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ICEPT.2017.8046663

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Improved permittivity and breakdown strength of
PVDF composites filled with Ti02-SrTi03 hybrids
Xiaodong ZhU,,2, Suibin Luo', Shanjun Ding',3, Cao Wang',2, Zijie Song',2, Shuhui Yu'*, Rong Sun'*, and Ching-Ping
Wong4
2
I
Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
Department of Nano Science and Technology Institute, University of Science and Technology of China, Suzhou 215123, China
3
College of Material Science and Engineering, Shenzhen University, Shenzhen, Guangdong 518061, China
4
Department of Electronic Engineering, Faculty of Engineering, The Chinese University of Hong Kong, Hong Kong, China
sh,yu@siat.ac.cn; rong.sun@siat.ac.cn
were
16-18] High breakdown strength is beneficial for the dielectrics
synthesized by a facile hydrothermal reaction using Ti02 as the
to be applied under high voltage and to produce high dipole
Abstract-In
titanium
this
precursor
work,
under
the
Ti02-SrTi03
basic
condition.
hybrids
By
using
the
synthesized Ti02-SrTi03 hybrids as fillers, the films of the Ti02-
displacement. The improved displacement and voltage lead to
high stored energy density.
SrTi03/PVDF composites were prepared. The dielectric property
and insulation behavior of the films were investigated. High
permittivity and improved breakdown strength of the composites
Here, we report a PVDF-based composite filled with Ti02SrTi03 hybrids. The hybrids were fabricated by hydrothermal
were achieved. The breakdown strength of the composites filled
reaction using Ti02 as the titanium precursor. The reaction
with 1
process was conducted on the surface of Ti02 nanoparticles. So,
wt%
hybrids exhibited an improvement about 80%
the formed SrTi03 phases were deposited or coated on the
compared with the unfilled PVDF matrix.
surface of Ti02 nanoparticles. The PVDF-based composites
Keywords-hybrids; dielectric properties; breakdown strength;
nanocomposites
were fabricated by a common solution-casted method. The
dielectric properties and breakdown strength of the casted films
were investigated.
I.
INTRODUCTION
II.
Polymer-based dielectric nanocomposites have attracted
EXPERIMENTAL PROCEDURE
much attention because of their important applications in
various fields such as portable electronic devices, medical
A. Materials
debrillators, hybrid electric vehicles and power grids. [1-4]
Relatively
high
permittivity,
low
loss
and
high
voltage
breakdown strength are primary requirements of dielectric
materials in the above applications. The common methods for
enhancing the permittivity of the polymer matrix involve
introducing high-dielectric-constant ceramics or conductive
fillers.[5, 6] Either method has some limits. The ceramic filled
composites show limited enhancement of permittivity. And the
composites containing conductive filler exhibit high dielectric
loss at the percolation threshold. The breakdown strength of the
conductor
attempts such as fabrication of core-shell structured particles
and metal-ceramic hybrid particles have been made to reduce
the leakage current.[2, 7-13] However, the breakdown strength
is still much lower than that of the pure polymer matrix as the
filler content is high.
An effective way to improve the breakdown strength is
adding small amount of oxide nanoparticles into the polymer
matrix. When the filler content is lower than 5 vol%, the
composites exhibited a breakdown strength larger than that of
the matrix. This phenomenon is attribute to the interface effect,
has been explained by the multi-core model proposed
by Tanaka.[14,
improved
from Aladdin Industrial Corporation, China and used as the
titanium
hydroxide
and
strontium
(NaOH,
98%)
sources,
supplied
respectively.
by
Aladdin
Sodium
Industrial
Corporation was used as the alkaline medium. Deionized water
was prepared by Ulupure water purification system. N, N­
dimethyl formamide (DMF, Xilong Chemical Co. China) was
used as solvent.
Poly (vinylidene fluoride) (PVDF, Shanghai
3F Co. China) was chosen as the polymer matrix.
filled composites rapidly decreases due to the
formation of conductive pathway. To overcome this problem,
which
Titanium dioxide (Ti02, anatase, 99.8%) and Strontium
hydroxide octahydrate (Sr(OH)2 '8H20, 97%) were purchased
15]
breakdown
B.
Preparation ojTi02-SrTi03 hybrid nanoparticies
An amount of Ti02 nanoparticles with the size of 40nm
were mixed with the determined quality of Sr(OHk 8H20
powders. The mole ratio of Sr/Ti was set as 0.5. Then, 50 mL 5
mol L-' NaOH solution was added into the above mixture and
stirred for 2 hours. The obtained suspension was transferred to
a 100-mL Teflon-lined stainless steel autoclave and heated to
220°C. The reaction lasted 12 hours. The reactor was cooled to
about 30°C after the hydrothermal reaction was finished.
The products were washed with deionized water several
times
to
remove
excess
alkali.
To
eliminate
unreacted
Many reports have demonstrated the
hydroxides, dilute hydrochloric acid was added into the slurry
strength in the polymer composites
of the collected Ti02-SrTi03 (TO-STO) hybrids dispersed in
introduced with fillers like BaTi03, Ti02, MgO and BN et al.[4,
2017 18th International Conference on Electronic Packaging Technology
978-1-5386-2972-7/17/$31.00 ©2017 IEEE
deionized water. After being ultrasonicated for 10 min, the
1238
III.
A.
RESULTS AND DISCUSSION
Charaterization ofTi02-SrTi03 hybrids
Fig. 1 shows the XRD patterns of TO-STO hybrids
prepared by a hydrothermal reaction with the molar ratio of
Sr/Ti =50%. As shown in the figure, the crystal structures of
the TO-STO hybrids match exactly with the standard anatase
Ti02 (space group I411amd, Ref. code 01-089-4921) and cubic
perovskite SrTi03 (space group Pm3m, Ref. code 01-0741296). The XRD pattern of bare Ti02 nanoparticles (Sr/Ti = 0)
shows diffraction peaks at 29 = 25.39°, 37.99°, 48.09°, 53.95°,
55.110, and 62.77°, which are perfectly indexed to the (1 0 1),
(0 0 4), (2 0 0), (1 0 5), (2 1 1) and (2 0 4) crystal planes of
anatase Ti02, respectively. After being hydrothermally treated
in Sr(OH)2 solution with Sr/Ti = 50% at 220°C for 12 h,
additional diffraction peaks with 29 = 22.68°, 32.34°, 39.88°,
Fig. 1. XRD patterns of TiO, particles and the synthesized TiOrSrTi03
nanohybrids.
46.43°, 57.74°, and 77.12° appeare, corresponding to (1 0 0), (1
1 0), (1 1 1), (2 0 0), (2 1 1), (2 2 0) and (3 1 0) crystal planes
of cubic perovskite SrTi03, respectively. The results indicate
that part of Ti02 has successfully converted into SrTi03.
[mal slurry was centrifuged at 9000 rpm for 10 min and
washed repeatedly by hot deionized water until the pH value of
the centrifugation liquid reached about 7. The product was
SEM images show shat the synthesized TO-STO hybrids
maintain similar morphology of the Ti02 precursors (Fig. 2a &
b). The results indicate that the formation of TO-STO in the
dried in an oven for 12 h at 80 °C. Finally, the obtained product
hydrothermal reaction process occurred on the surface of Ti02
was characterized and used as the filler for preparing PVDF
precursor particles. The size of the collected TO-STO hybrids
composites.
is about 80nm. Fig.2c & d display the cross-section SEM
images of the TO-STOIPVDF nanocomposites, indicating that
C. Fabrication ofthe Ti02-SrTi03IPVDF composite films
The matrix polymer PVDF was dissolved in DMF under
the hybrid nanoparticles are uniformly distributed in the
composites.
ultrasonication. The weight ratio of PVDF to DMF is 1 :6.
Different amounts of TO-STO hybrids were added into the
PVDF solution. The TO-STO hybrids were homogeneously
dispersed by ultrasonication for 12 hours. Then the films of the
composites were obtained by spreading the suspension on the
glass substrate and dried in an oven under 80 °C for 12h to
remove residual solvent.
D. Characterization
The crystal structure of TO-STO hybrids was analyzed
using X-ray diffraction
(XRD,
D/max-2500/PC, Rigaku Co.)
with Cu Ka radiation, at a scanning speed of 201min in steps of
0.02°. The cross section morphology of the films of the TO­
STOIPVDF
composites
was
examined
using
a
scanning
electron microscope (SEM) (FEI Nova NanoSEM 450). The
thermal stability of the TO-STO hybrids was investigated by
thermalgravimetric analysis (TGA, Q800, TA Instruments)
with a heating rate of 5 °C/min under flowing N2 atmosphere
in a temperature range from 30°C to 1000 °C. The dielectric
permittivity and dielectric loss of the films were measured by
employing an Impedance Analyzer (Agilent 4294A) in the
frequency range of 100 Hz to 10 MHz. The measurement of
DC breakdown strength was carried out with a dielectric
strength tester (CS9912BX, Allwin Instrument Science and
Technology co.Ltd, China) at a ramping rate of 200Vs" and the
Fig. 2. SEM images of (a) TiO, nanoparticles and (b) the synthesized TO­
STO hybrids. The cross section SEM images of the TO-STO/PVDF
composites with the filler content of (c) I wt% and (d) 7 wt %, respectively.
maximum leakage current wad set at 5mA.
2017 18th International Conference on Electronic Packaging Technology
1239
the prepared PVDF composites contain few defects. All the
dielectric losses of the composites at 1 kHz is lower than 0.1
which is acceptable for real application.
C. Breakdown strength o/the TO-STOIPVDF composites
To study the insulation behavior of the TO-STO!PVDF
(Eb)
composites, the breakdown strength
is measured. The
breakdown strength was investigated using a two-parameter
Weibull-distribution equation as stated as follows: [19]
P(E)=I- [I-( %b r 1
where,
failure.
(1)
peE) is the cumulative probability of electric breakdown
Eb is the scale parameter which indicates the Weibull
breakdown strength with 63.2% probability to breakdown. �s is
the slope (or shape) parameter derived from logarithm equation
given as
In[-In(l-P(E))]
The
higher
value
of
�s
=
Ps lnE - Ps
indicates
less
1nEb
(2)
scattering
in
the
experimental data and better reliability.
Eb and �s are shown in
Eb of pristine PVDF is 125.34 kV/mm and reaches a
The calculated breakdown strength
Fig.4. The
maximum
value
incorporated
of
with
223.10
merely
kV/mm
1wt%
for
TO-STO
the
composite
fillers.
This
represents an enhancement about 80% compared with the
breakdown strength of the neat PVDF. Composite containing
3wt% TO-BTO filler also shows a higher
Fig. 3. Frequency-dependence of (a) pertmittivity and (b) dielectric loss of
the TO-STO/PVDF nanocomposites.
Eb than
pure PVDF.
Then the breakdown strength monotonically decreases to 80.13
kVImm as the filler content reaches 7 wt%. The reduced
breakdown strength is due to the overlapping of the interfacial
B. Dielectric properties o/the TO-STOIPVDF composites
Fig.3
shows
dielectric
properties
of
the
PVDF-based
nanocomposites as a function of frequency at 25 DC. The
permittivity of the composites increases with the TO-STO filler
loading. The permittivity of the pristine PVDF is about 12 at
100 Hz. When the filler content is 1 wt%, the permittivity is 15.
As the filler content is increased to 7%, the permittivity reaches
region. The charges in the composites are more easy to transfer
and forming electric breakdown trees. The �s of the TO­
STO/PVDF composites increases with the filler content. The �s
of the pure PVDF films is 7.09. It increases to 8.61 when the
filler content is 7 wt%.
The results suggested that the
reliability of the composites is enhanced with the introduction
of TO-STO hybrids.
19. The enhancement ratio of permittivity is about 60%. It
means that the TO-STO hybrids are effective in enhancing
permittivity of the polymer based composites.
Besides, the stability of permittivity with the frequency is
enhanced for the PVDF polymer filled with the TO-STO
hybrids. The permittivity of PVDF shows a decrease from 12 at
100 Hz to 6 at 10 MHz. The decreased ratio is 50%. For the
composites
filled with
1 wt%
TO-STO,
the permittivity
decreases from 14.8 at 100 Hz to 1l.7 at 10 MHz. The
decreased ratio of the composite is only 21%. The decreased
ratio is 28% for the composite filled with 7 wt% TO-STO
hybrids in the frequency range from 100 Hz to 10 MHz. Fig.3b
shows the dielectric loss of the composites in the frequency
range from 100 Hz to 10 MHz. The tendency of the dielectric
loss of the composites with the frequency is following the
variation of PVDF matrix but only shows slight increase in
comparison with PVDF. The dielectric loss of the composites
show little increase compared with the PVDF. It suggests that
2017 18th International Conference on Electronic Packaging Technology
Fig. 4.
Breakdown strength of the TO-STO/PVDF composites.
1240
IV.
core-shell structured BaTi03@A1203 nanoparticles," Ceramics
SUMMARY
In this report, we successfully synthesized TO-STO hybrids
international, vol. 43,pp. 3127-3132,2017.
[8]
via a facile hydrothennal reaction using Ti02 as titanium
precursor. The dielectric properties of the prepared TO-STOI
PVDF nanocomposites achieved a high permittivity about 19
and low loss (less than 0.1 at 1 kHz). The breakdown strength
[9]
reached a maximum value of 223.10 kV/mm for the composite
filled
with
1wt%
TO-STO
hybrids.
The
nanocomposites
possess increased permittivity, low dielectric loss and enhanced
breakdown
strength,
simultaneously,
which
[10]
demonstrate
potential applications in electrical and electronic devices.
[II]
ACKNOWLGMET
This work was financially supported by the National Natural Science
Foundation of China (No.51377157),
the Frontier Science Key
[12]
Program of the Chinese Academy of Sciences (QYZDY-SSW­
JSCOIO), Guangdong Provincial Key Laboratory (2014B030301014)
and
Shenzhen
Key
Fundamental
Research
Program
(JCYJ20160608160307181).
[13]
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