BST and Other Ferroelectric Thin Films by CCVD and Their Properties and Applications

25


0.5 1 1.5 2 2.5 3 3.5 4 4.5
Frequency (GHz)
-7
-6.5
-6
-5.5
-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
Insertion Loss in dB
3 GH z
-4.326 dB
DB(|S(2,1)|)
0V
DB(|S(2,1)|)
05 V
DB(|S(2,1)|)
10V

DB(|S(2,1)|)
15V
DB(|S(2,1)|)
20V
DB(|S(2,1)|)
25V
DB(|S(2,1)|)
30V
DB(|S(2,1)|)
35V


0.5 1 1.5 2 2.5 3 3.5 4 4.5
Frequency (GHz)
-40
-35
-30
-25
-20
-15
-10
-5
0
Return Loss in dB
3 GHz
-11.53 dB
DB(|S(1,1)|)
0V
DB(|S(1,1)|)
05V

DB(|S(1,1)|)
10V
DB(|S(1,1)|)
15V
DB(|S(1,1)|)
20 V
DB(|S(1,1)|)
25 V
DB(|S(1,1)|)
30V
DB(|S(1,1)|)
35V


Fig. 30. (a) Insertion loss, S21 and (b) return loss, S11 of 3 GHz phase shifter

11.522.533.544.55
Frequency (GHz)
0
20
40
60
80
100
120
140
160
180
200
220

240
260
280
300
320
340
360
380
400
Insertion Phase Shift in Degrees
3 GHz
376.3 Deg
05V ( Deg )
10 V (Deg)
15 V (Deg)
20 V (Deg )
25 V (Deg )
30V ( Deg )
35V ( Deg )


Fig. 31. Phase shift of the 3 GHz phase shifter at different frequencies and bias voltages
(a)
(b)

Ferroelectrics – Material Aspects

26
5. Conclusions
As a summary, high quality epitaxial or textured ferroelectric and dielectric thin films,

including BST (both single layer and nanostructured multilayer), PZT, and CCT, have been
successfully deposited by the proprietary CCVD process onto various substrates, including
sapphire and single crystal STO, MgO, and LAO etc. Excellent electrical properties have
been achieved on these ferroelectric and dielectric thin films. High performance microwave
devices that can be used up to Ka band, such as tunable MEMS filters and CDMA filters,
have been designed and fabricated on BST based ferroelectric thin films. The performance of
these microwave devices are summarized as following:
 MEMS Ka-band tunable bandpass filters (both center frequency and bandwidth are
tunable): the best insertion loss of 3 dB when biased, and the bandwidths of 3 and 7.8%
for 3-pole narrowband and wideband, respectively;
 CDMA Tx tunable filters: insertion loss <2 dB, VSWR <1.5:1, center frequency shifting
from 1.85 to 1.91 GHz, Rx zero (@1.93 GHz) rejection >40 dB, DC bias <10 V;
 X- to Ku-band tunable bandpass filters: insertion loss of ~5 dB @11.5 GHz (0V) to 3 dB
@14 GHz (30 V), VSWR <2:1, DC bias <30 V, 6 × 1.5 × 0.5 mm in footprint;
 X-band back-to-back 4-pole bandpass filters: Insertion loss from 5.4 dB at 9.1 GHz to
1.84 dB at 10.25 GHz with an analog tuning of 12.6%; return loss <10 dB over the whole
X-band frequency range;
 Ka-band ring filters: insertion loss of 2.3 and 2.0 dB for 0 and 30 V, respectively; 3-dB
bandwidth of 20% for both bias states; tuning from 31.6 to 33.7 GHz, a 6.3% tunability;
 3 GHz phase shifter: The insertion loss at is 4.3 dB at 15 V and 3 GHz. The figure of
merit is 89.4°/dB at 0V. A phase shift of 361° is measured at 30V.
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Ferroelectrics – Material Aspects

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0254-0584
2
Synthesis of Ferroelectric Na
0.5
Bi
0.5
TiO
3
by MSS
(Molten Salt Synthesis) Method
Teresa Zaremba
Silesian University of Technology
Poland
1. Introduction
Environmental destruction has been a serious problem worldwide. One problem is the
release of harmful materials (e.g., Cd, Hg, Pb) from electrical industries. Thus, the restriction
on hazardous substance (RoHS) will be enforced soon to prevent the release of harmful
waste (Hiruma et al., 2007; Panda, 2009). Lead – based ferroelectric ceramics represented by
Pb (Zr,Ti)O
3

(PZT), have been widely used for piezoelectric transducers, sensors and
actuators due to their excellent piezoelectric properties. However, the evaporation of
harmful lead oxide during preparation causes a crucial environment problem. Therefore, it
is necessary to develop environment – friendly lead – free piezoelectric ceramics to replace
the PZT – based ceramics, which has become one of the main trends in present development
of piezoelectric materials. Sodium bismuth titanate, Na
0.5
Bi
0.5
TiO
3
(abbreviate as NBT),
discovered in 1960 (Smolenskii et al., 1960), is considered to be a promising candidate of
lead – free piezoelectric ceramics (Pookmaneea et al., 2001; Isupov, 2005; Panda, 2009; Zhou
et al., 2010).
NBT is a relaxor ferroelectric material with the general formula A
’
x
A”
1-x
BO
3
. The
ferroelectricity in NBT ceramic is attributed to (Bi
1/2
Na
1/2
)
2+
ions, especially Bi

3+
ions at the
,,A” site of the perovskite structure (ABO
3
) and due to rhombohedral symmetry at room
temperature. It has high Curie temperature (T
c
= 320°C), and shows diffuse phase transition
(Suchanicz et al., 2000; Suchanicz et al., 2001; Raghavender et al., 2006). However, the
piezoelectric properties of NBT ceramics are not good enough for most practical uses. In
order to enhance the properties and meet the requirements for practical uses, it is necessary
to develop new NBT – based ceramics (Raghavender et al., 2006; Zhou et al., 2010).
Researches have investigated many dopants into NBT ceramics (Panda, 2009). Also, it is
desirable to fabricate ceramics with a textured microstructure in order to improve the
properties (Hao et al., 2007).
The ferroelectric ceramic powders are synthesized trough conventional solid – state method
which needs high calcination temperature and repeated grindings (Lu et al., 2010). In order to
eliminate these defects, the wet chemical synthesis techniques have been developed, for
instance hydrothermal method (Cho et al., 2006; Wang et al., 2009), sol – gel method (Xu et al.,
2006; Mercadelli et al., 2008), and molten salt method (Zeng et al., 2007; Li et al., 2009). But the
hydrothermal and sol – gel synthesis are usually long and complex processes, use hazardous
solvents such as 2-methoxyethanol, and result in agglomerated particles (Bortolani & Dorey,
2010). Moreover, in the sol –gel method the cost of starting materials is high (Li et al., 2009).

Ferroelectrics – Material Aspects

32
Molten salt synthesis (MSS) is a process that yields large amounts of ceramic powders in a
relatively short period of time. Moreover, it is a suitable method for preparation of complex
oxide compounds with anisotropic particle morphologies. In this technique starting materials

are mixed together with a salt (usually alkaline chloride and sulphate) and then heat treated at
a temperature higher than the melting point of the salt. The melting temperature of the salt
system can be reduced by using a eutectic mixture of salts, e.g. the use of NaCl – KCl instead of
pure NaCl reduces the melting point from 801 to 657°C. A reaction between the precursors
takes place in the molten salt (the flux) and the solid product obtained is separated by washing
of the final mixture with hot deionised water. The typical starting materials are oxides, but
carbonates, oxalates and nitrates can also be used. There are several requirements for the
selection of salt to be used for MSS. First, the melting point of the salt should be relatively low
and appropriate for synthesizing of the required phase. Second, the salt should possess
sufficient aqueous solubility in order to eliminate it easily after synthesis by washing. Finally,
the salt should not react with the starting materials or the product (Bortolani & Dorey, 2010;
Hao et al., 2007). MSS has been used to form various ceramic powders such as niobates
relaxors (Yoon et al., 1998), Bi
4
Ti
3
O
12
(Kan et al., 2003), ZnTiO
3
(Xing et al., 2006), BaTiO
3

(Zhabrev et al., 2008) and Pb(Zr, Ti)O
3
(Cai et al., 2008; Bortolani & Dorey, 2010).
It was found that ternary compound Na
0.5
Bi
0.5

TiO
3
was formed in the solid – state process
through the intermediate binary compound, i.e. bismuth titanate – Bi
4
Ti
3
O
12
(Zaremba,
2008). Bi
4
Ti
3
O
12
(abbreviate as BIT) belongs to the Aurivillius family with a general formula
(Bi
2
O
2
)[A
m-1
(B)
m
O
3m+1
], which consists of (Bi
2
O

2
)
2+
sheets alternating with (Bi
2
Ti
3
O
10
)
2

-
perovskite – like – layers (Aurivillius, 1949, as cited in Stojanović et al., 2008). In general
formula m represents the number of octahedra stacked along the direction perpendicular to
the sheets, and A and B are the 12- and 6- fold coordination sites of perovskite slab,
respectively. This kind of structure promotes plate – like morphology (Dorrian et al., 1971,
as cited in Stojanović et al., 2008).
In this paper, Na
0.5
Bi
0.5
TiO
3
powders were prepared by molten salt synthesis in the presence
pure NaCl or NaCl - KCl as fluxes. The first stage of the study related to direct synthesis of
NBT via MSS from Na
2
CO
3

, Bi
2
O
3
and TiO
2
. For comparison, the synthesis of NBT by the
conventional method (CMO – conventional mixed oxides) was investigated. The second
stage included obtaining intermediate binary compound BIT via MSS from oxide
precursors, i.e. Bi
2
O
3
and TiO
2
, and then synthesis of NBT via MSS using BIT, Na
2
CO
3
and
TiO
2
as starting materials.
The details pertaining to studies of synthesis of NBT and an Aurivillius – structured BIT
precursor are reported in the following sections.
2. Synthesis of ferroelectric Na
0.5
Bi
0.5
TiO

3
Chemically pure powders of Bi
2
O
3
, TiO
2
(rutile) and Na
2
CO
3
were used as starting
materials. The Na
0.5
Bi
0.5
TiO
3
(NBT) was prepared by the following two routes:
Na
2
CO
3
+ Bi
2
O
3
+ 4TiO
2
→ 4Na

0.5
Bi
0.5
TiO
3
+ CO
2
(1)
Bi
4
Ti
3
O
12
+ 5TiO
2
+ 2Na
2
CO
3
→ 8Na
0.5
Bi
0.5
TiO
3
+ 2CO
2
(2)
In route (1), the starting materials were weighed in the proportion to yield NBT and mixed

in isopropyl alcohol employing an agate mortar and pestle for 1 h. Using MSS method, the
dry mixture of the precursors in the stoichiometric composition was mixed with an aqual

Synthesis of Ferroelectric Na
0.5
Bi
0.5
TiO
3
by MSS (Molten Salt Synthesis) Method

33
weight of salt. Salts used in this experiment were NaCl and eutectic mixture of 0.5NaCl –
0.5KCl, i.e. 43.94% NaCl – 56.06% KCl (by weight). The mixture of the precursors and flux
was dried at 120°C for 2 h for complete removal of isopropyl alcohol, placed in a Pt crucible
and heated in a sealed alumina crucible (to prevent salt evaporation) at temperatures
between 800°C and 1100°C for a different time period. After thermal treatment the chlorides
were removed from the products by washing with hot deionized water several times until
the filtrates gave no reaction with silver nitrate solution. The powders were finally dried at
100°C for 2 h. NBT powders were also prepared by a conventional mixed oxide method
(CMO) for comparison. All the syntheses were carried out in a conventional electric furnace.
Platelike Bi
4
Ti
3
O
12
(BIT) particles were obtained by MSS method in 0.5NaCl – 0.5KCl flux
(abbreviate as NaCl – KCl) in the same way as described above. Temperature of thermal
treatment ranging from 700°C to 1100°C for a different time period.

In route (2), BIT crystals produced earlier were subjected to second molten salt synthesis.
Na
2
CO
3
and TiO
2
were added to give the total composition of NBT. Again, pure NaCl or
NaCl – KCl mixture was added (weight ratio of precursors to flux = 1:1).
Finally, the phase composition of the synthesized samples was analyzed by the powder X-
ray diffraction (XRD; model 3003 TT, Seifert) using Ni – filtered Cu K
α
radiation. The
microstructure was observed by a scanning electron microscope (SEM; model BS 340, Tesla).
The samples were coated by a gold layer by using a metal – coating plant under a vacuum.
X–ray energy dispersive spectra (EDS) were measured using a Hitachi S-3400 N scanning
electron microscope with an EDS system Thermo Noran.
2.1 Synthesis of Na
0.5
Bi
0.5
TiO
3
from Bi
2
O
3
, TiO
2
and Na

2
CO
3

Fig. 1 represents the XRD patterns of the selected powders synthesized through route (1), i.e.
directly from Bi
2
O
3
, TiO
2
and Na
2
CO
3
via MSS (NaCl flux) and CMO. Similar trends were
also observed for NBT produced using NaCl- KCl flux. The particle morphology of the
starting materials and synthesized powders is compared in Figs 2 – 4.
NBT perovskite phase was observed in all the prepared samples. A comparison of
interplanar spacings determined from XRD patterns of the samples prepared by a
conventional solid state reaction and via MSS shows that agreement is quite satisfactory.
Analysis of XRD patterns of NBT samples obtained via MSS has not shown displacement of
maxima of diffraction peaks as the NaCl-KCl flux was used.
Isometric particles are found to exist in the samples of NBT. Typical micrograph of the NBT
powder prepared by CMO is shown in Fig. 3a. There is high degree of agglomeration in this
powder. The NBT particles prepared directly by CMO and MSS (NaCl flux) are very small
(about 1 μm). The size of the particles increased with increasing temperature, especially, as
NaCl-KCl flux was used. Probably, this is mainly due to the different melting points for each
salt used. NaCl and 0.5 NaCl – 0.5 KCl have melting points of about 800°C and 650°C,
respectively.

According to (Cai et al., 2007, as cited in Bortolani & Dorey, 2010) the solubility of the
starting materials in the molten salt plays an important role in the synthesis as it has an
influence on the final product morphology. For a simple two reactant system, two different
cases can be distinguished: either both reactants are equally soluble in the molten salt or one
oxide is more soluble than the other (Li et al., 2007, as cited in Bortolani & Dorey, 2010). In
the first case (dissolution – precipitation mechanism) both reactants fully dissolve, react in
the molten salt and the final product precipitates from the molten salt after formation. The
shape of the product has no connection with the shape of the starting materials. In the
second case, the more soluble precursor dissolves in the salt and diffuses to the less soluble

Ferroelectrics – Material Aspects

34
one. Here, at the surface, it reacts to final product. This template formation mechanism
would result in a product morphology that is similar to that of the less soluble reactant
which has acted as a template.


Fig. 1. XRD patterns of Na
0.5
Bi
0.5
TiO
3
powders fabricated through route (1): (a) via MSS
(NaCl flux) at 950°C for 1.5 h; (b) via MSS (NaCl flux) at 1000°C for 4 h; (c) via CMO at
1000°C for 4 h

Synthesis of Ferroelectric Na
0.5

Bi
0.5
TiO
3
by MSS (Molten Salt Synthesis) Method

35

(a)

(b)

(c)
Fig. 2. SEM micrographs of the starting materials: (a) Na
2
CO
3
; (b) Bi
2
O
3
; (c) TiO
2
- rutile

Ferroelectrics – Material Aspects

36

(a)


(b)

(c)
Fig. 3. SEM micrographs of Na
0.5
Bi
0.5
TiO
3
powders obtained through route (1): (a) via CMO
at 950°C for 1.5 h.; (b) via MSS (NaCl flux) at 950°C for 1.5 h; (c) via MSS (NaCl flux) at
1000°C for 4 h

Synthesis of Ferroelectric Na
0.5
Bi
0.5
TiO
3
by MSS (Molten Salt Synthesis) Method

37

(a)

(b)

(c)


(d)
Fig. 4. SEM micrographs of Na
0.5
Bi
0.5
TiO
3
powders obtained through route (1) via MSS
(NaCl - KCl flux) at different temperatures for 4 h: (a) 800°C; (b) 900°C; (c) 1000°C; (d)
1100°C

Ferroelectrics – Material Aspects

38
In the case of NBT the mechanism is further complicated due to the presence of (at least) 3
reactants. According to (Cai et al, 2007, as cited in Bortolani & Dorey, 2010) TiO
2
is not
soluble in molten alkali chlorides. The final NBT morphology should be similar to the
morphology of TiO
2
.


Fig. 5. XRD patterns of Bi
4
Ti
3
O
12

powders obtained via MSS at: (a) 700°C for 15 min; (b)
900°C for 30 min; (c) 900°C for 240 min; (d) 1000°C for 15 min (indexed peaks are those of
Bi
4
Ti
3
O
12
)

Synthesis of Ferroelectric Na
0.5
Bi
0.5
TiO
3
by MSS (Molten Salt Synthesis) Method

39

(a)

(b)

(c)

(d)
Fig. 6. SEM micrographs of Bi
4
Ti

3
O
12
powders obtained via MSS at 700°C for: (a) 15 min; (b)
30 min; (c) 60 min; (d) 120 min

Ferroelectrics – Material Aspects

40

(a)

(b)

(c)

(d)
Fig. 7. SEM micrographs of Bi
4
Ti
3
O
12
powders obtained via MSS at 1000°C for: (a) 15 min; (b)
30 min; (c) 60 min; (d) 120 min

Synthesis of Ferroelectric Na
0.5
Bi
0.5

TiO
3
by MSS (Molten Salt Synthesis) Method

41

(a)

(b)

(c)

(d)
Fig. 8. SEM micrographs of Bi
4
Ti
3
O
12
powders obtained via MSS at different temperatures
for 4 h: (a) 700°C; (b) 800°C; (c) 900°C; (d) 1000°C

Ferroelectrics – Material Aspects

42
2.2 Synthesis of Bi
4
Ti
3
O

12
The XRD patterns of selected samples BIT prepared from the mixture of Bi
2
O
3
and TiO
2
via
MSS (NaCl-KCl flux) are presented in Fig. 5. At 700°C, the phase Bi
12
TiO
20
co-existed with
BIT. Pure crystalline BIT was obtained after thermal treatment at 800°C for 15 min
Increasing the temperature to 1100°C, the intensities of the (00l) diffraction lines were
increased. These results indicate that during sample preparation for X-ray diffraction
characterization, Bi
4
Ti
3
O
12
crystals with platelet morphology may align with (00l) planes
parallel to the flat specimen holder.
Figs 6 – 8 show morphology and size of BIT crystals prepared at different temperatures. The
synthesizing temperature could significantly influence the growth rate and crystallization
habit of the BIT particles. Between 700°C and 800°C aggregate particles were formed. The
powder synthesized at 700°C was composed of fine particles. The size of the primary
particles increased and their shape changed from lumpy to plate-like with increasing
temperature. Above 800°C discrete plate-like particles with increased particle size were

formed. On the other hand, the effect of heating time on morphology and particle size is
smaller. The degree of aggregation decreased with increasing prepare temperatures.
According to (Kimura & Yamaguchi, 1987) Bi
4
Ti
3
O
12
is formed via MSS by mechanism,
when two reactants have comparable dissolution rates in molten salt. If this mechanism
dominates during the formation process, the complex oxide powder with a characteristic or
lumpy shape is formed, depending on the degree of interaction between the complex oxide
and salt.
2.3 Synthesis of Na
0.5
Bi
0.5
TiO
3
from Bi
4
Ti
3
O
12
, TiO
2
and Na
2
CO

3
Fig. 9 shows the XRD patterns of the selected powders synthesized through route (2), i.e.,
from Bi
4
Ti
3
O
12
(BIT), TiO
2
and Na
2
CO
3
via MSS (NaCl-KCl flux) at different temperatures.
The diffraction lines were indexed based on the pseudocubic unit cell because of a small
rhombohedral distortion of Na
0.5
Bi
0.5
TiO
3
.
BIT has a BLSF (bismuth layer-structured ferroelectric) structure that is highly anisotropic,
with the grain growth rate along the c-axis much lower than that along the a (b)-axis. So it is
easy for them to form a plate-like morphology. Similar to the BIT particles, most of the NBT
particles laid down with the c-axis aligning along the vertical direction during the sample
preparation for the XRD analysis. So, they exhibit strong (100) and (200) diffraction peaks,
especially, for higher temperatures of synthesis.
Fig. 10 shows the SEM micrographs of the NBT samples prepared from the BIT particles at

different temperatures in the presence NaCl-KCl flux. Similar to the BIT particles, most of
the NBT particles are large and of plate-like shape. Much larger crystals were grown at
1100°C, but the XRD pattern (Fig. 9d) shows that NBT co-existed with other crystalline
phase (phases), probably it was related to the beginning of thermal decomposition of NBT.
It has also been found that the salt has a significant effect on the size of the synthesized
particles. Fig. 11 shows the SEM micrographs of the ceramic powders synthesized in
different fluxes at 1100°C. The particles for the powder synthesized in NaCl-KCl flux are
larger than those synthesized in NaCl flux. NaCl-KCl flux at eutectic has a low melting point
(650°C), so ions have a high diffusion rate at the synthesing temperature 1100°C. In order to
determine the composition of the prepared samples, energy dispersive X-ray spectroscopy
(EDS) data (Fig. 12) performed on a samples synthesized in the presence NaCl-KCl and
NaCl flux show that the chemical components of the samples are the elements Na, Bi, Ti and
O (without K from KCl for the sample obtained in the presence NaCl-KCl).

Synthesis of Ferroelectric Na
0.5
Bi
0.5
TiO
3
by MSS (Molten Salt Synthesis) Method

43
As a member of the BLSFs, BIT consist of the (Bi
2
Ti
2
O
10
)

2-
(pseudo-) perovskite layers
interleaved by (Bi
2
O
2
)
2+
fluorite layers. After the reaction with the complementary reactants
(Na
2
CO
3
and TiO
2
), the layer-structured BIT particles were transformed to the perovskite
NBT. Although there are works reporting the transformation as a process from a lamellar
phase to a perovskite phase (Schaak & Mallouk, 2000), the process involving the (Bi
2
O
2
)
2+
layers changing to the perovskite structure is still unclear.


Fig. 9. XRD patterns of Na
0.5
Bi
0.5

TiO
3
powders fabricated through route (2) via MSS (NaCl -
KCl flux) at different temperatures for 4 h: (a) 800°C; (b) 900°C; (c) 1000°C; (d)
1100°C(indexed peaks are those of Na
0.5
Bi
0.5
TiO
3
)

Ferroelectrics – Material Aspects

44

(a)

(b)

(c)

(d)
Fig. 10. SEM micrographs of Na
0.5
Bi
0.5
TiO
3
powders obtained through route (2) via MSS

(NaCl - KCl flux) at different temperatures for 4 h: (a) 800°C; (b) 900°C; (c) 1000°C; (d)
1100°C

Synthesis of Ferroelectric Na
0.5
Bi
0.5
TiO
3
by MSS (Molten Salt Synthesis) Method

45

(a)

(b)

(c)
Fig. 11. SEM micrographs of Na
0.5
Bi
0.5
TiO
3
powders obtained through route (2) via MSS at
1100°C for 4 h: (a) NaCl - KCl flux; (b, c) NaCl flux

Ferroelectrics – Material Aspects

46


Fig. 12. EDS spectra of of Na
0.5
Bi
0.5
TiO
3
powders obtained through route (2) via MSS: (a)
NaCl- KCl flux; (b) NaCl flux
3. Conclusion
NBT has a perovskite structure with high symmetry, therefore it is difficult to obtain large
anisotropic NBT particles by methods as conventional solid-state reaction process or molten
salt synthesis. Using Bi
2
O
3
, TiO
2
and Na
2
CO
3
as starting materials, the equiaxed particles NBT

Synthesis of Ferroelectric Na
0.5
Bi
0.5
TiO
3

by MSS (Molten Salt Synthesis) Method

47
were obtained. NBT anisotropic particles with grain orientation were synthesized by
conversion of BIT crystals with layered structure. Owing to its highly anisotropic structure,
plate-like BIT was firstly fabricated in the NaCl-KCl flux. The plate-like BIT was reacted with
the complementary Na
2
CO
3
and TiO
2
in the presence of chloride flux, finally transformed to
the perovskite NBT and maintained its morphology nearly unchanged. NBT particles show
preferred orientation with the (h00) plane. The powder synthesized in 0.5 NaCl – 0.5 KCl flux
has the larger particles than those synthesized in pure NaCl. The increase of temperature and
soaking time of synthesis can make the plate-like grains of NBT more distinct and discrete. The
NBT particles prepared in this experiment can be used to prepare ceramics with more uniform
grain orientation, i.e., textured ceramics for improving piezoelectric properties.
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