Synthesis of ternary varieties of ε-Fe N: Experiment and theory. Joint ...

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03-10
Synthesis of ternary varieties of -Fe 3N:
Experiment and theory.
Joint Project:
Rainer Niewa, Dieter Rau, Univ. Stuttgart
Ulrich Schwarz, Carola Müller, MPI CPfS
Richard Dronskowski, Michael Wessel, RWTH Aachen
Max-Planck-Institut
für Chemische Physik fester Stoffe

www.iac.uni-stuttgart.de
03-10
Max-Planck-Institut
für Chemische Physik fester Stoffe
RhFe 3N
A. Houben, P. Mueller, J. von Appen, H. Lueken,
R. Niewa, R. Dronskowski, Angew. Chem. Int. ed.
(2005), 44, 7212-7215.

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03-10
Theoretical Method & Strategy
Used Programs:
• DFT calculations using the program VASP
- generalized gradient approximation (GGA) of PBE-type
- projector-augmented wave (PAW) potentials
- Energy cut-off: 500 eV
• Thermochemical properties using the program FROPHO
Procedure:
- Investigating the influence of pressure
- Investigating the influence of temperature
→ Finding the synthesis conditions
Max-Planck-Institut
für Chemische Physik fester Stoffe

www.iac.uni-stuttgart.de
03-10
→ no high-pressure synthesis
Max-Planck-Institut
für Chemische Physik fester Stoffe

www.iac.uni-stuttgart.de
03-10
→ no high-temperature synthesis
Max-Planck-Institut
für Chemische Physik fester Stoffe

www.iac.uni-stuttgart.de
03-10
→ no high-pressure synthesis
Max-Planck-Institut
für Chemische Physik fester Stoffe

www.iac.uni-stuttgart.de
03-10
→ high-temperature synthesis possible
Max-Planck-Institut
für Chemische Physik fester Stoffe

www.iac.uni-stuttgart.de
03-10
Phase Diagram Fe–N
K. H. Jack, Proc. Roy. Soc. A 208 (1951) 200.
H. A. Wriedt, N. A. Gokcen, R. H. Nafziger, Bull. Alloy Phase Diagrams 8 (1987) 355.
P
Max-Planck-Institut
für Chemische Physik fester Stoffe
-Fe 3N 1+x
(P6 322)

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03-10
Experimental Techniques
Multi Anvil Module with Uniaxial Press
• Walker-type module
• MgO/Cr 2O 3 octahedra, h-BN crucibles
• Resistance heating by graphite tubes surrounding the
sample crucible
• Pressure and temperature calibration via electrical
resistivity of Bi and thermocouples
• Max. P = 15(2) GPa and T = 1600(200) K
Max-Planck-Institut
für Chemische Physik fester Stoffe

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03-10
Treatment: Result:
Fe/Co in N 2, NH 3
T 1100 °C, P = 0.1 MPa -Fe 3N + Fe 1–xCo x
High pressure
High Temperature
Formation of
-phases
Intensity
CoK
30 40 50 60 70 80 90 100
Diffraction Angle 2/ Degree
Max-Planck-Institut
für Chemische Physik fester Stoffe
Co + Fe 4 N, 15 GPa, 1200°C
Co + Fe 3 N, 15 GPa, 1200°C
-Fe 3 N Educt
Fe 4 N Educt

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03-10
Synthesis Experiments
Treatment: Result:
Fe/Co in N 2, NH 3
T 1100 °C, P = 0.1 MPa -Fe 3N + Fe 1–xCo x
Hp ht synthesis
of -phases
Intensity
CoK
20 30 40 50 60 70 80 90 100
Max-Planck-Institut
für Chemische Physik fester Stoffe
Co + Fe 4 N, 7 GPa, 1100 °C
Co + Fe 3 N, 9 GPa, 700 °C
-Fe 3 N 0.75
hp-Fe 4 N
-Fe 3 N
Diffraction Angle 2 / Degree

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03-10
Intensity
CoK
7 GPa, 1100°C
30 40 50 60 70 80 90 100
Diffraction Angle 2/ Degree
Max-Planck-Institut
für Chemische Physik fester Stoffe
Co + Fe 4 N
15 GPa, 1200°C

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03-10
Intensity
CoK
30 40 50 60 70 80 90 100
Diffraction Angle 2 / Degree
Max-Planck-Institut
für Chemische Physik fester Stoffe
Co + Fe 3 N
15 GPa, 1200°C
7 GPa, 1100°C

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03-10
EDX
Co + Fe 3N
9 GPa, 1100 °C
Main Phase 1-3
Fe : Co
66(4):34(4)
Contamination
Fe : Co
50 : 50 4,5
90 : 10 6, 7, 10
Max-Planck-Institut
für Chemische Physik fester Stoffe

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03-10
Treatment: Result:
Fe/Co in N 2, NH 3
T 1100 °C, P = 0.1 MPa -Fe 3N + Fe 1–xCo x
-Fe 3N/Co -(Fe,Co) 3N + Fe 1–xCo x
Fe 4N/Co
P = 7 GPa
T 1100 °C
-Fe 3N/Co -(Fe,Co) 3N + -Fe(Co)
Fe 4N/Co
P = 15 GPa
T = 1200 °C
a = 4.6828 – 4.8016 Å
c = 4.3705 – 4.4269 Å
Fe3N0.75 – Fe3N1.5 a = 4.5771 Å
c = 4.3136 Å
Max-Planck-Institut
für Chemische Physik fester Stoffe

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03-10
Composition Determination
-(Fe,Co) 3N
930 °C, p > 7 GPa
Literature:
a = 4.5771 Å
c = 4.3136 Å
n(Fe) : n(Co) = 0.66 : 0.34
Fe 2Co 1N x
-Fe a = 4.283/3 Å (2.473 Å)
c = 3.962 Å
-Fe 3–xCo xN 0 x 0.8 nanoparticles
(multi-phase products)
unit cell parameters do not change with x
Mössbauer spectroscopy
-Fe 2.4Co 0.6N a = 4.774/3 Å (2.756 Å)
c = 4.403 Å
Mao Hokwang et al., J Appl. Phys. 1967.
N. S. Gajbhiye et al., Hyper. Interact. 2004, 2005; Mater. Res. Bull. in press.
Max-Planck-Institut
für Chemische Physik fester Stoffe

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03-10
Synthesis Experiments
Treatment: Result:
Fe/Ir in N 2, NH 3
T 1100 °C, P = 0.1 MPa -Fe 3N + Ir
High pressure
High temp.
Intensity
Co-K1
10 20 30 40 50 60 70 80 90 100
Max-Planck-Institut
für Chemische Physik fester Stoffe
-Fe 3 N 0.75
hp-Fe 4 N
Diffraction Angle 2 Degree
Ir + Fe 3 N
9 GPa, 1600 °C
9 GPa, 1450 °C

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03-10
Treatment: Result:
Fe/Ir in N 2, NH 3
T 1100 °C, P = 0.1 MPa -Fe 3N + Ir
-Fe3N/Ir -(Fe,Ir) 3N + ?
T > 1200 °C, P > 9 GPa
a = 4.794 Å
c = 4.419 Å
Fe 3N 0.75 – Fe 3N 1.5
a = 4.6828 – 4.8016 Å
c = 4.3705 – 4.4269 Å
Max-Planck-Institut
für Chemische Physik fester Stoffe

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03-10
DH (kJ/mol) DV (cm 3 /mol)
-Fe 3N + Co – Fe 0.0 0.00
2 Fe + N + Co 28.7 7.03
-Fe 2CoN 14.8 0.03
→ reaction not driven by pressure
- 8 structures (ordered and statist. distributed)
- a = 4.625 Å, c = 4.341 Å
- c/a ratio in all structures approx. 1.07
- Difference in energy less than 3 kJ/mol
→ statistical distribution of Fe and Co atoms
Max-Planck-Institut
für Chemische Physik fester Stoffe

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03-10
DH (kJ/mol) DV (cm 3 /mol)
-Fe 3N + Ir – Fe 0.0 0.00
2 Fe + N + Ir 28.7 7.03
-Fe 2IrN 95.3 0.69
→ reaction not driven by pressure
- 8 structures (ordered and statist.distributed)
- a = 4.820 Å, c = 4.476 Å
- c/a ratio in all structures approx. 1.08
- statistical distribution of Fe and Co atoms is lower
in energy by approx. 10 kJ/mol
Max-Planck-Institut
für Chemische Physik fester Stoffe

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03-10
-Fe 3N (COHP)
No antibonding states → stable
Max-Planck-Institut
für Chemische Physik fester Stoffe

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03-10
-CoFe 2N (COHP)
antibonding states → reduced stability compared to - Fe 3N
Max-Planck-Institut
für Chemische Physik fester Stoffe

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03-10
-IrFe 2N (COHP)
antibonding states → reduced stability compared to - Fe 3N
Max-Planck-Institut
für Chemische Physik fester Stoffe

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03-10
Conclusion
Predicted VON was not (yet) obtained at elevated temperatures
and pressures:
V 2O 5 decomposes into V 2O 3, VN does not react
From iron nitrides and Co at elevated temperatures and
pressures above 7 GPa a hexagonal phase (-type) with unit
cell parameters between -Fe and -Fe 3N 1–x is obtained.
According to EDX analysis the phase contains Fe and Co and
represents probably a new phase -Fe 2CoN 1–x
Similarly, from iron nitrides and Ir at elevated pressures and
temperatures -(Fe,Ir) 3N 1–x was obtained
The formation of -Fe 2CoN and -Fe 2IrN seems to be driven by
temperature; pressure needed to keep nitrogen in the reaction
(Co, Ir)-N and (Co, Ir)-Fe antibonding states result in the
reduced stability of -Fe 2(Co, Ir)N compared to -Fe 3N
Max-Planck-Institut
für Chemische Physik fester Stoffe