Workshop on Atomic-Scale Challenges in Advanced Materials: Defects in Materials Turku, Finland
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Transcript of Workshop on Atomic-Scale Challenges in Advanced Materials: Defects in Materials Turku, Finland
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Composition dependent properties of Ni2MnGa based ferromagnetic shape memory
alloys
Qing-Miao Hu
Institute of Metal Research, Chinese Academy of Sciences
Wenhua Road 72, Shenyang 110016, China
Workshop on Atomic-Scale Challenges in Advanced Materials:
Defects in MaterialsTurku, Finland
August 22-23, 2013
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Co-workers
Dr. Hu-Bin LuoInstitute of Metal Research, Chinese Academy of Sciences
Dr. Chun-Mei LiInstitute of Metal Research, Chinese Academy of Sciences
Royal Institute of Technology/Uppsala University , Sweden
Prof. Rui YangInstitute of Metal Research, Chinese Academy of Sciences
Prof. Börje JohanssonRoyal Institute of Technology/Uppsala University , Sweden
Prof. Levente VitosRoyal Institute of Technology/Uppsala University , Sweden
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Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
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Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
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Background and MotivationGeneral
Mn: 3.86, Ni: <0.3, Ga: 0.00
Magnetic Transition:
Ferromagnetic Paramagnetic
Ni2MnGa: Heusler Alloys
c/a = 1
Structure Transition:
Cubic L21 Austinite
Orthorhombic Martensite
Reversible: Shape Memory Effect
c/a >1
c/a <1
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202 K 376 K
Coupling between the structure and magnetic transitions leads to some unique properties:
•Giant magnetocaloric effect; •Magnetostriction; •Magnetoresistance.
Potential applications: •Magnetic refrigeration;•Magnetostrictive
transducers;•etc.
Background and MotivationGeneral
Perfect Ni2MnGa
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How to control composition to achieve desirable TM? Can we find some easy predictors to connect composition and TM?
Khovaylo, et al., Phys. Rev. B 72, 224408 (2005)
Background and MotivationGeneral
Tsuchiya, et al., ISIJ International 46, 1283 (2006)
Fe doped Ni2MnGa
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1. Number of valence electrons per atom (e/a) and TM
Chernenko, et al., Acat Mater. 50, 53 (2002)
Background and MotivationPredictors for the composition dependence of TM
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2. c/a ratio of martensite and TM
Lanska, et al., J. Appl. Phys 95, 8074 (2004)
Background and MotivationPredictors for the composition dependence of TM
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3. Energy difference between austinite and martensite (E) and TM
Chen, et al., Appl. Phys. Lett. 89, 231921 (2006)
Background and MotivationPredictors for the composition dependence of TM
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Bungaro and Rabe, Phys. Rev. B, 2003
cdcdT
10
dTdc
T1
Ren and Otsuka, Mater Sci Forum (2000)
NiTi SMA: Larger C of the austenite corresponding to lower TM.4. Elastic modulus Cand TM?
Background and MotivationPredictors for the composition dependence of TM
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Background and MotivationPhase stability: Structure of modulated martensite
The modulated structure is very complex: shear: changing c/a; shuffle: wave-like movement of atoms on [110]
Alloying effect on the modulated structure?
a
a
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Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
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MethodEMTO-CPA
First-principles method based on density functional theory
Basis Sets: Exact muffin-tin orbitials (EMTO), spdf
Exchange-correlation functional: GGA-PBE
Coherent potential approximation for the random distribution of alloying atoms.
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Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
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Geometry of Ni2MnGa projected to (001) plane
Ga
Mn
Ni
Ni2MnGa
Ni2-xMnGa1+x
Indirect site-occupancy
MnNi
GaMn
GaNi
Direct site-occupancy
Results and DiscussionSite-occupancy in Ni2MnGa based alloys
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Off-stoichiometric: Indrect: Ga-rich Ni-deficient alloys, forming
GaMn and MnNi.
Phys. Rev. B 79, 144112 (2009); 84, 024206 (2011)
Results and DiscussionSite-occupancy in Ni2MnGa based alloysFree energy of different site-occupancy configurations
Fe/Co/Cu doped:Indirect: Fe-doped Ga-deficient alloys
Co-doped Mn- or Ga-deficient alloysCu always take direct site-occupancy
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Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
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Results and DiscussionElastic modulus and TM
7.0 7.2 7.4 7.6 7.8141
144
147
150
153
156
7.0 7.2 7.4 7.6 7.810
15
20
90
95
100
105
Bulk
Mod
ulus (
GPa)
e/ a
Shea
r Mod
ulus
(GPa
)
C44 C
e/ a
9 12 15 180
100
200
300
400
500
600
T M (K
)
C7.35 7.50 7.65 7.80
0
100
200
300
400
500
600
T M (K
)
e/ a
Off-stoichiometric Ni2MnGa
Phys. Rev. B 79, 144112 (2009)
Fe/Co/Cu doped Ni2MnGa
7.4 7.5 7.6 7.7 7.8 7.9
2
4
6
8
10
Ni2+xMnGaCux
Ni2Mn1-xGaCux
Ni2MnGa1-xCux
Ni2+xMnGaCox
Ni2Mn1-xGaCox
Ni2MnGa1-xCox
Ni2+xMnGaFex
Ni2Mn1-xGaFex
Ni2MnGa1-xFex
C' (G
Pa)
e/ a
2 4 6 8 1050
100150200250300350400450
7.44 7.52 7.60 7.68 7.7650100150200250300350400450
Ni2+xMnGaCox
Ni2Mn1-xGaCox
Ni2MnGa1-xCox Ni2+xMnGaFex
Ni2Mn1-xGaFex
Ni2MnGa1-xFex
T M (K
)
C' (GPa)
Ni2+xMnGaCux
Ni2Mn1-xGaCux
T M (K
)
e/ a
Phys. Rev. B 84, 024206 (2011)
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Results and DiscussionElastic modulus and TM
0.0 0.2 0.4 0.6 0.8 1.0
6
8
10
12
14
16
C' (G
Pa)
Atomic fraction of Al, c
C'
100
120
140
160
180
200
TM
T M (K
)
Ni2Mn(Ga1-xAlx)
Acta Mater. 59, 5938(2011)
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Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
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Results and DiscussionPhase stability of Ni2Mn(Ga1-xAlx)
)sinsin(sin 56
254
152 jAjAjj
Acta Mater. 59, 5938(2011)
Martynov et al.. J. Phys. III 2, 739(1992)
a
a
Two degrees of freedom optimization:
Shear: c/a; Shuffle:
5L modulated martensite:
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Results and DiscussionPhase stability of Ni2Mn(Ga1-xAlx)
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
-1
0
1
2
3 (a) Ni2MnGa
non-modulated modulated
E (m
Ry)
c/a
0.90 0.92 0.94 0.96-0.12-0.10-0.08-0.06-0.04
E
(mR
y)
c/a
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
-1
0
1
2
3 (b) Ni2Mn(Ga0.9Al0.1)
non-modulated modulated
E (m
Ry)c/a
0.90 0.92 0.94 0.96-0.08-0.06-0.04-0.020.00
E (m
Ry)
c/a
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
-1
0
1
2
3 (c) Ni2Mn(Ga0.8Al0.2)
non-modulated modulated
E (m
Ry)
c/a
0.90 0.92 0.94 0.96-0.030.000.030.060.09
E (m
Ry)
c/a
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.03
0.06
0.09
0.12
E
AM
(m
Ry)
c
Critical point
0.0 0.1 0.2 0.3 0.9 1.00
50100150200
T M (K
)
c
No MT
Exp.
EAM=EA-EM
Martensite more stable
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Results and DiscussionPhase stability of Ni2(Mn1-xFex)Ga
2 4 6 8 1050
100150200250300350400450
7.44 7.52 7.60 7.68 7.7650100150200250300350400450
Ni2+xMnGaCox
Ni2Mn1-xGaCox
Ni2MnGa1-xCox Ni2+xMnGaFex
Ni2Mn1-xGaFex
Ni2MnGa1-xFex
T M (K
)
C' (GPa)
Ni2+xMnGaCux
Ni2Mn1-xGaCux
T M (K
)
e/ a
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Results and DiscussionPhase stability of Ni2(Mn1-xFex)Ga
L21 austinite becomes elastically softer with increasing Fe: Lattice vibration contribute more to the free nergy accordingly, stabilizing L21
EAM=EA-EM
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Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
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Summary
• We predict that indrect site-occupation occurs in some of the off-stoichiometric and Fe/Co/Cu doped Ni2MnGa alloys.
• The general TM~C′ correlation works for some of the alloys for which the TM~e/a correlation fails. However, there are several cases where both the general TM~C′ and TM~e/a correlations break down.
• We present a feasible approach to study the 5-layer modulated (5M) martensitic structure of Ni2MnGa-based alloy using first-principles methods. By using this approach, the 5M martensitic structure of Ni2MnGa is reasonably reproduced and the Al/Fe-doping effects are predicted.
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Thank you for your attention!