M. Kumar, U. Chandra, and G. Parthasarathy, Mater. Lett, pp.2066-2068, 2006.

G. Parthasarathy, . Mater, and . Lett, , pp.4329-4331, 2007.

P. E. Zhang, J. S. Zhang, L. D. Yao, F. Y. Li, Z. X. Bao et al., J. Mater. Sci, issue.22, pp.7374-7379, 2006.

L. D. Yao, P. Zhang, J. S. Zhang, W. Li, F. Y. Jin et al., Phys. B Condens. Matter, pp.2241-2245, 2008.

M. Santoro, F. A. Gorelli, R. Bini, J. Haines, and A. Van-der-lee, Nat Commun, 1557.

J. Gao, H. Xiao, and H. Du, Scr. Mater, vol.45, pp.1063-1068, 2001.

L. X. Qiu, B. Yao, Z. H. Ding, Y. J. Zheng, X. P. Jia et al., J. Alloys Compd, vol.456, issue.1-2, pp.436-440, 2008.

X. Zhou, J. Zang, L. Dong, X. Cheng, T. Li et al., Mater. Lett, vol.144, pp.69-73, 2015.

R. Z. Valiev, Y. Estrin, Z. Horita, T. G. Langdon, M. J. Zehetbauer et al., , vol.58, pp.33-39, 2016.

R. Vafaei, M. R. Toroghinejad, and R. Pippan, Mater. Sci. Eng. A, vol.536, pp.73-81, 2012.

J. Gonzalez, A. Segura, C. Ferrer-roca, D. Martinez-garcia, V. M. Jose et al., , vol.22, pp.271-275, 2002.

M. Kobayashi, H. Iwata, H. Hanzawa, T. Yoshiue, and S. Endo, Phys. Status Solidi, vol.198, issue.1, pp.515-520, 1996.

J. Gonzalez, A. Segura, C. Ferrer-roca, D. Martinez-garcia, V. M. Jose et al., , vol.23, pp.29-33, 2003.

J. González, J. Marquina, and F. Rodríguez, , vol.29, pp.594-599, 2009.

A. R. Oganov, V. L. Solozhenko, . Superhard, and . Mater, , pp.285-291, 2009.

B. Albert, H. Hillebrecht, V. L. Solozhenko, O. O. Kurakevych, A. R. Oganov et al., Angew. Chem. Int. Ed, vol.48, issue.46, pp.428-429, 2008.

A. R. Oganov, J. Chen, C. Gatti, Y. Ma, Y. Ma et al., Nature, vol.457, issue.7231, pp.863-867, 2009.

A. R. Oganov,

N. Orlovskaya and M. Lugovy, NATO Science for Peace and Security Series B: Physics and Biophysics, 2011.

A. R. Oganov, V. L. Solozhenko, C. Gatti, O. O. Kurakevych, Y. J. Godec et al., , vol.33, pp.363-379, 2011.

S. Carenco, D. Portehault, C. Boissière, N. Mézailles, and C. Sanchez, Chem. Rev, vol.113, issue.10, pp.7981-8065, 2013.

A. W. Laubengayer, D. T. Hurd, A. E. Newkirk, J. L. Hoard, D. E. Sands et al., J. Am. Chem. Soc, vol.65, issue.10, pp.5582-5583, 1943.

L. V. Mccarty, J. S. Kasper, F. H. Horn, B. F. Decker, and A. E. Newkirk, J. Am. Chem. Soc, vol.80, issue.10, pp.2592-2592, 1958.

F. H. Horn, G. Parakhonskiy, N. Dubrovinskaia, L. Dubrovinsky, S. Mondal et al., J. Electrochem. Soc, vol.106, issue.10, pp.162-166, 1959.

M. Terauchi, Y. Kawamata, M. Tanaka, M. Takeda, and K. Kimura, J. Solid State II-4-References

D. Portehault, S. Devi, P. Beaunier, C. Gervais, C. Giordano et al., Angew. Chem. Int. Ed, vol.50, issue.14, pp.3262-3265, 2011.

B. Terlan, A. A. Levin, F. Börrnert, J. Zeisner, V. Kataev et al., Eur. J. Inorg. Chem, pp.2003-2006, 2005.

B. Terlan, A. Levin, F. Börrnert, F. Simon, M. Oschatz et al., Approche moléculaire vers des nanomatériaux inorganiques composés de bore : nouvelles nanostructures fonctionnelles, vol.27, pp.5106-5115, 2015.

G. Gouget, P. Beaunier, D. Portehault, C. F. Sanchez, and . Discuss, , 2016.

D. Portehault, G. Gouget, C. Gervais-stary, and C. Sanchez, Matériau nanostructuré de bore amorphe, vol.15, p.55878, 2016.

C. E. Johnson, E. J. Cairns, and R. Sridhar, J. Chem. Eng. Data, vol.15, issue.2, pp.244-245, 1970.

A. S. Basin, A. B. Kaplun, A. B. Meshalkin, N. F. Uvarov, and . Russ, J. Inorg. Chem, vol.53, issue.9, pp.1509-1511, 2008.

C. H. Liu and L. R. Lieto, J. Chem. Eng. Data, vol.14, issue.1, pp.83-84, 1969.

C. L. Turner, R. E. Taylor, and R. B. Kaner, J. Phys. Chem. C, vol.2015, issue.24, pp.13807-13813

A. J. Mannix, X. Zhou, B. Kiraly, J. D. Wood, D. Alducin et al., Science, vol.2015, issue.6267, pp.1513-1516

B. Feng, J. Zhang, Q. Zhong, W. Li, S. Li et al., Nat. Chem, vol.8, pp.563-568, 2016.

C. Pallier, J. Leyssale, L. A. Truflandier, A. T. Bui, P. Weisbecker et al., Chem. Mater, vol.25, issue.13, pp.2618-2629, 2013.

S. Aydin and M. Simsek, Phys. Status Solidi Basic Res, vol.246, issue.1, 2009.

. Chapter, HPHT treatments on oxygen-containing nanocomposites 94

, III-5-Associated content Supporting Information. Figure III-S1: FTIR spectra of the precursors

I. Figure, Fourier Transform Infrared spectra of the (a) HfB 2 /amorphous boron and (b) CaB 6 /amorphous boron nanocomposites after exposure to air during seven days

, III-6-References

J. S. Knyrim and H. J. Huppertz, Solid State Chem, vol.180, pp.742-748, 2007.

M. Marezio, J. P. Remeika, and P. D. Dernier, Acta Crystallogr. Sect. B Struct. Crystallogr. Cryst. Chem, vol.25, issue.5, pp.965-970, 1969.

E. J. Gonzalez, B. Hockey, G. J. Piermarini, and . Mater, , vol.11, pp.951-967, 1996.

J. S. Olsen, L. Gerward, and J. Z. Jiang, , vol.22, pp.385-389, 2002.

H. Chang, J. Jiang, M. Kuo, D. Hsu, and S. H. Lin, Phys. Chem. Chem. Phys, vol.17, pp.21143-21148, 2015.

B. Liu, M. Yao, B. Liu, Z. Li, R. Liu et al., Z. J. Phys. Chem. C, issue.111, pp.4546-4551, 2011.

S. Shah, M. Shahabuddin, M. Parakkandy, J. M. Alzayed, N. S. Madhar et al., , vol.28, pp.481-485, 2014.

V. L. Solozhenko, O. O. Kurakevych, and Y. Le-godec, Adv. Mater, vol.2012, issue.12, pp.1540-1544

N. Dubrovinskaia, V. L. Solozhenko, N. Miyajima, V. Dmitriev, O. O. Kurakevych et al., Appl. Phys. Lett, issue.10, pp.1-4, 2007.

A. Nagakubo, H. Ogi, H. Sumiya, and M. Hirao, Appl. Phys. Lett, issue.8, p.81906, 2014.

B. Liang, Y. Xie, W. Li, W. Wu, and X. Zhang, J. Phys. D. Appl. Phys, issue.19, p.195010, 2008.

T. Irifune, A. Kurio, S. Sakamoto, T. Inoue, and H. Sumiya, Nature, vol.421, issue.6923, pp.599-600, 2003.

N. Dubrovinskaia, L. Dubrovinsky, F. Langenhorst, S. Jacobsen, and C. Liebske, Diam. Relat. Mater, vol.14, issue.1, pp.16-22, 2005.

Y. Zhao, D. W. He, L. L. Daemen, T. D. Shen, R. B. Schwarz et al., J. Mater. Res, vol.17, issue.12, pp.3139-3145, 2002.

V. L. Solozhenko, D. Andrault, G. Fiquet, M. Mezouar, and D. C. Rubie, Appl. Phys. Lett, issue.10, pp.1385-1387, 2001.

Y. Tian, B. Xu, D. Yu, Y. Ma, Y. Wang et al., Z. Nature, vol.493, issue.7432, pp.385-388, 2013.

V. L. Solozhenko, S. N. Dub, and N. V. Novikov, Diam. Relat. Mater, vol.10, issue.12, pp.2228-2231, 2001.

R. H. Wentorf, J. Chem. Phys, vol.34, issue.3, p.809, 1961.

X. Zhou, J. Zang, L. Dong, X. Cheng, T. Li et al., Mater. Lett, vol.144, pp.69-73, 2015.

H. Huppertz and D. A. Keszler, In Encyclopedia of Inorganic and Bioinorganic Chemistry, pp.1-12, 2014.

U. S. Survey, L. N. Demianets, H. Kouta, Y. Kuwano, K. Ito et al., Prog. Cryst. Growth Charact. Mater, vol.21, issue.22, pp.676-682, 1991.

J. Brinker, Silica Glass and its Application, Glass Science and Technology

N. Venkatasubramanian, B. Wade, P. Desai, A. S. Abhiraman, and L. T. Gelbaum, J. Non. Cryst. Solids, vol.130, issue.2, pp.144-156, 1991.

H. G. Snowman, Sol-gel technology for thin films, fibers, preforms, electronics, and specialty shapes

L. C. Klein, H. Huppertz, H. Emme, and H. Huppertz, Acta Crystallogr. Sect. C, vol.47, issue.1, pp.3623-3633, 1988.

G. Sohr, N. Ciaghi, M. Schauperl, K. Wurst, K. R. Liedl et al., Angew. Chemie Int. Ed, vol.17, issue.5, pp.2707-2715, 2005.

H. Huppertz, B. J. Eltz, J. S. Knyrim, F. Roessner, S. Jakob et al., Angew. Chem. Int. Ed, vol.124, issue.32, pp.9097-9100, 2002.

D. Portehault, S. Devi, P. Beaunier, C. Gervais, C. Giordano et al., Angew. Chem. Int. Ed, vol.50, issue.14, pp.3262-3265, 2011.

S. Carenco, D. Portehault, C. Boissière, N. Mézailles, and C. Sanchez, Chem. Rev, vol.113, issue.10, pp.7981-8065, 2013.

X. H. Ji, Q. Y. Zhang, J. Q. Xu, and Y. M. Zhao, Prog. Solid State Chem, issue.51, p.39, 2011.

T. Mori, J. Phys. Conf. Ser, vol.176, issue.1, p.12036, 2009.

J. B. Levine, S. H. Tolbert, and R. B. Kaner, Adv. Funct. Mater, vol.19, issue.22, pp.3519-3533, 2009.

Y. Godec, M. T. Le;-dove, S. A. Redfern, M. G. Tucker, W. G. Marshall et al., , vol.21, pp.263-280, 2001.

J. M. Besson, R. Nelmes, G. Gouget, P. Beaunier, D. Portehault et al., J. Phys. B Condens. Matter, vol.56, issue.42, pp.978-982, 1939.

J. S. Olsen, L. Gerward, J. Jiang, H. Chang, J. Jiang et al., Phys. Chem. Chem. Phys, vol.22, issue.45, pp.21143-21148, 2002.

S. Dogra, N. D. Sharma, J. Singh, H. K. Poswal, and S. Sharma, , vol.31, pp.292-303, 2011.

H. Mehrer, Diffusion in Solids Fundamentals,Methods,Materials, DiffusionControlled Processes, 2007.

. Chapter, HPHT formation of non-oxidised nanocomposites 114

A. R. Oganov, J. Chen, C. Gatti, Y. Ma, Y. Ma et al., Nature, vol.457, issue.1, pp.863-867, 2009.

N. Orlovskaya and M. Lugovy, NATO Science for Peace and Security Series B: Physics and Biophysics, 2011.

Y. Zarechnaya, E. Dubrovinsky, L. Dubrovinskaia, N. Miyajima, N. Filinchuk et al., Phys. Rev. Lett, vol.9, issue.4, pp.8-11, 2008.

.. R. Oganov, V. L. Solozhenko, C. Gatti, O. O. Kurakevych, Y. J. Godec et al., , vol.33, pp.363-379, 2011.

R. H. Wentorf, Science, vol.147, issue.3653, pp.49-50, 1965.

G. A. Slack, C. I. Hejna, M. F. Garbauskas, and J. S. Kasper, J. Solid State Chem, vol.76, issue.1, pp.52-63, 1988.

F. H. Horn, . Electrochem, G. Soc-;-parakhonskiya, N. Dubrovinskaia, E. Bykova et al., Synthesis and investigation of boron phases at high pressures and temperatures, J. Cryst. Growth, vol.106, issue.10, pp.60-63, 1959.

J. M. Besson, R. J. Nelmes, . Phys, Y. Condens-;-godec, M. T. Le;-dove et al., Matter, Acta Crystallogr., Sect. B, vol.21, issue.14, pp.1951-1954, 1977.
URL : https://hal.archives-ouvertes.fr/hal-01977851

J. S. Knyrim and H. J. Huppertz, Solid State Chem, vol.180, pp.742-748, 2007.

J. Z. Jiang, W. Rozeker, M. Sikorski, Q. P. Cao, and F. Xu, App. Phys. Lett, vol.84, issue.11, pp.1871-1873, 2004.

. Chapter, HPHT treatments of nanostructured amorphous boron, p.142

, Note that boron carbides can be crystallised at room pressure and high temperature, in the solid-solution domain comprised between ca. 9 and 22 at% of carbon. 18 At lower carbon content, a mixture of ?-B and B 4 C is obtained. 18 At 5 GPa, the solid-solution domain is possibly extended, so that C-doped ?-B could be obtained. The 11 B NMR spectrum (Figure V-5, Figure V-6) shows peaks similar to those obtained at 1350 and 1550 °C for 10 min dwell, which calls for the likely presence of small amounts of ?-B in previous experiments (though not seen on XRD patterns). The related spectra also enable attributing the peak at ca. 15 ppm to ?-B. The strong contamination under the electron beam precludes any HRTEM observation. Comparison of the XRD patterns of samples 3 (1550 °C, 8/10) and 5 (1750 °C, 8/10) (Figure V-5) show the presence of phases A and B. XRD patterns (Figure V-5) show neither ?-B nor the C phase. The 11 B NMR spectra of both samples show peaks at ca. 15, 0,-15 and-38 ppm, which indicate a mixture of A, B, C and ?-B. The relative amounts of phases A and B indicated by both 11 B NMR and XRD are consistent (Figure V-5) and show that the A phase is favoured vs. B above 1550 °C for short dwell times. Still at 1750 °C but for longer dwell time (90 min, experiment 6), XRD indicates the formation of a single crystalline phase: ?-B (Figure V-5 and Figure V-6). No reflections associated to the phases A, B and C are seen on the XRD pattern (Figure V-5). The 11 B NMR spectrum (Figure V-6) displays an intense peak at ca. 15 ppm, associated with ?-B. An additional broad peak (or two superimposed peaks) is seen at ca. 26 ppm, which may also be assigned to ?-B. The 11 B NMR spectrum also indicates low amounts of the A phase, the XRD pattern of the recovered sample (Figure V-6) shows two crystalline phases: B and reflections matching ?-B, in addition to unavoidable h-BN (sample capsule)

A. R. Oganov, J. Chen, C. Gatti, Y. Ma, Y. Ma et al., Nature, vol.457, issue.7231, pp.863-867, 2009.

Y. Zarechnaya, E. Dubrovinsky, L. Dubrovinskaia, N. Miyajima, N. Filinchuk et al., Adv. Mater, vol.9, p.44209, 2008.

G. Parakhonskiya, N. Dubrovinskaia, E. Bykova, R. Wirth, and L. Dubrovinsky, , vol.33, pp.673-683, 2013.

C. P. Talley, S. La-placa, B. Post, and . Iucr, Acta Crystallogr, vol.13, issue.3, pp.271-272, 1960.

E. A. Ekimov, I. P. Zibrov, and A. V. Zoteev, Inorg. Mater, vol.47, issue.11, pp.1194-1198, 2011.

C. L. Turner, R. E. Taylor, and R. B. Kaner, J. Phys. Chem. C, vol.2015, issue.24, pp.13807-13813

S. Komatsu and Y. Moriyoshi, J. Cryst. Growth, vol.102, issue.4, pp.899-907, 1990.

X. Wang, J. Tian, T. Yang, L. Bao, C. Hui et al., , vol.19, pp.4480-4485, 2009.

Y. Zhang, H. Ago, M. Yumura, T. Komatsu, S. Ohshima et al., Chem. Commun, vol.354, issue.23, pp.2806-2807, 2002.

Z. Wang, Y. Shimizu, T. Sasaki, K. Kawaguchi, K. Kimura et al., Chem. Phys. Lett, vol.368, issue.5-6, pp.663-667, 2003.

H. Bai, D. Dai, J. H. Yu, K. Nishimura, S. Sasaoka et al., Appl. Surf. Sci, vol.292, pp.790-794, 2014.

B. J. Bellott, W. Noh, R. G. Nuzzo, and G. S. Girolami, Chem. Commun, issue.22, pp.3214-3215, 2009.

Y. Wu, B. Messer, and P. Yang, Adv. Mater, vol.13, issue.19, pp.1487-1489, 2001.

X. M. Meng, J. Q. Hu, Y. Jiang, C. S. Lee, and S. T. Lee, Chem. Phys. Lett, vol.370, issue.5-6, pp.825-828, 2003.

J. D. Casey and J. S. Haggerty, J. Mater. Sci, vol.1987, issue.2, pp.737-744

A. L. Pickering, C. Mitterbauer, N. D. Browning, S. M. Kauzlarich, and P. P. Power, Chem. Commun, issue.6, pp.580-582, 2007.

T. T. Xu, J. G. Zheng, N. Wu, A. W. Nicholls, J. R. Roth et al., Nano Lett, vol.4, pp.963-968, 2004.

F. J. Thévenot and . Eur, Ceram. Soc, vol.6, pp.205-225, 1990.

G. Gouget, Approche moléculaire vers des nanomatériaux inorganiques composés de bore : nouvelles nanostructures fonctionnelles, 2016.

S. Komatsu and Y. Moriyoshi, J. Cryst. Growth, vol.102, issue.4, pp.899-907, 1990.

X. Wang, J. Tian, T. Yang, L. Bao, C. Hui et al., Adv. Mater, vol.19, issue.24, pp.4480-4485, 2009.

H. Bai, D. Dai, J. H. Yu, K. Nishimura, S. Sasaoka et al., Appl. Surf. Sci, vol.292, pp.790-794, 2014.

, operating at 200 kV) apparatus at the Microscopy Centre of Institut of Materials of Paris Centre, Sorbonne Universités-UPMC, Paris. The STEM-HAADF and STEM-DF observations were performed by Ovidiu Ersen and Simona Moldovan on a JEOL 2100 F operating at 200 kV and equipped with aberration correction on the electronic probe at the Institut de Physique et Chmie de la Matière de Strasbourg. STEM-EELS and STEM-EDS, not shown in this manuscript, were performed by Dario Taverna at the Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie on a JEOL 2100F equipped with a Schottky field emission gun, a post-column GIF 2001 device from Gatan for EELS and a SiLi detector from Jeol for EDS analysis. SAED pictures are calibrated on a gold reference sample. Particle size distribution diagrams (HfB 2 , nano-B am ) were based on measurements for 150 particles at least, Most TEM and HRTEM analyses were performed using a Tecnai spirit G2 apparatus (LaB 6 , operating at 120 kV). HRTEM analyses of the CaB 6 /B nanocomposite (Chapter II and III) were performed by Patricia Beaunier on a JEOL JEM 2011

, The powders were dissolved in nitric acid (2 to 5 mol.L-1 ) prior to dilution in deionised water (10 fold). For all elements dosed, the error is ca, ICP-OES analyses were realised by Domitille Giaume at the Institut de Recherche de Chimie Paris on a iCAP 6000 apparatus from ThermoFisher

, The acceleration voltage is set to 10 kV and the EDS signal calibrated for quantitative analysis on the K-line of titanium. The composition corresponds to mean values obtained on at least three different regions of the sample. The data were analysed with the INCA software from Oxford. Samples were deposited on a conductive carbon tape. For SMS-derived samples, the powders were recovered with a ca. 20 nm thick carbon layer prior to analysis, which was not the case for HPHT treated sample