effect of pressure and chemical substitution on the structural,...

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).

Isovalent substitution of As by P in SmFeAsO

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)

Isovalent substitution of As by Sb in LaFeAsO

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.

Part 1:

Isovalent substitution of Se by S in TlFe2-zSe2

� 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


- 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


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

)


�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.)


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


interplane Fe-Se/S distanceliterature

Fe-

Se/

S h

eigh

t (Å

)

1.39


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


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


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

)


� No superconductivity observed in S- (or Te) substituted samples� direct linear relationship between TNéel & Fe-Se/S height

TlFe2-z(Se1-xSx)2: conclusion


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)?

effect of pressure and chemical substitution on the structural,...

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