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P. Toulemonde , S. Karlsson, D. Santos-Cottin, D. Freitas, M. Núñez Regueiro,P. Strobel, A. Sulpice, J. Marcus, S. Pairis, F. Lévy-Bertrand Institut Néel, GrenobleC. Marcenat INAC, CEA, GrenobleG. Garbarino ESRF, GrenobleV. Nassif, Th. Hansen, J.A. Rodríguez Velamazán ILL, GrenobleF. Morales IIM, Universidad Nacional Autónoma de México, México
Effect of pressure and chemical substitution on the structural, magnetic and superconducting properties of
iron based arsenides and chalcogenides
- Introduction: some key parameters of iron based sup erconductors
Outline
- Isovalent substitution of Se by S (or Te) in the Tl 1-yFe2-zSe2 compoundToulemonde et al. JPCM (2013)
- Isovalent substitution of As by P in the SmFe AsO compound& comparison with the high pressure study Garbarino et al. Phys. Rev. B 84, 024510 (2011)
- Conclusion
- Isovalent substitution of As by Sb in the LaFe AsO compoundKarlsson et al. Phys. Rev. B 84, 104523 (2011)
Some words about our previous work:
In more details in this talk:
LnFeAsO“1111”
Tc max = 55 K
(AE,A)Fe2As2“122”
Tc max = 38 K
Fe1+δ(Se1-xTex)“11”
Tc = 8K to 15K
Fe-As: 2.40ÅFe-Fe: 2.80Å & 6.51Å
As-Fe-As:111.1° & 108.7°
Fe-As: 2.435ÅFe-Fe: 2.85Å & 8.74Å
α,βα,βα,βα,β(As-Fe-As):111.6° & 108.4°
Fe-Se: 2.367 ÅFe-Fe: 2.66 Å & 5.52 Å
Se-Fe-Se:111.6° & 105.4°
Introduction: new iron -based superconductors
The non superconducting parent compound:Long range AFM order (Spin Density Wave) below TNéel
� Superconductivity (SC) appears when AFM order is destabilized by chemical doping or mechanical pressure
Introduction: from Anti Ferro Magnetism to Super Conductivity
Fukazawa et al. JPSJ 77 (2008)
LnFeAs(O1-xFx)
� Superconductivity (SC) appears when AFM order is destabilized by chemical doping or mechanical pressure
Introduction: phase diagram T vs composition or T vs pressure
Zhao et al. Nat. Mat. (2008) Paglione & Green. Nat. Phys. (2010)
1111(O1-xFx) 122/HP
Lee et al.JPSJ 77 (2008)
( )
−=
= −−
12tan22tan2 11
zAsca
hAsaα
- Tc max when Fe(As/Se) 4tetrahedron is regular
i.e. @ optimized h(As/Se) and c/a values
Introduction: Crystal structure – SC relationship ?
True in compounds doped outside of the FePn layers:LnFeAs(O,F), (AE,A)Fe2As2
False in compounds substituted isoelectronically inside the FePn layers:AE(Fe1-xRux)2As2AEFe2(As1-xPx)2
Rullier-Albenque et al.PRB82
(2010)
Our previous study: isovalent substitution of As by P (chemical pressure)
or Sb in LnFeAsO (Ln=Sm,La)?
α1(x=0):111.2°α2(x=0):108.62
� Garbarino et al. Phys. Rev. B 84, 024510 (2011). & Karlsson et al. Phys. Rev. B 84, 104523 (2011).
0.0 0.2 0.4 0.6 0.8 1.0
8.20
8.25
8.30
8.35
8.40
8.45
8.50
0 1 2 3 4 5 6 7
8.20
8.25
8.30
8.35
8.40
8.45
8.50
SmFe(As1-x
Px)O series
c ax
is (
Å)
refined P content
Pressure (GPa)
SmFeAsO SmFeAs(O
0.9F
0.1)
0.0 0.2 0.4 0.6 0.8 1.0
3.88
3.89
3.90
3.91
3.92
3.93
3.940 1 2 3 4 5
3.88
3.89
3.90
3.91
3.92
3.93
3.94
SmFe(As1-x
Px)O series
a-ax
is (
Å)
refined P content
Pressure (GPa)
SmFeAsO SmFeAs(O
0.9F
0.1)
Effect of mechanical P≠ effect of chemical subst.
SmFe(As 1-xPx)O: mechanical pressure VS chemical pressure
a-axis : 100% P ↔ 5.5 GPac-axis : 100% P ↔ 7.5 GPa
Toulemonde et al, unpublished.
belt
Pistons
HP gasket
Pressure
Pressure
Sample
WC belt
High pressure –high temperature
synthesis« belt » system (Institut Néel)
6GPa - 1100°C
0.0 0.2 0.4 0.6 0.8 1.00
10
20
30
40
50
0 1 2 3 4 5
0
10
20
30
40
50SmFeAs(O
0.9F
0.1)
Tc (
K)
refined P content (x)
Tc onset (Res) Tc middle (Res) Tc onset (SQUID)
SmFe(As1-x
Px)O series
Pressure (GPa)
Tc onset Tc middle
0.0 0.2 0.4 0.6 0.8 1.0105
106
107
108
109
110
111
112
113
114
115
116
117
angle1 (x2) angle2 (x4)
(As,
P)-
Fe-
(As,
P)
angl
e (d
eg.)
refined P content (x)
SmFe(As 1-xPx)O
P substitution in SmFeAsO induces superconductivity with a T cvariation different from the one obtained under pre ssure
In strong contrast with BaFe 2(As 1-xPx)2 system !!!� Explanation: electronic structure changes (nesting, N(EF)) are different
0.0 0.5 1.00.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50Fe
As
Sm
z po
sitio
n
refined P content
O
Tc max ~ 45 K (x = 0.1)
0.0 0.5 1.02.2
2.4
2.6
2.8
3.0
3.2
Sm-As/P
Fe-Fe
Fe-As/Pinte
rato
mic
dis
tanc
e (Å
)
refined P content
Sm-O
SmFe(As 1-xPx)O series: correlation Tc ����crystallo structure.
Toulemonde et al, unpublished.
BaFe2(As 1-xPx)2 series: literature
Ba-122 system: mechanical P ~ chemical pressure (isovalent subst. P/As)
Kasahara et al. PRB 81 (2010)
Isovalent subtitution by P induces SC with Tc max = 31K for x~0.3
Pressure on BaFe2(As1-xPx) induces SC with Tc max = 31K
Klintberg et al. JPSJ 79 (2010)
LaFe(As 1-xSbx)O: M(T), Cp(T) and R(T)
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
x=0.4x=0.2
x=0.4x=0.2
∆cp/
TN
orm
.
(a)
x=0
120 140 1600.84
0.88
0.92
0.96
x=0.2
c p/TN
orm
.
80 100 120 140 160 180
0.80
0.84
0.88
0.92
M/H
Nor
m.
(b)
-6
-4
-2
0
M/H
Nor
m.
100 120 140 160
0.0
0.2
0.4
0.6
0.8
1.0
1.2
x=0.2x=0.4
d(M
/H)/
dTN
orm
.
25 50 75 100 125 150 175 200 225 250 2750.6
0.8
1.0
1.2
1.4
1.6
1.8
x=0
x=0.2
x=0.4
ρ/ρ 28
0K
(c)
Temperature (K)
80 100 120 140 160 180-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
x=0
x=0.2
x=0.4
dρ/d
TN
orm
.
����TS and TNéeldecrease with x(Sb)
S. Carlsson et al. Phys. Rev. B84, 104523, 2011.
0.0 0.1 0.2 0.3 0.4
100
110
120
130
140
150
160
170
180
-0.2 0.0 0.2 0.4 0.6 0.8 1.00.90
0.95
1.00
1.05
1.10
1.15
1.20
PM tetrag.
TN ρ T
N M/H T
N C
P T
N ND
TS ρ T
S M/H T
S C
P T
S ND
Sb content
Tra
nsiti
on te
mpe
ratu
re (K
)
(a)AFM ortho.
Fe2Sb2 thickn. Fe-As/Sb dist. Fe-Fe dist. Fe-As-Fe angle La2O2 thickn.
Nor
m. s
truc
tura
l par
amet
ers
-P content Sb content
Lébegue et al.
Wang et al.
(b)
LaFe(As 1-xSbx)O: phase diagram
�Successful replacement of As by Sb in LaFeAsO up to 40%�Physical measurements show a decrease of TNéel but no superconductivity (in the contrary of P substitution)
� NPD shows a slight increase of m(Fe) with Sb content in the low T AFM structure as expected by DFT calculations�Our analysis suggest that the crucial structural parameter controlling the magnetic interaction and the occurrence of superconductivity in 1111 arsenides is the Fe-As bond length
S. Carlsson et al. Phys. Rev. B84, 104523, 2011.
� Superconductivity is strongly enhanced by mechanical pressure:From Tc= 8K to ~35K under 6-12GPa
Introduction: sensitivity of superconductivity to pressure
G. Garbarino et al. EPL 86 (2009)
In the Fe1+δδδδSe chalcogenide ?
Okabe et al. Phys. Rev. B 81 (2010)
Guo et al. Phys. Rev. B 82 (nov. 2010)
Superconductivity at T c= 30K in K 1-yFe2-zSe2 !
i.e. at Tc similar to the one of FeSe/HP!
Could Tl1-yFe2-zSe2 be SC by adequate substitution or pressure?In this talk: Se substitution by Sulfur
Pressure effect on TlFe1.6Se2
Introduction: superconductivity in AFe 2-zSe2 !
Structure analogous to the one of 122
arsenides
But iron vacancies !(ordered or not)
A=K,Rb,Cs
Crystallographic structure of TlyFe2-zSe2
I4/mmm (N°139) space group
Atomic
site
Wyckoff
position x y z
Tl 2a 0 0 0
Fe 16i 0 1/2 3/4
Se 4e 0 0 0.3534(1)
Tunable Se/Te/S height
TlFe2-zSe2: a parent phase to induce superconductivity?
TlFe2-z(Se1-xSx)2: synthesis and x-ray diffraction- Synthesis : Tl pieces + Fe + Se/S powders reacted at 700°C in sealed quartz tube and cooled down to 280°C at 5°C/h
� Full solid solution 0<x(S)<100% in Tl0.8Fe1.5(Se1-xSx)2� Nearly single phase
Toulemonde et al, accepted in JPCM (2013).
10 15 20 25 30 35 40 45 50 55 60 65 70
+ +++
*
*
+
**
*
*
Tl0.8Fe1.5S2
100%
93(2)%
87(2)%
72(2)%58(2)%
50(2)%
45(1)%
35(1)%
16(1)%
11(1)%
inte
nsity
(a.
u.)
2 theta (deg.)
0%
refinedSulfurcontent
Tl0.8Fe1.5Se2
*
25 26 27 28 46 47 48 49 50 51
(200
)
Tl0.8Fe1.5S2
inte
nsity
(a.
u.)
2 theta (deg.)
Tl0.8Fe1.5Se2
(004
)
100%
93(2)%
87(2)%
70(2)%
58(2)%
52(2)%
45(1)%
35(1)%
16(1)%
11(1)%
0%
I4/mtetragonal supercell
typecaa ×× 55
Ibamorthorhombic supercell
type caa ×× 222
I4/mmmtetragonal cell
caa ××
z=0 (no iron vacancies)z=0.4
- Observation of supercell peaks in XRD patterns corresponding to ordered vacancies in iron plane:
Observed supercells by XRD and ED (by TEM)
z=0.5
TlFe2-z(Se1-xSx)2: crystallographic study by XRD & ED/TEM
Toulemonde et al, accepted in JPCM (2013).
- Observation of supercell peaks in XRD patterns corresponding to ordered vacancies in iron plane:
TlFe2-z(Se1-xSx)2: crystallographic study by XRD & ED/TEM
10 12 14 16 18 20 22 24 26 28
0.1
0.2
(200
) t
0.60
0.50
0.50z
0.20
0.60
(112
) t
(202
) t
(200
) t
(110
) t
x(S)
(112
) o
(022
) o
(110
) o
(020
) o
(101
)
(004
)
(202
) t
(112
) t
(110
) t
inte
nsity
(a.
u)
2 theta (deg.)
(002
)
0.20
I4/mtetragonal supercell
typecaa ×× 55
Ibamorthorhombic supercell
type caa ×× 222
Toulemonde et al, accepted in JPCM (2013).
0 10 20 30 40 50 60 70 80 90 1000.346
0.348
0.350
0.352
0.354
0.356
0.358
Sulfur content (from Rietveld refinement)
z(S
e,S
) po
sitio
n�nearly isotropic decrease (~3.5%) of the lattice with S content�c/a ratio quasi constant (~3.58)
TlFe2-z(Se1-xSx)2: lattice parameters & bond length versus x(S)
�continuous decrease ofFe-Ch bond length & Fe- Ch height
with S content
-40 -20 0 20 40 60 80 100
3.75
3.78
3.81
3.84
3.87
3.90
3.93
3.9640 20 0 -20 -40 -60 -80 -100
c-axis (Te subst.)a-axis (Te subst.)
Tellurium content (nominal)
c-axis (S subst.)c-axis (literature)a-axis (S subst.)a-axis (literature)
Sulfur content (refined)
a-ax
is (
Å)
13.3
13.4
13.5
13.6
13.7
13.8
13.9
14.0
14.1
c-ax
is(Å
)
2.30
2.32
2.34
2.36
2.38
2.40
2.42
2.44
2.46
our study literature
Fe-
Se/
S b
ond
leng
th(Å
)
Toulemonde et al, accepted in JPCM (2013).
�optimized Fe-Ch height reached (i.e. the one for Tc ~30K in FeSe/HP)
TlFe2-z(Se1-xSx)2: Fe-(Se/S) height & (Se/S)-Fe-(Se/S) angle versus x( S)
�distorted FeSe4tetrahedron becomes nearly
regular in Tl0.8Fe1.5S2
But No superconductivity!…
0 10 20 30 40 50 60 70 80 90 100104
105
106
107
108
109
110
111
112
α-angle literature
β
α S
e/S
-Fe-
Se/
S a
ngle
(de
g.)
Sulfur content (from Rietveld refinement)
α
104
105
106
107
108
109
110
111
112 β-angle literature
ββ ββ S
e/S
-Fe-
Se/
S a
ngle
(de
g.)
0 10 20 30 40 50 60 70 80 90 100
1.32
1.34
1.36
1.38
1.40
1.42
1.44
1.46
1.48
1.50
Sulfur content (from Rietveld refinement)
interplane Fe-Se/S distanceliterature
Fe-
Se/
S h
eigh
t (Å
)
1.39
Toulemonde et al, accepted in JPCM (2013).
TlFe2-z(Se1-xSx)2: low T and high T M(T) and R(T)
200 250 300 350 400 450 500
0.04
0.06
0.08
0.1
0.12
0.14
0.16
1.8x10-4
1.8x10-4
1.9x10-4
1.9x10-4
2.0x10-4
R(O
hm)
T(K)
R(T)
TNéelx=0.40
M(A
.m2 )
M(T)
0.1
1
10
R (
Ohm
)
TNéel
= 344K
0.1
1
10
R (
Ohm
)
Tl0.8
Fe1.5
S2
T2 ~ 55K
0 50 100 150 200 250 300 350 400 450 500 550
0.1
1
10
100
1000
10000
TNéel
= 425K
T(K)
R (
Ohm
)
T2 ~ 120K
0.1
1
10
100
1000
10000Tl0.8
Fe1.5
Se2
R (
Ohm
)
� AFM with high T Néel� insulating @ low T
Toulemonde et al, accepted in JPCM (2013).
TlFe2-z(Se1-xSx)2: low T and high T M(T) and R(T)
� Tnéel decreases with S content� but No superconductivity induced by S substitution
300 330 360 390 420 450 480 510 540 570
2
4
6
8
10
R/R
(573
K)
T(K)
nominalx(S) content
0 0.2 0.45 0.75 0.9 1
Toulemonde et al, accepted in JPCM (2013).
0 10 20 30 40 50 60 70 80 90 100
340
360
380
400
420
440
460
our series (from R(T)) literature our series (from M(T))
TN
éel(K
)
Sulfur content (from Rietveld refinement)
� No superconductivity observed in S- (or Te) substituted samples� direct linear relationship between TNéel & Fe-Se/S height
TlFe2-z(Se1-xSx)2: conclusion
Toulemonde et al, accepted in JPCM (2013).
1.30 1.35 1.40 1.45 1.50320
340
360
380
400
420
440
460
480
our series literature
TN
éel (
K)
Fe-Se/S height (Å)
2.30 2.35 2.40 2.45320
340
360
380
400
420
440
460
480
our series literature
TN
éel (
K)
Fe-Se/S bond length (Å)
Conclusion
• SmFeAs(O 0.81F0.19) under HP- 1st study showing the direct correlation between the regularity of the tetrahedron FeAs4 & Tc
• SmFe(As 1-xSbx)O
- Sb substitution = “negative” chemical pressure
- phase diagram: T(SDW) ���� with Sb content
- superconductivity in HP-HT synthesized samples (probably because of oxygen vacancies)!
• SmFe(As 1-xPx)O
- ISOelectronic substitution but Superconductivity (!) like in BaFe2(As1-xPx)2
- Chemical pressure (As/P) effect ≠ mechanical pressure in 1111 system
- Evolution of the electronic structure with P substitution? Need theoretical investigation…
• TlFe2-y(Se1-xSx)2
- direct linear relationship between T Néel & Fe-Se/S height (or Fe-Se/S bond length)
- no superconductivity observed over the full substitution range!
- which ingredient is missing? Higher N(EF)? No phase separation (Tl content fixed)?