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October/November 2006, Huenfeld

Nitride chemistry of geomaterials Earlier findings, perspectives and new results Prof. Dr. Rainer Niewa, TU München PD Dr. Ulrich Schwarz, MPI Dresden. October/November 2006, Huenfeld. Outline. • Earlier findings Perowskites ( RE 3 X ) A

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October/November 2006, Huenfeld

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  1. Nitride chemistry of geomaterials Earlier findings, perspectives and new results Prof. Dr. Rainer Niewa, TU München PD Dr. Ulrich Schwarz, MPI Dresden October/November 2006, Huenfeld

  2. Outline • Earlier findings Perowskites (RE3X)A RE = f-metal; X = N, C, O, ; A = d-metal • Target compounds • Systems Fe-N-C; Fe-N-C-O (meteorites, terrestrial minerals) • New ternary iron nitrides (potential materials) • First results: hp-Cu3N Max-Planck-Institut für Chemische Physik fester Stoffe

  3. Techniques • In-situ hp x-ray diffraction (ESRF, M. Hanfland) Laser heating (ESRF) • In-situ hp neutron diffraction (ISIS, M. Tucker,  FRM-II, Garching) • In-situ hp XAS (DESY) • Multianvil set-up + press • Chemical analysis • Metallography Max-Planck-Institut für Chemische Physik fester Stoffe

  4. Rare-earth perovskites (RE3N)M at high pressures B0 = 107(6) GPa • Low-pressure range B0 > 80 GPa • High-pressure range (Ce3N)In B0 ~ 40 GPa Valence change? B0 = 85(3) GPa B0 = 88(8) GPa B0 = 43(1) GPa Max-Planck-Institut für Chemische Physik fester Stoffe

  5. Pressure (GPa) 12.7 10.0 8.0 6.8 CeO2 (reference) XAS of (Ce3N)In • Ce LIII threshold • P > PT Constant signal of Ce3+ (4f1)  No evidence for a valence change Max-Planck-Institut für Chemische Physik fester Stoffe

  6. Relevance of iron nitrides Max-Planck-Institut für Chemische Physik fester Stoffe

  7. Relevance of binary iron nitrides • Fe4N • Fe(Fe3N) perovskite-type at ambient conditions • Mineral roaldite in the impact zone of meteorites • Relevance for the earth’s core? • Formation conditions unknown • Hexagonal high-pressure phase at P > 32 GPa [Adler, Williams, J. Geophys. Res. 110 (2005) 1203] • “Fe5N2” (Fe3N1+x) Aetna: Silvestrite [A. Silvestri, Pogg. Ann. 157 (1867) 165]  2 of 8 known nitride minerals are iron compounds • Hard materials – Surface hardening • Spinell-type hp-Fe3N4 predicted, B0 = 304 GPa [Xu, Ruhs, Ching, J. Appl. Phys. 91 (2002) 7352] Max-Planck-Institut für Chemische Physik fester Stoffe

  8. Ternary iron nitrides • Ternary nitrides ambient pressure (predicted and synthesized): (Fe3N)Rh [Appen, Dronskowski, Angew. Chem. 117 (2005) 1230] [Houben, Müller, Appen, Lueken, Niewa, Dronskowski, Angew. Chem. 117 (2005) 7379] high-pressure (predicted) P > 37 GPa: (Fe3N)Ir [Appen, Dronskowski, Angew. Chem. 117 (2005) 1230] • Homogeneity range of phases • Substitution of N by O and C • Characterization of the samples Chemical composition Physical properties Max-Planck-Institut für Chemische Physik fester Stoffe

  9. Copper nitride Cu3N: Crystal structure and phase transitition • Ambient pressure d(Cu-N) 191 pm CN(Cu) 6 CN(N) 2 • Predicted high-p phases Li3P, -UO3 or K3N, P > 25 GPa [Cancarevic, Schön, Jansen ZAAC 631 (2005) 1167] • HP-synthesis of a quenchable phase failed (P 8 - 10 GPa) lp-Cu3N, Cu ReO3 type Max-Planck-Institut für Chemische Physik fester Stoffe

  10. Cu3N • In-situ x-ray increasing pressure PT > 7 GPa • PT reversible with hysteresis •Cu subcell I4/mmm Cu 0,0,0 c/a ~ 1.47  In partial-structure Max-Planck-Institut für Chemische Physik fester Stoffe

  11. Cu3N: TOF Neutron diffraction data Four phases •Cu3N • Pb pressure marker • WC anvil • Ni crucible Scattering factors b(Cu) = 7.9  fm b(N) = 9.4  fm Cu3N Cu3N Cu3N Pb/WC Ni Pb WC 10 to 25 to 40 to 55 to 70 to 85 to Max-Planck-Institut für Chemische Physik fester Stoffe

  12. Structure refinement of hp-Cu3N + Pb, Ni, WC f = 85 to Non-linear background No indication for symmetry reduction with respect to X-ray data Max-Planck-Institut für Chemische Physik fester Stoffe

  13. Hp-Cu3N: structure model (L. Akselrud, MPI CPfS) I4/mmm (sg 139) a = 265.3 pm c = 390.8 pm c/a = 1.473 Cu (0,0,0) N (1/2, 1/2, 0) SOF(N)= 0.37(2)  Cu3N1.1(1) d(Cu-N) = 187.6(1) pm [4/3 ] d(Cu-N) = 195.4(1) pm [2/3 ] Cu 1/3 N Max-Planck-Institut für Chemische Physik fester Stoffe

  14. Summary Hp phase of Cu3N In-situ: nitrogen-disordered I4/mmm Quenching not successful Outlook Preparation in Systems Fe-N-C; Fe-N-C-O Preparation of (predicted) ternary iron nitrides (Cooperation Prof. Dronskowski) Mechanical properties (Cooperation Prof. Riedel) Crystal growth (Cooperation Dr. Gross) Max-Planck-Institut für Chemische Physik fester Stoffe

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