Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Synthesis and Characterization of Electrospun Ba 0.6 Sr 0.4 TiO 3 Nanofibers and 3-3 Nanocomposites
Yahya Toprak, 1 Ebru Menur Alkoy 2 and Sedat Alkoy 1,*
1 Department of Materials Science and Engineering, Gebze Institute of Technology, Kocaeli 41400, Turkey
2 Faculty of Engineering, Maltepe University, Istanbul 34857, Turkey
Abstract— Barium strontium titanate – Ba 0.6 Sr 0.4 TiO 3 (BST) nanofibers with diameters of 50–200 nm were prepared
using electrospun BST/polyvinylpyrrolidone (PVP) fibers by calcination for 1 h at temperatures in the range of 650–800ºC
in air. The morphology and crystal structure of calcined BST/PVP nanofibers were characterized using SEM and XRD.
Nanocomposites with 3-3 phase connectivity were prepared by infiltrating an epoxy matrix phase into the nanofiber mats.
Dielectric properties of the BST/epoxy nanocomposites were evaluated for tunable microwave dielelectric applications.
BST powders were also prepared by gelation and drying of BST precursor sol-gel solutions. Dried gels were then
calcined, ground, pressed and sintered to obtain dense BST ceramics. Electrical properties of BST ceramics were
determined through dielectric and PE hysteresis measurements.
Barium strontium titanate - Ba 1x Sr x TiO 3 (BST) is a
perovskite type material with a ferroelectric-paraelectric
transition temperature that can be tuned from 30 to 400 K by
varying the Ba/Sr ratio [1]. Solid solutions with x = 0.2 to
0.5 are normally used to shift the transition temperature to,
or just below, room temperature. BST solid solutions have
unique combination of large dielectric constant, high
tunability, low dc leakage, low loss tangent, and stable
operation at high temperature [2]. With this combination of
favorable properties, BST finds niche in tunable microwave
devices such as microwave tunable phase shifters, tunable
filters, and high-Q resonators for radar and communication
applications [3]. Fiberization of the functional ceramics
expand their utility into the micro and nanodevices, and
incorporation of these fibers into composite structures
provides an added flexibility and mechanical integrity [4].
Electrospinning represents a simple and versatile method for
preparing ceramic fibers in the nanoscale range [5].
In the preparation of BST precursor sol-gel solution
barium acetate, strontium acetate and titanium isopropoxide
were used as source materials. A mixture of acetic acid and
2-methoxyethanol with 1:2 mix ratio was used as solvent.
Poly(vinylpyrrolidone) (PVP) was used as the carrier
polymer. The Ba:Sr molar ratio was 0.6:0.4 and the molarity
of the final precursor solution was 0.27 M. Various PVP
additions from 5 to 30 wt% were studied. The electric field
during the electrospinning process was varied from 10 to 20
kV/cm and the pumping rate from 1 to 5 l/h.
Electrospun BST/polyvinylpyrrolidone (PVP) fibers were
obtaind by calcination for 1 h at temperatures in the range of
650–800ºC in air. The morphology and crystal structure of
calcined BST/PVP nanofibers were characterized using
SEM and XRD. Nanocomposites with 3-3 phase
connectivity were prepared by infiltrating an epoxy matrix
phase into the nanofiber mats. Dielectric properties of the
BST/epoxy nanocomposites were evaluated for tunable
microwave dielelectric applications. BST powders were
also prepared by gelation and drying of BST precursor solgel
solutions. Dried gels were then calcined, ground, pressed
and sintered to obtain dense BST ceramics. Electrical
properties of BST ceramics were determined through
dielectric and PE hysteresis measurements.
X-ray diffraction patterns presented in Fig. 1 for calcined
BST powders indicate that a calcination temperature of
700ºC was enough to obtain pure BST phase with perovskite
structure. The scanning electron micrograph shown in Fig.
2 indicates that nanofibers with diameters ranging from 50
to 200 nm can be obtained without the formation of
undesired beads.
Figure 1. XRD pattern of BST powders calcined at 700ºC-1 h.
Figure 2. SEM micrograph of the as deposited BST/PVP
nanofibers.
The dielectric constant of the bulk BST ceramic pellets
were as high as 2000 with a dielectric loss of less than 2%
measured at room temperature at 100 kHz. The polarization
vs. electric field hysteresis loops indicates a ferroelectric
behavior with a remnant polarization of 5 C/cm 2 and a
coercive field of 15 kV/cm measured under an electric field
of 50 kV/cm.
*Corresponding author: sedal@gyte.edu.tr
[1] K.V. Saravanan et al., Mater. Chem. Phy. 105, 426 (2007).
[2] S. Maensiri et al., J. Colloid Interface Sci. 297, 578 (2006).
[3] D.Y. Lee et al., J Sol-Gel Sci Technol 53, 43 (2010).
[4] E.M Alkoy et al., J. Amer. Ceram. Soc. 92, 2566 (2009).
[5] R. Ramaseshan et al., J. Appl. Phys. 102, 111101 (2007).
6th Nanoscience and Nanotechnology Conference, zmir, 2010 328