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High- pressure -high- temperature synthesis , characterization and q uantum-chemical calculations of metal nitrides. Joint Project : K ai Guo , Ulrich Schwarz, MPI CPfS Rainer Niewa, Dieter Rau, Univ. Stuttgart Richard Dronskowski , RWTH Univ. Aachen. 28. 09. 2012. Outline.
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High-pressure-high-temperaturesynthesis, characterization and quantum-chemicalcalculationsofmetalnitrides Joint Project: Kai Guo, Ulrich Schwarz, MPI CPfS Rainer Niewa, Dieter Rau, Univ. Stuttgart Richard Dronskowski, RWTH Univ. Aachen 28. 09. 2012
Outline γʹ-Fe4N, cubic Fe ② ② ε-Fe3N, hexagonal/trigonal Fe N ① ③ ζ-Fe2N, orthorhomic TM • Phase diagram of the binary system Fe-N. High-pressurebehaviorsand single-crystalgrowthofε-Fe3Nxunder high-pressure, high-temperature (HPHT). Phase transitionfromγʹ -Fe4N and ζ-Fe2N to ε-Fe3Nx and subsequent recrystalizationunder HPHT. Synthesis andcharacterizationofε-Fe2TMN (TM = Co, Ni), ε-Fe2IrNxandε-Fe3(N, C). Theoreticalpredictionofnewpernitrides2La3+(N2)2- (N2)4-. K.H. Jack, Proc. Roy. Soc. A 1951, 208, 200.
1. ε-Fe3Nx: high-pressurebehaviors Fe3N1.05±3O0.017±1 B0= 172(4) GPa, B‘ = 5.7 Experimental data Theoreticalsimulation Theoreticalsimulation • Pressure-volume dataofε-Fe3N. Nophasetransitionoccursunder high pressure. c/a ratio of the hexagonal unit-cell parameters of ε-Fe3N as a functionofpressure. Upon pressureincrease, thec/aratioincreasestowardthe ideal value (0.943 = 1.633/). R. Niewa et al. Chem. Mater.2009, 21, 392.
MgO/Cr2O3 p= 15(2)GPa, T = 1600(200) K Zirconia Starting material: Fe3N1.05±3O0.017±1 Molybdenum TheoreticalanalysisrevealsthatP312 is moreenergeticallyfavoredfor Fe3N1.1. MgO Graphite Boron Nitide The compositionrefinedfromP312 is muchcolser to theexpectedcomposition. Sample Two-stage multianvildevicewith a walker-type module Refinedfomulaforε-Fe3Nx in sapcegroupP312 andP6322. Formation enthalpiesandaveragemagneticmoments on Featomsforε-Fe3N andε-Fe3N1.1. 1. ε-Fe3Nx: HPHT single-crystalgrowth
2. Phase transition from γʹ-Fe4N to ε-Fe3N0.75 0 K Endothermic ② Energy–volumediagramforthesystemε-Fe3N+Fe, γʹ-Fe4N andε-Fe4N as calculated by density-functional theory. TM Inducedbypressure! 0 K ε-Fe4N Herein, a phasetrantionfromγʹ-Fe4N to ε-Fe4N(Fe3N0.75) at 7 GPaispredictedbased on density-functionaltheory! γʹ-Fe4N Enthalpy-difference–pressurediagramfor Fe4N as calculated by density-functional theory. R. Niewa et al.,J. AlloysCompd. 2009, 480, 76.
2. Phase transition from γʹ-Fe4N to ε-Fe3N0.75 Starting material: γʹ -Fe4N0.995(5) Conditions: p = 8.5 GPa, T = 1373 K Phase transitionfromγʹ-Fe4N to ε-Fe3N0.75 underHPHT isobserved The nitrogencontentdeducedfromtheeqationsisreasonabllyagreementwithresultsby CA. ε-Fe3N0.75 γʹ-Fe4N Fe3N0.77(4) XRPD patterns of the precursor γ’-Fe4N and the product ε-Fe3N0.75 after HPHT treatments. CA: Fe3N0.760(6)O0.018(2) Latticeparametersvsnitrogencontent in Fe3Nx. K. Guo, R. Niewa, D. Rau, Y.Prots, W, Schnelle, U. Schwarz, in preparation.
2. Crystal structureofε-Fe3N0.75 Refinedfomulaforε-Fe3Nx in spacegroupP312 andP6322. CA: Fe3N0.760(6)O0.018(2) Bothdescriptionsforthecrystalstructure in spacegroupP312 andP6322looklikereasonableresults. P312 Landau theoryindicates that a change in space group within a homogeneity range is not possible! P6322 Combinedtheearlierresults, spacegroupP312 issuggested.
2. Thermal propertiesofε-Fe3N0.75 ε-Fe3N0.76 γʹ-Fe4N+ ε-Fe3Nx (x > 0.75) ε-Fe3N0.75 remains metastable up to Tonset= 516 K before transforming into thermodynamically stable γ’-Fe4N at ambient pressure.
2. Magneticpropertiesofε-Fe3N0.75 2 K: 183 emu/g = 5.83 μB ε-Fe3N0.75 FM-Fe3N0.75 γʹ-Fe4N NM-Fe3N0.75 FM-Fe4N NM-Fe4N
2. Magneticmoments in ε-Fe3N andε-Fe3N0.75 (□-FeΙ-N) (N-FeΠ-N) Density-functionaltheory!
2. Phase transition from ζ-Fe2N to ε-Fe3N1.5 ② U. Schwarz, et al., Eur. J. Inorg. Chem. 2009, 12, 1634.
2. High-pressurebehaviorsofζ-Fe2N Starting material: ζ–Fe2N0.986(6)O0.0252(8) Nophasetransitionoccursunder high pressure Bulkmodulus: B0= 172.1(8) GPa B0ʹ= 5.24(8) XRPD taken on ζ-Fe2N at different pressures in a DAC. • Enthalpy-differenceforε-Fe3N1.5 in spacegroupP312 andP6322, aswellas 2Fe+α-Ncomparedto ζ-Fe2N. Theoreticalsimulation Pressure–volumedataofζ-Fe2N. This phasetransitioncanʹtbeinducedonlybythepressure!
2. Phase transition from ζ-Fe2N to ε-Fe3N1.5 Conditions: p = 15(2) GPa, T = 1600(200) K The phasetransitionisprobablyinducedbythetemperature RefinementswithP312 leadtounreasonableresultsalthoulhitisenergeticallyfavoredbaesd on quantumtheoreticalomputations • Enthalpy-differenceforε-Fe3N1.5 in spacegroupP312 andP6322, aswellas 2Fe+α-Ncomparedto ζ-Fe2N. XRPD diagrams of ζ-Fe2N and the product of the HPHT treatment. Refinedfomulaforε-Fe3Nxin sapcegroupP6322.
3. Synthesis ofε-Fe2TMN (TM = Co, Ni) Starting material: ζ–Fe2N0.986(6)O0.0252(8) and TMpowders Conditions: p = 15(2) GPa, T = 1473(150) K Si Si Si Si Si BN TM XRPD for the starting material ζ-Fe2N, the products -Fe2CoN and -Fe2NiN. XRPD resultsrevealpure phasesforε-Fe2TMN (TM = Co, Ni)! K. Guo, R.Niewa, D. Rau, U.Burkhardt, W.Schnelle, U. Schwarz, submitted.
3. Characterizationofε-Fe2TMN (TM = Co, Ni) ε-Fe2CoN ε- Fe2NiN Typical optical micrographs of (a) -Fe2CoN and (b) -Fe2NiN. The compositions detected by EDXS and CA. Homogeneouscomposition Metal ration: Fe : Co = 1.99(6) : 1.01(6) Fe : Ni = 1.97(2) : 1.03(2)
3. Thermal propertiesofε-Fe2TMN (TM = Co, Ni) ε-Fe2CoN ε-Fe2NiN Enthalpy-differenceforε-Fe2TMN andthiercompetitivephasesundervaringpressure Based on DFT, bothε-Fe2CoNandε-Fe2NiNaremetalstable The reactions are triggered by the temperature but the pressure play an important role in the preservation of nitrogen content
3. Thermal propertiesofε-Fe2TMN (TM = Co, Ni) ε-Fe2CoN N: 6.92±0.32% ε-Fe2NiN N: 8.08±0.45% TG-DSC forε-Fe2TMN. ε-Fe2TMN decomposeabove 750 K involvingthelossofnitrogen
3. Magneticpropertiesofε-Fe2TMN (TM = Co, Ni) Fe2CoN: 4.3μB/f.u. Fe2CoN: 488(5) K Fe2NiN:3.1μB/f.u. Fe2NiN: 234(3) K Fe3N: Ms= 6μB;Tc = 575(3) K A. Leineweberet al., J. AlloysCompd., 1999, 288, 79.
3. Synthesis ofε-Fe2IrNx No experimental evidence! DRHth (kJ mol–1) γʹ -IrFe3N: high-pressurephase, stablebeyond37GPa,ferromagnetic Enthalp-pressurediagramforγʹ-IrFe3N andthiercompetingphases J. von Appen, R. Dronskowski, Angew. Chem. Int. Ed.2005, 44, 2
3. Synthesis ofε-Fe2IrNx Changingsyntheticpressure Changingsynthetictemperature
3. Synthesis ofε-Fe2IrNx Fe3N,a = 4.6982(3) Ǻ, c= 4.3789(4) Ǻ
3. Synthesis ofε-Fe2IrNx 12 Gpa, 1100 oC 12 Gpa, 1100 oC 5 Gpa, 1300 oC 0 Gpa 0 Gpa Characterizationofcompositionandphysicalpropertiesareneededtobedone.
3. Synthesis ofbulkε-Fe3(N,C) The nitrogencontent in ε-Fe3(N,C) canbetunedto a certainextent.
4. Predictionofnewpernitrides2La3+(N2)2- (N2)4- DHR = –11 kJ mol–1at absolute zeroT B0 = 86 GPa N–N = 1.30 Å M. Wessel, R. Dronskowski, J. Am. Chem. Soc. 2010, 132, 2421.
4. Predictionofnewpernitrides 2La3+(N2)2- (N2)4- 300 K Density-functional Gibbs free energy-pressure diagram for the synthesis of LaN2 in the [ThC2] type at a projected synthetic temperature of T =300 K.
Conclusions • Nophasetransition but recrystallizationoccursforε-Fe3N1.05±3O0.017±1 under HPHT. • Phase transitionsfromγʹ-Fe4N and ζ-Fe2N toε-phasearestudied. • Ternarymetastablenitridesε-Fe2TMN (TM = Co, Ni) areobtainedunder HTHP. Bothε-Fe2CoN andε-Fe2NiN areferromagnetic (ε-Fe2CoN: Ms = 4.3 μB/f.u., Tc = 488(5) K; ε-Fe2NiN: Ms = 3.1 μB/f.u.Tc = 234(3) K). • ε-Fe2TMNxisobtainedbymodified HPHT treatments. • New binarypernitridesFe2+(N2)2-and2La3+(N2)2- (N2)4-arepredicted. In parallel, potential syntheticconditionsaregiven. Further works Synthesis ofε-Fe2TMNx(TM= Ir, Cr, Mn, etc.) under HTHP. Synthesis andcharacterizationofε-Fe3(N,C) asbulkmaterialsunderHTHP. …
Acknowledgement Philipp Marasas andSusann Leipe: HPHT experimental support Yurii Prots and Horst Borrmann: collectionofpowderand single-crystaldiffractiondata Ulrich Burkhardt: EDX and EXAFS measurements Gudrun Auffermann and Anja Völzke: chenmicalanalysis Susann Scharsach, Stefan Hoffmann and Marcus Peter Schmidt: Thermal analysis Walter Schnelle: characterizationofmagneticproperties Ralf Riedel and Dmytro Dzivenko: measurementsofhardness Michael Hanfland: beamtimeofsynthrotronradiation Financial support from SPP 1236!
