Effect of Heat Treatment on the Grain Orientation of Bi3.25Nd0.75Ti3O12 Ceramics.

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Malaysian Joumai olNlicroscopy 7 : 132 - 136 (2011) ISSN: 1823-7010

Effect

of Heat

Treatment

on

the

Grain Orientation of

Bi3.2sNdo.75Ti3O12

Ceramic

A.

UmarAl-Amanir,

S.

Srimala.r, M.N. Ahmad

Fauzir,

A.R.

Khairunisakl,

S. Tanaka2 and

K.

UematsuT

tschool of Materials and

Mineral

Resou'ce's Engineering'

tJniversiti

sains lulalaysia, 14300

Niltong

Tebal, Penang, MALAYSIA

2Department _{of Materials}_{Science and}Engineering, Faculty of Engineering Nagaoka [Jniversity of Technology,

1603-1 KamitorniokQ, Nagaoka,

Niigata

940-2188' JAPAN

Neodymium substituted-bismgth titanate, Bir.25Ndo.7iTirOL (BNT075) ceramic was prepared using soft combustion technique. The dependence ofheat treatment on the grain orientation ofceraniic r'vas

observed. With increasing temperature, the BNT075 ceramic tumed from offc-axis-preferential-oriented to c-axis-oriented. The result also corresponded to the change from equiaxed structure to plate-1ike structure, indicating that the grain orientation had a significance influence on grain grorvth,

Keyrvords: c-axis, heat treatment, grain orientation

INTRODUCTIOI\

Over the last decade, much attention has been

paid

to

lanthanide substituted-bismuth titanate

for

their potential applications

in

nonvolatile

ferroelectric random

access

memories [1,2].

N eodymium-sdbstituted'uismuth trtanate ts one

of

the most popular materials investigated

for

this purpose

[3].

The outstanding fenoelectricity such as

high

remanent

polarization

(2P,),

low

coercive

fleld

(2E"), good fatigue

endurance

and

low

leakage

current

are essential

in

this application

[4].

As

reported, the 2P. is

highly

dependent on

their grain orientation

[5].

The

2P.

value

of

the c-axis-oriented

BNT films

is

-100

pC/cm2 whereas the

off

c-axis

oriented

thin

films

has

the

2P.

of

51

pC/cm2

16,71.

Based on this resutt,

it

would

be expected that

the 2P. value of c-axis-oriented

BNT

thin

films

is much higher than that

of off

c-axis-oriented

films.

In the case to enhance the c-axis-oriented,

several works have been reported over the last

10

years,

Bae and co-workers have reported a

fabrication of c-axis-oriented lanthanurn-dopt; bismuth titanate resulting

from

the increase

i:

annealing temperature

[8].

The other way is i.,

use

template-grain growth

(TGG)

method t,-'

orient

the textured Nb-doped

bismuth titana;t

in. t'a.y,is r.91.,. Ta.nak-a. a-nrl a.nd- ,itJ-wacks,.-s h&l.: fabricated c-axis-oriented

ZtO with

a rotati::g

high magnetic

field

[10].

In this work, we

h::;

prepared the grain orientation in c-axis-orieni,;,,

and

off-c-axis-oriented BNT075

ceratnic

*.ii::

various

heat-treatments,

whereby the

resul::r

were presented

in X-ray

stnrctural, Lotgeri:i,.

degree of c-oriented and grain morphologies

E XP ERI1VI E N

TAL

PRO CE D

URE

Materials

and Reagents

The

following

materials and reagents rvere

ttsci

bismuth nitrate penthahydrate

(Bi

(NO3)r.5FI:i,i.

98%, Sigma

Aldrich),

neodymium

nitr::r

hexahydrate

(Nd

(NO3)3.6H2O, 99.9olo, Sigr:r',

Aldrich), titanium

(IV)

isopropoxide

iT

'Corresponding _author.Tel: + 6{04)-5995255; Fax: + 6(04)-5941011

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Eltbct of Heat Treatment on the Crain Orientation of Bi::.Ndo::Ti3O,2 Ceramic

f

OCH

(CH.).11, 97o/o.

Merck),

acetylacetone

(C.HsOr, Merck) and 2-Methaoxyethanol

( C H.OCHTCH,OH, Merck).

Preparation

of

BNT075

The required amounts of Bi (NO,)r.sHrO and Nd

(NO.h.6lir0

were sirnultaneously dissolved

in

CH.OCH:CHTOH by stirring at 40oC and 25oC,

respectively,

tor

30

min.

Separately,

Ti

IOCH (CH:):],r r,vas also dissolved

in

the

mixture

of

CH.OCHTCH,OH

and C5HsO2

with

constant

stiring

at 25"C

for

30

min.

Then,

Nd

solution

rvas

slowly

added

into

Bi

solution

while

being constantiy

stirred.

It

was then

followed by Ti

solution

rvas added

drop-by-drop

into Bi-Nd

solution

and

continuously stirred

at

40"C

for

alloaher 2

h.

Aflow

chart is illustrated in

Fig.

l.

Fig.

L

Sirtrple.flou, chart r;f tlte preparution d' B NT1 7 -5 v'i t h vo r i ous h eo t - I reelnzen ts

Malaysian Jor.rmal ol lvlicroscopy Vol. 7 201 I

Stages

of heat-treatment

Various heat-treatments were used to investigate

their effect on grain orientation and

grain

morphoiogies

of BNT07-s,

The correspondrns

samples HT 1,

HTI

and HT3 u.ere ob:ained

a;er

calcination.

pre-sinlerin-e and

posl-silterr::.

respectivel),. HT4

ri'as obiained

t-,'' a.mosi

same samples as HT3. excepi iha[ pre-s1i:eni1:

was skipped in the processing

route. I: car le

simplified

as listed in Table 1.

TABLE 1

List of parameter of heat-treatment rvith heating rate of 5'C/rnin

Sample

Heat

treatment

Temperature Soaking

HTi

Calcination

800"C

HT2 Pre-sintering

700"C

HT3

Post-sintering

1 100'C

HT4

Direct

sintering

1100"C

3h

2h

3h

Characterization

X-ray diffraction (XRD,

Bruker D8 Advanced)

analysis was carried out to determine the grain

orientation as a result of different heaGtreatment.

The

grain

morphologies

were

displayed by

fleld-ernission

scanning

electron

microscopy

(FE-SEM, Zeiss Supra 55VP PGT/HKL).

The Lotgering degree

of

grain orientation was

calculated according to the

following

equation

flll:

u(c-axis)

:

Itool)

Iruon

*

Irrrl

(l)

(2) Irrrzt

a(otf

_' c-axts)

110u11 + I1l1z1

RESULTS

AND DISCUSSIONS

XRD Analysis

Frg

2 shows

XRD

patterns of the BNT075

with

various heat-treatments. The

XRD

analysis

confirmed that various heat treatments can be used

to

form

single phase

of

bismuth-layered

stnlcture.

For the sample produced

from

HTl

and HT2, the most intense peak was dominated

133

Rtu'ruatelia ls

('onrpIcration

Er rr prlrirtion

Pr c-sirrterirrg

Pri

[image:3.595.68.585.21.804.2]

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A. Umar Al-Arnani, S. Srinrala, M.N. Ahmad Fauzi, A.R. Khairunisak, s. Tanaka and K' l]ematsu

by

(117),

suggesting

the formation

of

highly

off-c-axis

orientation.

On

the other hand, the

indexed peak was

found to

decreasc

in

the

sample

produced

from HT3

and

HT4.

The

increase

in

intensity

of (000

plane

is

clearly

seen in

XRD

pattern,

implying

that significance shifted to c-axis-orientation.

It

is reasonable to suggest that

different

axis

in

grain orientation

is produced

with

various type of heat treatment'

In

addition

to

that,

the degree

orientation

(u)

of

c-axis

and

off-c-axis

was calculated

for

respective sample. As calculated, o.-u";. for

HTl,

HT2, HT3

and

HT4

was about

ll.60/0,30.1oh,

7

l.4Yo

and 84.7o/o, respectively,

indicating

the

increase in c-axis-orientation and decreasing

in

off-c-axis-orientation.

The calculated value is

shown in Table 2.

TABLE 2

Degree oforientation for c-axis and offc-axis

Sample a(c-axis)

a(off c-axis)

HT1 HT2 HT3 HT4

1r.60% 30.10% 71.40% 84.'70%

88.40% 69.90% 78.60% 15.30%

SEM Analysis

Fig.

j

shows

the grain morphologies

of

thc

BNT075

ceramic

with

various heat-treatmeuts.

In Frg.

3(a),the

HT1

grains

mostly

consist

of

equiaxed-like strucrure

with

average grain size

of

100 nm

to

600

nm,

As

the porvder

is

pre-heated, the

HT2

grain

size

is

almost

unifornr

due to grain growth of equiaxed-like grain (Flg.

.c

{!

'a

o

C

60

5B

40 ?fl

10

I l+

2o _{,,)

Fig. 2 : X-ray dffi'actian patterns o.f BNT07 5 at

dffirent

heat tteatment

$l

sl

I

sB

t

i?

"H

I

pti?iil

A4: direct sinte ring

ll

A3: post-sintering

,l

A2: pre-sinlering

I

A1: calcination I

[image:4.595.279.443.99.169.2] [image:4.595.11.578.277.834.2] [image:4.595.127.416.306.639.2]

(5)

I

Eltcct ol Hcat Treatment on thc Grain

-116l). This particular grain growth occurs very ertensive during post-sintering resulted in HT3 plate-like stmctr.rre (Fig.

3(c)).

The platey grain rs more

unifonn

with average grain size

of2

pm

to 8

prn,

The laryest

HT4 plate-like

structure

is clearly seen resuiting from direct sintering as

shor,vn

in

FiS

3(cl). The morphoiogy results are

consistcnt rvith the results of

XRD

and degree

of orientation as reported earlier.

CONCLUSION

In

summary, the grain orientation

of

BNT075

cerarnic is

highly

dependent on heat treatment.

Orientation of Bi,,,Nd, rr1i.Or: Ccramic

Similar

observation was

found

in

the sample

produced from

HTI

and HT2, whereby the

off-c-axis became a dominant orientation. However,

it

did not occur in the sample produced from HT3 and

HT4.

The

increase

in

c-axis-orientation

was also confirmed by degree

orientation.

The

change

in

grain orientation

r,vas

clearly

seen

in

grain morphology, whereby

highly-c-axis-orientation corresponds to plate-like structure.

ACKNOWLEDGMENT

The

authors appreciate

the technical

support

from School ofMaterials and Mineral Resources

Istr"W

[image:5.595.37.433.259.624.2]

I

Fig. 3: Grain morphologies of'BNT075

tith

vorious heot-teottilents. (a) HTl,

(h) IIT2, (c) H7'3 und (d) HT4

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A. UmarAl-Amani, S. Srimala, M.N' Ahmad Fauzi, A.R. Khairunisak, S. Tanaka and K. Uematstt

Engineering,

Universiti

Sains

Malaysia'

This

research was supported

by

the E-science Fund

305/Pbahan/ 6013357,

USM-RU grant

1 001/

Pbahanl80420 1 8 and 8 1 1069.

REFERENCES

[1]

Park, B.H., Kang, B.S., Bu, S.D', Noh, T.W., Lee, J., Jo, W. (1999). Nahrre (401) 682'

[2]

Giridharan, N.V., Subramanian,

M',

Jayavel, R. (2006). Appl. Phys. A (83) 123.

[3]

Chen, X.Q., Qi, H.Y., Qi, Y.J., Lu,

C'i'

(2005). Phys. Lett. A (346) 204.

[4]

Noh, T.W, Kang, B.S., Seo, S., So, Y.W., Park' 8.H., Bu, S.D.. Yoon, J.G. (2002) Ferroelectrics' 267 (1) r21.

[5]

Uong, C., Jeong, S.S., HyLrn' M.l. (2003)' J' Appl'

Phys.93 (8) 4769.

[6]

Chon, U., Jang, H.M., Kirn, M'G', Chang' C'H' (2002). Phys. Rev. Lett. (89) 087601'

[7]

Yang, B.,Zhang, D.M., Zhou, 8., Huang, L H', Zheng, C.D., Wu, Y.Y. Guo, D'Y., Yu, J' (2008)' J. Cryst Grov'th (3 10) 45 I 1 '

[8]

Bae, J.C., Kim, S.S., Choi, E.K., Song, T'K., Kim, WJ., Lee, Y.I. (2005). Thin Solid Filns (4'12)90

[9]

Hong, S.H., Susan, T.M., Gary,

L'M'

(2000)..r. Am. Ceratn.,loc.83 (1) 1i3.

l10l

Satoshi, T., Atsushi,

M.,

Zenji'

K.,

Keizo, U

(2009).J. Eur. Cerarn. Soc. (29) 955.

tl1l

Ni,2.,

Tadashi, S. (2007). Mat' Lett, (61) 2935.