Effect of Li2CO3 addition on the structural, optical, ferroelectric, and electric field induced strain of lead free BNKT based ceramics

Author’s Accepted Manuscript
Effect of Li2CO3 addition on the structural, optical,
ferroelectric, and electric-field-induced strain of
lead-free BNKT-based ceramics
Nguyen Van Quyet, Luong Huu Bac, Dang Duc
Dung
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To appear in: Journal of Physical and Chemistry of Solids
Received date: 22 January 2015
Revised date: 30 April 2015
Accepted date: 10 May 2015
Cite this article as: Nguyen Van Quyet, Luong Huu Bac and Dang Duc Dung,
Effect of Li2CO3 addition on the structural, optical, ferroelectric, and electricfield-induced strain of lead-free BNKT-based ceramics, Journal of Physical and
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Effect of Li2CO3 addition on the structural, optical, ferroelectric, and
electric-field-induced strain of lead-free BNKT-based ceramics

Nguyen Van Quyet1, Luong Huu Bac2, and Dang Duc Dung2,*
1

School of Materials Science and Engineering, University of Ulsan, Ulsan 680-749,
Republic of Korea
2

School of Engineering Physics, Ha Noi University of Science and Technology,
1 Dai Co Viet Road, Ha Noi, Viet Nam
Abstract

In this work, we reported the effect of Li2CO3 addition on the structural, optical,
ferroelectric properties and electric-field-induced strain of Bi0.5(Na,K)0.5TiO3 (BNKT)
solid solution with CaZrO3 ceramics. Both rhombohedral and tetragonal structures
were distorted after adding Lithium (Li). The band gap values decreased from 2.91 to
2.69 eV for 5 mol% Li-addition. The maximum polarization and remanent polarization
decreased from 49.66 C/cm2 to 27.11 C/cm2 and from 22.93 C/cm2 to 5.35
C/cm2 for un-doped and 5 mol% Li- addition BNKT ceramics, respectively. The
maximum Smax/Emax value was 567 pm/V at 2 mol% Li2CO3 access. We expected this
work will help to understand the role of A-site dopant in lead-free ferroelectric BNKT
materials.
Keywords: A. Ceramics; B. Crystal growth; D. Optical properties; D. Ferroelectricity;
D. Piezoelectricity
*) Corresponding e-mail:

I. Introduction
The Pb(Ti1-xZrx)O3 (PZT)-based piezoceramics currently dominate the electronic
industry, however the search for an appropriate lead-free replacement due to
environmental and human health concerns continues [1]. Among various lead-free
systems, modified-Bi0.5(Na,K)0.5TiO3 (BNKT) ceramics seem to be a candidate for

1


real application in piezoelectric devices due to giant electric field-induced strain
(EFIS) [2]. Recently, the current development BNKT-based indicated that the
dynamic coefficient (Smax/Emax) could be compared with soft PZT-based materials [3].
The dynamic coefficient in BNKT ceramics was around 225 pm/V and can be
enhanced when the mostly A-site and/or B-site were modified [4-8]. Dinh et al.
reported the enhancement Smax/Emax up to 715 pm/V due to replace Bi3+ by 3 mol%
La3+ as A-site [4]. Do et al. reported that trivalent Y3+ and alionvalent Ta5+ modified
Ti4+ resulted in increasement the Smax/Emax values of 278 pm/V and 566 pm/V,
respectively [5, 6]. Similarly, Hussain et al. obtained the enhancement of Smax/Emax to
475 and 614 pm/V by replacement of isovalent ions Hf4+ and Zr4+ for Ti4+ at B-site,
respectively [7, 8]. Recently, Nguyen et al. archived strongly enhancement of the
electric-field-induced strain due to the co-substitution in both A-site (Li+ substituted
Na+) and B-site (Ta5+ or Sn4+ substituted Ti4+) [9, 10].
In addition, the solid solutions of secondary ferroelectric perovskite materials with
lead-free BNKT-based were also found to be enhanced Smax/Emax values. In fact, the
solid solution of A’B’O3 perovskite materials to BNKT ceramics which could consider
as co-dopants at both A- and B-site, with similar concentration, because of diffuse
element during sintering process. Thank to well solid-solution with lead-free
Bi0.5(Na,K)0.5TiO3-based ceramics, Ullah et al. reported the highest value of Smax/Emax
of 391 pm/V for 5 mol% BiAlO3 solid solution in Bi0.5(Na0.8K0.2)0.5TiO3 which resulted
from phase transition from the coexistence of rhombohedral and tetragonal into
pseudocubic phase [11]. Interestingly, Ullah et al. pointed out that the Smax/Emax
value was 533 pm/V in 0.975[Bi0.5(Na0.78K0.22)0.5TiO3]–0.025BiAlO3 due to the
tetragonal side of the mophotropic phase boundary composition and 592 pm/V in
2

0.970[Bi0.5(Na0.78K0.22)0.5TiO3]-0.030BiAlO3 at near the tetragonal-pseudocubic phase
boundary [12, 13]. However, Fu et al. reported that only distorted structure was
obtained and phase transition did not happen in BiAlO3 solid solution with
Bi0.5(Na0.82K0.18)0.5TiO3 [14]. In fact, co-modifications at A-site and B-site in BNKT
ceramics were further enhancement the Smax/Emax up to 579 pm/V when the
tetragonal structure of lead-free 0.99Bi0.5(Na0.78K0.22)0.5TiO3–0.01(Bi0.5La0.5)AlO3
composition was distorted [15]. Lee et al. obtained the normal strain of 549 pm/V for
3 mol.% Ba0.8Ca0.2ZrO3-modified BNKT [16]. Moreover, the solute solution of CaZrO3
into BNKT was found to display in larger Smax/Emax values than BaZrO3 modification
of BNKT [17, 18]. The explanation for different enhancement of Smax/Emax in BNKT
solid solutionoriginated from phase transition from polar to non-polar due to
expansion tolerance factor and/or promotion of oxygen vacancies [4, 9, 19]. In fact,
the tolerance factors just only evaluated the perovskite or non-perovskite and it could
not show the relationship between tolerance factors with structure symmetry [20-22].
Therefore, these results were important to point out that: i) the mechanism in
enhancement Smax/Emax values were still unclear in their research, and ii) the
modification of A-site were more sensitive to Smax/Emax values than that of only
modified at B-site.
The A-site modification by ion Li+ in lead-free BNKT-based ceramics have been
reported with interesting phenomena and attractive results. The Li+ ions were found
to be suppressed formation of the second phase and Ti3+/4+ valence transitions when
it substituted at Na-site in BNKT [17, 18]. Co-doped Li+ (at Na+-site) and Ta5+ (at Ti+site) ions in BNKT ceramics were found to be strongly enhanced the Smax/Emax value
up to 727 pm/V which resulted from transition from coexist of rhombohedral and
3


tetragonal phase to pseudocubic phase [9]. Unlikely, the co-doped Li+ (at Na+-site)
and Sn4+ (at Ti+-site) ions caused phase transition from pseudocubic to tetragonal
phase with Smax/Emax value of 646 pm/V [10, 25]. Recently, we reported that the
distorted tetragonal and rhombohedral structure due to Li+ ions modified

Bi0.5(Na0.78K0.22)0.5Ti0.97Zr0.03O3 lead-free piezoceramics which were possible to
increase the Smax/Emax from 600 pm/V to 643 pm/V for 2 mol% Li+-added [26].
In this work, we reported the effect of Li2CO3 addition on the structural, optical,
ferroelectric properties and electric-field-induced strain of BNKT solid solution with
CaZrO3 ceramics. The both rhombohedral and tetragonal structures distorted after
adding Li. The band gap (Eg) values decreased from 2.91 to 2.69 eV with 5 mol % Liadded. The maximum polarization decreased from 49.66 C/cm2 to 27.11 C/cm2 as
increasing the Li concentration from 0 to 5 mol%. The Smax/Emax value was 567 pm/V
with 5 mol Li-added.
II. Experiment
The 0.97Bi0.5Na0.4-xLixK0.1TiO3-0.03CaZrO3 (BNKTCZ-xLi) (x = 0.00, 0.01, 0.02, 0.03,
0.04, and 0.05) ceramics were prepared by a conventional solid state reaction route.
The raw materials were Bi2O3, K2CO3, TiO2, Li2CO3, CaCO3 (99.9%, Kojundo
Chemical), Na2CO3 (99.9%, Ceramic Specialty Inorganics) and ZrO2 (99.9%, Cerac
Specialty Inorganics). The details of fabrication processing were found in elsewhere
[26]. The green compacts were sintered in a covered alumina crucible at 1180 °C for
2 h in ambient condition. The surface morphology was observed with a field emission
scanning electron microscope (FE-SEM). The crystalline structures of the samples
were characterized by X-ray diffraction (XRD). The optical properties were studied by
UV-VIS spectroscopy. The temperature dependence of the dielectric properties was
4


measured using an impedance analyzer. The polarization-electric fields (P-E) and
electric field-induced strain hysteresis loops were measured in silicon oil using a
modified Sawyer–Tower circuit and linear variable differential transducer system,
respectively.
III. Result and discussion
Fig. 1 shows the X-ray diffraction pattern of BNKTCZ-xLi with x=0.00, 0.01, 0.02,
0.03, 0.04 and 0.05. The all samples show the single perovskite structure without
impurity phase, indicating that Li+ ions were successfully diffused to lattice. The

magnifications of Fig. 1 in the range 2 from 39.0 to 41.0 and 44.0 to 48.0 are
shown in Fig. 2 (a) and (b), respectively. The results show that the peaks were
unsymmetrical with shoulder peak which revealed the overlap of multi-peaks. The
each peak was carefully fitted by using the Lorentzian as shown in the red dash line.
The peaks were indexed as (003)/(021) and (002)/(200) in the range from 39.0 to
40.5 and 44.0 to 48.0, respectively, indicating that both rhombohedral and
tetragonal phases were coexisted. In addition, the peaks position trended to shift to
higher angle when Li was added with content up to 3 mo%, indicating that Li+ ions
gave the local compression strain when it filled at Na+ site. The result can be
understood based on the different ionic radii between Li+ (0.092 nm in 8-fold
coordination) and Na+ (0.136 nm in 12-fold coordination) [27]. Interestingly, the
peaks position was shifted back to lower angle when Li+ concentration was higher
than 3 mol%. This phenomenon was suggested that the Li+ ions can be also filled at
the octahedral site when Li+ addition was higher a threshold value and consequently
resulted in expansion the lattice constants because the ionic radius of Ti4+ (0.0605
nm in 6-fold coordination) was larger than that ionic radius of Li+ (0.076 nm in 6-fold
coordination) [27]. The effect of multisite Li+ was well known in both lead-based and
5


lead-free piezoelectric material [25, 26, 28, 29]. We recently obtained the effect of
multisite Li+ occurred in BNKT-modified with Sn or Zr piezoelectric materials [25, 26].
Fig. 3(a)–(f) shows FE-SEM micrographs of the BNKTCZ–xLi ceramics with x =0.00,
0.01, 0.02, 0.03, 0.04 and 0.05, respectively. A dense microstructure with some
distinct pores is observed for the BNKTCZ ceramic and 1 mol% Li-added BNKTCZ,
as seen in Fig. 3(a) and (b). The compact structures were obtained when Li+ ions
further added, as shown in Fig. 3(c)-(f) indicating that the samples exhibited dense
and uniform grains. We suggested that the effect of Li on the grain size resulted from
liquid phase sintering process because of low melting point of Li2CO3 and/or
promotion oxygen vacancies during sintering process [25, 26].

The room temperature absorption spectra of the Li addition in BNKTCZ are shown in
Fig. 4(a). All of the specimens exhibited absorption in the visible light region. The
absorption spectra show a red shift slightly as the Li concentration increases,
indicating that the Li+ ions addition modified the band gap of lead-free BNKTCZ
piezoelectric specimen. The Eg values was associated with the absorbance and
photon energy by following equation αh ~ (h-Eg)n, where α is the absorbance
coefficient, h the Planck constant,  the frequency, Eg the optical band gap and n a
constant associated with different types of electronic transition (n=1/2, 2, 3/2 or 3 for
direct allowed, indirect allowed, direct forbidden and indirect forbidden transitions,
respectively) [30]. The Eg values of lead-free piezoelectric BNKTCZ–xLi ceramics
were evaluated by extrapolating the linear portion of the curve or tail. The band gap
estimated with n=1/2 for direct transition as shown in Fig. 4(b). The optical band gap
decreased with increase in Li+ ions addition. It decreased from 2.91 eV to 2.69 eV as
Li+ ions concentration increased from 0 to 5 mol%. This results were consisted with
our recently reported for effect of Li-modified BNKT-based ceramics on the optical
6


properties which Eg values decreased from 2.88 eV to 2.68 eV and 2.99 eV to 2.84
eV for Li-doped BNKT-modified with Zr and BNKT-modified with Sn, respectively [25,
26]. Thus, we suggested that the reduction of band gap in Li-modified BNKTCZ
ceramics is strongly related to the ionics bonding between A-site and oxygen
and/or distorted structure.
Fig. 5(a) shows the temperature dependence of the dielectric constant of lead-free
BNKTCZ–xLi ceramics at frequencies of 1 kHz. Similar to the lead-free ferroelectric
Bi0.5Na0.5TiO3 ceramics, the curves show two distinct anomalies for all samples
which correspond to the depolarization temperature (Td) and maximum dielectric
constant temperature (Tm), respectively [31]. The curves for different samples look
similar, all exhibiting two-phase transition at Td and Tm. The two dielectric peaks can
cause by the phase transitions from ferroelectric to antiferroelectric (Td) and

antiferroelectric to paraelectric phase (Tm), which is consistent with the previous
reports of lead-free BNKT-based ceramic [26, 32, 33]. The variations in the values of
Td and Tm with different amount of Li addition for BNKTCZ ceramics are presented in
Fig. 5 (b). From Fig. 5 (b), it is found that both Td and Tm exhibited an obvious
dependency on amount of Li+ cations dopants concentration. However, the first
phase transition temperature change in narrow range from 427 K to 405 K while the
secondary phase transition temperature increased from 531 K to 607 K as Li content
increased from 0 to 5 mol%. Compared with BNKTCZ ceramics, the increase of Tm
in Li-added BNKTCZ specimen as increasing the Li concentration is probably
consequence of the enhancement of antiferroelectric phase stability by Li addition.
Dai et al. proposed that the dielectric maximum around Tm is related to relaxation of
tetragonal phase emerged from rhombohedral polar nanoregions [34]. According to
Zhu et al., the reversed dependence of Td and Tm on Li amount dopants
7


concentration can be attributed to the lattice distortion [35]. In addition, Zhou et al.
reported that the vacancies facilitate the movement of the ferroelectric domain and
result in a decrease of depolarization temperature [36]. Moreover, according to the
theory of dielectric response of relaxor ferroelectric discovered by Thomas that the
stability of ferroelectric domain decreases as the coupling reaction between A-site
cation and BO6 octahedron decreases [32]. Yang et al. reported that the coupling
reaction between A-site cation and BO6 octahedron is weakened and the Td moves
to lower temperature region when A-site is vacancies [37]. Therefore, we suggested
that the decrease of depolarization temperature was strongly related with multisite
occurrence of Li+ ions in BNKTCZ ceramics.
To better understanding the dielectric behavior, we used the modified Curie-Weiss
law which is described as follows: m/=1+(T-Tm)/(22) where m is the peak value of
the dielectric constant and Tm is the temperature at with  reaches the maximum,  is
the degree of diffuseness, and  is peak broadening parameter that indicates the

diffuseness degree [38, 39]. When =1, the materials with this type of phase
transition belongs to normal ferroelectrics; when 1<<2, the materials belongs to
relaxor ferroelectrics; and when =2, the materials belongs to ideal relaxor
ferroelectric. Fig. 6 (a)-(f) shows ln[(m-)/] as a function of ln(T-Tm) for BNKTCZ-xLi
ceramics with x=0.00, 0.01, 0.02, 0.03, 0.04 and 0.05, respectively, at 1 kHz. The
results indicated that a linear relationship is observer in all un-doped and Li-added
BNKTCZ ceramics. The  and  values were extracted from Fig. 6 by linear fitting.
The values of  and  as function of Li-dopant BNKTCZ ceramics were shown in Fig.
7. The  values were in range from 1.79 to 2.00 indicating that our samples
exhibited relaxor ferroelectric feature. The  values were 1.86 for Li-undoped
8


BNKTCZ specimen, and it increased close to 2.00 for 3 mol% Li addition. However,
the  values trend to decrease to 1.79 for 5 mol% Li addition. A similar trend has
been found for  values that it increased from 108.5 K to 254.6 K for un-doped and 2
mol% Li addition and then decreased to 94.4 K for 5 mol% Li access. Santos et al.
proposed that the higher  values displayed a higher diffusivity during study in
comparing the dielectric properties of Sr0.61Ba0.39Nb2O6 and PbMg1/2Nb2/3O6
ceramics [39].
The dielectric constant and dielectric loss as function of temperature with
various frequencies were shown in Fig. 8(a)-(f) for x = 0-0.05, respectively. The
dielectric curves of Li-addition lead-free piezoelectric BNKTCZ ceramics
exhibit broad transition peaks around Td and Tm, which shows the
characteristics of diffuse phase transition. In addition, frequency dispersion
around Td and Tm indicate that Li-addition lead-free piezoelectric BNKTCZ
samples exhibit relaxor characteristics. Our result was in agreement with
report of Samara for the relaxational properties of compositionally disordered
ABO3 perovskites [40]. Setter et al. reported that diffused phase transition of
Pb(Sc0.5Ta0.5)O3 ceramics system is considered due to random distribution of

Sc3+ and Ta5+ cations at B-site [41]. Rahman et al. reported that the observed
frequency dependent of the BaZrO3-modified 0.935Bi0.5Na0.5TiO3–0.065BaTiO3
ceramics dispersed diffuseness at Tm could be attributed to the disordering of
A- as well as B-sites cations [42]. Zheng et al. reported that the observation the
frequency dispersion is considered due to random distribution of La3+ and
Ba2+ at A-site in La-modified Bi0.5Na0.5TiO3-BaTiO3 ceramics [43]. Yang et al.
reported that the coexistence of Na+, K+, Li+ and Bi3+ disordering at A-site
causes the reason for observation of the relation behavior [44]. This is in
9


accordance with the results of Fig. 2 where the multisite dopant occurred in Limodified BNKT-based ferroelectric materials.
Fig. 9 (a) shows the polarization-electric field (P-E) hysteresis loops of BNKTCZ-xLi
ceramics at room temperature. All samples exhibited P-E hysteresis loops at room
temperature indicated that all specimens were typical ferroelectric materials. The
effective of Li concentration dopants to maximum polarization (Pm), remnant
polarization (Pr) and coercive field (EC) showed in Fig. 9 (b). The both Pm and Pr
values were found to be decease from

49.7 C/cm2 to 27.1 C/cm2, and 22.9

C/cm2 to 5.4 C/cm2, respectively, as the Li amount increased from 0 to 5 mol%. In
addition, the HC values were also obtained to significantly decrease from 1.7 to 0.9
kV/mm within the corresponding composition range. Recently, the reduction of Pm
and Pr values were widely reported in BNKT-modified with Zr, Y, Nb etc. cause of
phase transition from polar to non-polar via dopants and/or promotion via oxygen
vacancies [4-10]. As we mentioned above that the origin of phase transitions were
still debated. However, our results indicated that no phase transition existed. There
were instated by distorted structure when Li added BNKTCZ ceramics. Thomas et al.
reported that the manifestation of ferroelectric properties in ABO3-perovskite were

strongly relative with the BO6 oxygen octahedral [32]. Therefore, the degree of the
coupling between neighboring BO6 octahedral will be significantly weakened by
introducing defects that acts to break the translational invariance of polarization,
result in a decrease in the coupling of ferroelectrically active BO6 octahedral [32, 34,
45, 46]. Grinberg et al. predicted that the B-cation displacement was highest in case
of Ti which were expected for strong ferroelectric activation [47]. Moreover, Yuan et
al. reported that both A-site and B-site vacancies decreased the degree of coupling
between dipoles in ABO3-type perovskite resulting in reduced the coupling of
10


ferroelectricly active BO6 octahedra, moreover, the effect of A-site vacancies on the
decoupling of BO6 octahedral was more significant than that of B-site vacancies [48].
Our result showed that the structure was distorted when the Li + content added and
the multisite were occurred. Therefore, the vacancy was created when Li+ filled to
Ti4+-site possible and resulted in rapidly decreasing both Pm and Pr values. This
results were consisted with our recently reported for Li-modified BNKT-based
materials [26].
Fig. 10 (a) shows the bipolar electric-field-induced strain curves of the BNKTCZ-xLi
ceramics. All the ceramics showed butterfly-shaped curves that are distinct features
of ferroelectric materials. The effect of Li-doped BNKTCZ on the maximum strain
(Smax) and negative strain (Sneg) values as a function of Li addition showed in Fig. 10
(b). The Li-undoped BNKTCZ exhibited a butterfly-shaped curve with a Smax of
0.21% and Sneg of 0.15%. Noted that the negative strain denoted the difference
between zero field strain and the lowest strain [13]. The Li-added BNKTCZ displayed
increased Smax values up to 0.34% at 2 mol% then decreased to 0.15% at 5 mol%.
In addition, the Sneg values slightly increased to 0.17% at 1 mol% then gradually
decreased to 0.004% which corresponded to 5 mol% Li-added BNKTCZ. The
estimation of Smax/Emax values was 350 pm/V and 567 pm/V for undoped and 2 mol%
Li-added BNKTCZ ceramics specimen, respectively. The results were solid evident

for enhancement of electrical induced strain in lead-free BNKTCZ via Li-addition.
The maximum Smax/Emax value was 567 pm/V which was higher than that of pure
BNKT ceramics with Smax/Emax around 230 pm/V or only CZ-modified BNKT with
Smax/Emax value around 500 pm/V as reported by Hong et al. [17, 49]. Our
observation was consisted with recently reported for Li-doped BNKT-modified with Zr
[26]. Moreover, the observation maximum Smax/Emax values were presented in
11


comparison with previously reported for lead-free piezoelectric BNKT-based
materials, as shown in Fig. 11. Our results indicated that Li-modified BNKTCZ
ceramics resulted in enhancement of Smax/Emax values which overcome the pure
BNKT [49] or Cu-[50], Y-[6], Zn-[51], Hf-[7] and (Cu,Nb)-[49] modified BNKT
ceramics. However, the Smax/Emax values were smaller than that single element Zr[8], Sn-[19], La-[4], Nb-[52], Ta-[5], or co-doped-(Li,Sn)-[10], (Li,Ta)-[9] modified
BNKT ceramics materials.
VI. Conclusion
The distorted structures of the BNKTCZ ceramics samples were happened when Li
amount was added up to 5 mol%. The multisite Li ions occurred was observation.
The band gap values decreased with increasing Li concentration. The both
maximum polarization and remanent polarization values was reduced from 49.66
C/cm2 to 27.11 C/cm2 and from 22.93 C/cm2 to 5.35 C/cm2 respectively as Li
concentration increased from 0 to 5 mol%. The maximum Smax/Emax value was
enhancement up to 567 pm/V. We expected this work will help to understand the role
of A-site dopant in lead-free ferroelectric BNKT materials.
Acknowledgments
This work was financially supported by the Ministry of Education and Training,
Vietnam, under project number B 2013.01.55.
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Figure captions

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Fig. 1. (color online) X-ray diffraction pattern of Li-addition lead-free BNKTCZ
ceramics as a function of Li doping level x.
Fig. 2. (color online) The magnified XRD patterns in the 2 ranges of (a) 39.0–41.0
and (b) 44.0-48.0.
Fig. 3. FE-SEM images of the Li-modified BNKTCZ ceramics with (a) x=0.00,
(b) x=0.02, (c) x=0.04, (d) x=0.06, (e) x=0.08 and (f) x=0.10.
Fig. 4. (color online) (a) UV-vis absorption spectra of the BNKTCZ ceramics, and (b)
the dependence of (αh)2 on h of the BNKTCZ ceramics as function of Li
concentration addition. The inset of Fig. 4(b) shows the band gap Eg of the BNKTCZ
ceramics as function of Li-addition.
Fig. 5. (color online) (a) Relative dielectric constants at a frequency of 1 kHz of
BNKTCZ-xLi ceramics as a function of temperature, and (b) variations of Td and Tm
with different amount of Li+ cations additive for the lead-free piezoelectric BNKTCZ
ceramics at 1 kHz. The red line indicated the linear fitting.
Fig. 6. (color online) The ln[(m-)/] as a function of ln(T-Tm) at the frequencies of 1
kHz for Li-addition lead-free piezoelectric BNKTCZ ceramics at (a) x= 0, (b) x=0.02,
(c) x=0.04, and (d) x=0.05.

Fig. 7. (color online) Effects of doping level on the diffuse () and the diffuseness
degree ().
Fig. 8. (color online) The temperature dependence of dielectric constant and
dielectric loss for lead-free BNKTCZ-xLi ceramics at (a) x= 0, (b) x=0.01, (c)
x=0.02, (d) x=0.03, (e) x=0.04 and (d) x=0.05.
17


Fig. 9. (color online) (a) Room temperature P–E hysteresis loops of the BNKTCZ–xLi
ceramics as a function of x mol% Li+ ions content, and (b) effects of doping level on
the maximum polarization (Pm), the remnant polarization (Pr), and coercive field (EC).
Fig.10. (color online) (a) Bipolar strain hysteresis loops of Li doped BNKTCZ
ceramics, (b) the Smax and Sneg values as a function of Li addition.
Fig.11. (color online) Role of various dopant in electric-field-induced strain in BNKTbased ceramics pure BNKT [45], Cu-[46], Y-[6], Zn-[47], Hf-[7], (Cu,Nb)-[45], Zr-[8],
Sn-[19], La-[4], Nb-[48], Ta-[5], (Li,Sn)-[10], and (Li,Ta)-[9].

Quyet et al. Fig. 1

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Quyet et al. Fig. 2

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Quyet et al. Fig. 3
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Quyet et al. Fig. 4

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Quyet et al. Fig. 5

Quyet et al. Fig. 6

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Quyet et al. Fig. 7

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Quyet et al. Fig. 8

Quyet et al. Fig. 9

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