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Substitution effects in Bi2Sr2(Ca1−xYx)Cu2O8+δ studied by X-ray absorption spectroscopy
PHYSICA® ELSEVIER
Physica C 341-348 (2000) 383-386
www.elsevier.nl/locate/physc
Substitution effects in Bi2Sr~(Cav~YOCu~Os+~ studied by X-ray absorption spectroscopy R. S. Liu', I. J. Hsu", J. M. Chen b and R. G. Liub 'Department of Chemistry, National Taiwan University, Taipei, Taiwan, R.O.C. bSynchrolxon Radiation Research Center (SRRC), Hsinchu, Taiwan, R.O.C.
The Bi2Sr2(Cal.xYx)Cu2Os+6 system over the homogeneity range x = 0 -
1.0 has a maximal
superconducting transition temperature (To) of around 92 K at x = 0.2. The hole distribution of overdoped, optimum doped and underdoped states in Bi2Sr2(CavxY×)Cu2Os+shas been investigated by high-resolution O Kedge X-ray-absorption near-edge-structure (XANES) spectra. Near the O ls edge, a well-pronounced pre-edge peak with maximum at -528.3 eV is found, which is ascribed to the excitations o f O ls electron to O 2p hole states located in the CuO2 planes. The intens!ty of this pre-edge peak decreases as the Y doping increases, demonstrating that the chemical substitution of Y3+ for Ca 2+ in BizSr~(Cal.xYOCu2Os+sgives rise to a decrease in hole concentrations within the CuO2 planes. Moreover, the correlation between To and critical current density (J~) as a function of doping concentration has been studied. It is important to point out that the highest Jo across the system is appeared at the overdoped side with x = 0 in Bi2Sr2(Ca~.~Yx)Cu2Os+~.
1. INTRODUCTION
interpreted as a result of hole filling due to the additional electrons contributed by the trivalent ~+
The
Bi2Sr2(Cal.xYx)Cu2Os+~system
exhibiting
a
composition-induced metal-superconductor-insulator transition may offer a great potential for investigating the important structural and electronic characteristic, which
can
lead
to
superconductivity
at
such
extraordinary high temperature [1]. The system over the homogeneity range x = 0 - 1.0 has a maximal superconducting
transition
temperature
(To) of
around 92 K at x = 0.2. The depression of Tc and the decreasing
carrier
concentration
have
been
0921-4534/00/$ - see front matter C, 2000 Elsevier Science B.~ Pll S0921-4534(00)00517-7
ion relative to the divalent Ca 2÷ ion. The X-ray absorption spectra are determined by electronic transitions from a selected atomic core level to the unoccupied electronic states near the Fermi level. Xray absorption near edge structure (XANES) is therefore a direct probe to the character and local density of hole states responsible
for high-T¢
superconductivity. In this study, an attempt was made to use XANES All rights reserved.
for
providing
electronic
structural
384
R.S. Liu et al./Physica C 341-348 (2000) 383-386
information across the system. Moreover, the
shown in Figure l, mainly consists of a pre-edge
correlation between To and critical current density
arotmd 528 eV and a broad peak above 530 eV. The
(Jc) as a fimction of doping concentration has also
pre-edge peak at - 528.3 eV in Figure 1 can be
been studied. The results reported here may be able
ascribed to the transition from 3dg_L to Ol__s3d9 (_L
to stimulate further experiments and theories, since
denotes
the titled system offers a remarkable opporttmity of
corresponding to creation of a core hole on the O 1s
testing
level and a filling of the O2px,y states admixed to the
and
evaluating
a theory
of high-T~
a hole
in
an
O2px,y
orbital)
states
upper Hubbard band [3]. The transition is strongly
superconductivity.
related to the variation of the hole concentration 2. EXPERIMENTAL
within the CuO2 planes. The contribution of the broad peak above 530 eV is due to the wide
The
polycrystalline
samples
of
Bi2Sr2(Cat.xYx)Cu2Os+6 with Y content in the range
antibonding
Bi6pxy~-O(1) and
O(2)2t~y-O(3)2Pz
band [3].
0.0 < x < 1.0 were synthesized by the conventional solid state reaction [2]. All the samples are confirmed by powder X-ray diffraction (XRD) as a single phase.
HF
The magnetic properties of the samples were measured
by
magnetometer.
a
Quantum
Design
:--02
SQUID ~'~
The facility of the synchrotron
radiation was supported from Synchrotron Radiation
/
x=0.4
1.
x =0.6
Research Center (SRRC), Hsinchu, Taiwan. The XANES measurements of O-K-edg were performed at
the
6-m
high-energy
spherical
grating
o 2
monochromator (HSGM) beamline [2]. i
525
$28
I
531
i
I
i
534
I
537
i
540
E n e r g y ( eV )
3. RESULTS AND DISCUSSION
In Figure 1 we show the O K-edge XANES spectra for the series of Bi2Sr2(Ca~.xY~)Cu2Os÷~
Figure 1. O K-edge XANES spectra for the series of
samples with x = 0 ~ 1.0 in the energy range of 525 -
Bi2Sr2(Ca].xYx)Cu208+~ samples with x = 0 - 1,0 in
540 eV obtained with a bulk-sensitive total X-ray-
the energy range of 525 - 540 eV obtained with a
fluorescence yield technique. The O K-edge X-ray
bulk-sensitive
absorption spectrum for the sample with x = 0, as
technique.
total
X-my-fluorescence
yield
R.S. Liu et al./Physica C 341-348 (2000) 383-386
The pre-edge peaks were analyzed by fitting
385
estimated form the Bean critical model Assuming the grains are spherical, then
[4].
Gaussian functions to each spectrum. In Figure 2 the J¢ (A/cm 2)
integrated intensity of the pre-edge peaks is plotted as a function of compositional parameter x in Bi2Sr2(Ca~.xYOCu2Os÷8. It can be seen from Figure 2 that the intensity of the pre-edge peak at ~ 528 eV originating from the CuO2 planes decreases in
=
30 AM/d
Where AM (emu/cm 3) is the difference in magnetization for increasing and decreasing field (H > Hcl), and d is the average diameter (cm) of the grains (d - 10 0m for the series Bi2Sr2(Cat.~Y~)Cu2Os+ ~powdered samples ).
intensity as the Y doping increases. This effect may indicate that the hole concentration within the CuO2
10~
,
,
,
,
,
plane sites decreases with increasing Y doping. T=SK 0.55
I
I
I
I
I
I
0.50 0.45 0.40 e~
0.35
"'~ -5
-t~
0.30
.S,;)~
'~-
-o---~= 0.0
f
0.i
.B 0.25 -10
0.20
v---- x
0 3
x--0.4
0.15 x=0.5 0.10 -15
,
0
0.05
I
1
,
I
2 Field
,
I
,
3 (Tesla)
I
4
,
I
5
0.00 0.0
0.2
0.4
0.6
0.8
1.0
X
Figure 3. The magnetic hystersis curves at 5 K of the series Bi2Srz(Cal.xYOCu2Os+8 (x = 0 - 0.5 ) samples.
Figure 2. The integrated intensity of the pre-edge at 528.3 eV as a function of Y content x in Bi2Sr2(Cal.xYOCthOs+~.
The magnetic hysteresis curves at 5 K of the Bi2Sr2(Cal.xY~)Cu2Os+~samples are shown in Figure 3. The intragrain critical current density, Jc, has been
In Figure 4 we show the critical current, Jc, at T = 5 K and H = 1 Tesla as a function of the chemical composition x in Bi2Sr2(Ca~.xYx)Cu2Os+5. The intragrain critical current of the series Bi2Sr2(Ca~.xYx)Cu20,+~samples decreases as the Y doping increases, demonstrating that a decrease in hole concentrations within the CuO2 planes may effect the critical current of the material.
R.S. Liu et al./Physica C 341-348 (2000) 383-386
386
demonstrate that To varies more or less symmetrically with doping about a broad maximun at x = x~, = 0.68 100
80
4 . 5 x 1 0 '~
(optimal doping) in YosCaozBa2Cu306+~. This is
4.0x10 ~
similar to the x = 0.2 sample with the maximum T¢ in
3.5x10 7
Bi2Sr2(Ca~.xYx)Cu2Os+~, In contrast, the condensation energy U(0) has s sharp maximum situated at x = Xcrit
3 . 0 x 10"~--,,
0.77 (the overdoped site) in Y08Cao2Ba2Cu306+~
60 2.5x10"~-
which is corresponding to the highest J¢ sample
< 2 . 0 x l O ~V"
(x
40
0)
in
Bi2Sr2(Ca:.~Yx)Cu2Os+~ Further
experiments (e.g. specific heat etc.) are needed in
1.5x107
order to offer an important way forward in
1.0xl07
20
=
understanding the mechanism of high-temperature of 5.OxlO 6
superconductivity. 0
II
0.~0
' 0~2
' 0.:4
0.6
0.0
, 0 .:8
1.0
ACKNOWLEDGlVlENTS
X
This research was financially supported by the Figure 4. Critical current (Jo) at T = 5 K and H = 1
National Science Council of the Republic of China
Tesla and critical temperature (I'¢) as a function of
under the grant number ofNSC88-2113-M-002-029.
the
chemical
composition
x
in
BizSr2(Ca~.~YOCu20~+~. Moreover, both Tc and Jc dependence of x in BizSr2(Cal.xYOCuzOs+6are shown in Figure 4. The sample with the highest T¢ ( - 92 K) is appeared at x
REFERENCES
(1)A. Manthiram and J.B. Goodenough, Appl. Phys. Lett. 53 (1988) 420. (2)I.J. Hsu, R.S. Liu, J.M. Chen, R.G. Liu, L.Y.
= 0.2 in BizSr2(Ca~.xYOCu2Os÷6. However, the
Jang, J. F. Lee and K. D. M. Harris, Chem. Mater.,
sample with the highest Jo is exhibited at x = 0 in
in press (2000).
Bi2Sr2(Cal.xYOCuzOs÷6. This means that the highest
(3)J. Fink, N. NiJcker, E. Pellergin, H. Romberg, M.
T¢ sample is not corresponding to the highest Jc one
Alexander and M. Knupfer, J. Electron Spectrosc.
and the highest Jc is appeared in the overdoped region
Relat. Phenom. 66 (1994) 395.
in Bi2Sr2(Cal.xYx)Cu2Os+~.Such controversial effect
(4)C.P. Bean, Rev. Mod. Phys. 36 (1964) 31.
can be explained by Liang [5] using the condensation
(5)W.Y. Liang, J. Phys.: Condens. Matter 10 (1998)
energy, U(0) = Hc2(0)/8n (where Hc2 - Ho:H¢2is the thermodynamic critical field) of the materials. They
11365.
Physica C 341-348 (2000) 383-386
www.elsevier.nl/locate/physc
Substitution effects in Bi2Sr~(Cav~YOCu~Os+~ studied by X-ray absorption spectroscopy R. S. Liu', I. J. Hsu", J. M. Chen b and R. G. Liub 'Department of Chemistry, National Taiwan University, Taipei, Taiwan, R.O.C. bSynchrolxon Radiation Research Center (SRRC), Hsinchu, Taiwan, R.O.C.
The Bi2Sr2(Cal.xYx)Cu2Os+6 system over the homogeneity range x = 0 -
1.0 has a maximal
superconducting transition temperature (To) of around 92 K at x = 0.2. The hole distribution of overdoped, optimum doped and underdoped states in Bi2Sr2(CavxY×)Cu2Os+shas been investigated by high-resolution O Kedge X-ray-absorption near-edge-structure (XANES) spectra. Near the O ls edge, a well-pronounced pre-edge peak with maximum at -528.3 eV is found, which is ascribed to the excitations o f O ls electron to O 2p hole states located in the CuO2 planes. The intens!ty of this pre-edge peak decreases as the Y doping increases, demonstrating that the chemical substitution of Y3+ for Ca 2+ in BizSr~(Cal.xYOCu2Os+sgives rise to a decrease in hole concentrations within the CuO2 planes. Moreover, the correlation between To and critical current density (J~) as a function of doping concentration has been studied. It is important to point out that the highest Jo across the system is appeared at the overdoped side with x = 0 in Bi2Sr2(Ca~.~Yx)Cu2Os+~.
1. INTRODUCTION
interpreted as a result of hole filling due to the additional electrons contributed by the trivalent ~+
The
Bi2Sr2(Cal.xYx)Cu2Os+~system
exhibiting
a
composition-induced metal-superconductor-insulator transition may offer a great potential for investigating the important structural and electronic characteristic, which
can
lead
to
superconductivity
at
such
extraordinary high temperature [1]. The system over the homogeneity range x = 0 - 1.0 has a maximal superconducting
transition
temperature
(To) of
around 92 K at x = 0.2. The depression of Tc and the decreasing
carrier
concentration
have
been
0921-4534/00/$ - see front matter C, 2000 Elsevier Science B.~ Pll S0921-4534(00)00517-7
ion relative to the divalent Ca 2÷ ion. The X-ray absorption spectra are determined by electronic transitions from a selected atomic core level to the unoccupied electronic states near the Fermi level. Xray absorption near edge structure (XANES) is therefore a direct probe to the character and local density of hole states responsible
for high-T¢
superconductivity. In this study, an attempt was made to use XANES All rights reserved.
for
providing
electronic
structural
384
R.S. Liu et al./Physica C 341-348 (2000) 383-386
information across the system. Moreover, the
shown in Figure l, mainly consists of a pre-edge
correlation between To and critical current density
arotmd 528 eV and a broad peak above 530 eV. The
(Jc) as a fimction of doping concentration has also
pre-edge peak at - 528.3 eV in Figure 1 can be
been studied. The results reported here may be able
ascribed to the transition from 3dg_L to Ol__s3d9 (_L
to stimulate further experiments and theories, since
denotes
the titled system offers a remarkable opporttmity of
corresponding to creation of a core hole on the O 1s
testing
level and a filling of the O2px,y states admixed to the
and
evaluating
a theory
of high-T~
a hole
in
an
O2px,y
orbital)
states
upper Hubbard band [3]. The transition is strongly
superconductivity.
related to the variation of the hole concentration 2. EXPERIMENTAL
within the CuO2 planes. The contribution of the broad peak above 530 eV is due to the wide
The
polycrystalline
samples
of
Bi2Sr2(Cat.xYx)Cu2Os+6 with Y content in the range
antibonding
Bi6pxy~-O(1) and
O(2)2t~y-O(3)2Pz
band [3].
0.0 < x < 1.0 were synthesized by the conventional solid state reaction [2]. All the samples are confirmed by powder X-ray diffraction (XRD) as a single phase.
HF
The magnetic properties of the samples were measured
by
magnetometer.
a
Quantum
Design
:--02
SQUID ~'~
The facility of the synchrotron
radiation was supported from Synchrotron Radiation
/
x=0.4
1.
x =0.6
Research Center (SRRC), Hsinchu, Taiwan. The XANES measurements of O-K-edg were performed at
the
6-m
high-energy
spherical
grating
o 2
monochromator (HSGM) beamline [2]. i
525
$28
I
531
i
I
i
534
I
537
i
540
E n e r g y ( eV )
3. RESULTS AND DISCUSSION
In Figure 1 we show the O K-edge XANES spectra for the series of Bi2Sr2(Ca~.xY~)Cu2Os÷~
Figure 1. O K-edge XANES spectra for the series of
samples with x = 0 ~ 1.0 in the energy range of 525 -
Bi2Sr2(Ca].xYx)Cu208+~ samples with x = 0 - 1,0 in
540 eV obtained with a bulk-sensitive total X-ray-
the energy range of 525 - 540 eV obtained with a
fluorescence yield technique. The O K-edge X-ray
bulk-sensitive
absorption spectrum for the sample with x = 0, as
technique.
total
X-my-fluorescence
yield
R.S. Liu et al./Physica C 341-348 (2000) 383-386
The pre-edge peaks were analyzed by fitting
385
estimated form the Bean critical model Assuming the grains are spherical, then
[4].
Gaussian functions to each spectrum. In Figure 2 the J¢ (A/cm 2)
integrated intensity of the pre-edge peaks is plotted as a function of compositional parameter x in Bi2Sr2(Ca~.xYOCu2Os÷8. It can be seen from Figure 2 that the intensity of the pre-edge peak at ~ 528 eV originating from the CuO2 planes decreases in
=
30 AM/d
Where AM (emu/cm 3) is the difference in magnetization for increasing and decreasing field (H > Hcl), and d is the average diameter (cm) of the grains (d - 10 0m for the series Bi2Sr2(Cat.~Y~)Cu2Os+ ~powdered samples ).
intensity as the Y doping increases. This effect may indicate that the hole concentration within the CuO2
10~
,
,
,
,
,
plane sites decreases with increasing Y doping. T=SK 0.55
I
I
I
I
I
I
0.50 0.45 0.40 e~
0.35
"'~ -5
-t~
0.30
.S,;)~
'~-
-o---~= 0.0
f
0.i
.B 0.25 -10
0.20
v---- x
0 3
x--0.4
0.15 x=0.5 0.10 -15
,
0
0.05
I
1
,
I
2 Field
,
I
,
3 (Tesla)
I
4
,
I
5
0.00 0.0
0.2
0.4
0.6
0.8
1.0
X
Figure 3. The magnetic hystersis curves at 5 K of the series Bi2Srz(Cal.xYOCu2Os+8 (x = 0 - 0.5 ) samples.
Figure 2. The integrated intensity of the pre-edge at 528.3 eV as a function of Y content x in Bi2Sr2(Cal.xYOCthOs+~.
The magnetic hysteresis curves at 5 K of the Bi2Sr2(Cal.xY~)Cu2Os+~samples are shown in Figure 3. The intragrain critical current density, Jc, has been
In Figure 4 we show the critical current, Jc, at T = 5 K and H = 1 Tesla as a function of the chemical composition x in Bi2Sr2(Ca~.xYx)Cu2Os+5. The intragrain critical current of the series Bi2Sr2(Ca~.xYx)Cu20,+~samples decreases as the Y doping increases, demonstrating that a decrease in hole concentrations within the CuO2 planes may effect the critical current of the material.
R.S. Liu et al./Physica C 341-348 (2000) 383-386
386
demonstrate that To varies more or less symmetrically with doping about a broad maximun at x = x~, = 0.68 100
80
4 . 5 x 1 0 '~
(optimal doping) in YosCaozBa2Cu306+~. This is
4.0x10 ~
similar to the x = 0.2 sample with the maximum T¢ in
3.5x10 7
Bi2Sr2(Ca~.xYx)Cu2Os+~, In contrast, the condensation energy U(0) has s sharp maximum situated at x = Xcrit
3 . 0 x 10"~--,,
0.77 (the overdoped site) in Y08Cao2Ba2Cu306+~
60 2.5x10"~-
which is corresponding to the highest J¢ sample
< 2 . 0 x l O ~V"
(x
40
0)
in
Bi2Sr2(Ca:.~Yx)Cu2Os+~ Further
experiments (e.g. specific heat etc.) are needed in
1.5x107
order to offer an important way forward in
1.0xl07
20
=
understanding the mechanism of high-temperature of 5.OxlO 6
superconductivity. 0
II
0.~0
' 0~2
' 0.:4
0.6
0.0
, 0 .:8
1.0
ACKNOWLEDGlVlENTS
X
This research was financially supported by the Figure 4. Critical current (Jo) at T = 5 K and H = 1
National Science Council of the Republic of China
Tesla and critical temperature (I'¢) as a function of
under the grant number ofNSC88-2113-M-002-029.
the
chemical
composition
x
in
BizSr2(Ca~.~YOCu20~+~. Moreover, both Tc and Jc dependence of x in BizSr2(Cal.xYOCuzOs+6are shown in Figure 4. The sample with the highest T¢ ( - 92 K) is appeared at x
REFERENCES
(1)A. Manthiram and J.B. Goodenough, Appl. Phys. Lett. 53 (1988) 420. (2)I.J. Hsu, R.S. Liu, J.M. Chen, R.G. Liu, L.Y.
= 0.2 in BizSr2(Ca~.xYOCu2Os÷6. However, the
Jang, J. F. Lee and K. D. M. Harris, Chem. Mater.,
sample with the highest Jo is exhibited at x = 0 in
in press (2000).
Bi2Sr2(Cal.xYOCuzOs÷6. This means that the highest
(3)J. Fink, N. NiJcker, E. Pellergin, H. Romberg, M.
T¢ sample is not corresponding to the highest Jc one
Alexander and M. Knupfer, J. Electron Spectrosc.
and the highest Jc is appeared in the overdoped region
Relat. Phenom. 66 (1994) 395.
in Bi2Sr2(Cal.xYx)Cu2Os+~.Such controversial effect
(4)C.P. Bean, Rev. Mod. Phys. 36 (1964) 31.
can be explained by Liang [5] using the condensation
(5)W.Y. Liang, J. Phys.: Condens. Matter 10 (1998)
energy, U(0) = Hc2(0)/8n (where Hc2 - Ho:H¢2is the thermodynamic critical field) of the materials. They
11365.