Dielectric and Raman spectroscopic studies of
phase transitions in the (1-x)(Na0.5Bi0.5TiO3)x(BaSnO3) Lead-free ferroelectric system
Dillip K Pradhan a, Satya Narayan Tripathy a, Karuna Kara Mishra b
aDepartment of Physics, National Institute of Technology, Rourkela-769008, India
bCondensed Matter Physics Division, IGCAR, Kalpakkam-603102, India
Plan of presentation
Introduction.
Why Na0.5Bi0.5TiO3 (NBT)?
Problems to be addressed.
Objectives.
Results and Discussion
Summary and conclusions
Introduction
 Ferroelectric materials have permanent
dipoles and so there molecular structure
lack center of symmetry.
 All ferroelectric crystals must be
piezoelectric though the converse is not
true.
 All ferroelectric materials have one or
more phase transition temperatures.
 Structural change take place at the curie
temperature.
 Immediately above the curie temperature,
the dielectric constant of a ferroelectric
material obeys Curie -Wiess law .
 A ferroeletric is generally defined as one
of which exhibits hysterisis loop.
1)spontaneous Polarization (Ps)
2)Remnant Polarization (Pr)
3)Coercive Field (Ec)
Most studied material
 BT (BaTiO3)
 PZT (Pb(ZrxTi1−x)O3 )
 PLZT (Pb1−xLax(ZryT1−y)1−x/4O3)
 PMN (Pb(Mg1/3Nb2/3O3)- PT(PbTiO3)
Why Lead free
 Lead (Pb) release into the environment at time of processing and remain for
a long time in the environment and accumulates in living tissues which
damages the brain and nervous system.
 It could introduce to the ecosystem and cause “acid rain”.
 Restoring and recycling of lead-based materials is an extensive
environmental issues.
Why (Na0.5Bi0.5 )TiO3?
 Lead free compound.
 Ferroelectric at room temperature.
 Complex phase transitions sequence & anomalies dielectric
behaviors.
 High Curie temperature (Tc >320 0C) .
 Large Remnant polarization.
 Bi+3 ions are isoelectronic configuration with Pb+2, both
showing a lone pair effect.
Sequence of Phase transitions NBT
Rhombohedral (R3c)
Td
(200-280 oC) Modulated Orthorhombic (R3c+ Pnma)
TA-O
Orthorhombic (Pnma)
TC
Second order Phase transition (~320 oC)
Tetragonal (P4/mbm+P42/mnm)
First order phase transition
Cubic (520-540 oC) (Pm-3m)
•G. Trolliard and V. Dorcet, Chem. Mater. 20, 5074 (2008).
•V. Dorcet, G. Trolliard, and P. Boullay, Chem. Mater. 20, 5061 (2008).
Problems Addressed
 High coercive field 73 KV/cm.
 High conductivity cause problem during polling.
 High Dielectric loss.
 Low piezoelectric and electromechanical properties i.e. d33
of 92 pC/N and Kp coupling coefficients 18.6.
To overcome the above mentioned problems, we have synthesized
(1-x)Na0.5Bi0.5TiO3–xBaSnO3 ( 0 ≤ x ≤ 0.15)
Objective
Our main objective is to
(i) reduce the high dielectric loss and conductivity
(ii)improve the dielectric and ferroelectric properties.
(iii)study the fundamental physics related to phase
transition of NBT-BaSnO3 System.
1.Ferroelectric to relaxor crossover(1-x)BaTiO3-xBaSnO3
2.Relaxor ferroelectric behavior of BaSnO3-PbTiO3 solid solution with MPB
1. C. Lei, A. A. Bokov, and Z. G. Ye, J. Appl. Phys. 101, 084105 (2007).
2. X. Han, X. Li, X. Long, H. He, and Y. Cao, J. Mater Chem. 19, 6132 (2009).
(Na0.5Bi0.5) Ti O3
(A and B site Modification)
Na2CO3
BaCO3
Bi2O3
SnO2
TiO2
Dry Mixing
Wet Mixing
Calcination
Formation
Grinding
Recalcination
Cold Pressing
Materials
Preparation
Sintering
Polishing
Electroding
Characterization
Checked by XRD
NO
YES
Materials Characterization
Structure
Determination
XRD analysis
(PANalytical's X'Pert
PRO)
Raman
Spectroscopy
Ranishaw micro-Raman
spectrometer (ModelINVIA)
Dielectric,
Impedance
Measurement
PSM LCR 4NL, Model:
1735, UK
10
Structural Studies
* ICDD No 74-1318
*
x = 0.15
Intensity (A.U)
x = 0.12
x = 0.1
x = 0.08
x = 0.05
x = 0.03
x = 0.00
20
30
40
50
60
o
Bragg Angle (2 )
70
80
*Na0.5Bi4.5Ti4O15 (ICDD No 74-1318).
For, 0≤ x ≤ 0.08; Rhombohedral
For, 0.1≤ x ≤ 0.15; Orthorhombic
For, NBT a = b = 5.4972(17) Å and c = 13.4551(21) Å
Dielectric Studies
3.0
1.0
0.5
(a) x = 0.00
Zone-I
100
200
300
400
o
Temperature( C)
tan
0.3
Td
1.5
0.4
TA-O
Zone-II
2.0
TC
1 kHz
5 kHz
10 kHz
50 kHz
100 kHz
500 kHz
r 
103
2.5
0.5
0.2
0.1
0.0
500
350
300
o
Temperature( C)
100 kHz
250
Td
TA-O
150
TC
100
0.00
0.05
0.10
Composition (x)
0.15
a) Appearance and enhancement of modulated orthorhombic phase
b) Decrease in ferroelectric transition temperature
2nd Order Phase transition
6
0.8
TC= 335 C

2
0.6
0
0.4
-2

-4
-6
4
1/
200
300
o
Temperature( C)
400
0.2
0.0
 o 
 C 
o
1.0
x = 0.05
100 kHz
(b)
0.8
o
TC= 303 C
2

(a)

x = 0.00
100 kHz
1/ 

  
C 
4
1.0
0.6
0
0.4
-2

-4
-6
1/
200
For, x=0.00 ξ 320oC/ ξ 350oC ≈ 2.6
300
o
Temperature( C)
1/ 
6
400
0.2
0.0
Raman Spectroscopy
A. Compositional Dependence
100
600
(a)
x = 0.08
x = 0.05
x = 0.03
x = 0.00
85
(b)
(a)
IA/IQ
x = 0.1
500
-1
x = 0.12
90
Mode frequency (cm )
Intensity (arb. units)
x = 0.15
95
400
80
75
70
300
65
200
60
55
100
100 200 300 400 500 600 700
-1
Raman shift (cm )
50
0.00
0.05
0.10
Composition (x)
0.15
0.00
0.04
0.08
0.12
Composition (x)
 Mode (~278 - ~585 cm-1) are associated with the TiO6 octahedral vibration.
 Disappearance of A1-mode at ~134 cm-1 as the sample undergoes a structural phase
transition from rhombohedral to orthorhombic at x = 0.1 composition.
0.16
Conclusion
To conclude, lead free solid solutions of (1-x)NBT-xBSN (0≤ x
≤ 0.15) were synthesized by solid-state reaction method.
Phase transition temperatures Td, TA-O and TC were obtained
from the detailed dielectric data analysis.
A decrease in ferroelectric phase transition temperature as a
function of x is obtained and finally TC merges with TA-O at
composition x = 0.15.
In-situ temperature dependent Raman spectroscopy shows
disappearance and discontinuous changes in the phonon mode
frequencies across the orthorhombic-tetragonal phase transition.
Acknowledgement
We acknowledge Prof. R. N. P
Choudhary & Prof. A. K. Arora for
fruitful discussions.