Powders of high microwave dielectric material Barium Zinc Tantalate (BZT) and Barium Zinc Niobate (BZN) have been prepared by wet chemical procedure at moderately low temperature ~5000C. Co-precipitate and mechanical mixtures of hydroxide of Ba(II), Ta(V)/Nb(V) & Zn(II) in 3:2:1 mole proportion on thermal decomposition, showed formation of the desired perovskite phase at 5000C. The product of co-precipitate and mechanical mixture of hydroxides heated upto7400C produced single phase BZT. Thermal decomposition of mixture was studied in static air atmosphere by TG & DTA. XRD studies on a sample heated to 500, 740, 780 & 9000C confirmed the formation of single phase BZT formation at 7400C and that of BZN at7800C.

1. Sep. 30 IJASCSE, Vol1 Issue 2, 2012
Low Temperature Synthesis of Ba3Ta2ZnO9 (BZT) and Ba3Nb2ZnO9
(BZN) by Wet Chemical Route
Namrata Saraf, Manisha Khaladkar, Imtiaz Mulla
Rajashree Kashalkar, Department of Applied Science Emeritus Scientist(CSIR)
Department of Chemistry, College of Engineering, Pune CMET, Pune India
S.P.College, Pune India Pune India
Abstract: found applications as small electronic
component for use in hand held
Powders of high microwave dielectric communication device like cellular phone.
material Barium Zinc Tantalate (BZT) and Miniaturization of electronic devices and
Barium Zinc Niobate (BZN) have been adding more functionalities have given rise to
prepared by wet chemical procedure at a need for small size microwave resonators
moderately low temperature ~5000C. Co- with good frequency selectivity and high
precipitate and mechanical mixtures of temperature stability. Since the discovery of
hydroxide of Ba(II), Ta(V)/Nb(V) & Zn(II) in excellent microwave dielectric properties
3:2:1 mole proportion on thermal exhibited by Ba(Zn1/3Nb2/3)O3 and
decomposition, showed formation of the Ba(Zn1/3Ta2/3)O3 ceramics with perovskite
desired perovskite phase at 5000C. The structure. Many researchers [1-12] have
product of co-precipitate and mechanical prepared the material and there are several
mixture of hydroxides heated upto7400C patents on preparation of BZT [13].
produced single phase BZT. Thermal
decomposition of mixture was studied in Most of these procedures utilize oxides of
static air atmosphere by TG & DTA. XRD Ba, Ta/Nb, Mg/Zn in 3:2:1 mole proportion.
studies on a sample heated to 500, 740, 780 Although the material is used by many
& 9000C confirmed the formation of single workers; the reports in print are very few and
phase BZT formation at 7400C and that of especially reports on wet chemical route for
BZN at7800C. synthesis are rare except for work done by
Maclaren et al. [9], they have used barium
Key words: BZT, BZN, DTA, TG, XRD, acetate, zinc acetate, tantalum oxalate and
dielectric ceramics, Wet chemical route. Ganguly et al. [8] have used Mg(NO3)2.6H2O
for the formation of Magnesium Niobate
I. Introduction: (MN) and Magnesium Tantalate (MT). More
popular route for preparation of BZT is solid
Mixed metal oxide ceramics with Perovskite state route, where stoichiometric amounts of
(ABO3) structure are of great importance for corresponding oxides viz. 3BaO, ZnO,
various electronic applications. Among this Ta2O5/Nb2O5 are mixed, milled together
family BZT and BZN are very significant manually or using ball-mill and heated at
members because of their high dielectric temperature of about 13000C [11-14] for few
constant, low loss factor at resonant hours.
frequency and near zero temperature
coefficients at resonant frequency. BZT has
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2. Sep. 30 IJASCSE, Vol1 Issue 2, 2012
for studying the decomposition. Thermo-
gravimetric Analysis (TG) was employed to
The main problem associated with high study the decomposition. After plotting the
temperature (above 13000C) sintering is weight loss curves as a function of
volatility of ZnO. This leads to non- temperature few temperatures were selected
homogeneity in ZnO concentration is and the precursors were heated to those
observed on the surface and in the bulk. temperatures. The XRD analyses of the
High temperature sintering results in above heated samples were carried out to
formation of undesirable binary oxide barium monitor various products formed at the pre-
tantalate. Naturally the ZnO deficient phase decided temperatures. The experimentation
does not have desired dielectric constant is divided into three parts:
and hence device application fails. To 1) TG and DTA measurements were carried
eliminate the problem, sintering temperature out using equipments fabricated in house,
must be kept below 13000C. This is possible the decomposition were studied in static air
when powders are synthesized by wet atmosphere using heating rate of 100C /min,
chemical route [8]. Such chemically from ambient to 10000C, TG plots are shown
synthesized powders possess fine particle in figures 1to 4and DTA are shown in Fig 5
size distribution and low aspect ratio particle and 6.
morphology, as well as better homogeneity 2) Mixtures were heated up to 500, 740,
in micro-structure and chemical constitution 9000C and soaked for 1hr at the final
[1,2]. The resultant powder possesses better temperature. The products thus obtained
sintering ability. Hence wet chemical were analyzed by Bruker AXS D8 Advance X
synthesis is a promising route. ray diffractometer in 2θ range 20- 800.
3) Surface morphology was recorded on
In wet chemical method precursors are JEOL JSM 6360A Scanning Electron
added to give either mechanical mixtures or Microscope.
co-precipitate of metal salts in desired mole
proportion. Precipitate filtration, drying and List of samples studied is given below:
calcinations of dried precursor was carried
out. The dried precursors were then heated Table-1 Samples under study.
at constant pre decided rate. We have
successfully synthesized Barium Zinc Sr Precursor Sam Raw
Niobate (BZN), Barium-zinc-tantalate (BZT), N sample ple material
Zinc tantalate, Magnesium tantalate, Zinc o. abbr
Niobate by wet chemical route [1,2]. This eviat
paper reports results on synthesis of single ion
phase BZT and BZN using wet chemical 1. Binary mixture ZT Ta2O5 &
route at temperature as low as 7400C. of Tantalum & (cp) Zn (NO3)2
zinc
II. Experimentation: in 2:1 mole
proportion as
Co-precipitated hydroxides of Ba, Zn, Ta/Nb co-precipitate.
were prepared in 1:2:3 mole proportion and 2. Binary ZT Ta(OH)5 &
subjected to heating from ambient to 10000C mechanical (mm) Zn(OH)2
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3. Sep. 30 IJASCSE, Vol1 Issue 2, 2012
mixture of to the binary co-precipitate prepared by
Tantalum and method given above.
zinc In 2:1
3. Barium, BZT Ba(OH)2 & b) Mechanical mixtures (mm):
Tantalum and (cp) ZT
zinc 3:2:1 hydroxide In case of Mechanical mixtures individual
(cp) hydroxides were prepared from raw
materials as given in the flowchart No.1 and
4. Barium, BZT Ba(OH)2,T ammonium hydroxide was used as
Tantalum & (mm) a(OH)5 & precipitating agent. The resultant precipitates
zinc in 3:2:1 Zn(OH)2 were washed with distilled water till the pH of
5. Niobium & ZN(c Nb2O5 & filtrate was 7, and the precipitate was
zinc, 2:1 p) Zn (NO3)2 subjected to drying at 1100C for 5hr. The
6. Niobium & zinc ZN Nb(OH)5 & dried samples were mixed in required
2:1 (mm) Zn(OH)2 proportion (3:2:1 Ba: Ta: Zn) in agate mortar
7. Barium, BZN Ba(OH)2 & for 2 hrs and stored in vacuum desiccators.
Niobium & (cp) ZN
zinc, 3:1:2 hydroxide III. Results and Discussion:
(cp)
8. Barium, BZN Ba(OH)2,N It is observed that precipitate washing,
Niobium & zinc (mm) b(OH)5 & filtration and drying temperature play
, 3:1:2 Zn(OH)2 significant role in deciding the homogeneity,
and phase formation temperature of BZT and
Preparation of hydroxide mixtures: BZN.
TG interpretation
a) Co-precipitation method (cp): ZT(cp)
ZT(mm)
0
5
The procedure was chosen from earlier 10
% weight loss
reports by Ravi et al [1, 2] for preparation of 15
20
Mg4Ta2O9, MgNb2O6 etc. The major step is 25
dissolution of Ta2O5 and Nb2O5. It was 30
carries in fuming chamber using Teflon 35
0 200 400 600
0
800 1000
temperature C
beaker on a water bath. The beaker was
fitted with long air condenser. 20 hours
Fig.1 Decomposition pattern of co-precipitate
digestion time was required for Ta2O5 and 8
ZT (cp) and ZT mm –hydroxide
hours for Nb2O5. After the dissolution
required amount of Zinc nitrate was added
As can be seen from above figure
as solution and precipitation was carried out
decomposition of cp starts and completes at
using ammonium hydroxide solution till the
lower temperature. The actual weight loss
pH reached 9. Voluminous white precipitate
steps and reactions are given below.
was obtained. Filtration, washing and drying
For cp ZnTa2(OH)12.2NH4OH ZnTa2O6
was carried out. For preparation of ternary
For mm Zn (OH)2 +2 Ta
co-precipitate Barium hydroxide was added
(OH).2NH4OHZnTa2O6
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4. Sep. 30 IJASCSE, Vol1 Issue 2, 2012
400 69 H2O Ta-
Tem % Decom Residual intermedi
perat weig positio compound ate
ure ht n 400- 5.3 2.08 ZnTa2O6
o
C loss product 800 6 H2O
BZ 55- 12.98 -11.8 Partly
BZT (cp)
T 260 H2O dried 0
BZT (mm)
cp presursor.
10
260- 20.19 -14.11 ZnTa2(OH
% weight loss
20
400 H2O, )12 +
30
2 2BaO+
NH4OH 1 Ba(OH)2 40
400- 9.61 -7 H2O 3Ba2TaZn 50
0 200 400
temperature
0
600
C
800 1000
800 1from O9 (cp)
Ba, hydroxide Fig.2 Decomposition pattern of co-precipitate
6from BZT (cp) and BZT mm –hydroxide For cp
Ta + ZnTa2 (OH)12.2NH4OH
Zn cp +3Ba(OH)2Ba3ZnTa2O9
BZ 80- 4.77 -3H2O Amorphou For mm
T 180 (2from s Ba(OH)2.8H2O+Zn(OH)2+2Ta(OH)5Ba3ZnT
mm Zn and precursor a2O9
1from
Ta/Ba)
190- 5.53 -3.5 ZnO ZN (mm)
290 H2O 0
ZN (cp)
300- 3.15 -2 H2O Ba3Ta2Zn 10
730 O9 20
% wt loss
30
40
Sr. Tem % Decomp Residual 50
No perat wt osition compoun 60
0 200 400 600 800 1000
ure los product d Temperature
0
C
o
C s
ZT 115- 16. -2 partial Fig.3 Decomposition of co-precipitate ZN(cp)
cp 245 77 NH4OH Ammonia and ZN (mm) hydroxide ZnNb(OH)7 
-2 H2O expulsion ZnNb2O6
& Decomposition reactions for mm Zn(OH)2+
decompo Nb(OH)5.7H2O.(1H2O,1 NH4OH) ZnNb2O6
sition
255- 25. -4H2O ZnTa2O6
455 81 Decomposition reactions for cp
ZT 55- 10. 2 NH4OH
m 260 37 NH4OH Free ZT
m 260- 10. 4.15 ZnO +
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5. Sep. 30 IJASCSE, Vol1 Issue 2, 2012
Temp % Decom Residual
eratur W positio compound
e loss n adsorbed water, absorbed water, ammonia
produc water of crystallization and water released
t due to decomposition of hydroxide
respectively. The DTA plots obtained for
BZ 100- 14.2 -10.82 Dehydrated various samples are shown in Fig 5 and 6
N 200 1 H2O BZN (cp) below. The decomposition pattern of ZT mm
cp 273- 14.7 -11.23 Anhydrous & cp are almost identical. ZT mm
530 6 H2O BZN (cp) decomposition occurs in 55 to 350 and 350
560- 12 -9.1 BZN (cp) to 6000C in two steps and in ZT cp occurs in
660 H2O oxide four steps. Desorption, dehydration &
BZ 100- 7.24 - 5.5 Dehydrated decomposition are all endothermic reactions.
N 290 H2O BZN mm In all the four DTA samples a sharp
mm 350- 26.9 -21.6 BZN mm endothermic peak is observed at around
400 4 H2O anhydrous 3900C which is assigned to decomposition of
575- 7.65 -5.8 BZN mm ZT hydroxide.
695 H2O oxide
BZN (cp)
Tem % Deco Residual
0
BZN (mm)
pera W mpos compound
ture loss ition
10
0
C produ
% weight loss
20
ct
30
ZN 155- 16.7 -5 Dehydrate
cp 225 5 H2O d ZN
40
50
0 200 400
temperature in
600
0
C
800 1000
225- 6.04 -1.8 Anhydrous
305 H2O ZN
435- 9.36 - 2.85 ZN oxide
Fig.4 Decomposition pattern of co-precipitate 685 H2O
BZN (cp) and BZN mm –hydroxide ZN 55- 10.3 -1 Desorption
For cp m 155 8 NH4O of
Ba (OH)2.8 H2O+ ZnNb(OH)7 Ba3ZnNb2O9 m H 1ammonia
For mm -1 & water
Ba (OH)2.8 H2O+Zn(OH)2 + 2Nb(OH)5  H2O
Ba3ZnNb2O9 155- 21.5 - 3.5 Dehydratio
295 4 H2O n
c) DTA interpretation: 357- 8.72 2.66 Completion
435 H2O of
DTA measurements were carried out on dehydratio
DTA instrument fabricated in house. The n&
decompositions sequence was studied in decomposi
static air atmosphere using heating rate of At tion of Zn
100C /min, from ambient to 9000C. The high 500- 6.02 2 Formation
exothermic and endothermic peaks observed er 875 H2O of binary
in DTA plots were assigned to the loss of tem oxide of
Zn-Nb
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6. Sep. 30 IJASCSE, Vol1 Issue 2, 2012
perature around 660-670 0C co-precipitate
0.20
shows a small exothermic peak & mm shows 0.15
0.10
small endothermic peak which is little
ZN mm
0.05
0.00
conflicting but at temperature up to7500C -0.05
-0.10
shows same reversal reaction enthalpies. It -0.15
0.4
shows different stabilities of binary oxides 0.2
formed which lead us to select co- 0.0
ZN cp
-0.2
precipitated product over mechanical mixture -0.4
as starting material for ternary oxides. In -0.6
-0.8
DTA of BZT a broad endothermic peak 0.4
observed due to large amount of water of 0.2
0.0
BZN mm
crystallization at 100 for co-precipitate and at -0.2
-0.4
1400C for mechanical mixture. -0.6
-0.8
1
For BZN mm closely separated endothermic
peaks due to release of large amount of 0
BZN cp
associated water. In cp single endothermic -1
peak due to close association of molecules is -2
observed. 0 100 200 300 400 500 600 700 800
0
Temperature C
0.10
0.08
0.06
0.04
0.02 Fig. 6 DTA plots of ZN, BZN (cp, mm)
ZT mm
0.00
-0.02
-0.04
-0.06
-0.08
-0.10
0.10
0.05
0.00
ZT cp
-0.05
-0.10 d) XRD studies:
-0.15
0.2
0.1
Conformation of the phases formed at
0.0
various stages of decomposition was done
BZT mm
-0.1
-0.2
-0.3
-0.4 by XRD. XRD patterns recorded for
mechanical mixture of BZT – hydroxides
0.2
0.0
-0.2
BZT cp
heated up to 500, 7400C and on another
-0.4
-0.6
-0.8
0 100 200 300 400
Temperature
500
0
C
600 700 800
sample heated up to 9800C for 2 hrs are
shown in Fig 7-9. It can be easily seen that
the sample heated to 5000C shows very poor
Fig 5 DTA plots of ZT, BZT (cp, mm) crystallinity whereas the sample heated at
7400C shows single phase BZT, on heating
the sample up to 9000C the crystallinity
reduces and very low intensity peaks are
observed corresponding to BZT phase. The
XRD patterns were recorded for ternary
hydroxide Ba Zn Nb heated up to and heated
at 7400C for one hour. Fig 4 c shows the
XRD patterns for mm, cp and solid state
mixture of Ba, Zn and Nb oxides in 3:2:1
mole proportion. Comparison of the patterns
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7. Sep. 30 IJASCSE, Vol1 Issue 2, 2012
reveal that BZN cp mixture heated at 7400C
for one hr gives single phase BZN compound
as reported by C. T. Lee [14] where as the
solid state mixture shows binary oxides ZN in
addition to BZN . This indicates that for solid
state oxide mixture 7400C temperatures is
not sufficient for the formation of single
phase ternary BZN oxide.
900 C
0
740 C
0
2θ
Fig. 9 XRD of BZN cp, mm , ss heated to
7400C
500 C
0
e) SEM Studies:
Fig 10 a, b show SEM images of sintered
20 30 40 50 60 70 80
BZT powder and The SEM image shows
regions of about 1 micron size rods with
Fig. 7 XRD of BZT heated to various
uniform size and shape.
temperatures
0
BZT mm at 740 C
0
BZT cp at 740 C
Intensity
Fig.10 a SEM image of BZT
20 30 40 50 60 70 80
2 theta
Fig. 8 XRD for BZT cp & mm heated to
7400C
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8. Sep. 30 IJASCSE, Vol1 Issue 2, 2012
Formation of ZT occurs at Temperature as
low as 6800C for cp and single phase ZT
oxide is formed at 7400C for mm.
Formation of single phase BZT occurs at
temperature below 7400C and the crystalline
single phase disintegrates at temperatures
around 9000C as can be seen from Fig. 7,
the decomposition product of co-precipitate
Fig.10 b SEM image of BZT has better crystallinity; as compared to that
of mechanical mixture. No high temperature
sintering is required for the formation of
single phase BZT if hydroxide route is
adopted.
Decomposition of ZT is complete at 740 but
complete decomposition of ZN/BZN requires
temperature more than 8400C.Sintering time
of 1 hr. at 7400C for BZN & 1 hr at 8800C for
Fig. 10 (c) SEM image of BZN mm BZT is sufficient. In case of BZN cp and mm
(Fig. 10 c and d) it was observed in mm
sample there are two type of grains a needle
like which is in majority and flat plates in
lesser concentration. SEM image of cp
sample shows a single grain type which
more homogeneous hence it appears to
better than mm.
Fig. 10 (d) SEM image of BZN cp SEM images showed formation of uniform
rods with plumbite structure having 1micron
IV. Conclusions: size, on further magnification of a crystal
lump similar rod like structure is observed
Wet chemical route is better suited for within the lump. The high dielectric constant
preparation of binary and ternary oxides of of the material appears to be due to fractality
Zinc Tantalate and Barium Zinc Tantalate as observed in the crystal structure.
compared to Solid state route.
All hydroxides mixture cp as well as mm
seem to have high tendency to adsorb V. Acknowledgements:
ammonia as well as water. This Ammonia
M.Y. Khaladkar and Namrata Saraf are
and water is deeply embedded in the system
and require higher temperature (2600C for thankful to ISRO UoP STC, Pune and
ZN mm) for removal. Satellite application Centre (SAC)
Ahmadabad for their financial and technical
support. They are also thankful to the
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9. Sep. 30 IJASCSE, Vol1 Issue 2, 2012
Director, College of Engineering, Pune.
Namrata Saraf and R V Kashalkar are [11] H. Matsumoto, H. Tamura, K. Wakino,
thankful to Principal S.P.College for his Jpn. J. Appl. Phy, (1991), vol. 30, pp.2347.
timely help and encouragement for research
[12] X. M. Chen, Y. Suzuki, N. Sato, J.
work. I.S. Mulla is grateful to CSIR for Mater. Sci. Mater. Electron, (1994), vol.5,
awarding Emeritus Scientist scheme. pp.244.
VI. References: [13] M. Furuya, A. Ochi, J. J. Appl. Phys,
(1994), vol. 33, pp.5482.
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[2] V V Deshpande, M M Patil,S C Navale , V
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[4]H. Zhang, L. Fang, T. Huang, R. Yuan, J.
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[5] M. Bieringer, S. M. Moussa, L. D.
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