Novel multifunctional nitrides for fusion applications Andreas Zerr UPR 3407 - Laboratoire des Sciences des Procédés et des Matériaux CNRS, Université Paris Nord, 93430 Villetaneuse, France

Traditional binary nitrides At P= 1bar: product of the reaction M + x.N2 → 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 MN M3N4 M3N2 MN M3N

Novel high-pressure binary nitrides with N:M>1 At P > 5 GPa: product of the reaction M + x.N2 → 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 P3N5 W3N4 W2N3 M(N2) Novel dense phases of Si3N4, Ge3N4 Novel compound Sn3N4 M3N4, Ta2N3

Novel high-pressure binary nitrides with N:M>1 At P > 5 GPa: Our contribution 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Novel dense phases of Si3N4, Ge3N4 Novel compound Sn3N4 M3N4, Ta2N3

High-pressure synthesis

Synthesis of c-Zr3N4 / c-Hf3N4 having cubic Th3P4 structure LH-DAC ZrN + N2  c-Zr3N4 Hf + N2  c-Hf3N4 ~18 GPa; ~2800 K Size: up to 100 mm 50 mm Zerr, Miehe, Riedel, Nature Mater. 2, 185 (2003) Multianvil nc-Zr3N4+x  c-Zr3N4 nc-Hf3N4+x  c-Hf3N4 ~ 7-12 GPa; ~1600 K Size: up to 5 mm Dzivenko et al., Adv. Mater. 19, 1869 (2007)

Novel high pressure nitrides with N:M>1 As for any high-pressure products we expected : Higher density: ρproduct > ρstarting (Le Chatelier’s principal) Higher elastic moduli Higher hardness Possible Bonus(es): Novel compounds (e.g. M3N4 instead of MN) – novel properties - Elevated thermal or chemical stability - Toughness, wear resistance Optoelectronic applications (electronic structure, band gap) Resistant to neutron irradiation (?)

Radiation tolerant spinel nitride, g-M3N4 “structural vacancies” in spinel structure: - 7/8 of tetrahedral sites are free “self-healing” - 1/2 of octahedral sites are free Spinel-nitrides: Energetic costs of cation antisites formation = 0

Radiation tolerant spinel oxide, g-AB2O4 (e.g. MgAl2O4) “structural vacancies” in spinel structure: - 7/8 of tetrahedral sites are free “self-healing” - 1/2 of octahedral sites are free A O B Spinel-oxides: Energetic costs of cation antisites formation > 0

Spinel nitrides of the group 14 elements: g-M3N4 (M = Si, Ge, Sn)

Band gaps of g-M3N4 and exciton binding energies Experiment (SXS): band gap Theory (modified Becke-Johnson potential, MBJLDA): direct transition Direct or nearly direct band gaps Large Eexc – high conversion efficiency LEDs Lighting applications (true visible light?) g-Sn3N4 ↔ GaAs (LEDs, PV, mobile phones, HF) Experimentally confirmed for g-Si3N4 Museur, Zerr, Kanaev; Sci. Rep. (2016) Boyko et al., Phys. Rev. Lett. (2014)

Deposition of g-Sn3N4 spinel XRD Maruyama & Morishita (1995): RF magnetron sputtering 50 W, Sn + N2 substrate - glass, Tsubstrate=60 oC hexagonal structure CONFIRMED BY Caskey et al., J. Mater. Chem. C (2015) spinel 111 220 311 222 400 422 511 440 531 622 620 533 642 731 XRD

END