Synthesis and Dielectric Properties of Bi4-xNdxTi3O12 obtained by solution combustion synthesis.
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SYN
NTHESIS A
AND DIELECTRIC PROPERT
P
IES OF Bi4-x
NED BY
4 NdxTi3O12 OBTAIN
SOL
LUTION COMBUST
C
ION SYNT
THESIS
bUmarr Al-Amani*, Ahmad Ehsan,
E
Srim
mala Sreekanntan, Ahmad Fauzi Moohd Noor, Khairunisak
K
Abd. Razzak
School off Material and
a Minerall Resources Engineerinng,
Malaysia.
Univversiti Sains Malaysia,, 14300, Nibbong Tebal,, Penang, M
ABSTR
RACT
Bismuth
h neodymiuum titanate, BNdT (Bi4-xNdxTi3O12 where x=0.2,
x
0.4, 0.6, 0.8, 1.0) powderss
were syynthesized via
v solutionn combustioon synthesiis for ferroeelectric mem
mory devicces. The as-synthessized powdeers were callcined at 8000°C for 3 hhour and subbsequently, sintered at 1100oC forr
6 hourss. The form
mation of puure phase and
a c-axis-ooriented BN
NdT were ccharacterizeed by X-rayy
diffraction (XRD).. It was fouund that the orientationn degree of c-axis increeases with the
t increasee
c
in BNdT,
B
and at
a the same time
t
the graain morphollogy grows from rod-liike to plate-of Nd content
like struucture. Addditionally, thhe dielectricc properties of BNdT are
a greatly iinfluenced by
b the grainn
orientattion.
1.0 INT
TRODUCT
TION
Aurivillius material off bismuth-bbased has been widelyy studied duue to its outtstanding inn
ferroeleectric propeerties [1]. Bismuth
B
tittanate, Bi4T
Ti3O12 is a good canddidate for ferroelectric
f
c
memoryy devices appplication [2]. The subbstitution off rare-earth such as La33+, Pr3+, Sm
m3+ and Nd3++
in Bi4Ti3O12 has been extensiively perforrmed to impprove the feerroelectriciity in such devices
d
[3].
Howeveer, those raare-earths addded in Bi4Ti3O12 exhiibits differeent axis-orieented i.e. a--axis and c-axis [4]]. In a-axiss-oriented, the diffracttion peak iis indexed (1 1 7). O
On the otherr hand, thee
diffraction peak off c-axis-orieented corressponds to (00 0 6). Accoording to Fouskova annd Cross [5]]
the conductivity inn the a-direcction is apprroximately 30 times hiigher than inn the c-direection in thee
c
of B
Bi4Ti3O12. Therefore,
T
h
highly
a-axis crystal orrientation iss preferable in order too
single crystal
obtain high
h
conducctivity hence it can impprove the dielectric prooperties.
In this studdy, a solutioon combustiion synthessis was seleccted as an aalternative approach
a
too
preparee BNdT. This
T
methodd was devveloped froom the conncepts of sself-propagating high-temperaature synthesis (SHS) combined with wet chemical teechniques iin order to
o synthesizee
metal-ooxide-based ceramic powder.
p
Gennerally, thrree factors influence tthe generattion of fire,
which can
c be descrribed as selff-generatedd combustionn. These facctors are thee oxidizer, temperature
t
e,
and fueel, which produce
p
heaat, light, annd ash [6]. The fuel-frree combusstion methood does nott
employy fuel agentts such as citric acid,, urea, or glycine.
g
Thhe process is relativelly low-cost,
requiress a simple ssetup, and has high reprroducibilityy. In this woork, Nd3+ wiill be used to
t substitutee
Bi3+ ionns in Bi4Ti3O12 and thee peak charracteristic and grain morphology will
w be stud
died as welll
as dieleectric properrties.
PERIMEN
NTAL PRO
OCEDURE
2.0 EXP
Bi4-xNddxTi3O12 (B
BNdT) where x = 0.22, 0.4, 0.6,, 0.8 and 1 were synnthesized via
v solutionn
combusstion. Bismuuth nitrate penthahydra
p
ate, Bi(NO3)3.5H2O andd neodymiuum nitrate hexahydrate,
h
,
Nd(NO
O3)3.6H2O were
w
initiallyy dissolvedd in 2-Methhaoxyethanool, CH3OCH
H2CH2OH at 40oC onn
hot platte and stirreed for abouut 30 min. Separately,
S
t
titanium
(IV
V) isopropooxide, Ti[OC
CH(CH3)2]4
was dissolved in a homogeeneous soluution of 22-ME and acetylacetoone, C5H8O2 at room
m
olution with
h
temperaature and sttirred for 30 min. Thee Ti solutionn was then poured intto the Bi so
1
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continu
uous stirring
g at 40oC forr another 2 h. After thaat, the tempeerature of hhot plate wass then set to
o
o
reach att ~130 C too form a sticcky gel. Wiithin a few seconds, th
he temperatuure was theen increased
d
o
rapidly,, and when it reached to ~200 C,, large amoount of gasees (NH3, H2, CO2 and H2O) weree
liberateed and a darrk fluffy powder was produced
p
affter the com
mbustion proocess. The process
p
wass
o
consisteently repeatted for otheer Nd conteent. Those ppowders weere calcinedd at 800 C for 3 hourss
and preessed to form
m pellets wiith diameterr of 13mm. The pelletss were then sintered at 1100oC forr
6 hourss. Their phaase formatio
on was deteermined by XRD (Bruk
ker D8 Advvanced). A Zeiss
Z
Supraa
55VP PGT/HKL
P
F
Field
Emission Scannin
ng Electron
n Microscop
pe (FE-SEM
M) was used
d to observee
the miccrostructuree and morp
phology of BNdT sinttered pellets. The diellectric prop
perties weree
measureed by Hewllett Packard
d, 4291B im
mpedance an
nalyser.
3.0 RES
SULT AND
D DISCUSS
SION
Fig. 1a shows the XRD
X
patterrn of BIT an
nd BNdT w
with various Nd contentt calcined at
a 800°C forr
most all of the
t diffractiion peaks arre indexed according tto the stand
dard powderr
3 hourss in air. Alm
diffraction data of Bi4Ti3O12 (JCPDS
(
01--089-7500).. When the sintering teemperature increases
i
to
o
1100oC for 6 hourss, strong c-aaxis-orientaation reflecttion peaks dominate
d
X-ray diffracction pattern
n
(Fig. 1b
b). On the other hand
d, the refleection peak
k of (117) which
w
corrresponds to off-c-axis-orientattion decreasse with increasing of Nd
N addition. It demonstrates that 0.6BNdT, 0.8BNdT and
d
1.0BNd
dT show thee preferred c-orientatio
c
on, and the iintensity off 00l reflectiions (i.e. 00
04, 006, 008
8
and 0014) increasses with Nd
d content. Simplified approximaation of thee Lotgering
g degree off
a
to
o the follow
wing equatio
on [7]:
orientattion (f) was evaluated according
where I006 and I117 are 006 and
d 117 peak intensities.
i
(a)
(b)
1.0
1.0
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
Fig. 1:: Compilatio
on of XRD patterns forr BNdT (x=
=0.2, 0.4, 0.6
6, 0.8, and 11.0) powderrs calcined
and sinteered at (a) 800
8 oC and (b) 1100oC, respectivelyy
2
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The orientation deg
grees (f) off 0.6BNdT, 0.8BNdT aand 1.0BNdT are estim
mated to be 57.3%,
5
72.5
5%
gesting that the degree of orientattion increases with the increase off
and 79.4%, respectively, sugg
ntent which
h agrees with XRD in Fig. 1b. It is belieeved that thhe develop
pment of c-Nd con
orientattion closely relates to th
he anisotrop
pic growth of
o Bi4Ti3O12 grain.
Fig. 2 show
ws the grain
n morphology of BNdT
T sintered pellets
p
capttured by FE
E-SEM. Thee
rod-likee grains aree found in 0.2BNdT and 0.4BN
NdT whereaas the platee-like grainss appear in
n
0.6BNd
dT, 0.8BNd
dT and 1.0B
BNdT. Acco
ording to Y
Yu et al. rod
d-like grainns and platee-like grainss
correspond to off-cc-axis-orien
nted and c-aaxis-orientedd, respectiveely [4]. It caan be seen that
t most off
the graiins are rod-like while only
o
a few of
o them aree plate-like as
a shown in
n Fig. 2a an
nd b. On thee
other haand, more plate-like
p
grrains are ob
bserved in Fig.
F 2c, d, an
nd e. It is evvident that the result iss
consisteent with thaat observed using
u
XRD.
((b)
(a)
(cc)
(d)
(e)
Fig. 2: FESEM imagges of Bi4-xNdxTi3012 pelletss microstructuure with (a) x=
=0.2, (b) x=0.44, (c) x=0.6, (d
d) x=0.8 and
(e) x=
=1.0 sintered at
a 1100°C.
Fig. 3a an
nd b illustraate the Nd content in
n BNdT materials deppendence of
o dielectricc
nt and dielecctric loss att frequency of 1MHz and
a electric field at 5000mV, respecctively. Thee
constan
dielectrric propertiees also variees with the Nd contentt in BNdT. Combined with the XRD
X
results,,
the corrrelation bettween the dielectric
d
prroperties an
nd the grain
n orientatioon is very clear
c
that iss
better dielectric
d
pro
operties aree obtained with
w lesser pplate-like grrain. Apparrently, our results
r
show
w
that bettter dielectrric constantt was obtaiined with 0.2Nd
0
and 0.4Nd and slightly deecrease at a
subsequ
uent Nd con
ntent. In oth
her words, the
t dielectriic constant of BNdT iss much bettter with off-c-axis th
han c-axis.
3
300
0
0.1000
250
0
0.0800
Dielectric loss
Dielectric constant
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200
150
(a)
100
50
0
(b
b)
0
0.0600
0
0.0400
0
0.0200
0
0.0000
0.2 0.3 0.4 0.5 0.66 0.7 0.8 0.9
0
1.0
Nd conntent
0.2 0.3
3
0.4
0.5 00.6 0.7 0.8 0.9 1.0
Nd content
Fig. 3: Dielectriic properties of BNdT measured aat frequency
y of 1MHz with
w electricc field of
500mV:: (a) Dielecttric constant and (b) Diielectric loss
4.0 CO
ONCLUSIO
ON
BNdT (Bi
( 4-xNdxTi3O12 where x=0.2, 0.4,, 0.6, 0.8, 1..0) were succcessfully ssynthesized by solution
n
combusstion method. X-ray diffraction sh
hows that deegree of c-aaxis-orientaation increasses with thee
increasee of Nd content, accompanying with
w the ch
hange of grrain morphoology from rod-like to
o
plate-lik
ke. It was aalso found th
hat such oriientation annd grain mo
orphology hhas a great in
nfluence on
n
dielectrric propertiees.
EDGMENT
T
5.0 ACKNOWLE
The autthors apprecciate the tecchnical supp
port provideed by the Scchool of Maaterials and Mineral
M
Resourcces Engineeering, USM. This reseaarch was suppported by the
t E-sciencce Fund
305/Pbaahan/6013357 and the USM Fellowship.
6.0 REF
FERENCE
E
1. B. Aurivilliius, Arkiv Kemi,
K
1, 499
9 (1949).
2. M. Chen, Z.L.
Z Liu, Y. Wang, C.C
C. Wang, X.S. Yang, K.L.
K Yao, Soolid State Co
ommun.
130 (2004) 735–739.
3. X. Hu, A. Garg,
G
Z.H. Barber,
B
Thinn Solid Film
ms 484 (200
05) 188 – 1995.
4. J. Yu, B. Yang,
Y
J. Li, X.
X Liu, C. Zheng,
Z
Y. W
Wu, D. Gua,, D. Zhang, J. Phys. D:: Appl. Physs.
41 (2008).
5. A. Fauskovva and L.E. Cross, J. Apppl. Phys. 441, (1970) 2834.
2
6. K.C. Patil, M.S. Hed
dge, T. Ratttan, S.T. Aruna,
A
Cheemistry of N
Nanocrystalline Oxidee
Materials Combustioon Synthessis, Properrties and Applicationns, World
d Scientificc
Publishing Co. Pte. Ltd
d., Singapore, 2008, ppp. 42.
7. N. Zhong aand T. Shiossaki, Materiials Letters 61 (2007) 2935
2
– 29388.
4
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onal Postgradua
ate Colloquium on
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SYN
NTHESIS A
AND DIELECTRIC PROPERT
P
IES OF Bi4-x
NED BY
4 NdxTi3O12 OBTAIN
SOL
LUTION COMBUST
C
ION SYNT
THESIS
bUmarr Al-Amani*, Ahmad Ehsan,
E
Srim
mala Sreekanntan, Ahmad Fauzi Moohd Noor, Khairunisak
K
Abd. Razzak
School off Material and
a Minerall Resources Engineerinng,
Malaysia.
Univversiti Sains Malaysia,, 14300, Nibbong Tebal,, Penang, M
ABSTR
RACT
Bismuth
h neodymiuum titanate, BNdT (Bi4-xNdxTi3O12 where x=0.2,
x
0.4, 0.6, 0.8, 1.0) powderss
were syynthesized via
v solutionn combustioon synthesiis for ferroeelectric mem
mory devicces. The as-synthessized powdeers were callcined at 8000°C for 3 hhour and subbsequently, sintered at 1100oC forr
6 hourss. The form
mation of puure phase and
a c-axis-ooriented BN
NdT were ccharacterizeed by X-rayy
diffraction (XRD).. It was fouund that the orientationn degree of c-axis increeases with the
t increasee
c
in BNdT,
B
and at
a the same time
t
the graain morphollogy grows from rod-liike to plate-of Nd content
like struucture. Addditionally, thhe dielectricc properties of BNdT are
a greatly iinfluenced by
b the grainn
orientattion.
1.0 INT
TRODUCT
TION
Aurivillius material off bismuth-bbased has been widelyy studied duue to its outtstanding inn
ferroeleectric propeerties [1]. Bismuth
B
tittanate, Bi4T
Ti3O12 is a good canddidate for ferroelectric
f
c
memoryy devices appplication [2]. The subbstitution off rare-earth such as La33+, Pr3+, Sm
m3+ and Nd3++
in Bi4Ti3O12 has been extensiively perforrmed to impprove the feerroelectriciity in such devices
d
[3].
Howeveer, those raare-earths addded in Bi4Ti3O12 exhiibits differeent axis-orieented i.e. a--axis and c-axis [4]]. In a-axiss-oriented, the diffracttion peak iis indexed (1 1 7). O
On the otherr hand, thee
diffraction peak off c-axis-orieented corressponds to (00 0 6). Accoording to Fouskova annd Cross [5]]
the conductivity inn the a-direcction is apprroximately 30 times hiigher than inn the c-direection in thee
c
of B
Bi4Ti3O12. Therefore,
T
h
highly
a-axis crystal orrientation iss preferable in order too
single crystal
obtain high
h
conducctivity hence it can impprove the dielectric prooperties.
In this studdy, a solutioon combustiion synthessis was seleccted as an aalternative approach
a
too
preparee BNdT. This
T
methodd was devveloped froom the conncepts of sself-propagating high-temperaature synthesis (SHS) combined with wet chemical teechniques iin order to
o synthesizee
metal-ooxide-based ceramic powder.
p
Gennerally, thrree factors influence tthe generattion of fire,
which can
c be descrribed as selff-generatedd combustionn. These facctors are thee oxidizer, temperature
t
e,
and fueel, which produce
p
heaat, light, annd ash [6]. The fuel-frree combusstion methood does nott
employy fuel agentts such as citric acid,, urea, or glycine.
g
Thhe process is relativelly low-cost,
requiress a simple ssetup, and has high reprroducibilityy. In this woork, Nd3+ wiill be used to
t substitutee
Bi3+ ionns in Bi4Ti3O12 and thee peak charracteristic and grain morphology will
w be stud
died as welll
as dieleectric properrties.
PERIMEN
NTAL PRO
OCEDURE
2.0 EXP
Bi4-xNddxTi3O12 (B
BNdT) where x = 0.22, 0.4, 0.6,, 0.8 and 1 were synnthesized via
v solutionn
combusstion. Bismuuth nitrate penthahydra
p
ate, Bi(NO3)3.5H2O andd neodymiuum nitrate hexahydrate,
h
,
Nd(NO
O3)3.6H2O were
w
initiallyy dissolvedd in 2-Methhaoxyethanool, CH3OCH
H2CH2OH at 40oC onn
hot platte and stirreed for abouut 30 min. Separately,
S
t
titanium
(IV
V) isopropooxide, Ti[OC
CH(CH3)2]4
was dissolved in a homogeeneous soluution of 22-ME and acetylacetoone, C5H8O2 at room
m
olution with
h
temperaature and sttirred for 30 min. Thee Ti solutionn was then poured intto the Bi so
1
4th C
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esearch
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o Materials, Minerals and Polyymers 2010 (MA
AMIP 2010)
th
th
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continu
uous stirring
g at 40oC forr another 2 h. After thaat, the tempeerature of hhot plate wass then set to
o
o
reach att ~130 C too form a sticcky gel. Wiithin a few seconds, th
he temperatuure was theen increased
d
o
rapidly,, and when it reached to ~200 C,, large amoount of gasees (NH3, H2, CO2 and H2O) weree
liberateed and a darrk fluffy powder was produced
p
affter the com
mbustion proocess. The process
p
wass
o
consisteently repeatted for otheer Nd conteent. Those ppowders weere calcinedd at 800 C for 3 hourss
and preessed to form
m pellets wiith diameterr of 13mm. The pelletss were then sintered at 1100oC forr
6 hourss. Their phaase formatio
on was deteermined by XRD (Bruk
ker D8 Advvanced). A Zeiss
Z
Supraa
55VP PGT/HKL
P
F
Field
Emission Scannin
ng Electron
n Microscop
pe (FE-SEM
M) was used
d to observee
the miccrostructuree and morp
phology of BNdT sinttered pellets. The diellectric prop
perties weree
measureed by Hewllett Packard
d, 4291B im
mpedance an
nalyser.
3.0 RES
SULT AND
D DISCUSS
SION
Fig. 1a shows the XRD
X
patterrn of BIT an
nd BNdT w
with various Nd contentt calcined at
a 800°C forr
most all of the
t diffractiion peaks arre indexed according tto the stand
dard powderr
3 hourss in air. Alm
diffraction data of Bi4Ti3O12 (JCPDS
(
01--089-7500).. When the sintering teemperature increases
i
to
o
1100oC for 6 hourss, strong c-aaxis-orientaation reflecttion peaks dominate
d
X-ray diffracction pattern
n
(Fig. 1b
b). On the other hand
d, the refleection peak
k of (117) which
w
corrresponds to off-c-axis-orientattion decreasse with increasing of Nd
N addition. It demonstrates that 0.6BNdT, 0.8BNdT and
d
1.0BNd
dT show thee preferred c-orientatio
c
on, and the iintensity off 00l reflectiions (i.e. 00
04, 006, 008
8
and 0014) increasses with Nd
d content. Simplified approximaation of thee Lotgering
g degree off
a
to
o the follow
wing equatio
on [7]:
orientattion (f) was evaluated according
where I006 and I117 are 006 and
d 117 peak intensities.
i
(a)
(b)
1.0
1.0
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
Fig. 1:: Compilatio
on of XRD patterns forr BNdT (x=
=0.2, 0.4, 0.6
6, 0.8, and 11.0) powderrs calcined
and sinteered at (a) 800
8 oC and (b) 1100oC, respectivelyy
2
4th C
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esearch
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onal Postgradua
ate Colloquium on
o Materials, Minerals and Polyymers 2010 (MA
AMIP 2010)
th
th
27 -2
28 January 2010
The orientation deg
grees (f) off 0.6BNdT, 0.8BNdT aand 1.0BNdT are estim
mated to be 57.3%,
5
72.5
5%
gesting that the degree of orientattion increases with the increase off
and 79.4%, respectively, sugg
ntent which
h agrees with XRD in Fig. 1b. It is belieeved that thhe develop
pment of c-Nd con
orientattion closely relates to th
he anisotrop
pic growth of
o Bi4Ti3O12 grain.
Fig. 2 show
ws the grain
n morphology of BNdT
T sintered pellets
p
capttured by FE
E-SEM. Thee
rod-likee grains aree found in 0.2BNdT and 0.4BN
NdT whereaas the platee-like grainss appear in
n
0.6BNd
dT, 0.8BNd
dT and 1.0B
BNdT. Acco
ording to Y
Yu et al. rod
d-like grainns and platee-like grainss
correspond to off-cc-axis-orien
nted and c-aaxis-orientedd, respectiveely [4]. It caan be seen that
t most off
the graiins are rod-like while only
o
a few of
o them aree plate-like as
a shown in
n Fig. 2a an
nd b. On thee
other haand, more plate-like
p
grrains are ob
bserved in Fig.
F 2c, d, an
nd e. It is evvident that the result iss
consisteent with thaat observed using
u
XRD.
((b)
(a)
(cc)
(d)
(e)
Fig. 2: FESEM imagges of Bi4-xNdxTi3012 pelletss microstructuure with (a) x=
=0.2, (b) x=0.44, (c) x=0.6, (d
d) x=0.8 and
(e) x=
=1.0 sintered at
a 1100°C.
Fig. 3a an
nd b illustraate the Nd content in
n BNdT materials deppendence of
o dielectricc
nt and dielecctric loss att frequency of 1MHz and
a electric field at 5000mV, respecctively. Thee
constan
dielectrric propertiees also variees with the Nd contentt in BNdT. Combined with the XRD
X
results,,
the corrrelation bettween the dielectric
d
prroperties an
nd the grain
n orientatioon is very clear
c
that iss
better dielectric
d
pro
operties aree obtained with
w lesser pplate-like grrain. Apparrently, our results
r
show
w
that bettter dielectrric constantt was obtaiined with 0.2Nd
0
and 0.4Nd and slightly deecrease at a
subsequ
uent Nd con
ntent. In oth
her words, the
t dielectriic constant of BNdT iss much bettter with off-c-axis th
han c-axis.
3
300
0
0.1000
250
0
0.0800
Dielectric loss
Dielectric constant
4th C
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esearch
Natio
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ate Colloquium on
o Materials, Minerals and Polyymers 2010 (MA
AMIP 2010)
th
th
27 -2
28 January 2010
200
150
(a)
100
50
0
(b
b)
0
0.0600
0
0.0400
0
0.0200
0
0.0000
0.2 0.3 0.4 0.5 0.66 0.7 0.8 0.9
0
1.0
Nd conntent
0.2 0.3
3
0.4
0.5 00.6 0.7 0.8 0.9 1.0
Nd content
Fig. 3: Dielectriic properties of BNdT measured aat frequency
y of 1MHz with
w electricc field of
500mV:: (a) Dielecttric constant and (b) Diielectric loss
4.0 CO
ONCLUSIO
ON
BNdT (Bi
( 4-xNdxTi3O12 where x=0.2, 0.4,, 0.6, 0.8, 1..0) were succcessfully ssynthesized by solution
n
combusstion method. X-ray diffraction sh
hows that deegree of c-aaxis-orientaation increasses with thee
increasee of Nd content, accompanying with
w the ch
hange of grrain morphoology from rod-like to
o
plate-lik
ke. It was aalso found th
hat such oriientation annd grain mo
orphology hhas a great in
nfluence on
n
dielectrric propertiees.
EDGMENT
T
5.0 ACKNOWLE
The autthors apprecciate the tecchnical supp
port provideed by the Scchool of Maaterials and Mineral
M
Resourcces Engineeering, USM. This reseaarch was suppported by the
t E-sciencce Fund
305/Pbaahan/6013357 and the USM Fellowship.
6.0 REF
FERENCE
E
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