1. Non-stoichiometry in CaCu3Ti4O12 (CCTO) ceramics
Universidad Complutense de Madrid, Departamento Física Aplicada III Rainer Schmidt
Non-stoichiometry in
CaCu3Ti4O12 (CCTO) ceramics
Rainer Schmidt, Shubhra Pandey, Derek C. Sinclair
Universidad Complutense de Madrid
Engineering
Materials
Electroceramics
Research Group
Grupo de Física de
Materiales Complejos
Dpto. Fisica Aplicada III
21st June 2013
C-32

2. “CaCu3Ti4O12” (CCTO) ceramics
Universidad Complutense de Madrid, Departamento Física Aplicada III Rainer Schmidt
Non-stoichiometry in
“CaCu3Ti4O12” (CCTO) ceramics
- Introduction:
Giant dielectric permittivity er in CCTO
Non-stoichiometry models
- Phase diagram
- Lattice parameters
- Dielectric Spectroscopy
- Combined data analysis
- Conclusions

3. Crystal structure Giant dielectric permittivity
Introduction: Giant er Rainer Schmidt
Crystal structure
Giant dielectric permittivity
Giant dielectric permittivity er = 105 at high f
T-dependent drop to er = 80 at low f
Giant er has extrinsic origin!!!
Single crystals: Electrode interface effect
Polycrystalline ceramics:
Grain boundary (GB) effect
1:3 A-site ordered perovskite (A'A''3B4O12)
Strong octahedral tilting: a+a+a+ (Glazier)
Cu square planar coordination
Doubled simple cubic perovskite cell
Space group Im-3
Homes et al. Science 293 (2001) p.673 3

4. Internal Barrier Layer Capacitor (IBLC) structure
Introduction: Giant er Rainer Schmidt
Internal Barrier Layer Capacitor (IBLC) structure
Sinclair et al. Appl. Phys. Lett. 80 (2002) p.2153
The T-dependent drop to lower er is fully consistent with an IBLC model as represented by two RC element 4

5. Non-stoichiometry models in “CaCu3Ti4O12”
Introduction: Non-stoichiometry Rainer Schmidt
Non-stoichiometry models in “CaCu3Ti4O12”
(A) Oxygen vacancies + Ti-reduction
(B) High temperature Cu-reduction + Cu loss
(C) Cu reoxidation upon cooling + internal redox
Cu+ +Ti4+ → Cu2+ + Ti3+
(D) Cu-loss and Cu oxidation
(E) Cu-excess and oxygen vacancies
None of the models has been clealry confirmed experimentally!
Li et al. Appl. Phys. Lett. 88 (2006) p
Li et al. Solid State Commun. 135 (2005) 60
Fang et al. Acta Materialia 54 (2005) 2867
Schmidt et al. RSC Advances in Press (2013) 5

6. Internal Barrier Layer Capacitor (IBLC) structure
Introduction: Giant er Rainer Schmidt
Internal Barrier Layer Capacitor (IBLC) structure
Fang et al., J.Am.Ceram.Soc. 87 (2004) p.2072
M. Li, PhD Thesis (2008) Sheffield
Cu-rich
phase
bulk
TEM GB
Schmidt et al., J.Eur.Ceram.Soc. 87 (2004) p.2072
Cu-rich phase
Grain boundaries and bulk behave very different!
SEM: backscattered EDAX line-scan 6

7. Ternary CaO-CuO-TiO2 phase diagram
Phase diagram Rainer Schmidt
Ternary CaO-CuO-TiO2
phase diagram
1000 °C
1100 °C x y z D
B,C E 2 7 4 6 8 5 1 3 7

8. Ternary CaO-CuO-TiO2 phase diagram
Phase diagram Rainer Schmidt
Ternary CaO-CuO-TiO2
phase diagram
1000 °C
1100 °C x y z D
B,C E 2 7 4 6 8 5 1 3 8

9. CCTO Lattice parameters Cation ratio (fractions)
Lattice parameters Rainer Schmidt
CCTO Lattice parameters
Compos. Number
Cation ratio (fractions)
Expected phases (wt.)
Detected Phases (1100 °C )
a [Å] (1100 °C)
a [Å] (1000 °C) 1
Ca 0.125, Cu 0.375, Ti 0.5
CCTO (1)
CCTO, [CTO]
(1)
(4) 2
Ca 0.11, Cu 0.33, Ti 0.56
CCTO (0.88), TiO2 (0.12)
CCTO, TiO2, [[CTO]]
(1)
(3) 3
Ca 0.14, Cu 0.3, Ti 0.56
CCTO (0.84), CTO (0.07), TiO2 (0.09)
CCTO, CTO, TiO2
(3)
(2) 4
Ca 0.175, Cu 0.325, Ti 0.5
CCTO (0.88), CTO (0.12)
CCTO, CTO
(2)
(3) 5
Ca 0.145, Cu 0.435, Ti 0.42
CCTO (0.74), CuO (0.17), CTO (0.09)
CCTO, CTO, CuO
(2)
(2) 6
Ca , Cu , Ti 0.45
CCTO (0.9), CuO (0.1)
CCTO, [CTO], CuO
(4)
(2) 7
Ca , Cu 0.385, Ti
CCTO (0.81), CuO (0.08), TiO2 (0.11)
CCTO, TiO2, [CTO], CuO
(1)
(2) 8
Ca 0.06, Cu 0.52, Ti 0.42
CCTO (0.47), CuO (0.35), TiO2 (0.18)
CCTO, TiO2, [CTO], CuO,
(2)
(3) 9

10. Dielectric permittivity vs frequency Dielectric Spectroscopy
Dielectric spectroscopy Rainer Schmidt
Dielectric permittivity vs frequency
Dielectric Spectroscopy
Ceramics sintered at
1100 °C
Compositions 7 & 8 are different, 6 is intermediate. 10

11. Bulk dielectric permittivity vs CCTO lattice parameter
Combined data analysis Rainer Schmidt
Bulk dielectric permittivity vs CCTO lattice parameter
In compositions 1 – 4 a solid solution is obvious, which may be responsible for increased bulk er above Clausius-Mossotti predictions 11

12. Bulk resistivity vs CCTO lattice parameter
Combined data analysis Rainer Schmidt
Bulk resistivity vs CCTO lattice parameter
In compositions 5,7 & 8 a second solid solution is obvious, which may be responsible for increased GB resistivity 12

13. Conclusions Rainer Schmidt
Two different defect mechanisms were identified in CCTO ceramics
1.) In compositions with no CuO secondary phase the detected defect mechanism can explain the large bulk dielectric permittivity. Only small changes of the bulk CCTO resistivity occur along the solid solution. It may be associated with Ca-Cu anti-site defects [PRL 99 (2007) p037602]
2.) In compositions with a CuO secondary phase the detected defect mechanism exhibits large changes in the bulk CCTO resistivity along the solid solution. It may be associated with the differences in insulating and Cu-rich grain boundaries and semiconducting Cu-deficient bulk areas.
The separate analysis of the CCTO ternary phase diagram, lattice parameters of several compositions and impedance spectroscopy of sintered ceramics only gives some hints on the influence of Cu on the IBLC structure and non-stoichiometry in CCTO
Only the combined analysis of all 3 experimental results allows the clear identification of two distinct defect mechanisms