1. Effects of sintering temperature on the physical and
Contents Rainer Schmidt
Effects of sintering temperature on the physical and
chemical properties of CaCu3Ti4O12 ceramics
1. Introduction
2. Experimental
3. Dielectric properties
4. Thermal gravimetry and X-ray diffraction
5. Scanning Electron Microscopy Analysis
6. XANES and Raman spectroscopy
7. Conclusions

2. Crystal structure of 1:2 A-site ordered perovskite CaCu3Ti4O12
1. Introduction: Crystal structure Rainer Schmidt
Crystal structure of 1:2 A-site ordered perovskite CaCu3Ti4O12
Ti within
the green
octahedra Ca
Square-planar Cu O

3. Giant dielectric permittivity in CaCu3Ti4O12
1. Introduction: Giant dielectric permittivity Rainer Schmidt
Giant dielectric permittivity in CaCu3Ti4O12
Dielectric spectra represented in the
dielectric permittivity notation:
Real part e1 vs frequency w
Solid Lines are fits to a
Debye – model: C2 C2 R C1 C1
For one resistor only
one relaxation with
one relaxation peak
is expected
Homes et al., Science 293 (2001) p.673

4. Polycrystalline CCTO Dielectric spectra represented in the
1. Introduction: Impedance spectroscopy of CCTO Rainer Schmidt
Polycrystalline CCTO
Dielectric spectra represented in the
complex impedance notation:
Imaginary part –Z’’ vs real part Z’
The presence of two semicircles
indicates the presence of 2
relaxations with 2 resistors
Sinclair et al., Appl.Phys.Lett. 80 (2002) p.2153

5. Brickwork Layer Model (BLM)
1. Introduction: Brick-work layer model Rainer Schmidt
Brickwork Layer Model (BLM)
Semiconducting bulk: EA ≈ 0.01 – 0.1 eV
Insulating grain boundaries (GB) EA ≈ 0.6 eV
high dielectric permittivity has extrinsic origin
Adams et al., Phys.Rev.B 73 (2006) p
Rgb Rb
Cgb Cb
Cgb ~ 1 n F
Cb ~ 1 pF
where Rgb and Cgb are >> Rb and Cb

6. Internal Barrier Layer Capacitor
1. Introduction: Brick-work layer model Rainer Schmidt
Potential sources for chemical
differences in bulk and GB areas:
Variations in oxygen content
Ti valence state changes: Ti4+/Ti3+
Cu loss/non-stoichiometry/valency
Exact mechanisms are not known
Internal Barrier Layer Capacitor
In this work we investigate the
effect of sintering temperature
on the chemical and physical
properties of CCTO ceramics
Moulson & Herbert, Electroceramics,
Chapman & Hall London (1990) p.261
In this way we hope to find indications
for oxygen/Cu loss/non-stoichiometry
or valence state changes

7. Chemical and Physical Properties
2. Experimental Rainer Schmidt
Powder Processing
Mixed oxide route using dried CaCO % , CuO 99.99% , TiO %
Furnace reaction temperature of 975°C
Pellet Production
Pellet pressing using a 1 ton uni-axial hydraulic press
Pellet sintering at 975°C, 1000°C, 1025°C, 1050°C, 1075°C, 1100°C
Chemical and Physical Properties
Dielectric properties by impedance spectroscopy
Thermal Gravimetry, Lattice parameter determination by XRD,
Composition & Microstructure by SEM, Quantitative analysis by EDAX
Oxidation states by XANES and phonon modes by Raman spectroscopy

8. 3. Results: Dielectric properties Rainer Schmidt
Impedance spectroscopy data at 100 Kelvin from sintered pellets (975°C – 1100°C)
10-7
10-8
10-9
10-10
10-11
10-12
1,5x105
105
0,5x105
100 K
975C
Grain boundary
1100C
1075C
1050C
1000C
-Z'' (Wcm)
1025C
Real part capacitance C' (F/cm)
1000C
975C
1025C
1050C
Bulk
100 K
1075C
0,5x ,5x105
Frequency (Hz)
1100C
Real part impedance Z' (Wcm)
The grain boundary capacitance significantly
increases with sintering temperature
The bulk resistance significantly
decreases with sintering temperature

9. Cole-Cole and conductivity plots of impedance spectroscopy data
3. Results: Dielectric properties Rainer Schmidt
Cole-Cole and conductivity plots of impedance spectroscopy data
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
103
100 K
1100C
1100C
1075C
1050C
1075C
1025C
1000C
975C
C' ' (F)
Real part conductivity s' (1/Wcm)
1050C
1025C
1000C
100 K
,5x x ,5x
Real part capacitance C' (F)
Frequency (Hz)
975C
The grain boundary capacitance significantly
increases with sintering temperature
The bulk conductivity significantly
increases with sintering temperature

10. Reversible and unreversible weight loss was detected
4. Results: Thermal gravimetry Rainer Schmidt
Reversible and unreversible
weight loss was detected
Reversible: oxygen content
changes?
25C hold 10 min
C heat 10C/min
C heat 3C/min
1100C hold 60 min
C cool 3C/min
900C hold 30 min
C cool 10C/min
C – 25 C heat/
cool 3C/min
Unreversible: Cu content
changes?

11. CCTO lattice parameter vs sintering temperature
4. Results: Lattice parameter Rainer Schmidt
CCTO lattice parameter vs sintering temperature
from X ray diffraction using an internal Si standard

12. SEM/EDAX analysis on sintered CCTO pellets demonstrate Cu segregation
5. Results: Composition & microstructure by SEM Rainer Schmidt
SEM/EDAX analysis on sintered CCTO pellets demonstrate Cu segregation
1025ºC
1075ºC
Secondary
electrons Ti Ti
EDAX line
scans using
backscattered
electrons Cu Cu Ca Ca O O C C

13. 5. Results: Grain average by quantitative EDAX Rainer Schmidt
Quantitative EDAX analysis by averaging over large areas (large area average)
and localised EDAX measurements on single grains averaging over 25 grains
expected Cu
0,375
The measurements were calibrated using a CuTi alloy and ceramic CaTiO3

14. X-ray Absorption Near Edge Spectroscopy suggests mainly Cu2+
6. Results: XANES Rainer Schmidt
X-ray Absorption Near Edge Spectroscopy suggests mainly Cu2+
Cu1+ standard
Hints of Cu3+ ??
Cu2+ standard
975C
1100C
1100C:quenched

15. X-ray Absorption Near Edge Spectroscopy suggests Ti4+ exclusively
6. Results: XANES Rainer Schmidt
X-ray Absorption Near Edge Spectroscopy suggests Ti4+ exclusively
975C
1100C
Ti3+ standard
Ti4+ standard
Ti2+ standard
Ti0 standard

16. Raman spectroscopy suggests no changes in lattice structure
6. Results: Raman spectroscopy Rainer Schmidt
Raman spectroscopy suggests no changes in lattice structure

17. Conclusions Rainer Schmidt
1.) Changes in sintering temperature of CCTO ceramics between
C leads to dramatic changes in bulk resistivity (factor ≈103)
2.) A Cu rich phase segregates out of the ceramic by heating above 1025C
3.) Irreversible weight loss can occur suggesting Cu volatilization
4.) EDAX, XANES and Raman spectrocsopy analysis suggests that the
resulting Cu deficiency
5.) Only weak indications can be found that Cu segregation/volatilization
leads to increased bulk conductivity

18. Questions Rainer Schmidt