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Effects of Er3+–doping on dielectric and piezoelectric properties of 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr lead–free ceramics
Accepted Manuscript 3+ Effects of Er –doping on dielectric and piezoelectric properties of 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr lead–free ceramics Yongshang Tian, Shuiyun Li, Yansheng Gong, Dawei Meng, Jipeng Wang, Qiangshan Jing PII:
S0925-8388(16)32873-0
DOI:
10.1016/j.jallcom.2016.09.120
Reference:
JALCOM 38954
To appear in:
Journal of Alloys and Compounds
Received Date: 11 August 2016 Accepted Date: 11 September 2016
3+ Please cite this article as: Y. Tian, S. Li, Y. Gong, D. Meng, J. Wang, Q. Jing, Effects of Er –doping on dielectric and piezoelectric properties of 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr lead– free ceramics, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.09.120. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Effects of Er3+–doping on dielectric and piezoelectric properties of 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr lead–free ceramics
Qiangshan Jing a, b a
College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang
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464000, People’s Republic of China
Henan Province Key Laboratory of Utilization of Non–metallic Mineral in the South of
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b
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Yongshang Tian a, b, *, Shuiyun Li a, Yansheng Gong c, Dawei Meng c, Jipeng Wang c,
Henan, Xinyang 464000, People’s Republic of China c
Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan
* Corresponding author:
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430074, People’s Republic of China
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Yongshang Tian ([email protected])
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College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang 464000, People’s Republic of China Tel. +86–0376–6390603; Fax: +86–0376–6390603.
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ACCEPTED MANUSCRIPT Abstract 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr (x = 0–0.5%) lead–free ceramics were prepared by a modified Pechini polymeric precursor method, and the effects of erbium
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contents (x) on the crystal structure, dielectric and piezoelectric properties were investigated. The samples showed high densification (relative density: ~96.6 %) with fine grain size (~0.652 µm) under the synthesis conditions at x = 0.2%. The Curie temperature (TC) shifted
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toward lower temperature and orthorhombic–to–tetragonal phase transition temperature (TO–T)
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shifted toward higher temperature with addition of x, which was beneficial for elevating piezoelectric properties as pinched effect of the temperature. The diffuseness of the ceramics was receded with a small addition of x, because of disappeared oxygen vacancy and small area of polar nano–regions (PNRs) in the structure. The elevated piezoelectric constant (d33;
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~200 pC/N) and receded mechanical quality factor (Qm; ~70) at x = 0.2% showed “softening effect” by donor doping. However, erbium showed “hardening effect” by accepter doping
contents.
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with the substitution of B sites in the matrix of ABO3 structure with excessive erbium
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Keywords: Lead–free ceramics; Er3+–doping; Oxygen vacancy; Dielectric properties; Piezoelectric properties.
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ACCEPTED MANUSCRIPT 1. Introduction In recent years, lead–based materials with superior ferroelectric properties are restricted to use in electronic industry for their high toxicity [1]. Thus, it is urgent to find out lead–free
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ferroelectric materials for the substitution of the lead–based materials that was widely used in pyroelectric devices, actuators, memory storage, and sensors. Among many research on lead–free systems for the promising candidates, Barium calcium zirconate titanate
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(BCZT)–based ceramics with perovskite (ABO3) structure as the traditional ferroelectric
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materials has received increasing interest, because of the modified electrical performance by various preparation processes, forming the special crystal phase and structure [2–4]. Specifically, Z. Valdez–Nava et al. reported dielectric properties of BCZT–based materials were highly improved by spark plasma sintering technique [2]; W. Li et al. reported the
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formed polymorphic phase transition (PPT) regions in the structure of the BCZT–based materials at room temperature by doping [3]; W. Liu and X. Ren reported the formed morphotropic phase boundary (MPB) in the BCZT–based materials just like lead–based
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materials that featured high piezoelectric properties [4], etc. As we known, The significant
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merit of BCZT–based materials is of great solid solubility, and the substitution of different sites in the matrix of ABO3 structure is designable for the various applications on “soft” ceramics or “hard” ceramics [5,6]. Generally, the substitution of A or B sits in the ABO3 structure by higher stable iron valences could reduce oxygen vacancies, showing donor doping of “soft” ceramics. To the contrary, the substitution with lower iron valences indicated acceptor doping of “hard” ceramics. With the fundamental theory on the BCZT–based materials, there are a lot of researches on 3
ACCEPTED MANUSCRIPT intermediated ionic valence change or ionic radius with different substitution sits in ABO3 structure [7–9]. Among the researches, the rare earth ions doping BCZT–based materials were extensively studied as the outstanding electrical properties. For example, Z. Wang et al.
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reported Pr–doping BCZT–based materials showed high Strong photoluminescence and piezoelectricity properties [8]; W. Li et al. reported Ho–doping BCZT–based ceramics showed High piezoelectric coefficient and planar electromechanical coupling factor [9]; J. Ma
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et al. reported Ga–doping BCZT–based materials showed high piezoelectricity properties and
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temperature stability [10]; etc. However, the majority of rare earth ions doping BCZT–based system researches were single, and the co–doped studies were rarely reported. Z. Sun et al. reported La–doping BCZT–based materials showed high piezoelectric properties and positive temperature coefficient behavior with a small addition of lanthanum contents [11] and P. Du
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et al. reported Er–doping BCZT–based materials showed high ferroelectric properties and superior temperature sensing properties [12], but the synergistic effect of Er and La co–doped BCZT–based materials was not reported yet.
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In this work, La3+ and Er3+ co–doped 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr
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(BCT–BZT–La–xEr) ceramics were prepared by a modified Pechini polymeric precursor method sintered at a low temperature of 1250 °C. The influence on structure and electrical properties of the ceramics by Er–doping on varied substitution sits in ABO3 structure of the ceramics were investigated, when the addition of La content of 0.12% for decreasing part of oxygen vacancy [12]. Moreover, the origin of the diffuseness, the variation of dielectric properties between unpolarized and polarized process, and piezoelectric properties influenced by element electronegativity were all stated in detail. 4
ACCEPTED MANUSCRIPT 2. Experimental 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr (abbreviated as BCT–BZT–La–xEr; x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5%) ceramics were sintered with the as-synthesized
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BCT–BZT–La–xEr nanoparticles by a modified Pechini polymeric precursor method using Ba(CH3COO)2, Zr(NO3)4, Ti(OC4H9)4, Ca(NO3)2, La(NO3)3, Er(NO3)3, citric acid, and ethylene glycol as the raw materials, and the method of our study has been reported elsewhere
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[13,14]. The BCT–BZT–La–xEr nanoparticles were mixed with 2.5 wt.% polyvinyl alcohol
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solution binder homogeneously, and then uniaxially pressed into a discs of 16 mm in diameter at 200 MPa. Following burnt out the binder at 650 °C for 2 h in air, the green samples were buried in Al2O3 powders and were finally sintered at 1250 °C for 5 h in air for the ceramics. The silver electrodes were painted in both polished discs sides of the samples for the
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subsequent dielectric measurements. Then, the samples were polarized in a silicone oil bath at 25 °C under a direct–current electric field of 8 kV/cm. The phase structure of the ceramics was measured by X–ray powder diffraction (XRD;
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X’Pert PRO) using CuKα radiation at a 2θ scanning rate of 0.05°/s at room temperature. The
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precision electronic balance (ED–124S) was used to confirm the densification of the ceramics by Archimedes immersion principle. Field–emission scanning electron microscopy (FESEM; SUV–1080) was used to analyze the fractured microstructures, which were treated using a thermal etching process (1050 °C, 15 min in atmosphere). The relative permittivity (εr) and loss tangent (tan δ) of polarized and unpolarized ceramics were determined using a precision LCR meter (TH–2819). A radiant precision workstation was carried to investigate polarization–electric field (P–E) hysteresis loops. The planar and thickness vibration 5
ACCEPTED MANUSCRIPT electromechanical coupling (kp and kt) and mechanical quality (Qm) factors were calculated using Onoe and Jumonji formula [15,16] by a precision impedance analyzer (Agilent–4292A). Piezoelectric constant (d33) was determined by a quasistatic piezoelectric constant testing
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meter (ZJ–3A) at room temperatures. 3. Results and discussion
Fig. 1 shows the XRD patterns of the BCT–BZT–La–xEr ceramics doped with different
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erbium contents (x). All diffraction peaks can be indexed to desired pure perovskite structure
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(ABO3) without secondary phases, indicating that erbium was successfully diffused into the crystal lattice and showing high crystallinity. The XRD results showed a pure rhombohedral phase (R; JCPDS # 85–1796) with the diffraction peak (200) at ~45° (Fig. 1b), which suggested erbium could not induce the phase transition in our study. However, the apparent
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diffraction peak shift was detected around 45° and the full–width at half–maximum (FWHM) value was changed with increasing x in Fig. 1b, showing erbium could impact on lattice parameters of the ceramic crystal and ceramic crystallinity. The variation of diffraction peak
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shift with increasing x was due to different substitution site of erbium in ABO3, changing
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interplanar spacing of the crystal. The first higher diffraction peak shift was associated with the substitution of Ba2+ (ionic radius 0.161 nm) or Ca2+ (ionic radius 0.134 nm) with Er3+ (ionic radius 0.123 nm), and then the lower shift was attributed to the replacement of Ti4+ (ionic radius 0.0605 nm) or Zr4+ (ionic radius 0.74 nm) by Er3+ with excessive erbium contents [17,18]. Additionally, the FWHM value showed decreased first and then enhanced with increasing x. The lowest FWHM value was detected at x = 0.2%, indicating a relative highest crystallinity of the ceramics [19]. 6
ACCEPTED MANUSCRIPT The Rietveld refinement XRD pattern of BCT–BZT–La–0.2%Er ceramic using Fullprof software is shown in Fig. 2 that was refined by considering R3m space group. The detected experimental XRD pattern peak position fitted well with the model Bragg position, and the
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fitting parameters (Rp = 9.34, Rwp = 11.89, and χ2 = 2.07) suggested a good agreement between the detected and calculated XRD pattern [20]. After refining all the XRD pattern results of BCT–BZT–La–xEr ceramics, the lattice parameters (a, b, c, and Axial angle)
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information were obtained and shown in Table 1. The calculated lattice parameters (a, b, and c)
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receded first and then increased with increasing erbium contents, suggesting the variation of the structure and interplanar spacing, as consistent well with the XRD results in Fig. 1. Fig. 3 shows FESEM images of the fractured morphology of the BCT–BZT–La–xEr ceramics prepared with different erbium contents (x). All the samples featured dense packed
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microstructure, indicating a high ceramic densification in our study. The average grain size (GAV; 0.344–0.652 µm ) of the ceramics was estimated using the linear intercept method. The fine grain size in our study was related to the raw sintering materials of the as–prepared
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nanoparticles [21]. The GAV was first elevated to 0.652 µm and then decreased to 0.344 µm
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with excessive x, which was due to the fact that Er3+ had different diffusion position in the matrix of the ABO3 structure with addition erbium contents. Moreover, GAV was decreased with the formed fine grains at higher x, because the dissolving out elements at the grain boundaries as the solubility limits that inhibited grain growth [22]. Fig. 4 shows variations in the density and relative density of the BCT–BZT–La–xEr ceramics prepared with varying erbium contents (x). The densification was first elevated and then decreased with increasing x, which was associated with the various substitution of atomic mass in the ABO3 structure. 7
ACCEPTED MANUSCRIPT Moreover, the fine grain size and crystal lattice distortion (as shown in Fig. 3) were the other factors influencing densification of the ceramics. The high densification (~96.6%) with few cavities in our study indicated that the sintering ceramic process was effective.
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The temperature dependence of the relative permittivity (εr) and loss tangent (tan δ) of the of the BCT–BZT–La–xEr ceramics doped with varying erbium contents (x) assessed at a frequency of 10 kHz are shown in Fig. 5a. It was found that the dielectric peeks first
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strengthened and then broadened (receded) with increasing x, which was associated with
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various grain size in our study. However, the tan δ first decreased and then elevated with increasing x at around room temperature, which was due to the fact that the different substitution position in the ABO3 structure as shown in the defect Eq. (1–3). The first receded tan δ was attributed to the decreased oxygen vacancy (
), which weakened the carrier
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migration. The deteriorated tan δ with excessive erbium contents was associated with the substitution position (B site) in the matrix of ABO3 structure, which generated defect electron and
complex (Eq. (2–3)), increasing carrier migration and
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electron scattering at the grain boundaries [23,24]. Moreover, the disappeared and emerged
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might be the other reason for variation of grain size. Fig. 5b shows variations of the Curie temperature (TC) and orthorhombic–to–tetragonal phase transition temperature (TO–T) of the ceramics with various erbium contents. It was detected that TC had a little decreased with addition of x, because erbium could change internal stress in the structure [25]. However, TO–T shifted monotonously to a higher temperature with increasing x, indicating that erbium was helpful for pinching TO–T and TC that could elevate piezoelectric properties [26]. (1) 8
ACCEPTED MANUSCRIPT (2) (3) Fig. 6 shows temperature dependence of relative permittivity (εr) and loss tangent (tan δ) of
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BCT–BZT–La–xEr ceramics with erbium contents (x) under measuring frequencies of 100 Hz, 1 kHz, and 10 kHz. The increase in εr with the temperature could be associated with the change of electric dipole ordering, and then εr decreased at a high temperature (> TC) was due
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to the reduction of dipole ordering [27], indicating a flabby polarization behavior in our study
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[28]. As observed in the Fig. 6, tan δ and εr had a lower value under higher measuring frequency at the same temperature normally, which was attributed to the low charge accumulation at grain boundary [29]. The dielectric value had a sharper peak at x = 0.2%, because of the disappeared oxygen vacancy and less lattice distortion with a small addition of
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erbium contents. However, the dielectric peak boarded again with excessive erbium contents, which was associated with the more emerged oxygen vacancy and larger internal stress with lattice distortion. The results were in agreement with the analysis above. From Fig. 6b, the
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loss tangent peak emergence was earlier than the dielectric peak that was also corresponding
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to the phase transition, because there was some time requirement for the dipoles to orientate [30]. Fig. 6c shows a clear frequency dispersion of dielectric value, indicating a typical ferroelectric [31], and those ferroelectric properties would be discussed below. To study the degree of dielectric dispersion and diffuse phase transition, the quantitative parameters were calculated by Curie–Weiss law (Eq. (4)). 1
εr
=
T − TCW C
T > TC
(4)
where εr represents the relative permittivity; TCW represents the Curie–Weiss temperature; and 9
ACCEPTED MANUSCRIPT C represents the Curie–Weiss constant. The inverse permittivity (104/εr) as a function of temperature and the fitted Curie–Weiss curve (Eq. (5)) of the BCT–BZT–La–xEr ceramics under 10 kHz are shown in Fig. 7. (5)
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∆Tm = TB − Tm
where Tm represents the temperature associated with the maximum permittivity; TB corresponds to the temperature at which the permittivity starts to follow the Curie–Weiss law;
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and ∆Tm represents the temperature deviation that reveals the degree of diffusion. The
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detected and fitting results are shown in Table 2. ∆Tm was first decreased to 42.6 °C and then elevated with increasing erbium contents, indicating the diffuse phase transition of the ceramics was first deteriorated with the addition of x (x < 0.2%) and then enhanced with excessive erbium contents. The variation of C also revealed the degree of diffuse phase
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transition [32]. Moreover, the order (~105) of C value of the ceramics indicated that the high temperature paraelectric phase was driven by a displacive transition [33]. The modified Curie–Weiss law (Eq. (6)) has been used to investigate the dielectric
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behaviour of complex ferroelectric with diffuse phase transition.
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1
εr
−
1
εm
=
(T − Tm )γ C'
(6)
where εm represents the maximum relative permittivity; C′ represents the modified Curie–Weiss constant; and γ is the degree of the diffuseness exponent that ranged from 1 for normal ferroelectric to 2 for typical relaxor ferroelectric. Parameter γ is calculated by the slope of ln(1/εr − 1/εm) versus ln(T − Tm) under 10 kHz for avoiding space charge contributions in the lower frequency, which are shown in Fig. 8. The value was decreased from 1.798 to 1.721 with increasing of erbium content from 0 to 0.2%, indicating the phase 10
ACCEPTED MANUSCRIPT transition diffuseness was weakened. However, there were many oxygen vacancies cluster formed and rotated around Er'Ti/Zr with excessive erbium contents, following a short range motion of oxygen vacancy, which resulted in enhanced diffuseness of the phase transition [34].
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The different cationic substitution of A or B sites might hinder long–range ordering, which produced polar nano–regions (PNRs), resulting in the strengthened diffuseness [35]. In addition, a larger relaxor state and diffuseness were due to the fine grain sizes with large grain
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boundary volumes that might alter the balance between the long–range and short–range forces
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[36].
Fig. 9 shows Polarization–electric field (P–E) hysteresis loops of the BCT–BZT–La–xEr ceramics prepared with different erbium contents (x). All the samples showed typical saturated hysteresis loop, suggesting good ferroelectric properties. As detected in the selected
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enlarged regions (Fig. 8a), coercive field (Ec) were decreased with a small addition of erbium contents, which was associated with the inferior pinching effects in the domain wall with little oxygen vacancy. Remnant polarization (Pr) was also deteriorated, because the smaller ionic
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(Er3+) substitution position (A site) in the matrix of ABO3 structure, resulting in smaller
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inter-space octahedron [37]. Moreover, the decreased Ec was associated with the larger grain size with a small addition of x, because the domain reversal polarization is easier inside a large grain. Ec was enhanced with excessive erbium contents since the oxygen vacancy emerged again. Pr was first elevated and then weakened, which was attributed to the larger inter–space octahedron and internal stress [38]. Fig. 10 shows the schematic image of FESEM, optical microscope (OM), and domain for the BCT–BZT–La–xEr ceramic. The electric dipole in domain was isotropic before polarized 11
ACCEPTED MANUSCRIPT process, and the ceramic had no polarization, but the dipole had anisotropic properties after polarized process with the polarization. Fig. 11 shows the relative permittivity (ε33T/ε0) and loss tangent (tan δ) of the polarized BCT–BZT–La–xEr ceramics with different erbium
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contents (x) measured at room temperature under10 kHz. The ε33T/ε0 and tan δ had a similar variation tendency with the unpolarized ceramics. However, the ε33T/ε0 was little enhanced than the ε0 and the tan δ was little weakened than the upolarized ceramics, because the existed
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electric dipole anisotropy and electron scattering were decreased with the compensated
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defected dipole after polarized process [39].
Variations in the piezoelectric constant (d33), planar and thickness vibration electromechanical coupling factors (kp and kt), and mechanical quality factor (Qm) of the BCT–BZT–La–xEr ceramics with varying erbium contents (x) are shown in Fig. 12. d33 was
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elevated to ~200 pC/N with small addition of erbium contents, because of little domain wall pinching effect with decreased oxygen vacancy by donor doping. The substitution of the A sites (Ba: 1.00; Ca: 0.89) with higher electronegative Er (1.24) in the matrix of ABO3
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structure, resulting in sp3 hybridization of covalency with more covalent bonds and improved
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piezoelectric [40]. The decreasing d33 was also associated with the electronegative atomic substitution of the B sites (Ti: 1.54; Zr: 1.33) by accepter doping with excessive erbium contents. Moreover, the elevated d33 might be associated with the enlarged grain size, and the deteriorated d33 might be attributed to the distorted crystal structure with formed oxygen vacancy again. It was observed kp and kt featured a similar trend likewise d33, however, Qm showed an opposite tendency. The decreased Qm with a small addition of erbium contents indicated “softening effect”, but the elevated Qm with excessive erbium contents suggested 12
ACCEPTED MANUSCRIPT “hardening effect” in the system. In addition, the decreased Qm could enhance frequency bandwidth of the electron component [41]. The elevated Qm was associated with the high internal stress by distorted crystal structure and enhanced domain pinching effect caused by
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oxygen vacancy [42].
4. Conclusions
The high densification of Er3+–doping BCT–BZT–La–xEr ceramics were sintered at a low
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temperature of 1250 °C by a modified Pechini polymeric precursor method. Erbium first
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substituted A sites and then B sites in the matrix of ABO3 structure with increasing x, resulting in the change of interplanar spacing and the number of oxygen vacancy. The pinching TO–T and TC with increasing x indicated erbium was helpful for impacting on internal stress in the structure. The diffuseness of the ceramics was receded first and then enhanced
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with increasing x, because of internal stress in the distorted lattice and PNRs in the structure. The relative permittivity was elevated and loss tangent was receded after polarized process as the electric dipole anisotropy. The various piezoelectric properties with different x were
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associated with element electronegativity and doping method. Qm was first decreased and then
study.
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elevated with increasing x, showing “softening effect” first and then “hardening effect” in our
Acknowledgements
This work has been supported by Nanhu Scholars Program for Young Scholars of XYNU and Fundamental Research Funds for National University (CUG120118). The authors thank Prof. Yujun Liang for his help and raw materials supply.
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ACCEPTED MANUSCRIPT high–performance (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 lead–free piezoelectric ceramics, J. Am. Ceram. Soc. 95 (2012) 1998–2006. [34] J.Y. Miao, Z.Q. Zhang, Z.F. Liu, Y.X. Li, Investigation on the dielectric properties of
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ACCEPTED MANUSCRIPT Ferroelectric,
piezoelectric
and
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properties
in
lead
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(0.5)Ba(Zr0.2Ti0.8)O3–(0.5)(Ba0.7Ca0.3)TiO3 electroceramics, Ceram. Int. 41 (2015) 1980–1985.
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[42] M.A. Rafiq, M.N. Rafiq, K.V. Saravanan, Dielectric and impedance spectroscopic studies of lead–free barium–calcium–zirconium–titanium oxide ceramics, Ceram. Int. 41 (2015)
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ACCEPTED MANUSCRIPT Figure captions Fig. 1. (a) XRD patterns and (b) corresponding selected enlarged regions (42–50°) of the BCT–BZT–La–xEr ceramics with varying erbium contents (x)
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Fig. 2. The Rietveld refinement XRD pattern of BCT–BZT–La–0.2%Er ceramic using Fullprof software. The cross showed experimental detected intensity, the red line showed calculated pattern, the green vertical line showed Bragg position, and the blue line showed
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difference plot
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Fig. 3. FESEM images of the fractured morphology of the BCT–BZT–La–xEr ceramics prepared with different erbium contents (x) of (a) 0, (b) 0.1, (c) 0.2, (d) 0.3, (e) 0.4, and (f) 0.5%
Fig. 4. Variations in the density and relative density of the BCT–BZT–La–xEr ceramics
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prepared with varying erbium contents (x)
Fig. 5. (a) Temperature dependence of the relative permittivity (εr) and loss tangent (tan δ), (b) variations of the Curie temperature (TC) and orthorhombic-to-tetragonal phase transition
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temperature (TO–T) of the BCT–BZT–La–xEr ceramics with varying erbium contents (x)
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assessed at a frequency of 10 kHz
Fig. 6. Temperature dependence of relative permittivity (εr) and loss tangent (tan δ) of BCT–BZT–La–xEr ceramics with erbium contents (x) of (a) 0, (b) 0.1, (c) 0.2, (d) 0.3, (e) 0.4, and (f) 0.5% under different measuring frequencies Fig. 7. Temperature dependences of inverse permittivity (104/εr) of BCT–BZT–La–xEr ceramics with erbium contents (x) of (a) 0, (b) 0.1, (c) 0.2, (d) 0.3, (e) 0.4, and (f) 0.5% assessed at a frequency of 10 kHz 20
ACCEPTED MANUSCRIPT Fig. 8. The plots of ln(1/εr − 1/εm) versus ln(T − Tm) at 10 kHz for BCT–BZT–La–xEr ceramics with various erbium contents (x) Fig. 9. Polarization–electric field (P–E) hysteresis loops of the BCT–BZT–La–xEr ceramics
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prepared with different erbium contents (x). The inset (a) shows selected enlarged regions (−3.5 to 0 kV/cm)
Fig. 10. Schematic image of FESEM, Optical Microscope (OM), and domain for the
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BCT–BZT–La–xEr ceramic
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Fig. 11. The relative permittivity (ε33T/ε0) and loss tangent (tan δ) of the polarized BCT–BZT–La–xEr ceramics with different erbium contents (x) measured at room temperature under10 kHz
Fig. 12. Variations in the piezoelectric constant (d33), planar and thickness vibration
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electromechanical coupling factors (kp and kt), and mechanical quality factor (Qm) of the
Table captions
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BCT–BZT–La–xEr ceramics with varying erbium contents (x)
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Table 1 Lattice parameters, average grain size (GAV), density, and relative density (ρr) of the BCT–BZT–La–xEr ceramics prepared with varying erbium contents (x) Table 2 Temperature of the maximum permittivity (Tm); Curie–Weiss temperature (TCW); Temperature of the permittivity starts to follow Curie–Weiss law (TB); temperature deviation (∆Tm); and Curie–Weiss constant (C); and diffuseness exponent (γ) for the BCT–BZT–La–xEr ceramics with varying erbium contents (x) measured at 10 kHz
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ACCEPTED MANUSCRIPT Table 1 Lattice parameters, average grain size (GAV), density, and relative density (ρr) of the BCT–BZT–La–xEr ceramics prepared with varying erbium contents (x) b (Å)
c (Å)
0 0.1 0.2 0.3 0.4 0.5
3.9989(2) 3.9981(4) 3.9973(1) 3.9980(7) 3.9985(8) 3.9993(1)
3.9986(7) 3.9980(8) 3.9973(5) 3.9977(3) 3.9982(0) 3.9990(6)
3.9989(0) 3.9981(1) 3.9972(9) 3.9980(6) 3.9986(3) 3.9993(2)
Axial angle (o) GAV(µm) 89.84 89.86 89.90 89.88 89.85 89.82
0.627 0.636 0.652 0.580 0.419 0.344
Density
ρr
5.4501 5.4789 5.4956 5.5033 5.5028 5.4991
95.79 96.31 96.60 96.74 96.73 96.66
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a (Å)
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x (%)
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10 kHz
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(γ) for the BCT–BZT–La–xEr ceramics with varying erbium contents (x) measured at
Tm (°C)
Tcw (°C)
TB (°C)
∆Tm (°C)
C (×105 °C)
γ
0 0.1 0.2 0.3 0.4 0.5
73.1 73.2 73.7 73.5 73.3 72.9
82.9 88.8 76.9 87.7 86.2 87.2
124.3 120.9 116.3 122.0 125.2 126.8
51.2 47.7 42.6 48.5 51.9 53.9
1.341 1.472 1.675 1.477 1.282 1.245
1.798 1.782 1.721 1.762 1.867 1.906
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ACCEPTED MANUSCRIPT Highlights 1. The La and Er co–doped BCT–BZT–La–xEr ceramics were prepared at 1250 oC. 2. Er doped on various substituted sits in ABO3 structure with different contents.
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3. The piezoelectric properties could be improved by adding a small Er contents.
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4. The synergistic effect of La and Er co–doped mechanisms were stated.
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S0925-8388(16)32873-0
DOI:
10.1016/j.jallcom.2016.09.120
Reference:
JALCOM 38954
To appear in:
Journal of Alloys and Compounds
Received Date: 11 August 2016 Accepted Date: 11 September 2016
3+ Please cite this article as: Y. Tian, S. Li, Y. Gong, D. Meng, J. Wang, Q. Jing, Effects of Er –doping on dielectric and piezoelectric properties of 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr lead– free ceramics, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.09.120. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Effects of Er3+–doping on dielectric and piezoelectric properties of 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr lead–free ceramics
Qiangshan Jing a, b a
College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang
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464000, People’s Republic of China
Henan Province Key Laboratory of Utilization of Non–metallic Mineral in the South of
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b
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Yongshang Tian a, b, *, Shuiyun Li a, Yansheng Gong c, Dawei Meng c, Jipeng Wang c,
Henan, Xinyang 464000, People’s Republic of China c
Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan
* Corresponding author:
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430074, People’s Republic of China
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Yongshang Tian ([email protected])
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College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang 464000, People’s Republic of China Tel. +86–0376–6390603; Fax: +86–0376–6390603.
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ACCEPTED MANUSCRIPT Abstract 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr (x = 0–0.5%) lead–free ceramics were prepared by a modified Pechini polymeric precursor method, and the effects of erbium
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contents (x) on the crystal structure, dielectric and piezoelectric properties were investigated. The samples showed high densification (relative density: ~96.6 %) with fine grain size (~0.652 µm) under the synthesis conditions at x = 0.2%. The Curie temperature (TC) shifted
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toward lower temperature and orthorhombic–to–tetragonal phase transition temperature (TO–T)
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shifted toward higher temperature with addition of x, which was beneficial for elevating piezoelectric properties as pinched effect of the temperature. The diffuseness of the ceramics was receded with a small addition of x, because of disappeared oxygen vacancy and small area of polar nano–regions (PNRs) in the structure. The elevated piezoelectric constant (d33;
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~200 pC/N) and receded mechanical quality factor (Qm; ~70) at x = 0.2% showed “softening effect” by donor doping. However, erbium showed “hardening effect” by accepter doping
contents.
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with the substitution of B sites in the matrix of ABO3 structure with excessive erbium
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Keywords: Lead–free ceramics; Er3+–doping; Oxygen vacancy; Dielectric properties; Piezoelectric properties.
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ACCEPTED MANUSCRIPT 1. Introduction In recent years, lead–based materials with superior ferroelectric properties are restricted to use in electronic industry for their high toxicity [1]. Thus, it is urgent to find out lead–free
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ferroelectric materials for the substitution of the lead–based materials that was widely used in pyroelectric devices, actuators, memory storage, and sensors. Among many research on lead–free systems for the promising candidates, Barium calcium zirconate titanate
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(BCZT)–based ceramics with perovskite (ABO3) structure as the traditional ferroelectric
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materials has received increasing interest, because of the modified electrical performance by various preparation processes, forming the special crystal phase and structure [2–4]. Specifically, Z. Valdez–Nava et al. reported dielectric properties of BCZT–based materials were highly improved by spark plasma sintering technique [2]; W. Li et al. reported the
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formed polymorphic phase transition (PPT) regions in the structure of the BCZT–based materials at room temperature by doping [3]; W. Liu and X. Ren reported the formed morphotropic phase boundary (MPB) in the BCZT–based materials just like lead–based
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materials that featured high piezoelectric properties [4], etc. As we known, The significant
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merit of BCZT–based materials is of great solid solubility, and the substitution of different sites in the matrix of ABO3 structure is designable for the various applications on “soft” ceramics or “hard” ceramics [5,6]. Generally, the substitution of A or B sits in the ABO3 structure by higher stable iron valences could reduce oxygen vacancies, showing donor doping of “soft” ceramics. To the contrary, the substitution with lower iron valences indicated acceptor doping of “hard” ceramics. With the fundamental theory on the BCZT–based materials, there are a lot of researches on 3
ACCEPTED MANUSCRIPT intermediated ionic valence change or ionic radius with different substitution sits in ABO3 structure [7–9]. Among the researches, the rare earth ions doping BCZT–based materials were extensively studied as the outstanding electrical properties. For example, Z. Wang et al.
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reported Pr–doping BCZT–based materials showed high Strong photoluminescence and piezoelectricity properties [8]; W. Li et al. reported Ho–doping BCZT–based ceramics showed High piezoelectric coefficient and planar electromechanical coupling factor [9]; J. Ma
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et al. reported Ga–doping BCZT–based materials showed high piezoelectricity properties and
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temperature stability [10]; etc. However, the majority of rare earth ions doping BCZT–based system researches were single, and the co–doped studies were rarely reported. Z. Sun et al. reported La–doping BCZT–based materials showed high piezoelectric properties and positive temperature coefficient behavior with a small addition of lanthanum contents [11] and P. Du
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et al. reported Er–doping BCZT–based materials showed high ferroelectric properties and superior temperature sensing properties [12], but the synergistic effect of Er and La co–doped BCZT–based materials was not reported yet.
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In this work, La3+ and Er3+ co–doped 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr
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(BCT–BZT–La–xEr) ceramics were prepared by a modified Pechini polymeric precursor method sintered at a low temperature of 1250 °C. The influence on structure and electrical properties of the ceramics by Er–doping on varied substitution sits in ABO3 structure of the ceramics were investigated, when the addition of La content of 0.12% for decreasing part of oxygen vacancy [12]. Moreover, the origin of the diffuseness, the variation of dielectric properties between unpolarized and polarized process, and piezoelectric properties influenced by element electronegativity were all stated in detail. 4
ACCEPTED MANUSCRIPT 2. Experimental 0.5Ba0.9Ca0.1TiO3–0.5BaTi0.88Zr0.12O3–0.12%La–xEr (abbreviated as BCT–BZT–La–xEr; x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5%) ceramics were sintered with the as-synthesized
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BCT–BZT–La–xEr nanoparticles by a modified Pechini polymeric precursor method using Ba(CH3COO)2, Zr(NO3)4, Ti(OC4H9)4, Ca(NO3)2, La(NO3)3, Er(NO3)3, citric acid, and ethylene glycol as the raw materials, and the method of our study has been reported elsewhere
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[13,14]. The BCT–BZT–La–xEr nanoparticles were mixed with 2.5 wt.% polyvinyl alcohol
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solution binder homogeneously, and then uniaxially pressed into a discs of 16 mm in diameter at 200 MPa. Following burnt out the binder at 650 °C for 2 h in air, the green samples were buried in Al2O3 powders and were finally sintered at 1250 °C for 5 h in air for the ceramics. The silver electrodes were painted in both polished discs sides of the samples for the
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subsequent dielectric measurements. Then, the samples were polarized in a silicone oil bath at 25 °C under a direct–current electric field of 8 kV/cm. The phase structure of the ceramics was measured by X–ray powder diffraction (XRD;
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X’Pert PRO) using CuKα radiation at a 2θ scanning rate of 0.05°/s at room temperature. The
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precision electronic balance (ED–124S) was used to confirm the densification of the ceramics by Archimedes immersion principle. Field–emission scanning electron microscopy (FESEM; SUV–1080) was used to analyze the fractured microstructures, which were treated using a thermal etching process (1050 °C, 15 min in atmosphere). The relative permittivity (εr) and loss tangent (tan δ) of polarized and unpolarized ceramics were determined using a precision LCR meter (TH–2819). A radiant precision workstation was carried to investigate polarization–electric field (P–E) hysteresis loops. The planar and thickness vibration 5
ACCEPTED MANUSCRIPT electromechanical coupling (kp and kt) and mechanical quality (Qm) factors were calculated using Onoe and Jumonji formula [15,16] by a precision impedance analyzer (Agilent–4292A). Piezoelectric constant (d33) was determined by a quasistatic piezoelectric constant testing
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meter (ZJ–3A) at room temperatures. 3. Results and discussion
Fig. 1 shows the XRD patterns of the BCT–BZT–La–xEr ceramics doped with different
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erbium contents (x). All diffraction peaks can be indexed to desired pure perovskite structure
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(ABO3) without secondary phases, indicating that erbium was successfully diffused into the crystal lattice and showing high crystallinity. The XRD results showed a pure rhombohedral phase (R; JCPDS # 85–1796) with the diffraction peak (200) at ~45° (Fig. 1b), which suggested erbium could not induce the phase transition in our study. However, the apparent
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diffraction peak shift was detected around 45° and the full–width at half–maximum (FWHM) value was changed with increasing x in Fig. 1b, showing erbium could impact on lattice parameters of the ceramic crystal and ceramic crystallinity. The variation of diffraction peak
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shift with increasing x was due to different substitution site of erbium in ABO3, changing
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interplanar spacing of the crystal. The first higher diffraction peak shift was associated with the substitution of Ba2+ (ionic radius 0.161 nm) or Ca2+ (ionic radius 0.134 nm) with Er3+ (ionic radius 0.123 nm), and then the lower shift was attributed to the replacement of Ti4+ (ionic radius 0.0605 nm) or Zr4+ (ionic radius 0.74 nm) by Er3+ with excessive erbium contents [17,18]. Additionally, the FWHM value showed decreased first and then enhanced with increasing x. The lowest FWHM value was detected at x = 0.2%, indicating a relative highest crystallinity of the ceramics [19]. 6
ACCEPTED MANUSCRIPT The Rietveld refinement XRD pattern of BCT–BZT–La–0.2%Er ceramic using Fullprof software is shown in Fig. 2 that was refined by considering R3m space group. The detected experimental XRD pattern peak position fitted well with the model Bragg position, and the
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fitting parameters (Rp = 9.34, Rwp = 11.89, and χ2 = 2.07) suggested a good agreement between the detected and calculated XRD pattern [20]. After refining all the XRD pattern results of BCT–BZT–La–xEr ceramics, the lattice parameters (a, b, c, and Axial angle)
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information were obtained and shown in Table 1. The calculated lattice parameters (a, b, and c)
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receded first and then increased with increasing erbium contents, suggesting the variation of the structure and interplanar spacing, as consistent well with the XRD results in Fig. 1. Fig. 3 shows FESEM images of the fractured morphology of the BCT–BZT–La–xEr ceramics prepared with different erbium contents (x). All the samples featured dense packed
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microstructure, indicating a high ceramic densification in our study. The average grain size (GAV; 0.344–0.652 µm ) of the ceramics was estimated using the linear intercept method. The fine grain size in our study was related to the raw sintering materials of the as–prepared
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nanoparticles [21]. The GAV was first elevated to 0.652 µm and then decreased to 0.344 µm
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with excessive x, which was due to the fact that Er3+ had different diffusion position in the matrix of the ABO3 structure with addition erbium contents. Moreover, GAV was decreased with the formed fine grains at higher x, because the dissolving out elements at the grain boundaries as the solubility limits that inhibited grain growth [22]. Fig. 4 shows variations in the density and relative density of the BCT–BZT–La–xEr ceramics prepared with varying erbium contents (x). The densification was first elevated and then decreased with increasing x, which was associated with the various substitution of atomic mass in the ABO3 structure. 7
ACCEPTED MANUSCRIPT Moreover, the fine grain size and crystal lattice distortion (as shown in Fig. 3) were the other factors influencing densification of the ceramics. The high densification (~96.6%) with few cavities in our study indicated that the sintering ceramic process was effective.
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The temperature dependence of the relative permittivity (εr) and loss tangent (tan δ) of the of the BCT–BZT–La–xEr ceramics doped with varying erbium contents (x) assessed at a frequency of 10 kHz are shown in Fig. 5a. It was found that the dielectric peeks first
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strengthened and then broadened (receded) with increasing x, which was associated with
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various grain size in our study. However, the tan δ first decreased and then elevated with increasing x at around room temperature, which was due to the fact that the different substitution position in the ABO3 structure as shown in the defect Eq. (1–3). The first receded tan δ was attributed to the decreased oxygen vacancy (
), which weakened the carrier
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migration. The deteriorated tan δ with excessive erbium contents was associated with the substitution position (B site) in the matrix of ABO3 structure, which generated defect electron and
complex (Eq. (2–3)), increasing carrier migration and
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electron scattering at the grain boundaries [23,24]. Moreover, the disappeared and emerged
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might be the other reason for variation of grain size. Fig. 5b shows variations of the Curie temperature (TC) and orthorhombic–to–tetragonal phase transition temperature (TO–T) of the ceramics with various erbium contents. It was detected that TC had a little decreased with addition of x, because erbium could change internal stress in the structure [25]. However, TO–T shifted monotonously to a higher temperature with increasing x, indicating that erbium was helpful for pinching TO–T and TC that could elevate piezoelectric properties [26]. (1) 8
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BCT–BZT–La–xEr ceramics with erbium contents (x) under measuring frequencies of 100 Hz, 1 kHz, and 10 kHz. The increase in εr with the temperature could be associated with the change of electric dipole ordering, and then εr decreased at a high temperature (> TC) was due
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to the reduction of dipole ordering [27], indicating a flabby polarization behavior in our study
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[28]. As observed in the Fig. 6, tan δ and εr had a lower value under higher measuring frequency at the same temperature normally, which was attributed to the low charge accumulation at grain boundary [29]. The dielectric value had a sharper peak at x = 0.2%, because of the disappeared oxygen vacancy and less lattice distortion with a small addition of
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erbium contents. However, the dielectric peak boarded again with excessive erbium contents, which was associated with the more emerged oxygen vacancy and larger internal stress with lattice distortion. The results were in agreement with the analysis above. From Fig. 6b, the
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loss tangent peak emergence was earlier than the dielectric peak that was also corresponding
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to the phase transition, because there was some time requirement for the dipoles to orientate [30]. Fig. 6c shows a clear frequency dispersion of dielectric value, indicating a typical ferroelectric [31], and those ferroelectric properties would be discussed below. To study the degree of dielectric dispersion and diffuse phase transition, the quantitative parameters were calculated by Curie–Weiss law (Eq. (4)). 1
εr
=
T − TCW C
T > TC
(4)
where εr represents the relative permittivity; TCW represents the Curie–Weiss temperature; and 9
ACCEPTED MANUSCRIPT C represents the Curie–Weiss constant. The inverse permittivity (104/εr) as a function of temperature and the fitted Curie–Weiss curve (Eq. (5)) of the BCT–BZT–La–xEr ceramics under 10 kHz are shown in Fig. 7. (5)
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∆Tm = TB − Tm
where Tm represents the temperature associated with the maximum permittivity; TB corresponds to the temperature at which the permittivity starts to follow the Curie–Weiss law;
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and ∆Tm represents the temperature deviation that reveals the degree of diffusion. The
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detected and fitting results are shown in Table 2. ∆Tm was first decreased to 42.6 °C and then elevated with increasing erbium contents, indicating the diffuse phase transition of the ceramics was first deteriorated with the addition of x (x < 0.2%) and then enhanced with excessive erbium contents. The variation of C also revealed the degree of diffuse phase
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transition [32]. Moreover, the order (~105) of C value of the ceramics indicated that the high temperature paraelectric phase was driven by a displacive transition [33]. The modified Curie–Weiss law (Eq. (6)) has been used to investigate the dielectric
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behaviour of complex ferroelectric with diffuse phase transition.
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1
εr
−
1
εm
=
(T − Tm )γ C'
(6)
where εm represents the maximum relative permittivity; C′ represents the modified Curie–Weiss constant; and γ is the degree of the diffuseness exponent that ranged from 1 for normal ferroelectric to 2 for typical relaxor ferroelectric. Parameter γ is calculated by the slope of ln(1/εr − 1/εm) versus ln(T − Tm) under 10 kHz for avoiding space charge contributions in the lower frequency, which are shown in Fig. 8. The value was decreased from 1.798 to 1.721 with increasing of erbium content from 0 to 0.2%, indicating the phase 10
ACCEPTED MANUSCRIPT transition diffuseness was weakened. However, there were many oxygen vacancies cluster formed and rotated around Er'Ti/Zr with excessive erbium contents, following a short range motion of oxygen vacancy, which resulted in enhanced diffuseness of the phase transition [34].
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The different cationic substitution of A or B sites might hinder long–range ordering, which produced polar nano–regions (PNRs), resulting in the strengthened diffuseness [35]. In addition, a larger relaxor state and diffuseness were due to the fine grain sizes with large grain
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boundary volumes that might alter the balance between the long–range and short–range forces
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[36].
Fig. 9 shows Polarization–electric field (P–E) hysteresis loops of the BCT–BZT–La–xEr ceramics prepared with different erbium contents (x). All the samples showed typical saturated hysteresis loop, suggesting good ferroelectric properties. As detected in the selected
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enlarged regions (Fig. 8a), coercive field (Ec) were decreased with a small addition of erbium contents, which was associated with the inferior pinching effects in the domain wall with little oxygen vacancy. Remnant polarization (Pr) was also deteriorated, because the smaller ionic
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(Er3+) substitution position (A site) in the matrix of ABO3 structure, resulting in smaller
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inter-space octahedron [37]. Moreover, the decreased Ec was associated with the larger grain size with a small addition of x, because the domain reversal polarization is easier inside a large grain. Ec was enhanced with excessive erbium contents since the oxygen vacancy emerged again. Pr was first elevated and then weakened, which was attributed to the larger inter–space octahedron and internal stress [38]. Fig. 10 shows the schematic image of FESEM, optical microscope (OM), and domain for the BCT–BZT–La–xEr ceramic. The electric dipole in domain was isotropic before polarized 11
ACCEPTED MANUSCRIPT process, and the ceramic had no polarization, but the dipole had anisotropic properties after polarized process with the polarization. Fig. 11 shows the relative permittivity (ε33T/ε0) and loss tangent (tan δ) of the polarized BCT–BZT–La–xEr ceramics with different erbium
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contents (x) measured at room temperature under10 kHz. The ε33T/ε0 and tan δ had a similar variation tendency with the unpolarized ceramics. However, the ε33T/ε0 was little enhanced than the ε0 and the tan δ was little weakened than the upolarized ceramics, because the existed
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electric dipole anisotropy and electron scattering were decreased with the compensated
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defected dipole after polarized process [39].
Variations in the piezoelectric constant (d33), planar and thickness vibration electromechanical coupling factors (kp and kt), and mechanical quality factor (Qm) of the BCT–BZT–La–xEr ceramics with varying erbium contents (x) are shown in Fig. 12. d33 was
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elevated to ~200 pC/N with small addition of erbium contents, because of little domain wall pinching effect with decreased oxygen vacancy by donor doping. The substitution of the A sites (Ba: 1.00; Ca: 0.89) with higher electronegative Er (1.24) in the matrix of ABO3
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structure, resulting in sp3 hybridization of covalency with more covalent bonds and improved
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piezoelectric [40]. The decreasing d33 was also associated with the electronegative atomic substitution of the B sites (Ti: 1.54; Zr: 1.33) by accepter doping with excessive erbium contents. Moreover, the elevated d33 might be associated with the enlarged grain size, and the deteriorated d33 might be attributed to the distorted crystal structure with formed oxygen vacancy again. It was observed kp and kt featured a similar trend likewise d33, however, Qm showed an opposite tendency. The decreased Qm with a small addition of erbium contents indicated “softening effect”, but the elevated Qm with excessive erbium contents suggested 12
ACCEPTED MANUSCRIPT “hardening effect” in the system. In addition, the decreased Qm could enhance frequency bandwidth of the electron component [41]. The elevated Qm was associated with the high internal stress by distorted crystal structure and enhanced domain pinching effect caused by
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oxygen vacancy [42].
4. Conclusions
The high densification of Er3+–doping BCT–BZT–La–xEr ceramics were sintered at a low
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temperature of 1250 °C by a modified Pechini polymeric precursor method. Erbium first
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substituted A sites and then B sites in the matrix of ABO3 structure with increasing x, resulting in the change of interplanar spacing and the number of oxygen vacancy. The pinching TO–T and TC with increasing x indicated erbium was helpful for impacting on internal stress in the structure. The diffuseness of the ceramics was receded first and then enhanced
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with increasing x, because of internal stress in the distorted lattice and PNRs in the structure. The relative permittivity was elevated and loss tangent was receded after polarized process as the electric dipole anisotropy. The various piezoelectric properties with different x were
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associated with element electronegativity and doping method. Qm was first decreased and then
study.
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elevated with increasing x, showing “softening effect” first and then “hardening effect” in our
Acknowledgements
This work has been supported by Nanhu Scholars Program for Young Scholars of XYNU and Fundamental Research Funds for National University (CUG120118). The authors thank Prof. Yujun Liang for his help and raw materials supply.
13
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ACCEPTED MANUSCRIPT Ferroelectric,
piezoelectric
and
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ACCEPTED MANUSCRIPT Figure captions Fig. 1. (a) XRD patterns and (b) corresponding selected enlarged regions (42–50°) of the BCT–BZT–La–xEr ceramics with varying erbium contents (x)
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Fig. 2. The Rietveld refinement XRD pattern of BCT–BZT–La–0.2%Er ceramic using Fullprof software. The cross showed experimental detected intensity, the red line showed calculated pattern, the green vertical line showed Bragg position, and the blue line showed
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difference plot
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Fig. 3. FESEM images of the fractured morphology of the BCT–BZT–La–xEr ceramics prepared with different erbium contents (x) of (a) 0, (b) 0.1, (c) 0.2, (d) 0.3, (e) 0.4, and (f) 0.5%
Fig. 4. Variations in the density and relative density of the BCT–BZT–La–xEr ceramics
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prepared with varying erbium contents (x)
Fig. 5. (a) Temperature dependence of the relative permittivity (εr) and loss tangent (tan δ), (b) variations of the Curie temperature (TC) and orthorhombic-to-tetragonal phase transition
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temperature (TO–T) of the BCT–BZT–La–xEr ceramics with varying erbium contents (x)
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assessed at a frequency of 10 kHz
Fig. 6. Temperature dependence of relative permittivity (εr) and loss tangent (tan δ) of BCT–BZT–La–xEr ceramics with erbium contents (x) of (a) 0, (b) 0.1, (c) 0.2, (d) 0.3, (e) 0.4, and (f) 0.5% under different measuring frequencies Fig. 7. Temperature dependences of inverse permittivity (104/εr) of BCT–BZT–La–xEr ceramics with erbium contents (x) of (a) 0, (b) 0.1, (c) 0.2, (d) 0.3, (e) 0.4, and (f) 0.5% assessed at a frequency of 10 kHz 20
ACCEPTED MANUSCRIPT Fig. 8. The plots of ln(1/εr − 1/εm) versus ln(T − Tm) at 10 kHz for BCT–BZT–La–xEr ceramics with various erbium contents (x) Fig. 9. Polarization–electric field (P–E) hysteresis loops of the BCT–BZT–La–xEr ceramics
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prepared with different erbium contents (x). The inset (a) shows selected enlarged regions (−3.5 to 0 kV/cm)
Fig. 10. Schematic image of FESEM, Optical Microscope (OM), and domain for the
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BCT–BZT–La–xEr ceramic
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Fig. 11. The relative permittivity (ε33T/ε0) and loss tangent (tan δ) of the polarized BCT–BZT–La–xEr ceramics with different erbium contents (x) measured at room temperature under10 kHz
Fig. 12. Variations in the piezoelectric constant (d33), planar and thickness vibration
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electromechanical coupling factors (kp and kt), and mechanical quality factor (Qm) of the
Table captions
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BCT–BZT–La–xEr ceramics with varying erbium contents (x)
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Table 1 Lattice parameters, average grain size (GAV), density, and relative density (ρr) of the BCT–BZT–La–xEr ceramics prepared with varying erbium contents (x) Table 2 Temperature of the maximum permittivity (Tm); Curie–Weiss temperature (TCW); Temperature of the permittivity starts to follow Curie–Weiss law (TB); temperature deviation (∆Tm); and Curie–Weiss constant (C); and diffuseness exponent (γ) for the BCT–BZT–La–xEr ceramics with varying erbium contents (x) measured at 10 kHz
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ACCEPTED MANUSCRIPT Table 1 Lattice parameters, average grain size (GAV), density, and relative density (ρr) of the BCT–BZT–La–xEr ceramics prepared with varying erbium contents (x) b (Å)
c (Å)
0 0.1 0.2 0.3 0.4 0.5
3.9989(2) 3.9981(4) 3.9973(1) 3.9980(7) 3.9985(8) 3.9993(1)
3.9986(7) 3.9980(8) 3.9973(5) 3.9977(3) 3.9982(0) 3.9990(6)
3.9989(0) 3.9981(1) 3.9972(9) 3.9980(6) 3.9986(3) 3.9993(2)
Axial angle (o) GAV(µm) 89.84 89.86 89.90 89.88 89.85 89.82
0.627 0.636 0.652 0.580 0.419 0.344
Density
ρr
5.4501 5.4789 5.4956 5.5033 5.5028 5.4991
95.79 96.31 96.60 96.74 96.73 96.66
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ACCEPTED MANUSCRIPT Table 2 Temperature of the maximum permittivity (Tm); Curie–Weiss temperature (TCW); Temperature of the permittivity starts to follow Curie–Weiss law (TB); temperature deviation (∆Tm); and Curie–Weiss constant (C); and diffuseness exponent
10 kHz
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(γ) for the BCT–BZT–La–xEr ceramics with varying erbium contents (x) measured at
Tm (°C)
Tcw (°C)
TB (°C)
∆Tm (°C)
C (×105 °C)
γ
0 0.1 0.2 0.3 0.4 0.5
73.1 73.2 73.7 73.5 73.3 72.9
82.9 88.8 76.9 87.7 86.2 87.2
124.3 120.9 116.3 122.0 125.2 126.8
51.2 47.7 42.6 48.5 51.9 53.9
1.341 1.472 1.675 1.477 1.282 1.245
1.798 1.782 1.721 1.762 1.867 1.906
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ACCEPTED MANUSCRIPT Highlights 1. The La and Er co–doped BCT–BZT–La–xEr ceramics were prepared at 1250 oC. 2. Er doped on various substituted sits in ABO3 structure with different contents.
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3. The piezoelectric properties could be improved by adding a small Er contents.
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4. The synergistic effect of La and Er co–doped mechanisms were stated.
1