1. Universidad Complutense de Madrid, Departamento Física Aplicada III, GFMC Rainer Schmidt
Microstructure and dielectric properties of CaCu3Ti4O12 (CCTO) multilayer capacitors
Jörg Töpfer 1, Romy Löhnert 1, S. Barth 2, Beate Capraro 2, Heike Bartsch 3, J. Müller 3, Rainer Schmidt 4
1 – University of Applied Sciences Jena, Jena, Germany
2 – Fraunhofer IKTS, Hermsdorf, Germany,
3- Technical University Ilmenau, Germany
4 – Universidad Complutense de Madrid, GFMC, Madrid, Spain
2nd July 2014

2. Universidad Complutense de Madrid, Departamento Física Aplicada III
Universidad Complutense de Madrid, Departamento Física Aplicada III Rainer Schmidt
Microstructure and dielectric properties of CaCu3Ti4O12 (CCTO) multilayer capacitors
- Introduction:
Giant dielectric permittivity er in CCTO
Defect chemistry in CCTO
- Powder processing
- Pellet pressing and sintering
- Pellet microstructure
- Tape casting of laminates
- Multilayer fabrication
- Dielectric properties

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. Introduction: Giant er Rainer Schmidt
Influence of sintering temperature on the Internal Barrier Layer Capacitor (IBLC) structure
Schmidt et al., J.Eur.Ceram.Soc. 87 (2004) p.2072 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. Defect chemistry in “CaCu3Ti4O12”
Introduction: Defect chemistry Rainer Schmidt
Defect chemistry 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) 7

8. Starting powders: CaCO3 (98.0 %, Merck) CuO (99.7 %, Alfa Aesar)
Powder processing Rainer Schmidt
Starting powders:
CaCO3 (98.0 %, Merck)
CuO (99.7 %, Alfa Aesar)
TiO2 (99.5 %, rutile, Tronox)
Conventional powder
processing
Homogenization
6 hours
X-rays: 8

9. Pellet pressing Dilatometry Powder additives:
Pellet pressing Rainer Schmidt
Powder additives:
1 wt%, 3 wt%, 5 wt% glass frit:
Bi2O3-B2O3-SiO2-ZnO (BBSZ)
Planetary ball milling to ≈ 1 mm particle size
Pellet pressing
Uniaxial pellet pressing
Dilatometry 9

10. Pellet microstructure
Pellet microstructure Rainer Schmidt
Pellet microstructure
FE-SEM
2 h
4 h
12 h
1050 °C
1150 °C
Cu/Ti intergranular phase near the eutectic point leads to liquid phase sintering 10

11. FE-SEM 1050 °C 900 °C 4 h without glass 5 wt.% BBSZ
Pellet microstructure Rainer Schmidt
FE-SEM
1050 °C
900 °C
4 h
without glass
5 wt.% BBSZ 11

12. Cofiring at 900°C with BBSZ additive
Tape casting of laminates and Multilayer fabrication Rainer Schmidt
Tape casting of laminates and formation of Multi-Layer Ceramic Capacitors (MLCCs)
Cofiring at 900°C with BBSZ additive 12

13. Dielectric properties
Dielectric properties Rainer Schmidt
Dielectric properties
with BBSZ additive 13

14. Dielectric properties
Dielectric properties Rainer Schmidt
Dielectric properties
X7R characteristics between f = 0,1 kHz … 0,2 MHz
Losses in the range of 14

15. Conclusions Rainer Schmidt
Anomalous grain growth in CCTO is facilitated by a Cu/Ti containing inter-granular phase
This anomalous grain growth occurs only above the eutectic point (1000 °C) of this phase
CCTO can be formed into tape-casted laminates and Multi-Layer Ceramic Capacitor (MLCC) structures
In Low Temperature Co-fired Ceramics (LTCC) (900 °C) the limited grain growth leads to a drop in dielectric permittivity
MLCC structures based on glass containing (BBSZ) CCTO sintered at 900 °C under LTCC conditions fullfill the X7R characteristics for ceramic capacitors but have relatively high losses

16. Rainer Schmidt
Acknowledgments
Ramón y Cajal program