24. P. Diko, Influence of Post-growth Thermal

24. P. Diko, Influence of Post-growth Thermal

Influence of Post-growth Thermal Treatments on
Critical Current Density
of TSMG YBCO Bulk Superconductors
P. Diko, V. Antal, K. Zmorayová, M. Šefčiková, J. Kováč,
Institute of Experimental Physics SAS, Watsonova 47, 04001 Košice, Slovakia
X. Chaud
CNRS/CRETA, 25, Avenue des Martyrs, 38042 Grenoble Cedex 9, France
M. Eisterer, H. W. Weber
Vienna University of Technology, Atominstitut, Stadionallee 2, 1020 Vienna, Austria
X. Yao
Department of Physics, Shanghai Jiao Tong University, 800 Shanghai, People’s Republic of China
I. Chen
Department of Materials Science and Engineering, NCKUTainan, Taiwan
Outline
Weak links caused by post growth treatment
- sample cross section reduction by a/b-microcracks
and oxygenation cracks
-elimination of oxygenation cracks by high pressure oxygenation
Chemical pining centers influenced by post growth treatment
- Optimum dopant concentration for chemical pinning
- clustering of Al in Y123 lattice
- Ag partition coefficient in YBCO TSMG bulk
Conclusions
Reduction of the effective cross section by
211 particles and a/b-microcracks
M. Eisterer at al. 2005, ATI Vienna
4 mm
dc211  400 nm for YBa2Cu3O7
c-OC
Formation of oxygenation cracks
a,b
a,b
3.5 x 3.5 x 10 mm3
100 mm
First oxygenation
a
c
a/b-OC
Oxygenation time 20-30 hours
Diffusin length 50 µm
a/b-MIC
c-OC
calculated oxygenation time > 2 years
Diko et al. 2006
Oxygenation at 450 °C
a,b
c
10 mm
Cross-section reduction by a/c- oxygenation cracks
Jc = Jc0{ 1 – 0.93 (l/ λ)1/2}
λ2
λ1
a
l
Line 2
Line 1
typical l/λ ≈ 0.5
Cross section reduced to ≈ 35%
l/λ
M. Eisterer at al. 2005, ATI Vienna
Oxygenation cracks in Nd123 single-crystal
Sample (X. Yao)
crystal pulling
oxygenation
340 °C for 200 hrs
l/d = 0.53 cross section reduction to 30 %
Oxygen gap
∆O
Map of cracking for TSMG bulks
∆Oc(a/c)
∆Oc(a/b)
a/c-OC
a/b-OC
a/c-OC
a/b-OC
0,2
0.085
a/b-OC
≈0.7
≈ 0.7
1- V211
a/b-MIC
a/b-OC
≈ 0.3
a/b-MIC
0.3
a/b-MIC
dc211≈ 400 nm
d211
211 particle size
Effective cross section
2 – 3 times higher Jc after HPO
4
6,5x10
4
6,0x10
4
5,5x10
B
4
5,0x10
4
4,5x10
4
2
Sample: 2 x 2 x 0.5 mm
YBa2(Cu1-xAgx)O7 (x=0.005)
Jc [A/cm ]
4,0x10
4
3,5x10
4
3,0x10
4
2,5x10
4
2,0x10
4
1,5x10
4
1,0x10
Oxygenation:
A
3
5,0x10
0,0
3
-5,0x10
A/ 400 ºC , Oxygen (1bar)
B/ 750 °C, 16 MPa, progresive oxygen
pressure Increasing (CRETA Grenoble)
0
1
2
3
B[T]
4
5
6
7
Influence of high pressure oxygenation on microstructure
HPO eliminates oxygenation cracks
a,b
c
Oxygenation at 400 °C
High pressure oxygenation at 16 MPa, 750 ° C
Thermochemical postgrowth treatment of
doped YBCO
Chemical pining by Cu substitutions
Al, Ga, Fe, Co, Ag, Mn
CuO – chains
Zn, Ni, Fe
YBa2Cu Cu2O7
CuO2 – plains
Zn Krabbes et al. Physica C 2000,
Li Shlyk at all., Appl. Phys. Lett. 2002
Pd, Ni Shlyk at all. 2002 Physica C,
Fe Shlyk at all., Journal of Physics, 2006
Zn, Ni, Co, Ga, Zhou, Scruggs, Salama 2006, SUST
Co, Fe, Ga, Zn, Ishii, Appl. Phys. Lett., 2006
Ag, T. Nakashima, Journal of Physics, 2008
Orthorhombic structure of REBa2Cu3O7
(RE) – rare earth elements, such as Y, Sm, Gd, Nd, Eu …..
Pining by substitutions in Y123 lattice – chemical pining
Chemical pinning centers in YBCO
CuO chain plane
CuO2 plane
Cu
M
O
dChP
Lattice distorsion
dChP ≈ 1 -2 nm
Zn impurity in CuO2 plane. Disturbed region (NMR) about 2 nm
Fuchs et al. 2003
Strong suppression of superconductivity (STM) within 1.5 nm
Zn in BISCO S. H. Pan et al. Phys.Rev.Lett. 2000
Source of pinning: local suppression of superconductivity
crystal lattice distortion
appearance of magnetic moment
Effective mean distance of chemical PC
No pinning
Efective pinning
Pining centre size
dChPC ≈ 1-2 nm
2= 6 nm
at 77 K
dChPC << 2
2
PC -mean distance between PC
2
PC ≥ 2
PC << 2
 Pining centers in the middle of FL core
 FL bending
FL without bending
Fp ≈fp
Fp ≈ 0
Effective substitution concentration in CuO or CuO2 plane in
YBa2Cu3O7
Ishii, J. Mat. Sci. Eng. B. 2008
 M [nm]
-
Cu-O plane with chains
Cu
1
1
M
O
a
a – lattice parameter (0.38 nm)
 M= a
/(xM)1/2
=> xefLM = 0. 004
YBa2Cu0.996 M0.004Cu2O7 = YBa2(Cu0.9987M0.0013)3O7
x
in YBa2Cu1-x MxCu2O7
xM - concentration of M ions in CuO layer
The spacing of CuO layers in the c-direction is 1.2 nm
xefLM < 0.0013
Referred nominal concentrations are much higher
than xefLM = 0.0013
xZn = 0.004
Shlyk L, Krabbes G, Fuchs G, Stover G and Nenkov K 2002 Physica C 377 437
xLi = 0.006
Shlyk L, Krabbes G, Fuchs G, Nenkov K, Verges P 2003 Physica C 392 540
xAg = 0.05
Diko P, Antal V, Kaňuchová M, Jirsa M and Jurek K 2010 Physica C 470 155
xAl = 0.0025, 0.05 Antal V, Kaňuchová M, Šefčíková M, Kováč J, Diko P, Eisterer M, Hörhager N,
Zehetmayer M, Weber H W and Chaud X 2009 Supercond. Sci. Technol. 22 105001
Reasons
 clustering of dopant atoms
 macroscopic inhomogeneity of dopant distribution in YBCO bulk
 redistribution of dopant between Y123 and Y211 phase
Pinning by Al substitution in TSMG YBCO
Antal et al. 2009
Standard oxygenation – single atom pinning
Pre-annealing in Ar at 800 °C
- Tc returns to 91 K
- Formation of Al clusters
Simmilar to Fe3+ and Co3+
Pre-annealing in Ar 1 hour at 800 °C
Pinning by Al clusters
16
a,b
a,b
Cu
O2
Al
O2 (1/2,0,0)
Standard oxygenation
CuCN = 4
AlCN = 5
Extra oxygen at Al
– dense twins
Al clustering
– higher twin
spacing
Annealing in argon
Chemical pinning by Ag doping
Oxygenation: Oxygen flow
800/2 hours
400/ 300 hourt
Peak effect
at x = 0.05
x in YBa2(Cu1-xAgx)O7
SEM and EDAX analyses
BaCeO2
BaCeO2
Ag
Ag
(a)
5 mm
5 mm
(b)
Growth direction
5 mm
(c)
Solidified melt at the sample rim
Sample YBa2(Cu0.95Ag0.05)O6.5
Nominal Ag content 1.2 at % Ag
No Ag detected in the Y123 matrix
EDAX spectrum of Ag particle
WDX measurement of Ag concentration
no Ag detected in Y211
R
YBa2(Cu0.95Ag0.05)O6.5 , 1.2 at % Ag
2R
Ag concentration : 0.12 at%. x= 0.005
Ag parttition coefficient
kAg = CAgS/CAg0 = 0.12/ 1,2 = 0.1
CAgS(g) = kAg CAg0 {1-g} kAg – 1
g = Vs/V0 = 4(Ra)3/(p R3) for Ra  R/(2)1/2
CAg0 - nominal Ag concentration in the melt,
kAg - partition coefficient of Ag between the S and L
g - fraction of the liquid solidified
V - solidified part of the sample at the distance Ra
V0 - volume of the sample,
R - radius and height of the cylindrical sample
Ag content in Y123 about 4 times higher than effective concentration for pining
Conclusions
Oxygenation cracks can be eliminated by high pressure oxygenation,
Jc increases by a factor of ~ 3.
Clustering of dopant atoms can be achieved by thermochemical treatments
Dopant partition coefficient mast be considered at chemical pining in TSMG bulks
Trapped field for YBCO and GdBCO TSMG bulks
77 K
Nariki et al
2004
7, IRRAD
4, Li
6
1
3
5, Zn
2
Gd123-air
Gd123-OCMG
Y123-air
Gd123 bulks data :D. Cardwell EUCAS
2009, Dresden
Influence of Y123 growth rate on kAg
30 mm
YBa2(Cu0.95Ag0.05)O6.5 , 1.2 at % Ag
High growth rate region (HGRR)
formed during cooling from the growth
temperature
kAg significantly decreases with growth rate
Cu
M
O
1
1
a
a – lattice parameter (0.38 nm)
Weak links formed during post growth treatment
a/b-microcracks induced by 211 particles
Thermal expansion coefficient 
 (K-1. 105)
YBa2Cu3O7
c-axis
YBa2Cu3O7
a/b-plane
Y2BaCuO5
3.2
0.86
1.24
RM  -2GPa
211
211
Thermal dilatation
stresses
M  1GPa
a/b-MIC length: some 211 inter-particle distances
P. Diko 1998
Crystal defects in TSMG YBCO bulks
Pinning centers
211 particles and stresses around them (dislocations, stacking foults, point defects
added nanoparticles
substituted atoms
twins
Weak links
crystal misalignments (grain and subgrain boundaries)
cracks induced by 211 particles
oxygenation cracks
Growth realed crystal defects
crystal misalignments
size and inhomogeneities in macroscopic distribution of 211 and other particles
inhomogeneities in macroscopic distribution of substitution atoms (dopants)
Crystal defects influenced by post growth thermal treatments
oxygention cracks
local arrangement of substitution atoms (dopants)
twin spacing
Weak links formed during post growth treatment
Elimination of oxygenation cracks
OC elimination: subcritical oxygen gap
Short oxygenation time: high temperature
Oxygen close to 7: high oxygen pressure
Technology of HPO
16 MPa
0.1 MPa
X. Chaud
CRETA CNRS Grenoble
Thin wall TSMG YBCO
O’Brian et al. J. Am. Ceram. Soc. 1989
x = 0.005
x = 0.05
Twinning structures in YBa2(Cu1-xAlx)3O7-δ bulks after standard oxygenation
x = 0.005
x = 0.05
Twinning structures in YBa2(Cu1-xAlx)3O7-δ bulks after argon annealing
SEM and EDAX analyses
BaCeO2
BaCeO2
Ag
Ag
(a)
5 mm
5 mm
(b)
Growth direction
5 mm
(c)
Solidified melt at the sample rim
Sample YBa2(Cu0.95Ag0.05)O6.5
Nominal Ag content 1.2 at % Ag
No Ag detected in the Y123 matrix
EDAX spectrum of Ag particle
WDX measurement of Ag concentration
R
YBa2(Cu0.95Ag0.05)O6.5 , 1.2 at % Ag
2R
Ag parttition coefficient
kAg = CAgS/CAg0 = 0.12/ 1,2 = 0.1
CAgS(g) = kAg CAg0 {1-g} kAg – 1
g = Vs/V0 = 4(Ra)3/(p R3) for Ra  R/(2)1/2
CAg0 - nominal Ag concentration in the melt,
kAg - partition coefficient of Ag between the S and L
g - fraction of the liquid solidified
V - solidified part of the sample at the distance Ra
V0 - volume of the sample,
R - radius and height of the cylindrical sample
Various oxygen configurations around the metal atom in the chains of CuO plane.
The solid circle indicates the metal atom.
Open and filled circles indicate in-plane and out-of-plane oxygen atoms, respectively.
(g – i):
The concentration of (d) configurations is lower when linear (h) or two dimensional (i)
Ag clusters are formed.
The smaller solid circles represent the Cu atoms and the larger ones represent the Ag atoms.
Possible Cu substitutions
Al, Fe, Co, Ag, Mn
CuO – chains
Zn, Ni
YBa2Cu Cu2O7
CuO2 – plains
Al T. Siegrist et al., Phys. Rev. B 36 (1987) 8365
Fe Y. Xu et al., Phys. Rev. B 39 (1989) 6667
Co J.M. Tarascon et al., Phys. Rev. B 37 (1988) 7458
Ag C.R. Taylor et al., Physica C 235 (1994) 853
Mn J. Yang et al., Solid State Communic. 70 (1989) 919
Zn G. Krabbes et al., Physica C 330 (2000)181
Ni Y. Zhu et al., Appl. Phys. Lett. 54 (1989) 374
Orthorhombic structure of (RE)BCO
(RE) – rare earth elements, such as Y, Sm, Gd, Nd, Eu
Defects - weak links
What causes oxygenation
cracking
Data by Jorgensen et al. 1987, Casalta et al.1966
0,14
c
0,12
(a+b)/2
difference [A°]
Oxygenated layer
CO
DCO
0,1
0,08
0,06
0,04
0,02
0
0
200
400
600
800
T [°C]
Difference in lattice parameters of core
and oxygenated layer Y123
Tensile stress
Core 123: annealed in O2 at 900 oC
Layer: oxygenation at temperature, T, in O2
1000
Microstructure in polarized light
Typical microstructure
of as grown samples
Y2BaCuO5
Lattice parameters by RTG
sample
a [Å]
b [Å]
c [Å]
undoped
3.8235(1)
3.8856(2)
11.6778(7)
Ag_001
3.8261(2)
3.8834(3)
11.6818(9)
Ag_005
3.8267(2)
3.8855(3)
11.6896(9)
 Bimodal distribution of Y211 particles with means size 1.4 µm
 Ce does form any compound with Ag in the YBCO system
 Ag substituted in Y123 lattice
Relation between equilibrium Y123 – Ag phase diagram
and partition coefficient kAg
T
123ss +211 + L’
undercooling
211 + L’
211 + L’+ L’’
123ss + 211 + L’’
123ss + 211
P. Diko et al., Supercond. Sci. Technol. 2001
CAgS
CAg0
Ag concentration
Solubility of Ag in Y123 at solidification temperature controls
kAg
Clustering of Ag atoms
Cu and Ag have different cordinatiom number CN: CuCN = 2 or 4, AgCN = 2
M
O
Cu
Ag
Ag cluster with 4 have: AgC = 6 nm
Clustering of substituents should be considered