresults indicate that it is possible to design new functional amorphous materials by tuning thetopology of the initial zeolitic crystalline phases.https://doi.org/10.1038/s42004-023-01075-1 OPEN1 Department of Materials and Chemistry, National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577,Japan. 2 Center for Basic Research on Materials, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan. 3 Institute ofEngineering Innovation, The University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-8656, Japan. 4 Photon Factory, Institute of Materials Structure Science,High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan. 5 Institute for Integrated Radiation and Nuclear Science,Kyoto University, 2-1010 Asashiro-nishi, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan. 6 Graduate School of Engineering, Kyoto University,Kyotodaigaku-katsura, Nishikyo-ku, Kyoto 615-8520, Japan. 7 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan. 8 Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), Kouto, Sayo-cho, Hyogo 679-5198,Japan. 9 Kanagawa Institute of Industrial Science and Technology (KISTEC), 705-1 Shimoimaizumi, Ebina, Kanagawa 243-0435, Japan. 10 Laboratory forMaterials and Structures, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama, Kanagawa 226-8503, Japan. 11 Institut Charles Gerhardt Montpellier,CNRS, Université de Montpellier, ENSCM, 34293 Cedex 5 Montpellier, France. 12 Laboratoire Charles Coulomb, CNRS, Université de Montpellier, 34095Montpellier, France. 13 CEA, DAM Le Ripault, F-37260 Monts, France. 14 ISIS Facility, Rutherford Appleton Laboratory, Harwell Campus, Didcot, OxfordshireOX11 0QX, UK. 15Present address: Center for Basic Research on Materials, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047,Japan. 16Present address: Faculty Materials for Energy, Shimane University, 1060 Nishikawatsu-cho, Matsue, Shimane 690-8504, Japan. 17Present address:Institut de Physique du Globe de Paris (IPGP), Université Paris Cité, Paris, France. ✉email: hirokazu.masai@aist.go.jp; KOHARA.Shinji@nims.go.jpCOMMUNICATIONS CHEMISTRY |           (2023) 6:269 | https://doi.org/10.1038/s42004-023-01075-1 | www.nature.com/commschem 11234567890():,;http://crossmark.crossref.org/dialog/?doi=10.1038/s42004-023-01075-1&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s42004-023-01075-1&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s42004-023-01075-1&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s42004-023-01075-1&domain=pdfhttp://orcid.org/0000-0003-2310-733Xhttp://orcid.org/0000-0003-2310-733Xhttp://orcid.org/0000-0003-2310-733Xhttp://orcid.org/0000-0003-2310-733Xhttp://orcid.org/0000-0003-2310-733Xhttp://orcid.org/0000-0001-9596-2680http://orcid.org/0000-0001-9596-2680http://orcid.org/0000-0001-9596-2680http://orcid.org/0000-0001-9596-2680http://orcid.org/0000-0001-9596-2680http://orcid.org/0000-0002-3080-6991http://orcid.org/0000-0002-3080-6991http://orcid.org/0000-0002-3080-6991http://orcid.org/0000-0002-3080-6991http://orcid.org/0000-0002-3080-6991http://orcid.org/0000-0003-0667-9782http://orcid.org/0000-0003-0667-9782http://orcid.org/0000-0003-0667-9782http://orcid.org/0000-0003-0667-9782http://orcid.org/0000-0003-0667-9782http://orcid.org/0000-0002-3134-512Xhttp://orcid.org/0000-0002-3134-512Xhttp://orcid.org/0000-0002-3134-512Xhttp://orcid.org/0000-0002-3134-512Xhttp://orcid.org/0000-0002-3134-512Xhttp://orcid.org/0000-0002-8427-4740http://orcid.org/0000-0002-8427-4740http://orcid.org/0000-0002-8427-4740http://orcid.org/0000-0002-8427-4740http://orcid.org/0000-0002-8427-4740http://orcid.org/0000-0002-7030-3213http://orcid.org/0000-0002-7030-3213http://orcid.org/0000-0002-7030-3213http://orcid.org/0000-0002-7030-3213http://orcid.org/0000-0002-7030-3213http://orcid.org/0009-0004-4720-4059http://orcid.org/0009-0004-4720-4059http://orcid.org/0009-0004-4720-4059http://orcid.org/0009-0004-4720-4059http://orcid.org/0009-0004-4720-4059http://orcid.org/0000-0003-0376-2767http://orcid.org/0000-0003-0376-2767http://orcid.org/0000-0003-0376-2767http://orcid.org/0000-0003-0376-2767http://orcid.org/0000-0003-0376-2767http://orcid.org/0000-0002-8378-321Xhttp://orcid.org/0000-0002-8378-321Xhttp://orcid.org/0000-0002-8378-321Xhttp://orcid.org/0000-0002-8378-321Xhttp://orcid.org/0000-0002-8378-321Xmailto:hirokazu.masai@aist.go.jpmailto:KOHARA.Shinji@nims.go.jpwww.nature.com/commschemwww.nature.com/commschemThe properties of solid-state materials are significantlyaffected by their preparation conditions and chemicalcompositions. Polymorphisms in crystalline materials withthe same chemical composition have been investigated usingvarious approaches1–4. In contrast, in non-equilibrium materials,such as glasses, in which various metastable structures exist,structural relaxation by external stimuli is one of the mostinteresting topics from both scientific and industrial perspectives.This metastability is one of the challenging factors for thestructural analysis of glass5.Non-equilibrium oxide materials, such as glasses and zeolites,possess nanosized cavities that are specific to their functions. Inmaterials with such large cavities, thermodynamically metastablestructures can be formed semipermanently or transiently byapplying a much higher pressure than the ambient pressure whilesimultaneously heating6–20. Densified samples fabricated at highpressures exhibit completely different functions from those fab-ricated under ambient pressure. Greaves et al. predicted that thesemicroporous materials could approach the “perfect” glass com-pressed sufficiently slowly6. Densified glassy silica (GS) is tenta-tively proposed as an example of a high-pressure-induceddensified material because pristine GS possesses large cavitiessurrounded by –Si–O–Si– rings of varying sizes. Recently,experimental and mathematical approaches have been combinedto investigate the behaviours of rings and cavities in amorphousmaterials19–22. Owing to their varied rings and cavities, oxidematerials containing many oxygen atoms with lone-pair electronsare interesting materials for study.From a material densification perspective, zeolites with theiropen-structured micropores are also interesting targets for con-trollable cavities1,2,23–30. Approximately 260 different zeolitestructures are known, ranging from those with one-dimensionalchannels to those with three-dimensional pores, a number ofwhich are smaller than 1 nm. Zeolites provide another route forpreparing distinct amorphous materials via pressure-inducedamorphization. Haines et al. reported the densification of amor-phous SiO2 by pressurising a single crystal of siliceous MFI zeolite(SZ) to 20 GPa at room temperature (RT) (i.e. coldcompression17–19,31). The Bragg peaks from the SZ disappearedand broad peaks corresponding to amorphous were observed.However, Onodera et al. reported that the density of densified GSprepared by cold compression decreased over time, i.e. glassprepared by cold compression was not permanently densified19.Considering that they used GS as the starting material, it isunclear whether permanent densification could be achieved in theamorphous SiO2 prepared from SZ. We also investigated whetherdifferent topologies of SZ could be obtained via ball milling.Mechanical milling is sometimes used to prepare reactive ceramicpowders, such as oxides, sulfides, and chalcogenides32,33. Theball-milling process is expected to break the cages in the SZ,producing more reactive fragments. This study analysed amor-phous SiO2 and SZ to clarify the relationship between the startingmaterials and the glass structures.Results and discussionPreservation of cage structure in SZ-derived amorphous SiO2.Figure 1a shows the X-ray powder diffraction pattern of amorphousSiO2 from SZ, prepared by applying 20GPa and 7.7 GPa at RT, alongwith previous data reported for densified GS19 and the densifiedamorphous SZ prepared from SZ single crystals31. All data, except forthose of the reference materials (pristine GS and pristine SZ), wereacquired from the samples recovered after densification. The struc-ture factor S(k) of various amorphous materials differs depending onthe preparation conditions. This study focused on the first sharpdiffraction peak (FSDP), which is referred to as k1 and observed atk ~ 1.53 Å–1 in the diffraction pattern of pristine GS (Fig. 1b). TheFSDP, a signature of intermediate-range ordering in glass, shifts to ahigher-k value upon applying pressure, suggesting that the inter-mediate correlation distances decrease with the reduction in cavityvolume. In addition, a pre-peak is observed at k ~ 0.63 Å–1 in allsamples obtained from SZs, and the peak height decreases withincreasing pressure. This peak can be referred to as k0 because theFSDP at a higher-k value is typically referred to as k1 and the secondprincipal peak is called k234. The k2 peak is only visible in the neutrondiffraction data (Fig. S1) because k2 reflects the packing of oxygenatoms, and relative to silicon, oxygen scatters neutrons better than itscatters X-rays35. Notably, the k0 peak was not observed for the GS orthe densified GS. Table 1 summarises the starting materials, fabri-cation conditions, densities, and coherence lengths estimated fromdiffraction peaks. The density ρ was measured using a He pycn-ometer or by the analysis of the slope of reduced pair distributionfunctions G(r) using the equation ρ= 14π∂GðrÞ∂r , where r is a length.These results clearly indicate that the structures of the densifiedGS and amorphous SiO2 prepared from the SZ are different. Thek value of the k0 peak has similar k value as that observed for thestrong Bragg peaks in the X-ray diffraction pattern of the pristineSZ, implying that the topology of the crystalline starting materialcan be preserved in the amorphous material even after high-pressure treatment. An illustration of the SZ, highlighted by the(101) and (020) planes, is presented in Fig. S2. Notably, the heightof k0 increased with k1. Therefore, it is expected that amorphousSiO2 with different topologies can be obtained by selectingappropriate starting materials.Permanent densification and relaxation of SZ-derived amor-phous SiO2. Because compression was performed at ambienttemperature, it is expected that the long-term thermal stability isalso affected by the topology of the samples. To analyse thethermal stability after densification, i.e. the permanency of den-sification, we measured the diffraction data from the same sam-ples after long delays. Figure 2a, b compares the S(k) values ofamorphous SiO2 prepared by cold compression after 11 and 2years, respectively. Note that the former was obtained from bulkSZ (bSZ) single crystals with typical maximum linear dimensionsof 25–80 µm and the latter from a SZ powder (pSZ) with micro-sized grains. Although the two sets of data are similar, thestructures of the samples depend on the starting material. Fig-ure 2c, d shows an enlarged portion of S(k) from amorphous SiO2and the differential S(k) and ΔS(k) values of bSZ and pSZ. ΔS(k) isthe difference in S(k) between the as-prepared sample and thesame sample after an extended period. The positions of the FSDPand the peak at k3 are indicated by the dashed lines in Fig. 2c, d.The amorphous SiO2 from bSZ was very stable and showed noremarkable difference in the diffraction pattern after 11 years (i.e.there was no peak shift in Fig. 2c). In contrast, shifts in FSDP andk3 were observed for pSZ even after 2 years (Fig. 2d). The k valueof FSDP decreased, whereas that of k3 increased. This behaviouris comparable to that of S(k) in pristine GS and densifiedamorphous SiO2 as shown in Fig. 1. It is clear that ΔS(k), asshown in Fig. 2d, corresponds to the structural relaxation of thedensified amorphous SiO2 to pristine GS. Hence, we can concludethat bSZ-derived amorphous SiO2 was permanently densified,whereas the amorphous SiO2 from pSZ was not. Considering thatGS densified from bulk GS exhibits permanent densificationbehaviour with thermal treatment19, we assume that singlecrystals are an important starting point for sustaining permanentdensification via cold compression. Monolithic materials areexpected to be advantageous for efficient densification becausethey do not require energy to remove grain boundaries or defects.ARTICLE COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-023-01075-12 COMMUNICATIONS CHEMISTRY |           (2023) 6:269 | https://doi.org/10.1038/s42004-023-01075-1 | www.nature.com/commschemwww.nature.com/commschemThe mechanism of permanent densification has recently beendiscussed in terms of the topology19. It has been suggested thatboth ring size distribution and cavity volume are correlated withdensification19. The ring-size distributions for a series of SZs andGS, calculated based on King’s criterion36, are shown in Fig. 3.The GS data show a variation in the ring size that is topologicallydisordered21,22; however, the SZ data have a large fraction of five-fold rings, which is not representative of topological disorders.Notably, the ring size distributions of both SZ and GS subjectedto cold compression at 20 GPa were similar to those of theirrespective compounds at ambient pressure. The GS results seemto conflict with previous results for densified SiO2 glass18.However, although the definition of an n-membered ring and thesimulation method used in the present study are different fromthe previous study, we assume that it is difficult to conclude that aremarkable difference in the ring size distribution is observed bythe cold compression of the GS.We also visualised the cavities (highlighted in green) in the SZ andGS, as shown in Fig. 3. The cavity volume ratio (CVR) of pristine GSwas 33 vol% at 0 GPa22. The CVR was highest for pristine SZ at 0GPa and lowest for amorphous SiO2 prepared by cold compressionat 20 GPa. Furthermore, when comparing the samples prepared bycold compression at 20GPa, the CVR of the GS is larger than that ofamorphous SiO2 from SZ by 3.8%. We suggest that the small fractionof cavities in amorphous SiO2 prepared by cold compression of SZ at20GPa is associated with the persistence of a large fraction of five-fold rings and that this is an important signature of permanentdensification induced by both atomistic and topological order.Here, we emphasise that permanent densification is onlyobserved in amorphous SiO2 obtained by the cold compression ofbulk crystalline siliceous zeolite (bSZ). Because permanentdensification was not achieved by cold compression of GS19 orpSZ, it is expected that, in general, heating is important forpermanent densification. The effects of temperature on compres-sion of SiO2 have been reported previous studies18,19,37,38. Inaddition to the compression of silica glass18,19,37,38 relaxation ofdensified silica glass by thermal annealing has also beenreported38,39. This expectation also raises the question of whetherpermanent densification persists even after annealing. To confirmthe thermal stability of the densified samples, we heated cold-compressed bSZ to 750 °C. The effect of thermal annealing on S(k)was apparent, as shown in Fig. 4a, b. As seen in Fig. 4b, the S(k) ofannealed amorphous SiO2 is not identical to that of pristine GSbelow 6 Å−1; there are differences in the FSDP heights and in thelow-k (small-angle) region below 1 Å–1. Notably, the tiny sharpdiffraction peaks in amorphous SiO2 diminished after annealing at750 °C, indicating that they were associated with SZ rather thanimpurities. Intriguingly, the GS densified by cold compression wasconverted into pristine GS using the same annealing process(Fig. S3). The recovered stishovite also became amorphous uponheating40. The change in S(k) after annealing clearly demonstratesthat permanent densification is maintained only at ambienttemperatures, and that another metastable structure (topology) ofdensified amorphous SiO2 is generated by thermal treatment. Sucha transformation (relaxation) has also been observed in otherpapers38,39, in which the saturation behaviour was dependent onthe annealing temperature. Elucidating the key structural detailsnecessary for maintaining a metastable densified SiO4 network isthe next goal for distinguishing between thermally metastable andreversible SiO4 networks.S(k)(101)(020)S(k)Pristine SZPristine GSC20-bSZ31C20-GS19bak0 k1k0 k1C20-pSZC7.7-pSZPristine SZPristine GSC20-bSZ31C20-GS19C20-pSZC7.7-pSZFig. 1 Comparison of X-ray diffraction data. a Total structure factors, S(k), of amorphous SiO2 materials prepared by cold compressions: pristine glassySiO2 (GS), densified GS after cold compression with 20 GPa (C20-GS), densified amorphous SiO2 from bulk crystal siliceous zeolite after cold compressionwith 20 GPa (C20-bSZ), densified amorphous SiO2 obtained from siliceous zeolite powder by 7.7 GPa and 20 GPa cold compression (C7.7-pSZ and C20-pSZ, respectively); the dashed lines indicate the position of the scattering vector for k0 and k1 in GS without densification. b Enlarged S(k) in the FSDPregion of amorphous SiO2.Table 1 Structural parameters of amorphous SiO2 (all densified samples are synthesised by cold compression).ID Starting material Press condition Density (g cm−3) k0 (Å−1) k1 (Å−1) 2π/k0 (Å) 2π/k1 (Å)Pristine GS Glassy SiO2 NA 2.2 − 1.53 − 4.12C20-GS Glassy SiO219 20 GPa 2.7 − 1.85 − 3.40C20-bSZ Bulk siliceous zeolite31 20 GPa 2.7 0.7 1.83 8.97 3.44C20-pSZ Siliceous zeolite powder 20 GPa 2.3 0.63 1.77 9.94 3.56C7.7-pSZ Siliceous zeolite powder 7.7 GPa 2.1 0.63 1.66 9.94 3.79COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-023-01075-1 ARTICLECOMMUNICATIONS CHEMISTRY |           (2023) 6:269 | https://doi.org/10.1038/s42004-023-01075-1 | www.nature.com/commschem 3www.nature.com/commschemwww.nature.com/commschemEffect of ball-milling on the structure of SZ. Figure 5a shows theS(k) values of the pristine SZ and ball-milled (BM) pSZ. Thesharp Bragg peaks from the crystalline structure of the SZ dis-appeared after ball milling, indicating amorphization. In thediffraction pattern of the BM-SZ, the FSDP is at k= 1.65 Å−1,which is similar to the position of a peak observed for amorphousSiO2 obtained by a compression at 7.7 GPa and RT. Also, a broadpeak at k= 5 Å−1, which is conventionally attributed to k322 inpristine GS, is observed. Notably, the scattering intensityincreased remarkably compared to that of pristine GS in the low-k region as a result of sample grinding. We also note that theBragg peaks observed at k ~ 0.6 Å−1, which are associated withthe zeolite cage in crystalline SZ, remarkably diminish in the BM-sample but do not completely disappear, suggesting that the cagebreakdown is incomplete. Considering that the k0 peak has thesame k value as the Bragg peaks, it is expected that the samplepartially retains its crystallinity, although the cage structureappears to be much more disordered because of the lack oftranslational periodicity. Figure 5b, c shows the 29Si magic anglespinning (MAS) NMR spectra of the SZs before and after ball-milling, respectively. As indicated by dashed lines, each silicateQn unit was separated by peak deconvolution. In the case of SZbefore the treatment, the Q4 peak observed at −110 ppm wasasymmetric41–44. The chemical shift of the Q4 peak in 29Si MASNMR changes depending on the Si–O interatomic distance r andρ (=cosθ/(1−cosθ)) determined by the Si–O–Si bond angle θ44,45.Because the G(r) of SZ exhibits a Si–O correlation represented bya single normal distribution similar to that of another zeolite46,the asymmetry of the Q4 peak in the MAS NMR spectrum shouldarise from the presence of sites in the SZ with different couplingangles. The fitting parameters for the materials used to analysethe G(r) and 29Si NMR spectra are listed in Tables S1 and S2,respectively. By calculating each Qn area, each Qn fraction isquantified by calculating its area. These data are presented inTable 2. Data for SiO2 (Fig. S4), and SZ without BM treatment47were also included for comparison. Notably, the Q4 peak at ahigher magnetic field in the SZ disappears after ball milling.Considering the S(k) and Q4 peaks of the sample after ball-milling(Table S2), the Q4 species at a higher magnetic field can beassigned to a silicate unit that contributes to the cage structure.Figure 5d shows the S(k) values of BM-pSZ and cold-compressedamorphous SiO2 from BM-pSZ by applying a pressure of 20 GPaand RT. S(k) of pristine GS is also shown for comparison.Although FSDP and k3 peaks were observed for amorphous SiO2,both peak heights were lower than those of pristine GS. The S(k)profiles of BM-SZ and the densified BM amorphous SiO2 aresimilar to that of pristine GS at k > 3 Å–1, suggesting that theshort-range structure of BM-SZ is also similar to that of amor-phous SiO2. Notably, a significant difference is observed in thelow-k region. Although the height of the small-angle scatteringpeak below k ~ 1 Å−1 in the milling-induced amorphous SZsample decreases after densification, it does not completely dis-appear. Figure 5e shows G(r) for all samples. The densities of ball-milled samples were estimated from the slope of the dotted linesusing ρ= 14π∂GðrÞ∂r (see Fig. S5 for details). We found that thedensity of the ball-milled amorphized SZ (2.2 g cm−3) is higherthan that of pristine SZ (1.6 g cm−3) and comparable to that ofGS (2.2 g cm−3). After cold compression at 20 GPa, the density ofthe ball-milled amorphized SZ increases (2.4 g cm−3). Based onthese density values, we suggest that densification occurs throughthe collapse of zeolite pores following the breaking of the SZ cageduring ball milling.1.61.20.80.41.61.20.80.42.01.51.00.50.0201510502.01.51.00.50.020151050S(k)S(k)S(k)badcC20-bSZC20-bSZ after 11 years S(k)ΔS(k)ΔS(k)Pristine SZ Pristine SZk1 k3 k1 k3S(k)S(k)C20-pSZC20-pSZ after 2 years C20-bSZ C20-pSZC20-pSZ after 2 years C20-bSZ after 11 years Fig. 2 X-ray diffraction data showing the time-dependent variation of densified amorphous SiO2. a Total structure factors, S(k), of densified amorphousSiO2 prepared by 20 GPa-cold compressions obtained from bulk crystal siliceous zeolite (C20-bSZ). b Total structure factors, S(k), of densified amorphousSiO2 prepared by 20 GPa-cold compressions obtained from siliceous zeolite powder (C20-pSZ). c, d Enlarged S(k) of amorphous SiO2 and differential S(k)between the as-prepared sample and the same sample after the stated elapsed time; the dashed lines indicate the positions of the k1 (FSDP) and k3.ARTICLE COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-023-01075-14 COMMUNICATIONS CHEMISTRY |           (2023) 6:269 | https://doi.org/10.1038/s42004-023-01075-1 | www.nature.com/commschemwww.nature.com/commschemFraction Pristine SZCVR=39%d=1.6 g cm–3Fraction Pristine GSCVR=33%d=2.2 g cm–3Fraction C20-bSZCVR=6.1%d=2.7 g cm–3n-fold ringFraction C20-GSCVR=9.9%d=2.7 g cm–3abcdFig. 3 Topology of amorphous SiO2 derived from siliceous zeolite (SZ) and glassy SiO2 (GS). a n-fold ring distribution of pristine SZ, b densifiedamorphous SiO2 after cold compression with 20 GPa (C20-bSZ), c pristine GS, and d densified GS after cold compression with 20 GPa (C20-GS). Theimages on the right show the cavities in these SiO2-based materials, indicating the densities and CVR ratios (green: cavity; orange: silicon; and red:oxygen).21050baS(k)S(k)Pristine GSC20-bSZ after 11 years Pristine GSC20-bSZ after 11 years Fig. 4 Effect of thermal annealing on structure of amorphous SiO2 derived from siliceous zeolite (SZ). a S(k) of densified amorphous SiO2 from b-SZafter cold-compressed with 20 GPa (C20-bSZ) and that of cold-compressed amorphous SiO2 after thermal annealing at 750 °C for 1 h; the S(k) of pristineGS is also shown for comparison. b Enlarged S(k) of densified SZs plotted together with that of pristine GS.COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-023-01075-1 ARTICLECOMMUNICATIONS CHEMISTRY |           (2023) 6:269 | https://doi.org/10.1038/s42004-023-01075-1 | www.nature.com/commschem 5www.nature.com/commschemwww.nature.com/commschemComparison of amorphous SiO2 in k space. Finally, to comparethe pristine GS with other densified amorphous silicas preparedfrom SZs, the small-k region of S(k) of the BM-pSZ is depicted inFig. 6, together with the data from previously reported SiO2materials. Vertical dashed lines A and B–D serve as visual guidesto clarify the positions of k0 and k1, respectively. For amorphousSiO2 derived from SZ, a peak at k0, which is characteristic of SZ,was observed. Although the FSDP position is sensitive topressure48, a distinct correlation between the position of theFSDP and density was observed only in the GS and not in the SZ.However, if we exclude the BM-pSZs, we believe that a correlationexists between the density and FSDP position of amorphous SiO2prepared from SZs. Notably, the k0 value of BM-pSZ, whoseFSDP position was at the lowest wavevector k, was the lowest k0peak among these materials. In SZ-derived amorphous SiO2, it issuggested that the values of the wave vectors k0 and k1 arecorrelated.The obtained results show that the crystalline topology affectspressure-induced material fabrication and thermal stability. Theamorphization of the SZ by cold compression is linked to thecollapse of the pores in the SZ, and a trace of the cage structurehas been already reported in a previous paper31. Notably, tracesof the SZ remained in the densified amorphous SiO2 after thermalannealing. These traces of SZ influence permanent densificationand provide evidence of the structural differences between thestarting materials SZ and GS in amorphous SiO2. Materials withthe same chemical composition but different topologies can befabricated by tailoring the starting materials, which will pave theway for the design of novel functional materials.Amorphous materials prepared by applying high pressure to theSZ at room temperature using various treatments were char-acterised. The results confirm that the structural changes dependon the stabilisation treatment and pressurisation conditions. TheX-ray structure factor S(k) of the amorphous SiO2 derived from asingle crystal of SZ changed slightly over an 11-year period. Inparticular, it was found for the first time that samples preparedfrom SZs by high-pressure synthesis have a characteristic k0 peakat a lower k than that of FSDP, which is a remnant of some Braggpeaks of SZs. Furthermore, the k0 peak is a disrupted structuralmotif of SZs or a long-distance correlation rather than a remnantBragg peak, as the peak is shifted to a higher k. The k0 peak, whichis characteristic of a cage within the SZ, disappeared aftermechanical ball milling. The results demonstrated that thetopology of the pressure-induced amorphous materials could betuned by tailoring the nature of the starting materials. We areconfident that the clarification of the unique structure existing atdistances beyond the intermediate will provide a guide for openingup a new science of amorphous materials.Materials and methodsSample details. SZ powder was purchased from Tosoh Corp.(890HOA, MFI-type zeolite), and 890HOA was selected becauseits Si/Al ratio is sufficiently high (>1000) and its Al content issufficiently low. The linear dimensions of the crystallites were2–5 µm, and the material contained additional H+ cations.Densification of samples. The densified SiO2 samples using SZ asa starting material were prepared using a Kawai-type apparatuswith a Walker-module (mavo press LPR 1000-400/50; MaxFig. 5 Effect of ball milling (BM) on the structure of siliceous zeolite (SZ). a X-ray total structure factors, S(k), of SZ with and without BM treatment. 29SiMAS NMR spectra of SZ (b) and SZ after BM-treatment (c). d X-ray total structure factors, S(k), of BM-SZ and densified BM amorphous SiO2 obtained bycold compression, shown together with that of pristine GS; inset: enlarged S(k) at the FSDP region. e Reduced pair distribution functions, G(r), of allsamples shown in (d). f S(k) of amorphous SiO2 (BM) measured soon after cold pressing and again after 1 year along with SiO2 and densified GS;successive BM-SZ and GS data are displayed upward at S(k) for clarity.Table 2 Ratio of Qn units in siliceous zeolite (SZ) and glassySiO2 (GS) before and after ball-milling (BM).Chemicals Treatment Q2 Q3 Q4SZ Before BM 0 0.15 (±0.01) 0.85 (±0.01)After BM 0.04 (±0.01) 0.39 (±0.01) 0.57 (±0.01)GS Before BM47 0 0 1.00After BM 0.06 (±0.01) 0.53 (±0.02) 0.41 (±0.02)ARTICLE COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-023-01075-16 COMMUNICATIONS CHEMISTRY |           (2023) 6:269 | https://doi.org/10.1038/s42004-023-01075-1 | www.nature.com/commschemwww.nature.com/commschemVoggenreiter GmbH, Mainleus, Germany) at the Frontier MaterialsLaboratory, Tokyo Institute of Technology. The powdered samplesthat formed into pellets were sealed in a gold capsule and pressed atRT at an applied pressure of 20GPa for 1 h. A 1500-ton belt-typehigh-temperature, high-pressure apparatus installed at the NationalInstitute for Materials Science (NIMS), with an applied pressure of7.7 GPa was used to prepare the samples. The strategy was as fol-lows: (1) the powdered sample was moulded into a cylindrical shapewith a diameter of 4 mm and height of 3 mm and (2) pressurised to7.7 GPa in 5 h. Subsequently, (3) the applied pressure was main-tained for 30min, after which (4) the applied pressure was reducedto 0 GPa in 5 h. The application of high pressure at an ambienttemperature is known as cold compression.Ball-milling treatments. To obtain a less-ordered SZ, it wasground (by ball milling) in air at 500 rpm using a Fritsch P6planetary ball-mill system, a silicon nitride pot, and silicon nitrideballs. To prevent the pot from heating, the system was allowed torun for 15 min, and then stopped running for another 15 min tocool. Overall, grinding was performed for 24 h.Thermal annealing treatments. To verify the permanent densi-fication of C20-bSZ, the sample was heat treated in air in acommercially available electric furnace. The heating strategy wasas follows: (1) the sample was heated to 750 °C at a heating rate of10 °C/min, (2) 750 °C was maintained for 1 h for thermalannealing, following which (3) the sample was cooled to roomtemperature without the use of cooling-rate control.NMR measurements. The local structures of the Si atoms in thepristine and ball-milled SZ were evaluated using 29Si MAS NMRspectroscopy (JEOL ECA 300 (7.1 T) spectrometer) at a Larmorfrequency of 59.7 MHz. The sample powder was packed in a 4.0-mm ZrO2 rotor and spun at 7.5 kHz. Single-pulse experimentswere conducted using 30° pulses with a repetition delay of 20 s.Tetramethylsilane (TMS) was used as the reference material (0ppm) to calibrate the 29Si chemical shift. To estimate the popu-lation and NMR parameters of each Si species, the spectra werefitted to Gaussian functions.High-energy XRD measurements. High-energy XRD measure-ments were performed on the BL04B2 beamline at SPring-8(Hyogo, Japan) using a two-axis diffractometer dedicated tostudying disordered materials. The energy of incident X-rays was61.34 keV. The raw data were corrected for polarisation,absorption, and background, and the contribution of Comptonscattering was subtracted using a standard data analysis software.The corrected X-ray diffraction data were normalised to obtainthe total structure factor, S(k).Topological analyses. Ring size distribution calculations wereperformed for SZ (reverse Monte Carlo (RMC) model)49 and GS(molecular dynamics–RMC model)19,22,50 using the R.I.N.G.S.code51,52. Cavity volume analysis was performed using PyMol-Dyn code53. The code can calculate three types of cavities:domain, centre-based (Voronoi), and surface-based cavities. Wecalculated the surface cavity volumes using a cutoff distancerc= 2.5 Å.Data availabilityAll relevant data supporting the findings of this study are available from thecorresponding author upon request.Received: 20 July 2023; Accepted: 22 November 2023;References1. Profeta, M., Mauri, F. & Pickard, C. J. Accurate first principles prediction of17O NMR parameters in SiO2: assignment of the zeolite ferrierite spectrum. J.Am. Chem. Soc. 125, 541–548 (2003).2. Piccione, P. M. et al. Thermochemistry of pure-silica zeolites. J. Phys. Chem. B104, 10001–10011 (2000).3. Mizokami, K., Togo, A. & Tanaka, I. 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Erratum: Ring statistics analysis of topologicalnetworks: new approach and application to amorphous GeS2 and SiO2systems. [Comput. Mater. Sci. 49, 70–83 (2010)]. Comput. Mater. Sci. 50, 1217(2011).53. Heimbach, I. et al. pyMolDyn: identification, structure, and properties ofcavities/vacancies in condensed matter and molecules. J. Comput. Chem. 38,389–394 (2017).AcknowledgementsThis work was partially supported by TIA Kakehashi TK19-004 (to S.K., Y.S., H.M.,T.W., and S.S.). Support was also received from JSPS Grant-in-Aid for TransformativeResearch Areas (A) “Hyper-Ordered Structures Science” (grant numbers 20H05878,20H05880, 20H05881 and 20H05882) and the Collaborative Research Projects ofLaboratory for Materials and Structures, Institute of Innovative Research, Tokyo Instituteof Technology. High-energy XRD measurements were performed at BL04B2 of SPring-8with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (pro-posal numbers 2019B1563 and 2021A1166). We are grateful to F. Kawamura, M.Miyakawa, and T. Taniguchi (High-Pressure Structural Controls Group, NIMS) for theirsupport with the high-pressure and high-temperature syntheses using a 1500-ton belt-type apparatus at NIMS.Author contributionsDesign: H.M. and S.K.; Methodology: H.M. and S.K.; Investigation: H.M., S.K., Y.S., Y.O.,A.M., S.S., K.O. and D.A.K.; Sample preparation: T.W., Y.Sh., Y.Sa., J.H., C.L., P.H., A.I. andM.A. Writing—original draft: H.M. and S.K.; Writing—review and editing: H.M., S.K., J.H.and D.A.K. All authors have read and agreed to the published version of the paper.Competing interestsThe authors declare no competing interests.Additional informationSupplementary information The online version contains supplementary materialavailable at https://doi.org/10.1038/s42004-023-01075-1.Correspondence and requests for materials should be addressed to Hirokazu Masai orShinji Kohara.Peer review information Communications Chemistry thanks Marcin Stachowicz and theother, anonymous, reviewer(s) for their contribution to the peer review of this work. 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To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.© The Author(s) 2023COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-023-01075-1 ARTICLECOMMUNICATIONS CHEMISTRY |           (2023) 6:269 | https://doi.org/10.1038/s42004-023-01075-1 | www.nature.com/commschem 9http://creativecommons.org/licenses/by/4.0/http://creativecommons.org/licenses/by/4.0/www.nature.com/commschemwww.nature.com/commschem Siliceous zeolite-derived topology of amorphous�silica Results and discussion Preservation of cage structure in SZ-derived amorphous SiO2 Permanent densification and relaxation of SZ-derived amorphous SiO2 Effect of ball-milling on the structure�of SZ Comparison of amorphous SiO2 in k�space Materials and methods Sample details Densification of samples Ball-milling treatments Thermal annealing treatments NMR measurements High-energy XRD measurements Topological analyses Data availability References References Acknowledgements Author contributions Competing interests Additional information