High-pressure-high-temperature synthesis,
characterization and quantum-chemical
calculations of metal nitrides
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
Fe
③
N
ε-Fe3N, hexagonal/trigonal
①
ζ-Fe2N, orthorhomic
TM
Phase diagram of the binary system Fe-N.
1.
2.
3.
4.
High-pressure behaviors and single-crystal growth of ε-Fe3Nx under high-pressure, hightemperature (HPHT).
Phase transition from γʹ -Fe4N and ζ-Fe2N to ε-Fe3Nx and subsequent recrystalization under HPHT.
Synthesis and characterization of ε-Fe2TMN (TM = Co, Ni), ε-Fe2IrNx and ε-Fe3(N, C).
Theoretical prediction of new pernitrides 2La3+(N2)2- (N2)4-.
2
K.H. Jack, Proc. Roy. Soc. A 1951, 208, 200.
1. ε-Fe3Nx: high-pressure behaviors
Fe3N1.05±3O0.017±1
B0 = 172(4) GPa, B‘ = 5.7
Experimental data
Theoretical simulation
Theoretical simulation
Pressure-volume data of ε-Fe3N.
No phase transition occurs under high pressure.
c/a ratio of the hexagonal unit-cell parameters of
ε-Fe3N as a function of pressure.
Upon pressureincrease,
thec/aratioincreasestowardthe ideal value
(0.943 = 1.633/ 3).
3
R. Niewa et al. Chem. Mater. 2009, 21, 392.
1. ε-Fe3Nx: HPHT single-crystal growth
MgO/Cr2O3
Zirconia
Molybdenum
MgO
Graphite
Boron Nitide
Sample
p = 15(2) GPa, T = 1600(200) K
Starting material: Fe3N1.05±3O0.017±1
Theoretical analysis reveals that P312 is
more energetically favored for Fe3N1.1.
The composition refined from P312 is
much colser to the expected composition.
Two-stage multianvil device with a walker-type module
Refined fomula for ε-Fe3Nx in sapce group P312 and P6322.
Formation enthalpies and average magnetic moments on
Fe atoms for ε-Fe3N and ε-Fe3N1.1.
4
2. Phase transition from γʹ-Fe4N to ε-Fe3N0.75
0K
Endothermic
②
Energy–volume diagram for the system εFe3N+Fe, γʹ-Fe4N and ε-Fe4N as calculated by
density-functional theory.
TM
Induced by pressure! 0 K
ε-Fe4N
Herein, a phase trantion from γʹ-Fe4N to εFe4N (Fe3N0.75) at 7 GPa is predicted based on
density-functional theory!
γʹ-Fe4N
Enthalpy-difference–pressure diagram for Fe4N as
calculated by density-functional theory.
5
R. Niewa et al., J. Alloys Compd. 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 transition from γʹ-Fe4N to ε-Fe3N0.75
under HPHT is observed
The nitrogen content deduced from the
eqations is reasonablly agreement with
results by 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)
Lattice parameters vs nitrogen content in Fe3Nx.
6
K. Guo, R. Niewa, D. Rau, Y. Prots, W, Schnelle, U. Schwarz, in preparation.
2. Crystal structure of ε-Fe3N0.75
Refined fomula for ε-Fe3Nx
in space group P312 and P6322.
CA: Fe3N0.760(6)O0.018(2)
P312
Both descriptions for the crystal structure
in space group P312 and P6322 look like
reasonable results.
Landau theory indicates that a change in
space group within a homogeneity range
is not possible!
P6322
Combined the earlier results, space
group P312 is suggested.
7
2. Thermal properties of ε-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.
8
2. Magnetic properties of ε-Fe3N0.75
2 K: 183 emu/g = 5.83 μB
FM-Fe3N0.75
NM-Fe3N0.75
ε-Fe3N0.75
γʹ-Fe4N
FM-Fe4N
NM-Fe4N
9
2. Magnetic moments in ε-Fe3N and ε-Fe3N0.75
(□-FeΙ-N)
(N-FeΠ-N)
Density-functional theory!
10
2. Phase transition from ζ-Fe2N to ε-Fe3N1.5
②
11
U. Schwarz, et al., Eur. J. Inorg. Chem. 2009, 12, 1634.
2. High-pressure behaviors of ζ-Fe2N
Starting material: ζ –Fe2N0.986(6)O0.0252(8)
No phase transition occurs under high
pressure
Bulk modulus: B0 = 172.1(8) GPa
B0ʹ = 5.24(8)
XRPD taken on ζ-Fe2N at different pressures in a DAC.
Enthalpy-difference for ε-Fe3N1.5 in space group P312 and
P6322, as well as 2Fe+α-N compared to ζ-Fe2N.
Theoretical simulation
Pressure–volume data of ζ-Fe2N.
This phase transition canʹt be induced only by the pressure!
12
2. Phase transition from ζ-Fe2N to ε-Fe3N1.5
Conditions: p = 15(2) GPa, T = 1600(200) K
The phase transition is probably
induced by the temperature
Refinements with P312 lead to
unreasonable results althoulh it
is energetically favored baesd on
quantum theoretical omputations
Enthalpy-difference for ε-Fe3N1.5 in space
group P312 and P6322, as well as 2Fe+α-N
XRPD diagrams of ζ-Fe2N and the product of the HPHT treatment.
compared to ζ-Fe2N.
Refined fomula for ε-Fe3Nx in sapce group P6322.
13
3. Synthesis of ε-Fe2TMN (TM = Co, Ni)
Starting material: ζ –Fe2N0.986(6)O0.0252(8) and
TM powders
Si
Si
Conditions: p = 15(2) GPa, T = 1473(150) K
Si
Si Si
BN
TM
XRPD for the starting material ζ-Fe2N, the products
-Fe2CoN and -Fe2NiN.
  Fe 2 N  TM  Fe 2 TMN
XRPD results reveal pure phases for ε-Fe2TMN (TM = Co, Ni)!
14
K. Guo, R. Niewa, D. Rau, U. Burkhardt, W. Schnelle, U. Schwarz, submitted.
3. Characterization of ε-Fe2TMN (TM = Co, Ni)
ε-Fe2CoN
ε- Fe2NiN
Typical optical micrographs of (a) -Fe2CoN and (b) -Fe2NiN.
The compositions detected by EDXS and CA.
Homogeneous composition
Nominal
composition
EDX
CA
(N, wt%)
Real composition
Fe1.931Co1.069Nx
Metal ration: Fe : Co = 1.99(6) : 1.01(6)
Fe : Ni = 1.97(2) : 1.03(2)
Fe2CoN
Fe2NiN
Fe2.020Co0.980Nx 6.92±0.32
Fe2.019Co0.981Nx
Fe1.976Ni1.024Nx
Fe1.952Ni1.048Nx 8.08±0.45
Fe1.973Ni1.027Nx
Fe1.99(6)Co1.01(6)N0.91(4)
Fe1.97(2)Ni1.03(2)N1.07(6)O0.03(1)
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3. Thermal properties of ε-Fe2TMN (TM = Co, Ni)
ε-Fe2CoN
ε-Fe2NiN
Enthalpy-difference for ε-Fe2TMN and thier competitive phases under varing pressure
Based on DFT, both ε-Fe2CoN and ε-Fe2NiN are metalstable
The reactions are triggered by the temperature but the pressure
play an important role in the preservation of nitrogen content
16
3. Thermal properties of ε-Fe2TMN (TM = Co, Ni)
ε-Fe2CoN
N: 6.92±0.32%
ε-Fe2NiN
N: 8.08±0.45%
TG-DSC for ε-Fe2TMN.
ε-Fe2TMN decompose above 750 K involving the loss of nitrogen
17
3. Magnetic properties of ε-Fe2TMN (TM = Co, Ni)
Fe2CoN: 4.3μB/f.u.
Fe2NiN: 3.1μB/f.u.
Fe2CoN: 488(5) K
Fe2NiN: 234(3) K
Fe3N: Ms = 6 μB; Tc = 575(3) K
A. Leineweber et al., J. Alloys Compd., 1999, 288, 79.
18
3. Synthesis of ε-Fe2IrNx
Fe
1.26
Co
1.25
–2
Ru
1.34
7
Rh
64
Os
1.35
1.34
Ir
1.36
1a
• Fe
3c
•N
1b
Pd
1.37
–47
Pt
2
DRHth (kJ mol–1)
1.24
–8
–23
108
•M
Ni
1.39
–74
No experimental evidence!
M rM
DRHth
γʹ -IrFe3N: high-pressure
phase, stable beyond 37 GPa,
ferromagnetic
Enthalp-pressure diagram for γʹ-IrFe3N and thier competing phases
19
J. von Appen, R. Dronskowski, Angew. Chem. Int. Ed. 2005, 44, 2
3. Synthesis of ε-Fe2IrNx
Changing synthetic pressure
Changing synthetic temperature
20
3. Synthesis of ε-Fe2IrNx
Fe3N, a = 4.6982(3) Ǻ, c = 4.3789(4) Ǻ
21
3. Synthesis of ε-Fe2IrNx
12 Gpa, 1100 oC
12 Gpa, 1100 oC
5 Gpa, 1300 oC
0 Gpa
0 Gpa
Characterization of
composition and
physical properties are
needed to be done.
22
3. Synthesis of bulk ε-Fe3(N,C)
The nitrogen content in ε-Fe3(N,C) can be tuned to a certain extent.
23
4. Prediction of new pernitrides 2La3+(N2)2- (N2)4-
DHR = –11 kJ mol–1 at
absolute zero T
B0 = 86 GPa
N–N = 1.30 Å
24
M. Wessel, R. Dronskowski, J. Am. Chem. Soc. 2010, 132, 2421.
4. Prediction of new pernitrides 2La3+(N2)2- (N2)4300 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.
25
Conclusions
1. No phase transition but recrystallization occurs for ε-Fe3N1.05±3O0.017±1 under HPHT.
2. Phase transitions from γʹ-Fe4N and ζ-Fe2N to ε-phase are studied.
3. Ternary metastable nitrides ε-Fe2TMN (TM = Co, Ni) are obtained under HTHP. Both ε-
Fe2CoN and ε-Fe2NiN are ferromagnetic (ε-Fe2CoN: Ms = 4.3 μB/f.u., Tc = 488(5) K; εFe2NiN: Ms = 3.1 μB/f.u. Tc = 234(3) K).
4. ε-Fe2TMNx is obtained by modified HPHT treatments.
5. New binary pernitrides Fe2+(N2)2- and 2La3+(N2)2- (N2)4- are predicted. In parallel, potential
synthetic conditions are given.
Further works
1. Synthesis of ε-Fe2TMNx (TM = Ir, Cr, Mn, etc.) under HTHP.
2. Synthesis and characterization of ε-Fe3(N,C) as bulk materials under HTHP.
…
26
Acknowledgement
Philipp Marasas and Susann Leipe: HPHT experimental support
Yurii Prots and Horst Borrmann: collection of powder and single-crystal diffraction data
Ulrich Burkhardt: EDX and EXAFS measurements
Gudrun Auffermann and Anja Völzke: chenmical analysis
Susann Scharsach, Stefan Hoffmann and Marcus Peter Schmidt: Thermal analysis
Walter Schnelle: characterization of magnetic properties
Ralf Riedel and Dmytro Dzivenko: measurements of hardness
Michael Hanfland: beamtime of synthrotron radiation
Financial support from SPP 1236!
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Thanks for your attention!
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