Studies of Oxygen Deficient Complex Cobaltates with Perovskite Related Structures

1
Studies of Oxygen Deficient Complex Cobaltates
with Perovskite Related Structures

• Doctoral Thesis
• Fredrik Lindberg

2
Contents

• Its a perovskite material world
• Where are (or where are not) the oxygens
• Based on what?
• Summary
• Acknowledgements

3
Its a perovskite material world
ABX3
The perovskite structure.
4
Its a perovskite material world
t lt 1superstructures
t gt 1hexagonal variants
t 1cubic, ideal
The toleranced factor for perovskites
5
Its a perovskite material world
Important properties
6
Its a perovskite material world
Spin state transitions in coboltates
LS
IS
HS
LaCoO3 (P.G. Radaelli et. al. Phys. Rev. B66
(2002) 094408)
Magnetism
7
Its a perovskite material world
Superexchange Anti-Ferromagnetism
Co3
Co3
Double-exchange - Ferromagnetism
Co3
Co4
Co3
Co4
Magnetism
8
Where are (or where are not) the oxygens
Oxygen deficiency
SrFeO3
Sr4Fe4O11
Sr2Fe2O5
Sr8Fe8O23
Homologous serie, AnBnO3n-1
Deficiency
(J.P. Hodges et. al. JSSC. 151, (2000) 190)
9
Where are (or where are not) the oxygens
The Brownmillerite structure
10
Where are (or where are not) the oxygens
The Brownmillerite structure
11
Where are (or where are not) the oxygens
Pcmn
Ibm2
Icmm
The Brownmillerite structure
12
Where are (or where are not) the oxygens
Icmm
Ibm2
Pcmn
The Brownmillerite structure
13
Where are (or where are not) the oxygens
314 - phase
14
Based on What?
Stabilise Brownmillerite Sr2Co2O5 by aliovalent
doping
Paper I Synthesis and structural studies of
Sr2Co2-xGaxO5, 0.3  x  0.8
Paper II Synthesis and structural studies of
Sr2Co2-xAlxO5, 0.3  x  0.5
Paper I and II
15
Based on What?
Sr2Co2-xGaxO5
100
001
Paper I
16
Based on What?
Sr2Co1.7Ga0.3O5
Paper I
17
Based on What?
Sr2Co1.7Ga0.3O5
Co3oct 2.8BM Co3tetr 2.5BM
IS 3BM
LS 0BM
Paper I
18
Based on What?
Sr1-xLnxCoO3-? 314-phase at x 0.3, Ln Y, Eu-Ho
Paper III Influence of Oxygen Defects on the
Structure and Magnetic Properties of
Sr1-xBixCoO3-y (0.1   x   0.2) Supercell
Perovskites.
Paper IV Synthesis and characterization of
Sr0.75Y0.25Co1-xMxO2.625? (M Ga, 0.125 x
0.500 and M Fe, 0.125 x 0.875),
Paper III IV
19
Based on What?
Sr1-xBixCoO3-y 314-phase for x 0.1 0.2
Sr0.75Y0.25Co1-xMxO2.625? 314-phase x 0.375
(M Ga) x 0.625 (M Fe)
Paper III IV
20
Based on What?
Paper IV
Paper IV, page 1439
21
Based on What?
TGA in O2
Sr1-xBixCoO3-y
Sr0.7Y0.3CoO2.62 (Istomin et al. Chem. Mater.
15, 4012)
x
8
0
6
0
0.10
4
2
0
-60
4
0
1
0.20
2
-5
200
1000
600
400
800
0
T/?C
-80
Paper III
200
800
400
600
T/?C
22
Based on What?
Chemically induced AFM FM transitions,
Sr1-xBixCoO3-y
Sr0.85Bi0.15CoO2.9
Sr0.85Bi0.15CoO2.7
Paper III
23
Summary
Brownmillerites Sr2Co2-xGaxO5 and
Sr2Co2-xAlxO5 Domain structure, AFM, IS Co3.
314 structure Sr0.75Y0.25Co1-xGaxO2.625 and
Sr0.75Y0.25Co1-xFexO2.625. Domain structure and
well ordered, FM from spin-canting, FM domains.
Sr1-xBixCoO3-y O2 uptake, 314 to cubic AFM FM
transition. FM due to Co3-Co4 double exchange..
24
Acknowledgements

• Sergey Istomin and Oleg Drozhzhin, Moscow State
  University.
• Christopher Knee, Chalmers/Gothenburg University.
• Peter Warnicke and Peter Svedlindh Uppsala
  University.

25
Its a perovskite material world
The toleranced factor for perovskites
26
Its a perovskite material world
The toleranced factor for perovskites
27
Its a perovskite material world
Double exchange
Magnetism
28
Based on What?
Paper III IV
29
Its a perovskite material world
Chemically induced AFM FM transitions,
Sr2/3Y1/3CoOx
Ferromagnetic domains to small to be detected by
NPD
Magnetism
A. Maignan et. al. J. Solid State Chem. 178
(2005) 868
30
Its a perovskite material world
B Metall d
Oxygen p
SrTiO3
LaNiO3, LaCuO3
Important properties
31
Where are (or where are not) the oxygens
Ba2In2O5 (K.R. Kendall et. al. Solid State Ionics
82 (1995) 215-223)
32
Where are (or where are not) the oxygens
The Brownmillerite structure
The Brownmillerite structure
33
Based on What?
Paper I
34
Its a perovskite material world
The toleranced factor for perovskites
35
Based on What?
Sr2Co1.5Al0.5O5
Page 19 in thesis
Paper II