Low-temperature combustion synthesis of Bi4Ti3O12 plate-like structure and some of its characteristics.

lv{alm,sian Joumal of ivlicroscopl' Vol 6 (20 ]0) pg. 69-74

LOW-TEMPERATURE COMBUSTION SYNTHESIS

OF

Bi,rTi:Ore

PLATE.LIKE

STRUCTURE AND SOME

OFITS CHARACTERIZATION

A. Umar Al-Amani, S. Srimala-, M.N. Ahmad Fauzi and A.R. Khairunisak

School of Material and Mineral Resow'ces Engineering, Universiti Sains Malaysia, 14300 Seberang Perai Selatan, Nibong Tebal, Penang

Bismuth titanate, BiaTiiOp was prepared at different hydrolysis temperatules ond characterized with XRD, Rietveld analysis, TG-DTA, FESEM and TEM. The results

indicated that the pure bismuth titanate was obtained after combtrstion at lo*et temperature of about 260 "C. Interestingly, no calcination step involved to obtain bisrnuth-strtrctured layered. The effect of hydrolysis temperatttre at 4A ''C, 50 ''C'

and 60 oC on phase.fotmation, lattice parameter, crystallite size, thennal behavior

as well as grain morphologies was investigated.

Keywords: Bi+Tr:Or:; Low-temperature combustion; Chmacterization

INTRODUCTION

Bismuth titanate, (Bi4TirOr2) has been

used for ferroelectric tandort access memory

(FRAM)

devices

due

to

its

outstanding

fenoelectricity _[1]. This compound has been prepared using a rvet chemicai technique such

as

sol-gel, hydrothamal, precipitation aud

molten-salt synthesis

l2l.

Wet

chemical technique is preferred because a single phase Bi4Ti3Or2 can be obtained at low temperature

[3]. In early stage, Bi.rTirOrz has been prepared

using conventional solid state which often results

in

high

aggiomeration

and

low sinterability

of

powders because

of

high calcination beyond 1000 oC and repeated

grinding [4].

Several studies have emerged as the leading techniques to lorm BiaTi3Or2 have been

reported.

Han and

Ko t5l

produced

nanocrystalline Bi4Ti3Or2 powder using an

intense meehanical activation of a rnixtr::'e of

o-BizO: and TiO2 after a milling time

of

9

hours. Gu et

al. [6]

reported that BiaTi3O12

nanopiates were synthesized by polyethylme

glycol-assisted hydrothermal rnethod

at

200

oC. However, there are some lirritations in

both

processes such

as the

difficulty

to understand the phase evolution and rnechanical

activation condition and the courplexity of hydrothermal process in terms of experimentai

set up.

Therefore,

in

this

wort

we use the

combustion method to produce Bi+Ti:Oi:. The

current approach offers great advantages such

as simple experimental set up, capability to

produce high purity powder

with

excellent homogeneity, eliminate calcination step and

relatively

low

fonnation ternperature

of

a

single phase _{[7-9]. However,} comprehensive

investigation

on

the

processing parameter needs to be conducted in order to r.mderstand

the relation between processing parameter with properties of the BiqTiror2. In this paper, the

effect

of

hydrolysis temperahre

on

the

formation of BirTi:Orz is reported.

i - r _{----. i -i-::r:} iJ \, _-4hmad Faci and A.R. Khoinnisak

\II

TH OD S .1.\D \I-A,TERL{LS

3,s:.-.-:: :t:::=r: oe;rrlahldrale, citric

::.::::

:':=1.--:-

f\',

riop:oporide iiere used

:: :=-::t:

::ia.:IrarS.

Inlialll',

bismuth nitrate

:=-:r11i::.

u'as added rnto a conical tlask

::a:

r.rl2neii

drstilled wata-. The conical flask

n:s -:i:r

placed

in a

water bath and the

:e:ce:a:r:e

\las

confolled at

40 0c

under

;lrjia:i

sILnng. Simultaneously, citric acid

+ai

di.solr.ed in distilled rvater and stirred at

rcc:n :arnperarure. After that, citric aqueous

u.ere added to bismuth aqueous and constantly

sired

to

iorm bismuth mixture. Separately,

titanium (IV) isopropoxide rvas dissolved in 2-)Iethaoxyethanol (Sigma-Aldnch, ?_99 %) to

torm aqueous solution of Tia- ion. Then, the

.lqueous

of

Ti'-

ion rvas slowly added into

bismuth mxflue. The obtained mixture (which

aiso knou.ri as precursor soiution) was adjusted

to pH 7 by usLng NFIaOH (29 % solution). The precusor solution

with milky

color

lvas

hldrolyzed at 40 oC, 50 'C, and 60

'C

and

stirred for 24 h to obtain more homogeneous

Fig.

1.

10

XRD

profile temperature.

solutron. After that, the temperuture rvas raised

to

80

'C to

form

a

dried powder rnixture,

subsequently, gently crushed using an agate

mortar pestle. 'Ihe crushed powder was placed

back on a hot plate to cornplete the cornbustion process. The combustion temperatue was then recorded by thermocouple.

The dried

powders

(belbre

combustion)

were

anaiyzed

using

il

thermogravimetry-differential thennal analysis

(TG-DTA).

On the

other hand,

the

as-combusted powders were characterized by using X-ray diffraction (XRD), fie1d emission

scanning electron microscopy (FESEN{) aad

transmission electron microscope (TEM). The

lattice parameter aad crystallite size of the

as-combusted powders were calculated using High-Score Pluss softrvare

and

Schener's formula, respectively.

20 (o!

for

the

as-combusted powders prepared

at

different hydrolvsis

N c o

50

40

30

t3,?141 Bi4Ti3Ol

[image:3.595.19.583.1.826.2]

LOIY-TEMPERATURE COMBUST]ON SYNTHESIS OF Bi'Ti30II PLATE-I}KE S?RUCTURE AND SOME OF ITS CHARACTENZATION

RESULTS AND DISCUSSIONS

XRD arulysis

The XRD profile for the as-combusted

porvders prepared

at

different hydrol;sis temperatue is shown in Fig. 1. The result show

that all ttre difliaction peaks are corresponding

to BiaTi3O12 phase and matched well with PDF

#

73-2181. The absence

of

any other peak

confinaing

a

single phase

of

BiqTir0rz was

successfully obtained

at

lorv-temperature

combustion synthesis. Besides that, it was also

noticed that the hydrolysis temperature had

significimt influence

on

diftaction

peak

characieristic.

It

was noted that the broadness

of

the

peak reduced

with

increasing of

hydrolysis

temperature,

indicating

high crystallinity degree. Based

or

Rietveld

arralysis, the variation of lattice parameter was

clearly affected by hydrolysis temperanre. We

also found that a- and b-parameters rvere not always close; thereiore

it

confirmed that

Bi4Ti3Orz compounds matched

well

with pseudo- orlhorhombic strucnrre.

With

the

hcrease

of

this parameter, the volume

of

orthorhombic sfiuctwe

of

BiaTi3012 also

siightly increased and the result obtained at 60

oC _{was considered very close to the standard}

file. As mentioned in the experimental section,

the crystallite size at the peak position (i17) was calculated using Scherrer's equation [10] and the result is shown

il

Table 1. The result

showed that the crystallite size was strongly

dependent on the hydrolysis temperature. This was attribute.d by the increase

of

grain size.

'I'able 1. Lattice parameter and crystallite size of the as-combusted powder at different hydrolysis temperature calculated fiom XRD data

Lattice pararneters 400c

50nc

600c

al A.

b/A

cl

A

V/

i06 pm3

Space group (No.)

R (expected)/ % R (profile)/ %

R (weighted proftle)/ o/o

Density (calculated)/ g/cm Crystallite size (nm)

5.4i50(1)

5.4400(1) 32.7730(6) 96s.3 804

Fmmm(69)

4.62321 10.458s 1 t2.3113

8.06 24.1

Fmmm(69)

Fmmm(69)

5.4140( 1)

s.4440( 1)

32.7840(6) 956.2748 4.32741

lt.86494

14.20051 8.052s 26.4 5,420(2) 5.447(2) 32;/75(8) 967.s442 4.92416 11.96359 14.25008 8.0419 26.5

TG-DTA analysis

The thermal behavior

of

the dried porvder rvith dilferent hydrolysis temperatures is shorvn in Fig. 2. As seen the decomposition

process can be divided into hvo distinct stages

in

the

TG

plot (Fig. 2(a)). This trend was

A. Umar Al-Amani, S. Srimala, M.N. Ahmad Fauzi and A.R. Khairunisak

temperatures. The first weight loss took place

at temperature rangc at temperatrue range of50

-

181 "C. This causes to the vaporization of the

residual water, organic solvent such as

2-methaoxyethanol, isopropoxide and hy&oxyl groups.

It

lvas

correlated

with

thg

small endothermic peak at 121 "C and 151 "C (not

shown

here) The

second

rveight

ioss accompanied by a sharp exothermic peak took

piace at different temperahrres i.e, 242 'C,244

'C

ard 246 "C for 40 oC, 50 oC and 60 'C, respectively. Large exothermic peak was due to

vigorous oxidation-reduction

reaction

or cornbustiq! between dgqoryposed citric acid

and nikate

ions

which then

led

to

crystallization of bismuth tiianate.

This frrding

confirmed

that

the

oombustion

reaction

dependent

on

the

hydrolysis temperatures

of

the

precursor

solution.

It

was wor& to note that no further weight changes and heat effects were observed

in the TG-DTA cun/e up to 500 nC, indicating

{a}

50"c

40'c

the temperature ofbelow 260 "C represents a

srtfficient temperature for the formation r,rf a

crystalline Bi+Ti:Or:

from the

con-rbuslion reaction.

Micro stru cture analysis

The FESEM (Fig.

3(a)) microstructures

of

the cornbusted powders

hydrolyzed at 60 "C are shown in Fig. 3, The images for 40 "C and 50 "C rvere not shorvn as

the change in terms of size and shape were not so obvious. The Bi+TirOrz povvder was mostly composed

of

plate-like

grains

and

the

approximate diameter of grains was about 200

nrn. Since the size was quite fine, the particles

formed

with

high agglomeration as clezrly

observed by TEM (Fie. 3(b)).

{b} 50'c 40'c i

60'c

240

femperatun (ocl

Fig.2,

Thermal behavior of as-combusted poxders with different hydrolysis temperatur.e: (a) TC and (b) DTA.

teo

:-3

3-4

200 300

LO'Y.TETIPERAN]RE COJI{BUSTION SYNTHESIS OF BiILOTJ PLATE'I,IKE STRUCTUKE AND SOME OF IT'S CTTARACTENZATION

Fig.

3.

Plate-like grains of as-comtrusted powder hydrolyzed at 60 "C: (a) FESEM and (b) TEM,

CONCLUSION

Bi+Tirorz powder rvas successfully obtained by a combustion synthesis at very low temperature.

It

rvas confirmed by XRD and

TG-DTA. Siudy

on

hydrolysis temperaure showed

the

variation

of

structure lattice parameter that was confirmed

by

Rietveld analysis.Dii-ferent exothennic telnperanres were aiso recorded

in

DTA,

intlicating tlte hydrolysis ternp emhrre was essenlial paralneter

to

produce Bi4TilOt2 powder. Nano-platey stnlchrre of BirTi:Or: rvas clearly observed by f E Slr.lvl ano I -ts.lVI.

ACKNOWLEDGMENT

The authors appreciate the technical sripport provided by the School of Materials and lvlineral Resources Engineering, USM. This research was suppofled by the E-science

Fund 305/Pbahx1601,3357, Short term USM 304.PBahan.6035267

and

USM-RU

grant

100l,PBahan/8042018.

REFER.ENCES

t1l

Chen,

M., Liu,

Z.L.,Wang,

Y.,

Wang,

C.C., Yang, X.S.,

Yao

K.L.

(2004).

Ferroelectric properties of Pr6O11-doped

BiaTi3Ol2, Solid State Commun., \30 735-739.

Lazarevii,

2.,

Stojanovi6, B.D., Varela"

J.A. (2005). An Approach to Analyzing Synthesis, Structure and Properties of

Bismuth Tiianate

Ceramics,

Sci.

Sintering,3T 199-216.

Pookmanee,

P.,

BoonphaPk,

P.,

Phanichphant,

S.

(2004).

Chemical

synthesis

oF

bismuth

titanate

microparticles, Ceram.

Int.,

30

1917-1919.

Kan, Y., Jin. X., Wang, P., Li, Y., Cheng,

Y.B., Yan, D. (2003). Anisorropic grain

grorvth of Bi+Tirorz in moiten salt fluxes,

lvlateL Res. Bull.,38 567-576.

Han,

I(,

Ko,

T.

(2009). SYnthesis and phase formation of ferroelectric Bi4TiiO12

nanoporvder by mechanicai alloying,

J

Allo1, Q6sO6., 473 490495.

Gu, H., Hu,2., Hu, Y., Yuan, Y., You, J.,

Zou,

W.

(2008).

The

structure aild photolurninesoence

of

Bi4Ti3Or2

nanoplates sl,nthesized by hydrothennal nrethod, Colloid Sutfaces A., 315 294-298.

Patil, K.C., Aruna, S.T., Mimani, T. (2002). Combustion synthesis: an update,

Cun'. Opin. Solid State tVat Sci., 6 50'1

512.

tLl

t3l

t4l

t5l

t6l

A. umar Al-Anani, S. Srinala, lrf.N. Ahnad Fqilzi ctld A.R. Khaintnisak

t8l

Luo, S., Tang, 2., Yao, W., Zhang, Z.

(2003).

lrw-temperature combustion

synthesis

and

characterization of

nanosized tetragonal

barium

titanate

powders, Mio'oelectron. Eng.,

66

141-152.

[9]

Franco Junior, de Olivera Lima, E.C,

Novak,

M.A.,

Wells

Jr,

P

R.

(2007)'

Synthesis of nanopadicles of Co,Fe13-'yO.r

by combustion reaction method, J. Iulagn.

Magn. Mater., 308 198--202.

[10] Burton, A.W., Ong, K., Rea, T., Chan,

I.Y. (2009). On the estirnation of average

crystallite

size

of

zeolites

from

the Scherrer equation: A critical evaluation of

its

application

to

zeolites

lvith