Bi-based Superconductors n - CCP14

winkwellmadeΠολεοδομικά Έργα

15 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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Electron Crystallographic Study

of

Bi
-
based Superconductors

using

Multi
-
dimensional Direct Methods

Why Electrons ?

1. Electrons are better for studying



minute and imperfect crystalline samples


2. Electron microscopes are



the only instrument that can produce


simultaneously EM’s and ED’s for the same


crystalline sample at atomic resolution


3. Electrons are better for revealing


light atoms in the presence of heavy atoms

Scattering of X
-
rays and Electrons

by Different Elements

Relative
scattering
power

O

O

Sin
q
/
l

~ 0.31

Bi

Sr

Ca

Cu

X
-
rays

Electrons

Bismuth

bi
-
layer

Perovskite

layer

Bismuth

bi
-
layer

Bi
-
based Superconductors

n
= 1
n
= 2
n
= 3

Bi
-
㈲〱2††††††䉩
-
㈲ㄲ2††††††䉩
-
㈲㈳

Bi
-
O

Bi
-
O

Sr
-
O

Cu
-
O

Sr
-
O

Sr
-
O

Cu
-
O

Ca
-
O

Cu
-
O

Sr
-
O

Sr
-
O

Cu
-
O

Ca
-
O

Cu
-
O

Ca
-
O

Cu
-
O

Sr
-
O

Bi
-
O

Bi
-
O

Bi
-
O

Bi
-
O

Bi
-
O

Bi
-
O

Bi
-
O

Bi
-
O

Bi
-
O

Bi
-
O


c

Bi
2
Sr
2
Ca
n
-
1
Cu
n
O
2
n
+4+
x

Electron diffraction analysis of

the Bi
-
2223 superconductor

Space group
:

P
[
B
bmb] 1
-
1 1

a
= 5.49,

b
= 5.41,

c

= 37.1Å;

q

= 0.117
b
*


*The average


structure is


known*

Bi
-
2223 [100]

projected potential

Space group
: P [Bbmb] 1
-
1 1

a
= 5.49,
b
= 5.41,
c

= 37.1Å;
q

= 0.117
b
*

R
symM

= 0.12 (
Nref.

=42)

R
symS
= 0.13 (
Nref.

= 70)

R
m

= 0.16

R
s

= 0.17

a
3

a
4

Bi
-
2223

cut at
a
2
= 0 and projected

down the
a
1
axis

Space group
: P [Bbmb] 1
-
1 1

a
= 5.49,
b
= 5.41,
c

= 37.1Å;
q

= 0.117
b
*


a
1

=
a
,
a
2
=
b
-

0.117
d,

a
3

=
c
,
a
4
=
d

4
-
dimensional metal atoms

Image Processing of Bi
-
2212

Space group
: N [Bbmb] 1
-
1 1

a
= 5.42,
b
= 5.44,
c

= 30.5Å;

q

= 0.22
b
* +
c
*

EM image from

Dr. S. Horiuchi

FT

FT
-
1

Phase

extension

Image Processing of

Bi
-
2212

(
continued
)

Bi

Sr

Cu

Ca

Cu

Sr

Bi

b

c

2

8

4

1

Oxygen

in Cu
-
O layer

Original
image

Enhanced
image

b

c

O atoms on the
Cu
-
O layer

Bi
-
O

Sr
-
O

Sr
-
O

Bi
-
O

Cu
-
O

O
(
extra
)

Electron diffraction analysis of Bi
-
2201

R
T

= 0.32
R
m

= 0.29
R
S1

= 0.29
R
S2

= 0.36
R
S3

= 0.52

Space group
:
P
[
B
2/b]
-
1];
a =
5.41,

b =
5.43,

c =
24.6Å,

b
㴠㤰
o
;
q

= 0.217
b
* + 0.62
c
*

Bi
-
2201


Influence of

thermal
motion
(
B
)

and
Modulation
(
M
)

to the
dynamical
diffraction

Experimental B and M

B set to zero

M set to zero

B,M set to zero

Sample thickness:


~5Å

Bi
-
2201

The effect of
sample
thickness

Bi
-
O

Bi
-
O

Sr
-
O

Sr
-
O

Cu
-
O

~100Å

~200Å

~300Å

Extra oxygen

Oxygen in

Cu
-
O layer