Accepted Manuscript

Structure, piezoelectric, dielectric and ferroelectric properties of lead-free (1-x)

(Ba0.85Ca0.15)(Ti0.93Zr0.07)O3-x(Bi0.5K0.5)TiO3 ceramics

Enpei Cai, Qibin Liu, Shunlong Zhou, Yizhi Zhu, An Xue

PII: S0925-8388(17)32811-6
DOI: 10.1016/j.jallcom.2017.08.083
Reference: JALCOM 42840

To appear in: Journal of Alloys and Compounds

Received Date: 22 January 2017

Revised Date: 14 July 2017
Accepted Date: 10 August 2017

Please cite this article as: E. Cai, Q. Liu, S. Zhou, Y. Zhu, A. Xue, Structure, piezoelectric, dielectric and
ferroelectric properties of lead-free (1-x)(Ba0.85Ca0.15)(Ti0.93Zr0.07)O3-x(Bi0.5K0.5)TiO3 ceramics,
Journal of Alloys and Compounds (2017), doi: 10.1016/j.jallcom.2017.08.083.

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 ACCEPTED MANUSCRIPT

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 ACCEPTED MANUSCRIPT

Structure, piezoelectric, dielectric and ferroelectric properties

of lead-free (1-x)(Ba0.85Ca0.15)(Ti0.93Zr0.07)O3-x(Bi0.5K0.5)TiO3

ceramics
Enpei Caia, Qibin Liua,b,§, Shunlong Zhoua, Yizhi Zhua, An Xuea

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a
College of Materials and Metallurgy, Guizhou University, Guiyang 550025, Guizhou, P.R. China
b
Key Laboratory for material structure and strength of Guizhou province, Guiyang 550025, Guizhou, P.R.
China

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§
Corresponding author. Tel.:+86 136 0855 3484, Address: College of Materials and Metallurgy, Guizhou
University, Guiyang 550025, P.R. China
E-mail address: qbliugzu@163.com (Qibin Liu), caienpei@139.com (Enpei Cai)

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Abstract: Lead free solid solution ceramics (1-x)(Ba0.85Ca0.15)(Ti0.93Zr0.07)O3 -
x(Bi0.5K0.5)TiO3 [(1-x)BCZT–xBKT, x = 0, 0.02, 0.04, 0.06, 0.08 mol%] were
fabricated by the traditional solid-state reaction technique. The crystalline

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phase was confirmed by X-ray diffraction (XRD) patterns and Raman spectra,
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the results show that a pure ABO3 perovskite structure was obtained in all of
these samples, suggesting that BKT diffused into BCZT to form a solid solution.
The microstructure and crystal structure were investigated by thermal field
emission scanning electron microscopy (TFESEM) and field emission
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transmission electron microscopy (FETEM) respectively. The results show that

all of these samples exhibited relatively higher density structure. Monocrystal
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and polycrystal coexistence structure was obtained in BKT doped ceramics at

room temperature. In addition, the piezoelectric, dielectric and ferroelectric
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properties were systematically studied. The ceramic with x = 0.04 mol% BKT
demonstrates good properties: d33 = 162 pC/N, Tc = 103.1 , kp = 46.2%, εr =
2,390, tanδ = 1.5%, Pr = 9.33 µC/cm2, Ec = 0.80 kV/mm.
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Keywords: Lead-free ceramics; (Ba,Ca)(Zr,Ti)O3-(Bi,K)TiO3; Structure;

Piezoelectric property; Dielectric property; Ferroelectric property
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1. Introduction
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Piezoelectric ceramics as a smart material have become essential for modern

society, especially in the fields of information and communications, industrial
automation, medical diagnostics, etc. For more than half a century, Pb-based
piezoelectrics are the piezoelectric ceramics with the most application[1,2].
Lead zirconate titanate (PZT) piezoelectric ceramics are the most widely used
piezoelectric materials due to their superior piezoelectric properties close to
the morphotropic phase boundary (MPB) between rhombohedral and
tetragonal phases[3,4]. However, the toxicity of lead is a serious threat to human
health and environment[5,6]. Therefore, the development of lead-free
piezoelectric ceramics has become one of worldwide materials topics as they

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represent an environmentally friendly alternative to the PZT-based
ceramics[3,5,7].
Over the past few years, extensive studies on lead-free materials, including
the perovskites barium titanate BaTiO3 (BT)-based ceramics, bismuth sodium
titanate (Na0.5Bi0.5)TiO3 (NBT)-based ceramics, potassium sodium niobate
(K0.5Na0.5)NbO3 (KNN)-based ceramics and their various modified solid
solutions, have been investigated[5]. Although much considerable efforts have
been conducted to improve their piezoelectric properties, their piezoelectric

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constant is still lower (d33 = 200~400 pC/N) than PZT. The newly discovered
lead-free BCZT ceramics by Liu and Ren[8] have attracted extensive attention
due to its excellent piezoelectric properties with d33 = 500~620 pC/N[9-14].

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However, its measured Tc was only 85 and this low Tc prevented its
piezoelectric application. Therefore, it’s urgent to increase the Tc to meet the
practical application.

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Recently, many solid solutions of BaTiO3 with Bi-based compounds have
attracted attention due to environmental protection issues and have been
investigated, such as BaTiO3-BiScO3[15,16], BiScO3-Bi(Zn0.5Ti0.5)O3-BaTiO3[17]

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and (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3-(Bi0.5Mg0.5)TiO3[18] system etc. However, there is
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no report on the (1-x)(Ba0.85Ca0.15)(Ti0.93Zr0.07)O3-x(Bi0.5K0.5)TiO3 solid solution
ceramics. Considering the higher Tc (~ 380 ) of BKT ceramics, our research
group put forward a bold vision that combine the BCZT with BKT to improve
the electrical properties. In this paper, the (1-x)(Ba0.85Ca0.15)(Ti0.93Zr0.07)O3
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-x(Bi0.5K0.5)TiO3 solid solution ceramics were designed and fabricated. The

structure, piezoelectric, dielectric and ferroelectric properties have been
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investigated systematically.
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2. Experimental procedure

The (1-x)(Ba0.85Ca0.15)(Ti0.93Zr0.07)O3-x(Bi0.5K0.5)TiO3 solid solution ceramics

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with x = 0, 0.02, 0.04, 0.04, 0.08 mol% were prepared by conventional ceramic
processing route, where the powders were firstly synthesized at 1,200 ≦for
4h by a solid-state reaction method. The oxides and carbonates of the
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respective elements are BaCO3 ( ≦99.0%, AR), CaCO3 ( ≦99.0%, AR), ZrO2
( ≦99.0%, AR), TiO2 ( ≦99.0%, AR), Bi2O3 (≧ 99.0%, AR), K2CO3 ( ≦99.0%,
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AR) were used as raw materials, ethanol ( ≦99.7%, AR) was used as medium
in this work and x is the mole percentage of BKT. After the calcination, the
powders were ball milled for another 16h to enhance the compositional
homogenization. The resulting powders were then pressed into disks of 12 mm
in diameter and 1 mm in thickness under 30 MPa. Such pellets were sintered
at 1,280 ≦in air for 3h.
The crystalline phase of the ceramics were characterized by X-ray diffraction
(XPERT-PRO, Holland PANAlytical Co., Ltd.) using a Cu-Kα≦radiation (λ =
1.5406Å). The molecular structure was confirmed by laser microscopic
confocal Raman spectrometer (LadRAM HR Evoluion, France HORIBAJobin

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Yvon). The morphologies of the sintered ceramics were observed using
TFESEM (SUPRA 40, German Zeiss Co., Ltd.). The crystal structure was
characterized by FETEM (Tecnai G2 F20, FEI Co., Ltd.).
For measuring electrical properties, silver paste was coated on both
polished surfaces of the sintered samples and fired at 750 for 30 min to form
Ag electrodes. Specimens for piezoelectric measurements were polarized at
room temperature in a silicone oil bath by applying a direct current electric field
of 3~4 kV/mm for 20~30 min. Piezoelectric properties were measured after

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laying the polarized specimens for 24h to release the remnant stress and
charge. Piezoelectric coefficient (d33) values were measured by a quasi-static
d33 meter (ZJ-3AN, Institute of acoustics, Chinese Academy of Sciences). The

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planar electromechanical coupling factor (kp) was determined by a resonance
antiresonance method by means of an impedance analyzer (HP4294,
American Agilent Co., Ltd.). Temperature dependence of dielectric constant (ɛr)

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and dielectric loss (tanδ) of the unpolarized samples were measured at 100Hz,
1kHz, 10kHz, 100kHz and 1MHz using an LCR meter (TH2618B, Guangzhou
Zhuo Yue electronic instrument and Equipment Co., Ltd.) from 0 to 325℃.

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Ferroelectric hysteresis loops (P-E) were measured at 1kV, 1.5kV, 2kV, 2.5kV,
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3kV, 3.5kV, 4kV by a ferroelectric tester (RT66A; Radiant Technologies Inc.,
Albuquerque, NM).

3. Results and discussion

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3.1 XRD patterns and Raman spectra

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Fig.1.1(a) shows the XRD patterns of (1-x)BCZT-xBKT (x = 0, 0.02, 0.04, 0.06,

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0.08 mol%) solid solution ceramics measured at room temperature. The XRD
patterns are analyzed by the software of PANalytical HighScore and OriginPro
9. It can be seen that all the ceramics with different compositions possess a
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pure perovskite structure with no detectable second phase within the

instrument's resolution limit, indicating that BKT have diffused into the BCZT
lattices to form a homogeneous solid solution. Therefore, the BKT doped
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BCZT ceramics exhibit a pure perovskite phase and the introduction of BKT
cannot change the crystal structure of BCZT ceramics. Fig.1.1(b) shows the
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partial enlarged XRD patterns of the (1-x)BCZT-xBKT ceramics in the 2θ range

of 44°~47°. It can be seen that the ceramics at x = 0 mol% present
rhombohedral phase, which is characterized by a single peak of (002)/(200)
reflection at around 2θ of 45°. With increasing BKT content, the diffracti on
peaks of (1-x)BCZT-xBKT ceramics exhibit tetragonal (P4mm) structure with
obvious splitting of the (002)/(200) peaks at 2θ of 45°. The existence of
tetragonal phase was confirmed by the splitting of the (002)/(200) peaks at 2θ
of 45°[8,19] and rietveld XRD pattern of (1-x)(BCZT)-xBKT ceramics with x =
0.04 mol% in Fig.1.2. It can be seen from Fig.1.2 that the main composition is
tetragonal phase (98.97%), containing a small amount of rutile phase (1.03%).

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Moreover, it is observed that the XRD peak position is shifted slightly to higher
angle with increasing the BKT content from x = 0~0.04 mol%. However, the
XRD peak position almost not shift to higher angles with further increasing BKT
contents from 0.04 to 0.08 mol%. It is expected from the tolerance factors[20]
that small ions (r(Rn+) < 0.87Å) occupy the B site, large ions (r(Rn+) > 0.94Å)
occupy the A site, and intermediate ions (0.87Å < r(Rn+) < 0.94Å) occupy both
sites with different portioning for each ion. Taking Bi3+ (r = 1.03 Å), K+ (r = 1.38
Å), Ba2+(r = 1.35Å), Ca2+(r = 1Å), Zr4+(r = 0.72Å), Ti4+(r = 0.605Å) into

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consideration, it is concluded that Bi3+ and K+ occupy A site ((Ba,Ca)2+ site),
which results in a change for the lattice parameter and cationic vacancies (A
vacancies) which promotes sintering and reduces sintering temperature.

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These results confirm that the Bi3+ and K+ partially enter the A site in the lattice
and induce the shrinkage of crystal lattice and decrease crystalline interplanar
spacing, which make the peaks shift to higher angles when x ≦ 0.04 mol%.

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While with further increasing BKT contents from 0.04 to 0.08 mol%, the
process of Bi3+ and K+ enter the A site ((Ba,Ca)2+ site) has reached saturated
state. The rest of the Bi3+ and K+ occupy B site ((Ti,Zr)4+ site) and induce the

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expansion of crystal lattice, which make the lattice contraction mentioned
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previously counteract each other. So the XRD peak position can’t continue
shifting to higher angles.

To further confirm the phase structure of BKT-modified BCTZ ceramics, their

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Raman spectra were measured in the range of 100~2,000 cm-1, which are
shown in Fig.2(a) and (b). The Raman spectra are plotted by the software of
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OriginPro 9. The cubic BaTiO3 with Pm3m symmetry has four triply degenerate
optical vibration modes (3F1u + F2u). In the tetragonal BaTiO3 with P4mm
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symmetry, the optical vibration modes of 3F1u split into 3 (A1 + E) modes, and
F2u into (B1 + E) mode. Each of the A1 and E modes splits further into
transverse (TO) and longitudinal (LO) components due to the presence of
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long-range electrostatic force[21]. Consequently, the distinct Raman active

optical vibration modes for barium titanate are 3A1(TO) + 3A1(LO) + 3E(LO)
+1E(LO + TO) + 1B1[22,23]. At 298 K, a weak E(TO) mode at 175 cm−1
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combining with an A1(TO1) mode at 238 cm−1, an A1(TO2) mode at 294 cm−1,
an A1(TO3) mode at 527 cm−1 and an A1(LO3)/E(LO3) mode at 735 cm−1
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indicates the existence of tetragonal BaTiO3[24]. Moreover, The tetragonal

structure of BaTiO3-based materials could be also confirmed by the E(TO)
phonon mode[24]. Therefore, the micro-Raman scattering spectra further
confirm the formation of a tetragonal phase in the BKT doped ceramics.

3.2 TFESEM micrographs and FETEM images

The TFESEM micrographs of the free surface of (1-x)BCZT–xBKT solid

solution ceramics with different BKT contents are shown in Fig.3(a)~(e). It is
clear that the average grain size of BKT-modified BCZT ceramics slightly

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decreases firstly, then increases, then decreases and finally increases again
with the introduction of BKT contents and reaches its best size at x = 0.04
mol%. The growth of the grains leads to the homogeneous and uniform
microstructure. The Bi3+ and K+ substitution into the (Ba,Ca)2+ site (A site)
results in the generation of cationic vacancy (A vacancy). It is believed that the
presence of A vacancy helps the mass transport in the ceramics during the
sintering process, which is responsible for the enhanced grain growth with a
small amount of BKT content. When x increasing from 0 to 0.02 mol%, the

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substitution into A site of a small amount of Bi3+ and K+ can’t generate enough
A vacancy. So the grain size decreases firstly. With x increasing from 0.02 to
0.04 mol%, the substitution into A site of Bi3+ and K+ generate enough A

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vacancy, which leads to the grain size increase. Moreover, with continuing to
add the BKT content, the grain size becomes not uniformity and small.
However, when x increasing to 0.08 mol%, the grain size increases again.

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Furthermore, many small grains which don’t fully grow appear. This is because
the BKT and BCZT base compositions are a limited solid solution. With the
development of the sintering process, the correction of lattice defects reduces

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the solubility of BKT. The additive of the BKT makes the solid solution
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precipitate at grain boundary, which plays an important role in inhibiting the
grain growth. In addition, it is observed that the ceramics at higher BKT content
x = 0.06 mol% and x = 0.08 mol% become porous, suggesting that excess
BKT doping degrades the sintering performance of the ceramics, and thus
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results in the significant decrease in densification. This suggested that a

reasonable addition of BKT contents to BCZT solid solution ceramics can
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modify the grain size of the samples.

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Fig.4 a~d exhibits TEM images of the (1-x)BCZT–xBKT solid solution ceramics
with different BKT contents. The TEM images are analyzed by the software of
Gatan DigitalMicrograph. a1, b1, c1 and d1 are the surface morphology of the
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powder samples, respectively. a2 and a3 ,b2 and b3, c2 and c3, d2 and d3 are the
diffraction diagrams of A and B area in a1, C and D area in b1, E and F area in
c1, G and H area in d1, respectively. Figure a2 is a simple order of electron
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diffraction pattern, which confirms A area is a single crystal with ordered phase.
Figure a3 is a discursive disorder of diffraction spots pattern, which confirms B
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area is a polycrystalline structure with disordered phase. Figure b2 presents

some messy loose spots but some diffraction rings loom, which confirms C
area is a polycrystalline structure with disordered phase. Figure b3 is a kind of
superlattice electron diffraction patterns which along the [101] direction with
twice times cycle, complex and ordered spots. This structure is evolved from
the single crystal electron diffraction patterns which appears six times period in
the direction of [111]p of ordered perovskite. It confirms D area is electron
diffraction patterns of ordered phase, which is consistent with the results of
XRD in Fig.1.1. c2 and c3 present some sloppy mess of diffraction spots, which
confirm both E and F area are electron diffraction patterns of disordered phase.

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d2 demonstrates some sloppy mess of diffraction spots, but some diffraction
rings loom, which confirms G area is a polycrystalline structure with disordered
phase. d3 presents some sloppy mess of diffraction spots, which confirms that
H area is a polycrystalline structure with disordered phase. In addition, a4, b4,
c4 and d4 are the high resolution transmission electron microscopy (HRTEM)
images of the dotted ellipse area of A, C, E and G, respectively. It can be seen
that some lattice fringes arrange regularly in a4, b4, c4 and d4. Moreover, a42,
b42, c42 and d42 are the reduced FFT images of a4, b4, c4 and d4, respectively.

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a42 demonstrates a simple order of electron diffraction pattern, which confirms
A area is a single crystal with ordered phase. b42 presents some messy loose
spots, but some diffraction rings loom, which confirms C area is a

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polycrystalline structure with disordered phase. c42 shows some sloppy mess
of diffraction spots, which confirms E area is a polycrystalline structure with
disordered phase. d42 exhibits some sloppy mess of diffraction spots but some

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diffraction rings loom, which confirms G area is a polycrystalline structure with
disordered phase. These results are consistent with a2, b2, c2 and d2.
Furthermore, a41, b41, c41 and d41 are the inverse fast Fourier transformation

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(IFFT) images in the selected dotted square area of the a4, b4, c4 and d4
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images, respectively. It is expanded 2 times than a4, b4, c4 and d4. It can be
known from a41, b41, c41 and d41 that the crystal plane spacing d1 = 4.05Å, d2 =
2.86Å, d3 = 4.01Å and d4 = 2.88Å, respectively.
According to the above statements, it can be known that BKT doped solid
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solution ceramics exhibit single crystal and polycrystalline structure

simultaneously at different content of BKT samples. Nevertheless, they still
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belong to ABO3 perovskite structure.

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3.3 The temperature dependence of the dielectric constant (ɛr) and dielectric
loss (tanδ)
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Fig.5 exhibits ɛr and tanδ of (1-x)BCZT-xBKT solid solution ceramics as a

function of T with different BKT contents at 100Hz, 1kHz, 10kHz, 100kHz and
1MHz within the temperature range of 0~325 . All samples showed a single
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ferroelectric tetragonal-paraelectric cubic phase transition peak, corresponding

to the Curie temperature (Tc). It can be observed that the maximum dielectric
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constant ɛm decreases with increasing frequencies, which indicates lead-free

(1-x)BCZT-xBKT ceramics are relaxor ferroelectrics. In addition, the frequency
dispersion of the dielectric constant and dielectric loss of (1-x)BCZT–xBKT
solid solution ceramics could be obviously observed, suggesting a relaxation
characterization. Interestingly, dielectric constant ɛr first increased then
decreased from low to high temperature. In contrast, dielectric loss tanδ first
decreased then increased at the low frequency of 100Hz and 1kHz. With
further increasing frequency (10k, 100k and 1MHz), dielectric loss tanδ first
decreased then almost kept a constant at high temperature (200~325 ). The
dielectric loss tanδ of all the ceramics were lower ( 0.8). The typical

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ferroelectric materials follow the Curie-Weiss law above the Curie temperature
and can be determined by equation (I)[26]:

εr =
C
(I)
T −Tc
where εr is the dielectric constant, Tc is the Curie temperature and C is the
Curie-Weiss constant. The plots of temperature dependence on the reciprocal
of dielectric constant according to the Curie-Weiss law (I) are shown in

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Fig.6(a)~(e). It can be seen that Tc value initially decreased, then increased,
then decreased and increased slightly again with the BKT content, reached a
maximum value at x = 0.04 mol%. The change in Tc value may be attributed to

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the microstructure of the samples, which is consistent with the results of SEM
in Fig.3. The Curie-Weiss constant C is approximately 106 (> 107) in magnitude,
indicating the relaxor ferroelectric characteristic of these ceramics with

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different BKT contents[27]. Moreover, the deviation ∆T from the Curie-Weiss
law is defined by equation (II)[26,28]:

∆T = TCW − TC

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(II)
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where ∆T is the deviation, TCW is the Curie-Weiss temperature, Tc is the Curie
temperature. The fitted values of Tcw according to the Eq.(II) are shown in
Fig.6(a)~(e) and Tab.1. The values of ∆T varied with the addition of BKT
content. This phenomenon is associated with a variety in the relaxor behavior
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when BKT was dissolved into the BCZT ceramics.

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The dielectric behavior of (1-x)BCZT-xBKT ceramic systems was further

elucidated by describing the dielectric constant of a second-order relaxor
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ferroelectric by the simple quadratic law (III)[29-31].

(T − TC )γ
− =
1 1
(III)
εr εm
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where εm is the maximum value of the dielectric constant at the phase
transition temperature Tc, and γ (1 ≦γ ≦2) is the degree of the diffuseness
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of the phase transition. γ is a constant. At γ = 1, a normal Curie–Weiss behavior

is observed. 1 < γ < 2 indicates that the material is relaxor ferroelectric. While γ
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= 2 implies that the material is a complete diffuse phase transition material. A

fitting curve of ln(1/ε–1/εm) as a function of ln(T–Tm) is shown in Fig.7(a)~(e) for
the (1-x)BCZT-xBKT ceramics. The fitted lines conform to the equation y = A +
Bx. The fitted values of A and B according to the Eq.(III) are shown in Tab.1.
And the values of γ are presented in Tab.1 also. The diffuseness γ values
depended on the BKT content. Moreover, given that the values of γ were
between 1 and 2, the ceramics did not have normal Curie–Weiss type phase
transformation but they exhibited the characteristic of a relaxor behavior.
Obviously, it can be noted that γ of x = 0.04 mol% is much lower than other
samples. γ can be used as a sign of the dispersivity of phase transformation,

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and it has definite physical meaning by means of gamma. The larger the
gamma value is, the wider the temperature distribution of the phase transition
temperature of each micro region is, so the dispersion is stronger. Small
gamma means that the degree of dispersion is small, that is to say the degree
of relaxation is minimum. It may be attributed to the substitution of Bi3+ and K+
in A-site and B-site for BCZT ceramics, which leads to increasement of cation
disorder [19]. It is anticipated that the substitution of these cations would create
isolated clusters of polar nano-regions (PNRs) with only weak coupling

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between the neighboring clusters, leading to difficulties in the establishment of
long-range dipole formation[21]. The deviation in the relaxor behavior from the
Curie–Weiss type can be assumed to be caused by the distortion of crystal

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lattice, which is corresponding to the XRD results in Fig.1.1[32].

3.4 The ferroelectric hysteresis loops (P-E)

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Fig.8(a) shows the P-E hysteresis loops of (1-x)BCZT-xBKT ceramics sintered
at 1,280 ≦with different BKT contents,≦measured at 4kV, 1Hz and room

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temperature.≦It can be seen that all the samples present a typical square
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ferroelectric polarization hysteresis loop with relatively high remnant
polarization and low coercive field, demonstrating that good ferroelectric
properties are obtained in the (1-x)BCZT-xBKT ceramics. Moreover, from the
insert we can know that the P-E loops appear non symmetrical distribution
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centered on the original point and slightly offset to the positive direction of the x
axis, which indicate the formation of internal bias field. The variations in
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remnant polarization Pr and coercive field Ec as a function of x are presented in

Fig.8(b). The remnant polarization of BCZT ceramics is greatly influenced by
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the amount of BKT. With increasing BKT contents from 0 to 0.02 mol%, Pr and
Ec of (1-x)BCZT-xBKT ceramics increase gradually and reach their maximum
values Pr = 13.21 µC/cm2 and Ec = 1.01 kV/mm at x = 0.02 mol%, respectively.
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With continue increasing BKT contents, Pr and Ec decrease and reach their
minimum values Pr = 3.87 µC/cm2 and Ec = 0.63 kV/mm at x = 0.06 mol%,
respectively. However, with further increasing BKT contents, Pr and Ec
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increase again and reach their values of Pr = 7.40 µC/cm2 and Ec = 0.84
kV/mm at x = 0.08 mol% respectively, which are lower than the values of Pr
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and Ec at x = 0.02 and 0.04 mol%. This behaviour may be related to the motion
of ferroelectric domain in ceramics. With the introduction of BKT, the remnant
polarization Pr and coercive field EC of ceramics firstly increase, then decrease
and finally increase, indicating the switching of 180 degree ferroelectric
domain in ceramics under external electric fields firstly becomes easy, then
difficult and finally easy. In addition, the degree of difficulty in ferroelectric
domain deflection has a great relationship on the the grain size. It is believed
that the variation trend of the 180 degree ferroelectric domain reflection is
consistent with the change of grain size. The larger the grain size is, the easier
the ferroelectric domain is to deflect and the remnant polarization Pr larger is;

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the smaller the grain size is, the harder the ferroelectric domain is to deflect
and the remnant polarization Pr smaller is. However, it appears an anomalous
case that the remnant polarization Pr of sample at 0.02mol% is larger than that
of 0.04mol%. It may be that A vacancies and defects[33,34] of specimen at
0.02mol% are less than that of 0.04mol%. Because A vacancies and defects
will restrain domain movement by screening the polarisation charge. Under the
combined influence of grain size, A vacancies and defects, the 180 degree
ferroelectric domain reflection of sample at x = 0.02 mol% is more easier than

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that of 0.04mol%. Therefore, the largest remnant polarization Pr occur in x =
0.02 mol% sample but not that of 0.04 mol%. Furthermore, the decrease of Pr
make deflection of non 180 degrees domain in ceramics easier under external

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electric field. In contrast, the increase of Pr make deflection of non 180 degrees
domain in ceramics harder under external electric field. These results are
corresponding to the results of SEM in Fig.3.

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3.5 The value of various parameters

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Fig.9(a) presents the variations in d33 and the planar electromechanical
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coupling coefficient kp as a function of the BKT content x and (b) depicts the
variations in dielectric constant εr and Curie temperature Tc as a function of the
BKT content x. Tab.2 shows the electrical properties of (1-x)BCZT-xBKT
ceramics as a function of BKT content. The (1-x)BCZT-xBKT ceramics show a
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strong composition dependence of the electrical properties. By adding a small

amount of BKT, d33, kp and Tc of BCZT-BKT ceramics decreased firstly, then
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increased, then decreased and finally increased again. ɛr decreased firstly

then increased. Pr, Ec and tanδ increased firstly, then decreased and increased
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again finally. With increasing x to 0.04 mol%, both d33, kp and Tc reached their
maximum values of 162 pC/N, 46.2% and 103.1 . However, ɛr, tanδ, Pr and Ec
decreased. Their values were 2,390, 1.5%, 9.33 µC/cm2, 0.80 kV/mm,
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respectively. The highest d33 (162 pC/N) of BCZT-BKT ceramics should be

attributed to the large grain size and the relative high Curie temperature.
However, with continuing to add BKT content, ɛr monotonously increased while
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d33, kp, tanδ, Tc, Pr and Ec firstly degraded and then increased. This is because
the grain size at x = 0.06 and 0.08 mol% is smaller than that of 0.04 mol%,
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which leads to the monotonous increase of ɛr. Grain size firstly decreases then
increases but pores and defects firstly increase then decrease with further
increasing BKT from 0.06 mol% to 0.08 mol%, which lead to d33, kp, Tc, tanδ, Pr
and Ec increase again when x = 0.08 mol%. This result agrees with the result
of SEM in Fig.3.

Tab.3 exhibits a comparison of several key parameters for the analogous

BaTiO3-based ceramic systems. It can be known that (Ba0.85Ca0.15)
(Ti0.93Zr0.07)O3-(Bi0.5K0.5)TiO3 system possess considerable performance
compared with BaTiO3-Bi(Mg2/3Nb1/3)O3, 0.75BiFeO3–0.25BaTiO3, Ba(Zr0.2Ti0.8)

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O3-x(Ba0.7Ca0.3)TiO3 and (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3-(Bi0.5Mg0.5) TiO3 system.
The result demonstrates that (1-x)BCZT-xBKT lead-free solid solution
ceramics is a promising candidate for lead-free piezoelectric materials.

4. Conclusions

The (1-x)BCZT-xBKT (x = 0~0.08 mol%) lead-free solid solution ceramics have

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been synthesized by the conventional solid-state reaction process. A pure
ABO3 perovskite structure could be obtained in all studied compositions. The
BKT free ceramic has rhombohedral phase. The BKT doped ceramics have

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tetragonal phase in the limited range of 0.02 mol% ≦≦x ≦ 0.08 mol%. All of the
BKT doped ceramics exhibit monocrystalline and polycrystalline structure
simultaneously at room temperature. The addition of BKT has a great influence

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on the structure, piezoelectric, dielectric and ferroelectric properties. When x ≦
0.04 mol%, the electrical properties of (1-x)BCZT-xBKT ceramics can be
improved obviously due to the growth of grain. However, when x ≧ 0.04 mol%,

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the electrical properties decrease due to the growth of grain is hindered. The
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0.96mol%BCZT-0.04mol%BKT specimen sintering for 3h at 1,280 obtained
relatively superior electrical properties: d33 = 162 pC/N, Tc = 103.1 , kp =
46.2%, ɛr = 2,390, tanδ = 1.5%, Pr = 9.33 µC/cm2, Ec = 0.80 kV/mm.
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Acknowledgements
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This work was supported by high-level innovative talents plan of Guizhou

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province (No. (2015) 4009) and specialized funds from industry and
information technology department of Guizhou province (No. 2016056).
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References
[1] T.R. Shrout, S. Zhang, Lead-free piezoelectric ceramics: alternatives for
C

PZT[J]. J. Electroceram. 19 (2007) 113-126.

[2] T. Takenaka, H. Nagata, Y. Hiruma, Current developments and prospective
AC

of lead-free piezoelectric ceramics[J]. Jpn. J. Appl. Phys. 47 (2008)

3787-3801.
[3] Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori, T. Homma, T.
Nsagaya, M. Nakamura, Lead-free piezoceramics[J]. Nat. 432 (2004), 84.
[4] E. Hollenstein, M. Davis, D. Damjanovic, N. Setter, Piezoelectric properties
of Li-and Ta-modified (K0.5Na0.5)NbO3 ceramics[J]. Appl. Phys. Lett. 87 (2005):
182905-182905-3.
[5] J. Rödel, W. Jo, K.T.P. Seifert, E.M. Anton, T. Granzow, D. Damjanovic,
Perspective on the development of lead-free piezoceramics[J]. J. Am. Ceram.
Soc. 92 (2009): 1153-1177.

10
 ACCEPTED MANUSCRIPT
[6] Y. Bai, A. Matousek, P. Tofel, V. Bijalwan, B. Nan, H. Hughes, Tim W. Button,
(Ba,Ca)(Zr,Ti)O3 lead-free piezoelectric ceramics-the critical role of processing
on properties[J]. J. Eur. Ceram. Soc. 35 (2015): 3445-3456.
[7] E. Cross, Lead-free at last[J]. Nat. 432 (2004), 24.
[8] W.F. Liu, X.B. Ren, Large Piezoelectric Effect in Pb-Free Ceramics[J]. Phys.
Revi. Lett. 103 (2009): 257602
[9] W. Li, Z. Xu, R. Chu, P. Fu, G. Zang, Piezoelectric and Dielectric Properties
of (Ba1−xCax)(Ti0.95Zr0.05)O3 Lead-Free Ceramics[J]. J. Am. Ceram. Soc. 93

PT
(2010), 2942.
[10] M. Porta, T. Lookman, A. Saxena, Effects of criticality and disorder on
piezoelectric properties of ferroelectrics[J]. J. Phys. 22 (2010), 345902.

RI
[11] W. Li, Z. Xu, R. Chu, P. Fu, G. Zang, High piezoelectric d33 coefficient in
(Ba1−xCax)(Ti0.98Zr0.02)O3 lead-free ceramics with relative high Curie
temperature[J]. Mater. Lett. 64 (2010), 2325.

SC
[12] W. Li, Z. Xu, R. Chu, P. Fu, G. Zang, Polymorphic phase transition and
piezoelectric properties of (Ba1-xCax)(Ti0.9Zr0.1)O3 lead-free ceramics[J]. Phys.
B. 405 (2010) 4513-4516.

U
[13] D.Damjanovic, A morphotropic phase boundary system based on
AN
polarization rotation and polarization extension[J]. Appl. Phys. Lett. 97 (2010),
062906.
[14] S.W. Zhang, H.L. Zhang, B.P. Zhang, S. Yang, Phase-transition behavior
and piezoelectric properties of lead-free (Ba0.95Ca0.05)(Ti1−xZrx)O3 ceramics[J].
M

J. All. Comp. 506 (2010) 131-135.

[15] H. Ogihara, C.A. Randall, S. Trolier-Mc Kinstry, High-energy density
D

capacitors utilizing 0.7BaTiO3–0.3BiScO3 ceramics[J]. J. Am. Ceram. Soc. 92

(2009) 1719–1724.
TE

[16] H. Ogihara, C.A. Randall, S. Trolier-Mc Kinstry, Weakly coupled relaxor

behavior of BaTiO3–BiScO3 ceramics[J]. J. Am. Ceram. Soc. 92 (2009)
110–118.
EP

[17] C.C. Huang, D.P. Cann, X. Tan, N. Vittayakorn, Phase transitions and
ferroelectric properties in BiScO3–Bi(Zn1/2Ti1/2)O3–BaTiO3 solid solutions[J]. J.
Appl. Phys. 102 (2007) 04410.
C

[18] B. Shen, W.F. Bai, J.G. Hao, J.W. Zhai. Dielectric properties and relaxor
behavior of high Curie temperature (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3-Bi(Mg0.5Ti0.5)O3
AC

Lead-free ceramics[J]. J. Ceram. In. 39 (2013) S19-S23.

[19] B.E. Vugmeister, M.D. Glinchuk, Dipole glass and ferroelectricity in
random-site electric dipole systems[J]. Rev. Mod. Phys. 62 (1990) 993-1026.
[20] Y. Tsur, T.D. Dunbar, C.A. Randall, Crystal and Defect Chemistry of Rare
Earth Cations in BaTiO3[J]. J. Electroceram. 7 (2001): 25-34.
[21] P.S. Dobal, R.S. Katiyar, Studies on ferroelectric perovskites and
Bi-layered compounds using micro-Raman spectroscopy[J]. J. Raman
Specrosc. 33 (2002) 405-423.
[22] N. Baskaran, A. Ghule, C. Bhongale, R. Murugan, H. Chang, Phase
transformation studies of ceramic BaTiO3 using thermo-Raman and dielectric

11
 ACCEPTED MANUSCRIPT
constant measurements[J]. J. Appl. Phys. 91 (2002): 10038-10043.
[23] D.V. Uma, M.N. Vaman, N. Ratna, High-pressure Raman studies of
polycrystalline BaTiO3[J]. Phys. Rev. B, 58 (1998): 14256-14260.
[24] G. Yang, Z.X. Yue, T.Y. Sun, J.Q. Zhao, Z.W. Yang, L.T. Li. Investigation of
ferroelectric phase transition for modified barium titanate in multilayer ceramic
capacitors by in situ Raman scattering and dielectric measurement[J]. Appl.
Phys. A. 91 (2008): 119-125.
[25] B.D. Begg, S. Kim, Finnie, E.R. Vance, Raman study of the relationship

PT
between room-temperature tetragonality and the curie point of barium
titanate[J]. J. Am. Ceram. Soc. 79 (1996) 2666-2672.
[26] X. Chao, J. Wang, C. Kang, Z. Li, Z. Yang, Microstructure, electrical

RI
properties, strain and temperature stability of (K,Na,Li)(Nb,Ta)O3 ceramics: the
effect of BiFeO3 additive[J]. J. Ceram. Int. 41 (2015) 12887-12895.
[27] C. Liu, X. Liu, D. Wang, Z. Chen, B. Fang, J. Ding, X. Zhao, H. Xu, H. Luo,

SC
Improving piezoelectric property of BaTiO3-CaTiO3-BaZrO3 lead-free ceramics
by doping[J]. J. Ceram. Int. 40 (2014) 9881–9887.
[28] S. Ye, J. Fuh, L. Lu, Y.L. Chang, J.R. Yang, Structure and properties of

U
hot-pressed lead-free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 piezoelectric ceramics[J].
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RSC Adv. 3 (2013) 20693-20698.
[29] U. Intatha, P. Parjansri, K. Pengpat, G. Rujijanagul, T. Tunkasiri, S.
Eitssayeam, Phase formation, dielectric and ferroelectric properties of Mn, Al
doped BCZT ceramics by molten salt method[J]. Integr. Ferroelectr. 139 (2012)
M

83-91.
[30] K. Uchino, S. Nomura, Critical exponents of the dielectric constants in
D

diffused phase transition crystals[J]. Ferroelectr. Lett. Sect. 44 (1982) 55-61.

[31] S. Mahajan, O.P. Thakur, D.K. Bhattacharya, K. Sreenivas, A comparative
TE

study of Ba0.95Ca0.05Zr0.25Ti0.75O3 relaxor ceramics prepared by conventional

and microwave sintering techniques[J]. Mater. Chem. Phys. 112 (2008)
858-862.
EP

[32] S. Sen, R.N.P. Choudhary, Effect of doping Ca ions on structural and

electrical properties of Ba(Zr0.05Ti0.95)O3 electroceramics[J]. J. Mater. Sci.:
Mater. Electron. 15 (2004) 671-675.
C

[33] Y. Qin, X.Q. Liu, X.M. Chen, Dielectric, ferroelectric and magnetic
properties of Mn-doped LuFeO3 ceramics[J]. J. Appl. Phys. 113 (2013)
AC

044113-1-044113-5.
[34] W. Cai, C. Fu, J. Gao, X. Deng, Effect of Mn doping on the dielectric
properties of BaZr0.2Ti0.8O3 ceramics[J]. J. Mater. Sci.: Mater. Electron. 21
(2010) 317-325.
[35] X. Chen, J. Chen, D. Ma, L. Fang, H. Zhou, et al. Thermally Stable
BaTiO3-Bi(Mg2/3Nb1/3)O3 Solid Solution with High Relative Permittivity in a
Broad Temperature Usage Range[J]. J. Am. Ceram. Soc. 98 (2015) 804-810.
[36] J. Chen, J. Cheng. Enhanced thermal stability of lead-free high
temperature 0.75BiFeO3-0.25BaTiO3 ceramics with excess Bi content[J]. J. All.
Comp. 589 (2014) 115-119.

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Tab.1 The parameters obtained according to the Curie–Weiss Law and Quadratic Law for the
(1-x)BCZT-xBKT ceramics at 1MHz.

Tc/(℃) Tcw/(℃) △T/(℃)

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x/(mol%) A γ(B) C(×10 )

0 100.0 120.8 20.8 -16.07 1.81 10.49

0.02 95.5 110.7 15.2 -15.78 1.79 7.13

0.04 103.1 108.4 5.3 -13.83 1.39 1.01

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0.06 66.8 111.5 44.7 -16.09 1.66 9.69

0.08 76.8 104.5 27.7 -16.01 1.68 9.01

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Tab.2 Electrical properties of (1-x)BCTZ-xBKT ceramics doped with various BKT contents

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x/(mol%) d33/(pC/N) kp/(%) εr tanδ/(%) Tc/(℃) Pr/(µC/cm ） Ec/(kV/mm)

0 153 45.5 4,510 1.7 100.0 3.63 0.32

0.02 120 45.1 2,960 1.8 95.5 13.21 1.01

0.04 162 46.2 2,390 1.5 103.1 9.33 0.80

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0.06 72 43.9 3,270 1.3 66.8 3.87 0.63

0.08 91 44.1 3,660 1.5 76.8 7.40 0.84

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Tab.3 A comparison of several key parameters for the analogous BaTiO3-based ceramic systems

Ceramic system εr Tc/℃ Sintering/℃ Reference

BaTiO3-Bi(Mg2/3Nb1/3)O3 6,800 133 1,250~1,410 35

0.75BiFeO3–0.25BaTiO3 442 508 900~1,000 36

Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 3,060 93 1,450~1,500 8

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(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3-(Bi0.5Mg0.5)TiO3 1,257 218 1,050~1,350 18

(Ba0.85Ca0.15)(Ti0.93Zr0.07)O3-(Bi0.5K0.5)TiO3 2,390 103.1 1,150~1,350 This work

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Fig.1.1.(a) X-ray diffraction patterns of (1-x)BCZT-xBKT ceramics sintered at 1,280 with x = 0~0.08
mol%, (b) partial enlarged drawing for XRD with 2θ range of 44°~47°

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Fig.1.2 Rietveld XRD pattern of (1-x)(BCZT)-xBKT ceramics with x = 0.04 mol%

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Fig.2. Raman spectrums of (1-x)BCZT-xBKT ceramics with x = 0.02, 0.04, 0.06, 0.08 mol% at T = 298K

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Fig.3. SEM surface morphologies of (1-x)BCZT-xBKT ceramics sintered at 1,280℃ with

(a) x = 0 mol%, (b) x = 0.02 mol%, (c) x = 0.04 mol%, (d) x = 0.06 mol%, (e) x = 0.08 mol%.

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Fig.4. TEM images of (1-x)BCZT-xBKT ceramics sintered at 1,280℃ with

(a) x = 0.02 mol%, (b) x = 0.04 mol%, (c) x = 0.06 mol%, (d) x = 0.08 mol%.
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Fig.5. Temperature dependence of dielectric constant and dielectric loss of (1-x)BCZT-xBKT solid
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solution ceramics with different BKT contents measured at various frequencies: (a) x = 0 mol%, (b) x =
0.02 mol%, (c) x = 0.04 mol%, (d) x = 0.06 mol%, (e) x = 0.08 mol%.
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Fig.6. The plots of temperature dependence on the reciprocal of dielectric constant according to the
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Curie-Weiss law (a) x = 0 mol%, (b) x = 0.02 mol%, (c) x = 0.04 mol%, (d) x = 0.06 mol%, (e) x = 0.08
mol%.
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Fig.7. The fitting curves of ln(1/ε-1/εm)-ln(T-Tm) at 1 MHz

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(a) x = 0 mol%, (b) x = 0.02 mol%, (c) x = 0.04 mol%, (d) x = 0.06 mol%, (e) x = 0.08 mol%.
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Fig.8 (a) Polarization–electric field (P–E) hysteresis loops at 4kV and 1Hz for (1-x)BCZT-xBKT ceramics
sintered at 1,280 and the partial enlarged drawing near the original point is presented in the inset. (b)
The variations in remnant polarization Pr and coercive field Ec as a function of the BKT content x.

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Fig.9 (a) The variations in d33 and the planar electromechanical coupling coefficient kp as a function of the
BKT content x. (b) The variations in dielectric constant εr and Curie temperature Tc as a function of the

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BKT content x.

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Highlights

The combination of BCZT with BKT is helpful to improve electrical properties.

Coexistence of monocrystalline and polycrystalline is found in BKT doping

ceramics.

The optimized performance is obtained when BKT doping content is 0.04

mol%.

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(1-x)BCZT-xBKT lead free ceramics exhibit relaxor ferroelectric
characteristics.

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