Appendix-I: Dielectric Properties of CaCu3Ti4O12
Under High DC-Bias Electric-Fields
Contents
Page No.
A.1: Effect of High Electric-Field
119
A.2: Tunability of the Dielectric Constant
120
A.3: References
120
Appendix-I……………………………………
Dielectric behaviour of CaCu3Ti4O12 under high dc electric fields was measured from room
temperature down to liquid-N2 temperatures. The dielectric constant is enhanced on applying the
bias-field mainly over the high-temperature (200K-300K) region. The dielectric constant shows
high-tunability; η(4.5kV/cm)= [ε′(EV)-ε′(E0)]/ε′(E0) = 138% at 300K/1kHz. Positive tunability of
dielectric constant is useful in the capacitor-based storage batteries. The temperature and the
electric field both seem to have the same effect on the dielectric constant of CaCu3Ti4O12. The
effect of various bias-voltages on the dielectric constant (mainly observed at the low-frequency
side) is shown in fig. (1).
7000
115.6 Hz
4k
ε'
6000
3k
Eps'
5000
10
4000
100
450
Volt/mm
3000
225K
0 Volt
10Volt
20 Volt
50 Volt
100 Volt
200 Volt
300 volt
400 volt
450 volt
100000
Eps''
10000
1000
100
10
0
10
1
2
10
Freq. [Hz]
10
3
10
4
Figure (1). Effect of electric field at 225K on CaCu3Ti4O12.
Page 118
Appendix-I……………………………………
A.1: Effect of High Electric-Field
In fig. (2) is shown the dielectric permittivity vs. temperature at 1 kHz of CaCu3Ti4O12 at the
various applied bias electric fields.
1kHz
Dielectric Cons
tant
5000
1000
150
200
Temperature
250
300 0
mm)
e(V/
70 100
g
Volta
500
400
300
200
100
(K)
Figure (2). Effect of the bias electric field on the CaCu3Ti4O12.
The dielectric constant has a high value and little variation vs. temperature for zero-field,
similar to the earlier published reports [1]. As dielectric constant shows plateau region and large
(frequency-dependent) drop around 100K, due to the anti-parallel correlation of the dipoles [1]
(for 1kHz the drop happens precisely at 85K). On increasing the temperature above 250K (no
bias-field), dielectric constant shows another step, due to the grain-boundary relaxation [2]. The
grain-boundary effect is one of the main reasons for the huge dielectric constant of CCTO.
Insulating grains and semiconducting grain-boundaries provide the platform for IBLC-based
dielectric properties. Application of electric field up to ~50V does not show any remarkable
effects, whereas the dielectric constant starts to exhibit huge field dependence at high fields. At
450V bias-field ε′ starts to increase from 200K onwards. This increment can be understood as the
separation of more and more ions which stack at the grain-boundaries, contributing to the
enhancement of dielectric constant. Increment of the dielectric constant on exposure to radiation
has been recently reported [3].
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Appendix-I……………………………………
A.2: Tunability of the Dielectric Constant
From the above results it is established that one can tune the value of dielectric constant by
applying an electric field across the sample. The tunability {η = [ε′(EV)-ε′(E0)]/ε′(E0)} of the
dielectric constant vs. temperature for various fields at 1kHz is shown in fig. (2).
125
1kHz
Tunability(%)
100
75
50
25
0
100
150
200
Temperature
250
t/mm
V ol
500
400
300
200
100
300
(K)
Figure (3). Tunability of dielectric permittivity vs electric field against temperature.
The tunability is obviously higher for the higher fields and at high-temperatures, and reaches
a very high value (123%) at room temperature. The increment of the tunability can be understood
easily from the increment of the free-charge carriers on increment of the temperature, and this
effect gets boosted up on applying the external bias-field. To check the isotherm tunability of the
dielectric constant, we have taken the dielectric data of the sample at room temperature in
positive and negative field directions, and fond out a beautiful butterfly diagram for 1kHz.
A.3: References
[1] A.M. Awasthi and Jitender Kumar, J. Appl. Phys. 112, 054108 (2012).
[2] Derek C. Sinclair, Timothy B. Adams, Finaly D. Morrison, and Anthony R. West,
Appl. Phys. Lett. 80, 2153 (2002).
[3] C. Masingboon et.al., Appl Phys Lett. 102, 202903 (2013).
Page 120