- Email: [email protected]
Zr co-substituted BaTiO3 through XRD and Raman spectroscopy
Accepted Manuscript Structural investigation of Ca/Zr co-substituted BaTiO3 through XRD and Raman spectroscopy Vijayeta Pal, O.P. Thakur, R.K. Dwivedi PII:
S0925-8388(18)30153-1
DOI:
10.1016/j.jallcom.2018.01.152
Reference:
JALCOM 44616
To appear in:
Journal of Alloys and Compounds
Received Date: 13 July 2017 Revised Date:
27 December 2017
Accepted Date: 10 January 2018
Please cite this article as: V. Pal, O.P. Thakur, R.K. Dwivedi, Structural investigation of Ca/Zr cosubstituted BaTiO3 through XRD and Raman spectroscopy, Journal of Alloys and Compounds (2018), doi: 10.1016/j.jallcom.2018.01.152. 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.
ACCEPTED MANUSCRIPT
Structural investigation of Ca/Zr co-substituted BaTiO3 through XRD and Raman spectroscopy Vijayeta Pal1, 2#, O. P. Thakur3 and R. K. Dwivedi2 1
Defence Materials and Stores Research and Development Establishment, Kanpur-208013,
2
RI PT
India Department of Physics and Material Science and Engineering, Jaypee Institute of Information Technology, Noida – 201307, India
Solid State Physics Laboratory, Timarpur, Delhi - 110054, India
SC
3
Corresponding Author, E-mail: [email protected]
M AN U
Abstract
The present work reports the synthesis of Lead free (Ba1-xCax)(ZryTi1-y)O3 with x = 0.13, y ≤ 0.15 (i.e. BCTZ) piezoceramics by semi-wet route and effect of additives viz., Ca2+, and Zr4+ on phase formation, microstructure, piezoelectric and electromechanical properties. Detailed structural analysis suggests the formation of tetragonal perovskite phase with P4mm symmetry, which was also confirmed by Rietveld refinement and Raman spectra. SEM
TE D
micrographs showed that the average grain size decreased with Zr4+ which acts as grain growth inhibitor. Composition with x = 0.13 and y = 0.10 exhibited the optimum piezoelectric and electromechanical properties (d33 = 367 ± 2 pC/N and kp = 0.39 ± 0.01) and
EP
showed higher densification (relative density ~ 98 %). Keywords: Lead-free ceramics; Microstructure; Dielectric properties; Piezoelectric
AC C
properties
1. Introduction
In the past few years, lead-free piezoelectric ceramics have received considerable attention due to its environmental friendly nature and alternatives to lead-based compositions such as Pb(Zr,Ti)O3 (PZT) [1-2]. In continuous search for lead-free piezoceramics, barium titanate (BaTiO3; BT) is one of the potential candidates [3] showing typical ferroelectric characters with three phase transitions: rhombohedral to orthorhombic (R-O) ~ –80 °C; orthorhombic to tetragonal (O-T) ~ 5 °C; and tetragonal to cubic (T-C) ~120 °C [1]. Barium titanate has been widely studied material because of its high dielectric constant, ferroelectric properties and
ACCEPTED MANUSCRIPT nonlinear optical coefficients [2]. However, it exhibited inferior piezoelectric properties (d33 ~ 190 pC/N) with low Curie temperature (Tc ~ 120°C). In the past, electrical and piezoelectric properties of BaTiO3 were modified by applying some pioneering method for example via the construction of phase boundary, employment of site engineering, sintering condition and the use of different preparation techniques [1-2, 4-6].
RI PT
The solid solutions of BaTiO3 based ceramics exhibited a wide range of applications in electronic and technological appliances [6-8]. Moreover, electrical properties and the Curie temperature (Tc) at either barium (Ba) or titanium (Ti) sites could be controlled by the doping of appropriate foreign elements (donor or acceptor) [6-9]. However, doping of calcium (Ca)
polymorphic
phase
transition
(PPT)
behaviour
SC
at Ba- site did not make any significant effect on Tc values, but it only reduced the [10-11]
while,
some
interesting
microstructural and phase transitional changes were obtained with the doping of Zr4+ at B-site
M AN U
(Ti4+) in BaTiO3 [7, 12]. Among various BT-based ceramic systems, BZT –BCT system i.e. (Ba1-xCax)(ZryTi1-y)O3 (abbreviated as BCTZ) exhibited interesting dielectric properties for MLCC applications. The different phase transition behaviors of BZT and BCT ceramics made it a potential candidate to design new lead-free piezoelectric materials such as BCTZ systems which showed excellent piezoelectric properties at R-T phase boundary [2, 13].
TE D
Recently, researchers are seeking to improve the properties of lead-free piezoceramics by using the specialized preparation methods and specific conditions such as oxidizing atmosphere, reducing process cycle time [14-16]. However, there are no detailed reports available in the literature on the structural study of BCTZ ceramics through Rietveld
EP
refinement and Raman spectroscopy prepared by the semi-wet method. In view of this, we are reporting herein the preparation of (Ba1-xCax)(ZryTi1-y)O3 (BCTZ)
AC C
ceramics with compositions x = 0.13 and y ≤ 0.15 by the semi-wet method. The semi-wet method was employed here due to low cost and relatively simple technique. By this route, it is easier to control the stoichiometric ratio with lower sintering temperature/time; one could achieve highly dense ceramics with fine grain size. However, to the best of our knowledge, this route was adopted for the synthesis of BCZT ceramics for the first time. In the present work, we studied the effects of Ca and Zr content on synthesis, crystal structure, microstructure and electrical properties of BCZT ceramics. A detailed investigation of a crystal structure for this system was explored with the help of Rietveld refinement and Raman spectroscopy at room temperature. Meanwhile, the outcome of our results would provide the information regarding the basic mechanisms behind the anomalous behavior and underlying physical mechanism of large piezoelectricity.
ACCEPTED MANUSCRIPT
2. Experimental Method The Ba1-xCaxTi1-yZryO3 ceramics (abbreviated as BCTZ) with x = 0.13 and y ≤ 0.15 were synthesized by novel semi-wet technique. The high purity analytical-grade metal oxide or nitrate powders of Sigma Aldrich such as i.e. Ba(NO3)2 (99.9%), Ca(NO3)2.4H2O (99.9%), TiO2 (99.9%), and ZrO2 (99.9%), ethylene glycol were used as starting chemicals. After
RI PT
drying the powders, raw materials were weighed in stoichiometric amounts according to the chemical compositions of BCTZ ceramics system. The precursor for A-site of BCTZ ceramics was prepared using ethylene glycol solution, which was expected to distribute the cations homogeneously at the atomic level and forming a slurry (gel) and further dried at an
SC
optimum temperature (T ≤ 100 °C for 24 hrs) to obtain the fine powders. The dried powders of mixed oxides of A-site constituents (homogeneous and highly reactive) were mixed with appropriate amount of TiO2 and ZrO2 in ethanol medium using mortar pestle for 6 h and
M AN U
resulting slurry was dried and calcined at 1200 ºC for 8 hrs. The flow chart of the synthesis process was shown in Figure 1. The novel synthesis process was employed to prepare some other lead-free ceramics [17-19]. After calcination, powders were reground and mixed with a binder (2 wt % Polyvinyl Alcohol) and compacted in a disc shape in a steel die of diameter 10 mm using the uniaxial hydraulic press. The green circular pellets of the different
TE D
compositions were kept at 400 ºC for 4 hrs to burn off the PVA binder. The pellets were sintered at 1400 ºC for 4 hrs in the furnace equipped with PID temperature controller followed by air cooling. The major faces of the pellets were ground with emery papers, thoroughly cleaned, dried and electroded with silver paste and then cured at 400 ºC for 30
EP
min for better electrical contacts.
In order to know the phase formation and crystal structure, X-ray diffraction (XRD)
AC C
patterns of sintered samples of all the compositions were recorded at room temperature using an X-ray Powder Diffractometer (XRD 6000, Shimadzu analytical, Japan) with CuKα radiation (λ=1.5418 Å) in the 2θ range from 20º to 70º with a step of 0.02º and a scan rate 1º/min. After confirming the phase formation, structural analysis was carried out by Rietveld refinement method using FULLPROF program [20]. Raman spectra of these samples were recorded by Nd-YAG laser, 1064 nm, and 500 mW laser power. The surface morphology of sintered specimens was studied by Field emission scanning electron microscopy (FE-SEM, QUANTA 200 FEG, FEI Netherlands). The bulk density of the sintered specimens was calculated by the Archimedes principle. The relative density was determined using bulk and theoretical densities. The dielectric constant (εr) and dielectric loss (tan δ) were measured as a
ACCEPTED MANUSCRIPT function of temperature over the temperature range from room temperature to 250 ºC using Impedance Analyzer (Nova control, α-AT Germany) at 10 kHz frequency. Piezoelectric charge coefficient (d33) was measured using Piezo-meter (Take Control, PM 35, UK) after poling the specimens under applied DC field of 6 kV/mm in a silicon oil bath at room temperature for 1 hr. The planar electromechanical coupling coefficient (kp) was calculated (Agilent, 4294A, USA) on the basis of IEEE standards [21].
3. Results and Discussion
RI PT
from the resonance and anti-resonance frequencies recorded by Impedance Analyzer
SC
Figure 2 shows the variation of bulk (ρbulk) and relative densities (ρrel) of all the studied samples that showing density greater than 95% of the theoretical density except for the specimen y = 0. In the BCTZ ceramics, bulk density and relative density both increases up to
M AN U
y = 0.10 (~98 %) and then decreases with further increase of Zr concentration. Hence, it is suggested that Zr substitution in BCT ceramics modify the densification to a certain extent. Figure 3 shows the XRD patterns of all the sintered BCTZ ceramics with x = 0.13 and y ≤ 0.15 recorded at room temperature. It is evident that all the specimens exhibit a pure polycrystalline perovskite structure without any trace of impurity/secondary phase (s) which
TE D
also suggests that Zr4+ substitution is well accommodated in the BCT lattice to form a homogeneous solid solution. All the diffraction peaks of these samples have been indexed according to the perovskite-type tetragonal structure with P4mm space group, which is in agreement with the respective Joint Committee on Powder Diffraction Standards (JCPDS)
EP
file no 05-0626 and reported literature [22-23, 15]. In order to find the precise value of lattice parameters and to confirm crystal structure,
AC C
XRD data of all samples were further analyzed by Rietveld refinement using the Fullprof software and displayed in Figure 4. Good agreement between the experimental and calculated values have been observed based on the consideration of relatively lower Rwp and Rp values. In Rietveld refinement, Profile R-Factor measures goodness of fit (GOF) and the background was fitted with sixth order polynomial. The peak shapes were described by Pseudo-Voigt profiles. It is observed from the literature that BaTiO3 exhibits tetragonal symmetry with P4mm space group at room temperature. A structural model is required that has an approximation for the actual structure in Rietveld refinement. For all the ceramics, Rietveld refinement of the XRD patterns have been carried out on the basis of the tetragonal structure with P4mm space group and the
ACCEPTED MANUSCRIPT structural model allowed us to reproduce all the observed peaks (shown in Figure 3). Further, it has been observed that the compositions with x = 0.13, y ≤ 0.15 showed a quite good fit of experimental data (dotted lines) with refined data (solid lines) for the reflection (200), shown as a magnified image of patterns indicated by an arrow in Figure 4. The fitting parameters Rwp, Rexp, and ‘χ2’ of all the studied compositions have been found to be within the limit of
RI PT
agreement (see Table-1). Based on the above analysis, it has been confirmed that all the samples of BCTZ ceramics showed a tetragonal structure with P4mm space group. Further, it was found that lattice distortion (c/a) increases up to y = 0.10 thereafter it decreases and volume of the unit
SC
cell continuously increases with increasing y. Moreover, the peak position of all the specimens has been shifted towards lower angle side with increasing ‘y’ due to the lattice distortion and resulting expansion of cell volume (Table-1). It was also pointed out that there
M AN U
is an effective substitution of Ti4+ by Zr4+ in octahedral coordination. This volume expansion may be attributed to the difference in ionic radii of Ti4+ (ionic radius = 0.605 Å) by Zr4+ (ionic radius = 0.72Å) [24-25].
The average crystallite size was determined from XRD peak broadening considering the most intense peak (near 2θ~ 30°) using the Debye Scherrer equation i.e. t = kλ/β cosθ, where,
TE D
‘t’ indicates the average crystallite size, ‘k’ is the Scherer constant (0.89), ‘λ’ is the wavelength of the X-ray (λ = 1.5406 Ǻ), ‘β’ is the full width at half maxima (broadening of diffraction line on the 2θ scale. It has been observed that the value of crystallite size gradually increases with increasing the concentration of Zr. The crystallite size has been observed to
EP
increase from 27.42 nm (y = 0) to 52.23 nm (y = 0.15) which may be ascribed to the distortion in the lattice caused by the difference in the ionic radii of dopants and host ions in
AC C
the BCTZ ceramics.
Figure 5 illustrates Raman spectra of all the samples collected in the wave number range 100 cm-1 - 1000 cm-1 at room temperature by Raman spectrometer. It is one of the most powerful non-destructive techniques for studying the onset ferroelectric order in the polar disordered system. This study provides the local structural information due to its shorter coherence length and time scale of phonons. Raman spectrum of specimen y = 0 has been de-convoluted together into their Lorentzian-shape peaks. For Tetragonal structure, the general irreducible representation of BaTiO3 are as follows: Г = 3T1u + T2u, which belong to C4v point group and each of the T1u modes further splits into A1+ E modes. Furthermore, on the basis of the direction of
ACCEPTED MANUSCRIPT propagation the scattered light with respect to incoming polarization, it can be categorized as longitudinal optical (LO) or transverse optical (TO) modes. Thus, we can observe four modes in C4v point group, which are as follows: A1 (TO), A1 (LO), E (TO), and E (LO) from each T1u mode and the T2u, known as “silent mode”, becomes a mixed B1+E mode. The combined mode being no longer silent but with a spectral separation between its components is so small
RI PT
that it is difficult to distinguish. Domenico et al. [26] reported the modified irreducible representation, as follows: Г Raman = 3 A 1 (TO) + 3 A 1 (LO) +6 E (TO) + 3E (LO) + 2 E (TO +LO) +1 B1. The BCT spectrum exhibits virtually identical modes, typical of tetragonally distorted ferroelectric BT-based perovskites [23]. All Raman bands seem to be
SC
broad due to the higher disorder in the sublattice of BCT, resulting also from the overlapping of Raman modes. All samples exhibit several weak modes A1(TO1)/E(LO), B1, E(LO2) /E(TO3) and E(LO3)/A1(LO2) at 183 cm-1, 252 cm-1, 302 cm-1/347 cm-1 and 443 cm-1
M AN U
respectively. The onset of asymmetry in the E(TO4)/A1(TO3) mode, broad E (LO4) and A1(LO3) bands are visible at 516 cm-1/ 561 cm-1, 629 cm-1, and 723 cm-1 respectively. The presence of various Raman modes of BCTZ ceramics for y ≤ 0.15 match well with reported results in the literature [23, 27-29]. Detailed assignment of the vibrational frequencies for these samples has been listed in Table 2. The mode centered at 300 cm-1 is sharper, indicating the higher tetragonality of the samples, seen in XRD results. In BCTZ ceramics, the modes in
TE D
the range 180-350 cm-1 correspond to phonon vibrations of Ti-O bonds while the modes around 500-750 cm-1 correspond to phonon vibrations of Ba-O bands. A Raman active weak asymmetric breathing mode (A1g) has been obtained at 820 cm-1 in
EP
a higher concentration of BCTZ ceramics (y = 0.15), although this mode is absent in pure BT sample [27]. From the spectra, it has been observed that the modes at 302 cm-1, 252 cm-1, and
AC C
183 cm-1 are shifted towards lower wave number. In general, higher frequency broad modes of compounds may be attributed to the presence of several dissimilar atoms at A and B- sites, forming complex perovskite solid solution [15]. The modes, centered at 516 cm-1, and 723 cm-1 are shifted towards higher wave number, which may be due to the difference between the ionic radius of Ba2+ and Ca2+ as well as Ti4+ and Zr4+ and thereby resulting distortion in the lattice. A downward shift in the phonon mode may be due to the decrease in the force constant with the substitution of Zr into BT lattice. It may also be attributed to the change of the effective mass of the vibrational mode because of the greater atomic number of Zr as compared to Ti [6]. Moreover, the phonon mode of A1 (TO1) shifts towards lower frequency region which corresponds to the replacement of Ti- site with Zr [7]. Generally, the positions of phonon mode can be affected due to the hydrostatic pressure effect that generates from
ACCEPTED MANUSCRIPT clamping of grains by their neighbors while crossing the phase transition from a cubic to a tetragonal distorted phase [30]. This study concurs with our Rietveld analysis. Therefore, it is suggested that these ceramics exhibit tetragonal structure over the composition range y ≤ 0.15. Figure 6 illustrates the surface morphological features of all the sintered samples of
RI PT
BCTZ ceramics with compositions y ≤ 0.15. Microstructures of all the samples have been recorded at the magnification (1,000X) and are clearly seen from the micrographs that all the samples featured a relatively uniform, homogeneous and highly dense microstructure except for y = 0.15. Meanwhile, it is evident that the grain sizes are strongly dependent on the
SC
doping element contents. It has been observed that larger grains are surrounded by the smaller ones in these ceramic compositions (y = 0.04, 0.08, 0.10 and 0.12). For all the specimens, average grain size (Dav) was determined using line intercept method and listed in
M AN U
Table 1. The average grain size decreases from 28.57 µm (y = 0) to 8.28 µm (y = 0.15) with increasing Zr concentration up to y ≤ 0.15..
Figure 7 illustrates EDX spectra of BCTZ ceramics for y = 0, 0.10 and 0.15. From the spectra, it is clearly indicated that the arbitrarily selected region contained an appropriate proportion of all elements of Ba, Ca, Ti, Zr, and O which further support complete solid
TE D
solution formation or diffusion of Zr and Ca into BT lattice site.
Figure 8 shows the temperature dependence of the dielectric permittivity (εr) and dielectric loss (tan δ) at 10 kHz for BCTZ ceramics. The sharp phase transition has been transformed into diffuse phase with Zr4+ concentration. The magnitude of εr increases from
EP
400 to 1900 up to y= 0.10 and then it decreases to 1470 for y = 0.15. From tan δ vs temperature plots, it is clearly seen that tan δ shows a hump near the Tc for all the ceramics.
AC C
The value of tan δ has been found to vary from 0.009 (y = 0) to 0.01 (y = 0.15) at room temperature (Inset Fig. 8a), which is very low for all the samples in the temperature range T ≤ 200 oC. Inset of Figure 8 (b) showed that Tc decreases with y from 128 oC (y = 0) to 70 oC (y = 0.15). Thus, the specimen y = 0.10 shows the high value of dielectric constant with low loss and Tc = 100 oC, which can be utilized as a potential candidate for capacitor applications. Figure 9 shows the room-temperature piezoelectric charge coefficient (d33) and planar electromechanical coupling coefficient (kp) of all the poled samples, as a function of composition y. It has been observed that the d33 value increased with y, attaining a maximum value at y = 0.10 and drops with a further increase in y. Both the piezoelectric parameters (d33 & kp) showed a similar trend. The specimen with x = 0.13 and y = 0.10 showed d33 of 367 ± 2 pC/N, and kp of 0.39± 0.01. Moreover, the peculiar composition (x = 0.13 and y = 0.10) has
ACCEPTED MANUSCRIPT been compared with some lead-free BT, BNT, KNN, and PZT based ceramic system and it is observed that optimum composition showed notably higher or almost comparable piezoelectric properties to reported results [16, 31-35]. In general, the excellent piezoelectric property could be ascribed to the proximity of morphotropic phase boundary to the tricritical triple point. Therefore, the higher piezoelectric properties are greatly attributed to the
RI PT
instability in the domain structure that might facilitate the polarization switching and result in the improvement of piezoelectricity in the ceramics [2].
4. Conclusions
In the present study, Ca and Zr co-substituted BT ceramics i.e. Ba1-xCaxTi1-yZryO3
SC
(BCTZ) with compositions x = 0.13 & y ≤ 0.15 were synthesized by the semi-wet method, and its structural, surface morphology and piezoelectric properties were systematically
M AN U
studied. All the samples showed single phase formation with the tetragonal structure at room temperature, which suggests that doping with Zr4+ could not affect the main crystalline phase of BCT ceramics. Tetragonal structure with P4mm symmetry had been confirmed by Rietveld refinement using XRD data, which was further supported by Raman spectra. Unit cell volume of all the specimens was found to increase with increasing y. The average grain size decreased with y which further ascribed the inhibition of grain growth. The specimen
TE D
with x/y = 0.13/0.10 exhibited high value of dielectric constant (εr ~9353) with low value of dielectric loss (tan δ ~ 0.01) near the Tc. Moreover, enhanced piezoelectric (d33 ~367 ± 2 pC/N) and electromechanical properties (kp ~ 0.39 ± 0.01) were obtained for this composition and the optimized composition may serve as a potential candidate for the capacitor and
EP
electromechanical applications.
AC C
Acknowledgements: Financial support from DST & DRDO, Govt. of India is gratefully acknowledged. We are thankful to Director of Solid State Physics Laboratory (DRDO) Delhi for providing the facilities of piezoelectric measurements.
References (1) T. R. Shrout, S. J. Zhang, Lead-free piezoelectric ceramics: alternatives for PZT, J. Electroceram., 19 (2007) 111–124. (2) W. F. Liu, X. B. Ren, Large piezoelectric effect in Pb-free ceramics, Phys. Rev. Lett., 103 (2009) 257602-1-4.
ACCEPTED MANUSCRIPT (3) W. Li, Z. Xu, R. Chu, P. Fu, G. Zang, High piezoelectric d33 coefficient in (Ba1xCax)(Ti0.98Zr0.02)O3
lead-free ceramics with relative high Curie temperature, Mater. Lett.,
64 (2010) 2325-2337. (4) D. Xue, Y. Zhou, H. Bao, C. Zhou, J. Gao, X. Ren, Elastic, piezoelectric, and dielectric properties of 50Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 Pb-free ceramic at the morphotropic
RI PT
phase boundary, J. Appl. Phys., 109 (2011) 054110. (5) H. Maiwa, Electromechanical properties of BaTiO3 ceramics prepared by spark plasma sintering and other methods, Jpn. J. Appl. Phys., 48 (2009) 09KD04-1-4.
(6) A. Dixit, S. B. Majumder, A. Savvinov, R. S.Katiyar, R. Guo, A.S. Bhalla, Investigations on
SC
the sol-gel-derived barium zirconium titanate thin films, Mater. Lett., 56 (2002) 933- 940. (7) P. S. Dobal, A. Dixit, R. S. Katiyar, Z. Yu, R. Guo, A. S. Bhalla, Micro-Raman scattering
Appl. Phys., 89 (2001) 8085–8091.
M AN U
and dielectric investigations of phase transition behavior in the BaTiO3–BaZrO3 system, J. (8) M. Aparna, T. Bhimasankaram, S. V. Suryanarayana, G. Prasad, G. S. Kumar, Effect of lanthanum doping on electrical and electromechanical properties of Ba1-xLaxTiO3, Bull. Mater. Sci., 24 (2000) 497–504.
(9) Li W., Xu Z., Chu R., Fu P., Zang G., Piezoelectric and dielectric properties of (Ba1lead-free ceramics, J. Am. Ceram. Soc., 93 (2010) 2942–2944.
TE D
xCax)(Ti0.95Zr0.05)O3
(10) B. Jaffe, W. R. Cook, H. Jaffe, Piezoelectric ceramics, Academic Press, London, U. K, 3 (1971) chapter-7.
(11) S. J. Zhang, R. Xia, T. R. Shrout, Modified (K0.5Na0.5)NbO3 based lead-free piezoelectrics
EP
with broad temperature usage range, Appl. Phys. Lett., 91 (2007) 132913. (12) Z. Yu, R. Guo, A.S. Bhalla, Piezoelectric and strain properties of Ba(Ti1-xZrx)O3 ceramics,
AC C
J. Appl. Phys., 92 (2002) 1489-1493 (13) H. Bao, C. Zhou, D. Xue, J. Gao, X. Ren, A modified lead-free piezoelectric BZT–xBCT system with higher TC, J. Phys. D: Appl. Phys., 43 (2010) 465401. (14) S. Mahajan, O. P. Thakur, D. K. Bhattacharya, K. Sreenivas, A comparative study of Ba0.09Ca0.05Zr0.025Ti0.75O3 relaxor ceramics prepared by conventional and microwave technique, Mater. Chem. Phys., 112 (2008) 858–862. (15) V. Sreenivas Puli., A. Kumar, B. Chrisey Douglas, M. Tomozawa, J. F. Scott, R. S. Katiyar, Barium zirconate-titanate/barium calcium-titanate ceramics via sol-gel process: novel highenergy-density capacitors, J. Phys. D: Appl. Phys., 44 (2011) 395403-395412.
ACCEPTED MANUSCRIPT (16) I. Coondoo, N. Pamwar, H. Amorin, M. Algucro, A. Kholkin, Synthesis and characterization of lead free 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 ceramic, J. Appl. Phy., 113 (2013) 214107-214113. (17) V. Pal, R. K. Dwivedi, O. P. Thakur, Effect of neodymium substitution on structural and ferroelectric properties of BNT ceramics, Mater. Res. Bull., 51 (2014) 189-196. Pal, O. P. Thakur, R. K. Dwivedi, Effect of La/Li on structure, microstructure,
RI PT
(18) V.
dielectric and piezoelectric behavior of BNT ceramics, Indian J. Phys., 89 (2015) 123–130. (19) V. Pal, O. P. Thakur, R. K. Dwivedi, Investigation of MPB region in lead free BLNT-BCT system through XRD and Raman spectroscopy, J. Phys. D: Appl. Phys., 48 (2015) 055301-
SC
1-055301-8.
(20) J. Rodrigues-Carvajal, FULLPROF A Rietveld refinement and pattern matching analysis program, laboratoire leon Brillouin (CEA-CNRS), France, (2000).
M AN U
(21) S. J. Zhang, E.F. Alberta, R.E. Eitel, C.A. Randall, T.R. Shrout, Elastic piezoelectric and dielectric characterization of modified BiScO3–PbTiO3 ceramics, IEEE Trans Utrason. Ferroelectr. Freq. Control, 52 (2005) 2131-2139.
(22) Joint committee on powder diffraction standards (JCPDS) card no 05-0626. (23) R. E. Venkata, A. Mahajan, M.P.F. Graca, S.K. Mendiratta, J.M. Monteiro, M. Valente, A
TE D
Structure and ferroelectric studies of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 piezoelectric ceramics, Mater. Res. Bull., 48 (2013) 4395-4401.
(24) R. D. Shannon, Revised effective ionic radii and systematic studies of inter-atomic distances in halides and chalcogenides, Acta Crystallogr. A., 32 (1976) 751-761.
EP
(25) F. Benabdullah, A. Simon, H. Khemakhem, C. Elissalde, M. Maglione, Linking large piezoelectric coefficients to highly flexible polarization of lead free BaTiO3-CaTiO3-
AC C
BaZrO3 ceramics, J. Appl. Phys., 109 (2011) 124116. (26) D. M. J. Domenico, S. H. Wemple, S. P. Porto, R. P. Bauman, Raman spectrum of singledomain BaTiO3, Phys. Rev. 174 (1968) 522–530. (27) U. D. Ventkateswaran, V. M. Naik, R. Naik, High-pressure Raman studies of polycrystalline BaTiO3, Phys. Rev. B., 58 (1998) 14256-14260. (28) U. M. Pasha, H. Zheng, O. P. Thakur, A. Feteira, K. R. Whittle, D. C. Sinclair, I. M. Reaney, In situ Raman spectroscopy of A-site doped barium titanate, Appl. Phys. Lett., 91 (2007) 062908-062911. (29) J. D. Freire, R. S. Katiyar, Lattice dynamics of crystals with tetragonal BaTiO3 structure, Phys. Rev. B, 37 (1988) 2074.
ACCEPTED MANUSCRIPT (30) J. A. Sanjurjo, E. Lopez-Cruz, G. Burns,High-pressure Raman study of zone-center phonons in PbTiO3, Phys. Rev. B, 28 (1983) 7260–7283. (31) P. Bharathi, K. B. R. Varma, Grain and the concomitant ferroelectric domain size dependent physical properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics fabricated using powders derived from oxalate precursor route, J. Appl. Phys., 116 (2014) 164107-1- 164107-10.
RI PT
(32) V. Pal, A. Kumar, O.P. Thakur, R.K. Dwivedi, N Eswara Prasad, Preparation, microstructure and relaxor ferroelectric characteristics of BLNT–BCT lead-free Piezoceramics, J. Alloys Comp., 714 (2017) 725–735.
(33) N. Binhayeeniyi, P. Sukvisut, C. Thanachayanont, M. Supasarote, Physical and
temperature, Mater. Lett., 64 (2010) 305–308.
SC
electromechanical properties of barium zirconium titanate synthesized at low-sintering
(34) W. Jiagang, X. Dingquan, W. Wenjuan, Z. Jianguo, W. John, Effect of dwell time during
M AN U
sintering on piezoelectric properties of (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 lead-free ceramics, J. Alloys Comp., 509 (2011) L359– L361.
(35) A. Kumar, S. K. Misra, Dielectric, piezoelectric, and ferroelectric properties of lanthanummodified PZTFN ceramics, International Journal of Minerals, Metallurgy and Materials, 21
TE D
(2014) 595-603.
List of figure captions
Figure 1: Flow Chart of Semi-wet Technique for Ba1-xCaxTi1-yZryO3 based ceramics. Figure 2: Variation of relative densities (ρrel.) of BCTZ ceramics with y ≤ 0.15; Inset shows
EP
bulk density (ρbulk).
Figure 3: X-ray diffraction patterns of BCTZ ceramics (x = 0.13, y ≤ 0.15) at room
AC C
temperature.
Figure 4: Rietveld refined X-ray diffraction patterns of all BCTZ ceramics. Figure 5: Room temperature de-convoluted Raman spectrum of all the specimens of BCTZ ceramics.
Figure 6: Microstructures of all the compositions of BCTZ ceramics with y ≤ 0.15. Figure 7: EDX spectra of BCTZ ceramics for y = 0, 0.10 and 0.15. Figure 8: εr vs. T (a) and tan δ vs. T (b) of BCTZ ceramics y ≤ 0.15 in the range from RT to 250 º C at 10 kHz. Inset of Fig.8 (a) shows the variations of εr and tan δ at RT and (b) shows the variations of Tc. Figure 9: Variation of piezoelectric charge coefficient (d33) and planar electromechanical coupling factor (kp) of BCTZ ceramics with y ≤ 0.15.
ACCEPTED MANUSCRIPT
List of table captions
grain size of all BCTZ ceramics with y ≤ 0.15.
RI PT
Table 1: Lattice parameters, volume and Rietveld refined agreement R-factors and average
AC C
EP
TE D
M AN U
SC
Table 2: Fundamental frequencies (cm-1) of BCTZ system with their symmetry modes.
ACCEPTED MANUSCRIPT
Structural investigation of Ca/Zr co-substituted BaTiO3 through XRD and Raman spectroscopy Source Files
AC C
EP
TE D
M AN U
SC
RI PT
Figure 1
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Figure 2
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Figure 3
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
Figure 4 (a)
AC C
EP
TE D
Figure 4 (b)
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
Figure 5
AC C
EP
TE D
Figure 6
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Figure 7
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Figure 8 (a)
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
Figure 8 (b)
AC C
EP
TE D
Figure 9
ACCEPTED MANUSCRIPT Table 1.
y = 0.10
y = 0.12
a = b = 3.9737(2) c = 4.0149(2) α = β = γ = 90 a = b = 3.9745(2) c = 4.0154(2) α = β = γ = 90 a = b = 3.9825(2) c = 4.0159(2) α = β = γ = 90
AC C
EP
y = 0.15
a = b = 3.9739(2) c = 4.0143(2) α = β = γ = 90
R-factors
Average grain size (Dav) (µm)
63.2609(1)
Rwp = 6.14; Rexp= 5.04 χ2 = 1.48
28.57
1.0099
63.3890(1)
1.0101
63.3916(1)
RI PT
y = 0.08
a = b = 3.9741(2) c = 4.0138(2) α = β = γ = 90
1.0077
V (Å3)
1.0104
63.3969 (1)
1.0102
63.3978 (1)
1.0083
Rwp = 7.56; Rexp= 4.88 χ2 = 1.40
Rwp = 8.15; Rexp= 5.00 χ2 = 1.66
SC
y = 0.04
a = b = 3.9743(2) c = 4.0052(2) α = β = γ = 90
c/a
M AN U
y=0
Lattice constants (Å)
TE D
BCTZ x = 0.13; y ≤ 0.15
63.4061 (1)
Rwp = 7.39; Rexp= 5.40 χ2 = 1.87 Rwp = 7.01; Rexp= 5.08 χ2 = 1.90
Rwp=5.94;Rex p= 5.05 χ2 = 1.39
25.08
20.86
18.74
12.49
8.28
ACCEPTED MANUSCRIPT Table 2.
E(TO1)
39
This work BCTZ system x = 0.13 & y ≤ 0.15 -
Experiment
A1(TO1)/E(LO1)
155/182
~176-183
178/180
A1(LO1)/E(TO2)
193/196
-
189/180
B1
282
~252
308
E(LO2)/E(TO3)
308/320
308/308
E(LO3)/A1(LO2)
462/466
~297302/347 ~443
E(TO4)/A1(TO3)
514/554
E(LO4)
Ref. 23
Ref. 27
Ref. 28
Ref. 29
38
<50
-
-
RI PT
Theory (Ref. 29) J. D. Freire et al.
178/180
185
148
185/180
185
182/182
307
303
275
305/305
303
275/300
SC
Mode
463/475
463
-
489/512
486,518/520
520
519
699
~516523/561 ~629
722
-
720
723
A1(LO3)
729
~723-725
740
720
720
723
A1g
-
~820*
-
-
-
816
M AN U
466/473
AC C
EP
TE D
*refers that modes which appears for higher concentration of y i.e. y = 0.15
ACCEPTED MANUSCRIPT Highlights First time, we synthesized BCTZ piezoceramics by semi-wet method. XRD and Raman spectroscopy revealed the phase formation with tetragonal structure. Grain size reduced with additives (x/y), leading to inhibit the grain growth.
RI PT
Specimen (x/y = 0.13/0.10) exhibits excellent piezoelectric/eletromechanical
AC C
EP
TE D
M AN U
SC
properties.
S0925-8388(18)30153-1
DOI:
10.1016/j.jallcom.2018.01.152
Reference:
JALCOM 44616
To appear in:
Journal of Alloys and Compounds
Received Date: 13 July 2017 Revised Date:
27 December 2017
Accepted Date: 10 January 2018
Please cite this article as: V. Pal, O.P. Thakur, R.K. Dwivedi, Structural investigation of Ca/Zr cosubstituted BaTiO3 through XRD and Raman spectroscopy, Journal of Alloys and Compounds (2018), doi: 10.1016/j.jallcom.2018.01.152. 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.
ACCEPTED MANUSCRIPT
Structural investigation of Ca/Zr co-substituted BaTiO3 through XRD and Raman spectroscopy Vijayeta Pal1, 2#, O. P. Thakur3 and R. K. Dwivedi2 1
Defence Materials and Stores Research and Development Establishment, Kanpur-208013,
2
RI PT
India Department of Physics and Material Science and Engineering, Jaypee Institute of Information Technology, Noida – 201307, India
Solid State Physics Laboratory, Timarpur, Delhi - 110054, India
SC
3
Corresponding Author, E-mail: [email protected]
M AN U
Abstract
The present work reports the synthesis of Lead free (Ba1-xCax)(ZryTi1-y)O3 with x = 0.13, y ≤ 0.15 (i.e. BCTZ) piezoceramics by semi-wet route and effect of additives viz., Ca2+, and Zr4+ on phase formation, microstructure, piezoelectric and electromechanical properties. Detailed structural analysis suggests the formation of tetragonal perovskite phase with P4mm symmetry, which was also confirmed by Rietveld refinement and Raman spectra. SEM
TE D
micrographs showed that the average grain size decreased with Zr4+ which acts as grain growth inhibitor. Composition with x = 0.13 and y = 0.10 exhibited the optimum piezoelectric and electromechanical properties (d33 = 367 ± 2 pC/N and kp = 0.39 ± 0.01) and
EP
showed higher densification (relative density ~ 98 %). Keywords: Lead-free ceramics; Microstructure; Dielectric properties; Piezoelectric
AC C
properties
1. Introduction
In the past few years, lead-free piezoelectric ceramics have received considerable attention due to its environmental friendly nature and alternatives to lead-based compositions such as Pb(Zr,Ti)O3 (PZT) [1-2]. In continuous search for lead-free piezoceramics, barium titanate (BaTiO3; BT) is one of the potential candidates [3] showing typical ferroelectric characters with three phase transitions: rhombohedral to orthorhombic (R-O) ~ –80 °C; orthorhombic to tetragonal (O-T) ~ 5 °C; and tetragonal to cubic (T-C) ~120 °C [1]. Barium titanate has been widely studied material because of its high dielectric constant, ferroelectric properties and
ACCEPTED MANUSCRIPT nonlinear optical coefficients [2]. However, it exhibited inferior piezoelectric properties (d33 ~ 190 pC/N) with low Curie temperature (Tc ~ 120°C). In the past, electrical and piezoelectric properties of BaTiO3 were modified by applying some pioneering method for example via the construction of phase boundary, employment of site engineering, sintering condition and the use of different preparation techniques [1-2, 4-6].
RI PT
The solid solutions of BaTiO3 based ceramics exhibited a wide range of applications in electronic and technological appliances [6-8]. Moreover, electrical properties and the Curie temperature (Tc) at either barium (Ba) or titanium (Ti) sites could be controlled by the doping of appropriate foreign elements (donor or acceptor) [6-9]. However, doping of calcium (Ca)
polymorphic
phase
transition
(PPT)
behaviour
SC
at Ba- site did not make any significant effect on Tc values, but it only reduced the [10-11]
while,
some
interesting
microstructural and phase transitional changes were obtained with the doping of Zr4+ at B-site
M AN U
(Ti4+) in BaTiO3 [7, 12]. Among various BT-based ceramic systems, BZT –BCT system i.e. (Ba1-xCax)(ZryTi1-y)O3 (abbreviated as BCTZ) exhibited interesting dielectric properties for MLCC applications. The different phase transition behaviors of BZT and BCT ceramics made it a potential candidate to design new lead-free piezoelectric materials such as BCTZ systems which showed excellent piezoelectric properties at R-T phase boundary [2, 13].
TE D
Recently, researchers are seeking to improve the properties of lead-free piezoceramics by using the specialized preparation methods and specific conditions such as oxidizing atmosphere, reducing process cycle time [14-16]. However, there are no detailed reports available in the literature on the structural study of BCTZ ceramics through Rietveld
EP
refinement and Raman spectroscopy prepared by the semi-wet method. In view of this, we are reporting herein the preparation of (Ba1-xCax)(ZryTi1-y)O3 (BCTZ)
AC C
ceramics with compositions x = 0.13 and y ≤ 0.15 by the semi-wet method. The semi-wet method was employed here due to low cost and relatively simple technique. By this route, it is easier to control the stoichiometric ratio with lower sintering temperature/time; one could achieve highly dense ceramics with fine grain size. However, to the best of our knowledge, this route was adopted for the synthesis of BCZT ceramics for the first time. In the present work, we studied the effects of Ca and Zr content on synthesis, crystal structure, microstructure and electrical properties of BCZT ceramics. A detailed investigation of a crystal structure for this system was explored with the help of Rietveld refinement and Raman spectroscopy at room temperature. Meanwhile, the outcome of our results would provide the information regarding the basic mechanisms behind the anomalous behavior and underlying physical mechanism of large piezoelectricity.
ACCEPTED MANUSCRIPT
2. Experimental Method The Ba1-xCaxTi1-yZryO3 ceramics (abbreviated as BCTZ) with x = 0.13 and y ≤ 0.15 were synthesized by novel semi-wet technique. The high purity analytical-grade metal oxide or nitrate powders of Sigma Aldrich such as i.e. Ba(NO3)2 (99.9%), Ca(NO3)2.4H2O (99.9%), TiO2 (99.9%), and ZrO2 (99.9%), ethylene glycol were used as starting chemicals. After
RI PT
drying the powders, raw materials were weighed in stoichiometric amounts according to the chemical compositions of BCTZ ceramics system. The precursor for A-site of BCTZ ceramics was prepared using ethylene glycol solution, which was expected to distribute the cations homogeneously at the atomic level and forming a slurry (gel) and further dried at an
SC
optimum temperature (T ≤ 100 °C for 24 hrs) to obtain the fine powders. The dried powders of mixed oxides of A-site constituents (homogeneous and highly reactive) were mixed with appropriate amount of TiO2 and ZrO2 in ethanol medium using mortar pestle for 6 h and
M AN U
resulting slurry was dried and calcined at 1200 ºC for 8 hrs. The flow chart of the synthesis process was shown in Figure 1. The novel synthesis process was employed to prepare some other lead-free ceramics [17-19]. After calcination, powders were reground and mixed with a binder (2 wt % Polyvinyl Alcohol) and compacted in a disc shape in a steel die of diameter 10 mm using the uniaxial hydraulic press. The green circular pellets of the different
TE D
compositions were kept at 400 ºC for 4 hrs to burn off the PVA binder. The pellets were sintered at 1400 ºC for 4 hrs in the furnace equipped with PID temperature controller followed by air cooling. The major faces of the pellets were ground with emery papers, thoroughly cleaned, dried and electroded with silver paste and then cured at 400 ºC for 30
EP
min for better electrical contacts.
In order to know the phase formation and crystal structure, X-ray diffraction (XRD)
AC C
patterns of sintered samples of all the compositions were recorded at room temperature using an X-ray Powder Diffractometer (XRD 6000, Shimadzu analytical, Japan) with CuKα radiation (λ=1.5418 Å) in the 2θ range from 20º to 70º with a step of 0.02º and a scan rate 1º/min. After confirming the phase formation, structural analysis was carried out by Rietveld refinement method using FULLPROF program [20]. Raman spectra of these samples were recorded by Nd-YAG laser, 1064 nm, and 500 mW laser power. The surface morphology of sintered specimens was studied by Field emission scanning electron microscopy (FE-SEM, QUANTA 200 FEG, FEI Netherlands). The bulk density of the sintered specimens was calculated by the Archimedes principle. The relative density was determined using bulk and theoretical densities. The dielectric constant (εr) and dielectric loss (tan δ) were measured as a
ACCEPTED MANUSCRIPT function of temperature over the temperature range from room temperature to 250 ºC using Impedance Analyzer (Nova control, α-AT Germany) at 10 kHz frequency. Piezoelectric charge coefficient (d33) was measured using Piezo-meter (Take Control, PM 35, UK) after poling the specimens under applied DC field of 6 kV/mm in a silicon oil bath at room temperature for 1 hr. The planar electromechanical coupling coefficient (kp) was calculated (Agilent, 4294A, USA) on the basis of IEEE standards [21].
3. Results and Discussion
RI PT
from the resonance and anti-resonance frequencies recorded by Impedance Analyzer
SC
Figure 2 shows the variation of bulk (ρbulk) and relative densities (ρrel) of all the studied samples that showing density greater than 95% of the theoretical density except for the specimen y = 0. In the BCTZ ceramics, bulk density and relative density both increases up to
M AN U
y = 0.10 (~98 %) and then decreases with further increase of Zr concentration. Hence, it is suggested that Zr substitution in BCT ceramics modify the densification to a certain extent. Figure 3 shows the XRD patterns of all the sintered BCTZ ceramics with x = 0.13 and y ≤ 0.15 recorded at room temperature. It is evident that all the specimens exhibit a pure polycrystalline perovskite structure without any trace of impurity/secondary phase (s) which
TE D
also suggests that Zr4+ substitution is well accommodated in the BCT lattice to form a homogeneous solid solution. All the diffraction peaks of these samples have been indexed according to the perovskite-type tetragonal structure with P4mm space group, which is in agreement with the respective Joint Committee on Powder Diffraction Standards (JCPDS)
EP
file no 05-0626 and reported literature [22-23, 15]. In order to find the precise value of lattice parameters and to confirm crystal structure,
AC C
XRD data of all samples were further analyzed by Rietveld refinement using the Fullprof software and displayed in Figure 4. Good agreement between the experimental and calculated values have been observed based on the consideration of relatively lower Rwp and Rp values. In Rietveld refinement, Profile R-Factor measures goodness of fit (GOF) and the background was fitted with sixth order polynomial. The peak shapes were described by Pseudo-Voigt profiles. It is observed from the literature that BaTiO3 exhibits tetragonal symmetry with P4mm space group at room temperature. A structural model is required that has an approximation for the actual structure in Rietveld refinement. For all the ceramics, Rietveld refinement of the XRD patterns have been carried out on the basis of the tetragonal structure with P4mm space group and the
ACCEPTED MANUSCRIPT structural model allowed us to reproduce all the observed peaks (shown in Figure 3). Further, it has been observed that the compositions with x = 0.13, y ≤ 0.15 showed a quite good fit of experimental data (dotted lines) with refined data (solid lines) for the reflection (200), shown as a magnified image of patterns indicated by an arrow in Figure 4. The fitting parameters Rwp, Rexp, and ‘χ2’ of all the studied compositions have been found to be within the limit of
RI PT
agreement (see Table-1). Based on the above analysis, it has been confirmed that all the samples of BCTZ ceramics showed a tetragonal structure with P4mm space group. Further, it was found that lattice distortion (c/a) increases up to y = 0.10 thereafter it decreases and volume of the unit
SC
cell continuously increases with increasing y. Moreover, the peak position of all the specimens has been shifted towards lower angle side with increasing ‘y’ due to the lattice distortion and resulting expansion of cell volume (Table-1). It was also pointed out that there
M AN U
is an effective substitution of Ti4+ by Zr4+ in octahedral coordination. This volume expansion may be attributed to the difference in ionic radii of Ti4+ (ionic radius = 0.605 Å) by Zr4+ (ionic radius = 0.72Å) [24-25].
The average crystallite size was determined from XRD peak broadening considering the most intense peak (near 2θ~ 30°) using the Debye Scherrer equation i.e. t = kλ/β cosθ, where,
TE D
‘t’ indicates the average crystallite size, ‘k’ is the Scherer constant (0.89), ‘λ’ is the wavelength of the X-ray (λ = 1.5406 Ǻ), ‘β’ is the full width at half maxima (broadening of diffraction line on the 2θ scale. It has been observed that the value of crystallite size gradually increases with increasing the concentration of Zr. The crystallite size has been observed to
EP
increase from 27.42 nm (y = 0) to 52.23 nm (y = 0.15) which may be ascribed to the distortion in the lattice caused by the difference in the ionic radii of dopants and host ions in
AC C
the BCTZ ceramics.
Figure 5 illustrates Raman spectra of all the samples collected in the wave number range 100 cm-1 - 1000 cm-1 at room temperature by Raman spectrometer. It is one of the most powerful non-destructive techniques for studying the onset ferroelectric order in the polar disordered system. This study provides the local structural information due to its shorter coherence length and time scale of phonons. Raman spectrum of specimen y = 0 has been de-convoluted together into their Lorentzian-shape peaks. For Tetragonal structure, the general irreducible representation of BaTiO3 are as follows: Г = 3T1u + T2u, which belong to C4v point group and each of the T1u modes further splits into A1+ E modes. Furthermore, on the basis of the direction of
ACCEPTED MANUSCRIPT propagation the scattered light with respect to incoming polarization, it can be categorized as longitudinal optical (LO) or transverse optical (TO) modes. Thus, we can observe four modes in C4v point group, which are as follows: A1 (TO), A1 (LO), E (TO), and E (LO) from each T1u mode and the T2u, known as “silent mode”, becomes a mixed B1+E mode. The combined mode being no longer silent but with a spectral separation between its components is so small
RI PT
that it is difficult to distinguish. Domenico et al. [26] reported the modified irreducible representation, as follows: Г Raman = 3 A 1 (TO) + 3 A 1 (LO) +6 E (TO) + 3E (LO) + 2 E (TO +LO) +1 B1. The BCT spectrum exhibits virtually identical modes, typical of tetragonally distorted ferroelectric BT-based perovskites [23]. All Raman bands seem to be
SC
broad due to the higher disorder in the sublattice of BCT, resulting also from the overlapping of Raman modes. All samples exhibit several weak modes A1(TO1)/E(LO), B1, E(LO2) /E(TO3) and E(LO3)/A1(LO2) at 183 cm-1, 252 cm-1, 302 cm-1/347 cm-1 and 443 cm-1
M AN U
respectively. The onset of asymmetry in the E(TO4)/A1(TO3) mode, broad E (LO4) and A1(LO3) bands are visible at 516 cm-1/ 561 cm-1, 629 cm-1, and 723 cm-1 respectively. The presence of various Raman modes of BCTZ ceramics for y ≤ 0.15 match well with reported results in the literature [23, 27-29]. Detailed assignment of the vibrational frequencies for these samples has been listed in Table 2. The mode centered at 300 cm-1 is sharper, indicating the higher tetragonality of the samples, seen in XRD results. In BCTZ ceramics, the modes in
TE D
the range 180-350 cm-1 correspond to phonon vibrations of Ti-O bonds while the modes around 500-750 cm-1 correspond to phonon vibrations of Ba-O bands. A Raman active weak asymmetric breathing mode (A1g) has been obtained at 820 cm-1 in
EP
a higher concentration of BCTZ ceramics (y = 0.15), although this mode is absent in pure BT sample [27]. From the spectra, it has been observed that the modes at 302 cm-1, 252 cm-1, and
AC C
183 cm-1 are shifted towards lower wave number. In general, higher frequency broad modes of compounds may be attributed to the presence of several dissimilar atoms at A and B- sites, forming complex perovskite solid solution [15]. The modes, centered at 516 cm-1, and 723 cm-1 are shifted towards higher wave number, which may be due to the difference between the ionic radius of Ba2+ and Ca2+ as well as Ti4+ and Zr4+ and thereby resulting distortion in the lattice. A downward shift in the phonon mode may be due to the decrease in the force constant with the substitution of Zr into BT lattice. It may also be attributed to the change of the effective mass of the vibrational mode because of the greater atomic number of Zr as compared to Ti [6]. Moreover, the phonon mode of A1 (TO1) shifts towards lower frequency region which corresponds to the replacement of Ti- site with Zr [7]. Generally, the positions of phonon mode can be affected due to the hydrostatic pressure effect that generates from
ACCEPTED MANUSCRIPT clamping of grains by their neighbors while crossing the phase transition from a cubic to a tetragonal distorted phase [30]. This study concurs with our Rietveld analysis. Therefore, it is suggested that these ceramics exhibit tetragonal structure over the composition range y ≤ 0.15. Figure 6 illustrates the surface morphological features of all the sintered samples of
RI PT
BCTZ ceramics with compositions y ≤ 0.15. Microstructures of all the samples have been recorded at the magnification (1,000X) and are clearly seen from the micrographs that all the samples featured a relatively uniform, homogeneous and highly dense microstructure except for y = 0.15. Meanwhile, it is evident that the grain sizes are strongly dependent on the
SC
doping element contents. It has been observed that larger grains are surrounded by the smaller ones in these ceramic compositions (y = 0.04, 0.08, 0.10 and 0.12). For all the specimens, average grain size (Dav) was determined using line intercept method and listed in
M AN U
Table 1. The average grain size decreases from 28.57 µm (y = 0) to 8.28 µm (y = 0.15) with increasing Zr concentration up to y ≤ 0.15..
Figure 7 illustrates EDX spectra of BCTZ ceramics for y = 0, 0.10 and 0.15. From the spectra, it is clearly indicated that the arbitrarily selected region contained an appropriate proportion of all elements of Ba, Ca, Ti, Zr, and O which further support complete solid
TE D
solution formation or diffusion of Zr and Ca into BT lattice site.
Figure 8 shows the temperature dependence of the dielectric permittivity (εr) and dielectric loss (tan δ) at 10 kHz for BCTZ ceramics. The sharp phase transition has been transformed into diffuse phase with Zr4+ concentration. The magnitude of εr increases from
EP
400 to 1900 up to y= 0.10 and then it decreases to 1470 for y = 0.15. From tan δ vs temperature plots, it is clearly seen that tan δ shows a hump near the Tc for all the ceramics.
AC C
The value of tan δ has been found to vary from 0.009 (y = 0) to 0.01 (y = 0.15) at room temperature (Inset Fig. 8a), which is very low for all the samples in the temperature range T ≤ 200 oC. Inset of Figure 8 (b) showed that Tc decreases with y from 128 oC (y = 0) to 70 oC (y = 0.15). Thus, the specimen y = 0.10 shows the high value of dielectric constant with low loss and Tc = 100 oC, which can be utilized as a potential candidate for capacitor applications. Figure 9 shows the room-temperature piezoelectric charge coefficient (d33) and planar electromechanical coupling coefficient (kp) of all the poled samples, as a function of composition y. It has been observed that the d33 value increased with y, attaining a maximum value at y = 0.10 and drops with a further increase in y. Both the piezoelectric parameters (d33 & kp) showed a similar trend. The specimen with x = 0.13 and y = 0.10 showed d33 of 367 ± 2 pC/N, and kp of 0.39± 0.01. Moreover, the peculiar composition (x = 0.13 and y = 0.10) has
ACCEPTED MANUSCRIPT been compared with some lead-free BT, BNT, KNN, and PZT based ceramic system and it is observed that optimum composition showed notably higher or almost comparable piezoelectric properties to reported results [16, 31-35]. In general, the excellent piezoelectric property could be ascribed to the proximity of morphotropic phase boundary to the tricritical triple point. Therefore, the higher piezoelectric properties are greatly attributed to the
RI PT
instability in the domain structure that might facilitate the polarization switching and result in the improvement of piezoelectricity in the ceramics [2].
4. Conclusions
In the present study, Ca and Zr co-substituted BT ceramics i.e. Ba1-xCaxTi1-yZryO3
SC
(BCTZ) with compositions x = 0.13 & y ≤ 0.15 were synthesized by the semi-wet method, and its structural, surface morphology and piezoelectric properties were systematically
M AN U
studied. All the samples showed single phase formation with the tetragonal structure at room temperature, which suggests that doping with Zr4+ could not affect the main crystalline phase of BCT ceramics. Tetragonal structure with P4mm symmetry had been confirmed by Rietveld refinement using XRD data, which was further supported by Raman spectra. Unit cell volume of all the specimens was found to increase with increasing y. The average grain size decreased with y which further ascribed the inhibition of grain growth. The specimen
TE D
with x/y = 0.13/0.10 exhibited high value of dielectric constant (εr ~9353) with low value of dielectric loss (tan δ ~ 0.01) near the Tc. Moreover, enhanced piezoelectric (d33 ~367 ± 2 pC/N) and electromechanical properties (kp ~ 0.39 ± 0.01) were obtained for this composition and the optimized composition may serve as a potential candidate for the capacitor and
EP
electromechanical applications.
AC C
Acknowledgements: Financial support from DST & DRDO, Govt. of India is gratefully acknowledged. We are thankful to Director of Solid State Physics Laboratory (DRDO) Delhi for providing the facilities of piezoelectric measurements.
References (1) T. R. Shrout, S. J. Zhang, Lead-free piezoelectric ceramics: alternatives for PZT, J. Electroceram., 19 (2007) 111–124. (2) W. F. Liu, X. B. Ren, Large piezoelectric effect in Pb-free ceramics, Phys. Rev. Lett., 103 (2009) 257602-1-4.
ACCEPTED MANUSCRIPT (3) W. Li, Z. Xu, R. Chu, P. Fu, G. Zang, High piezoelectric d33 coefficient in (Ba1xCax)(Ti0.98Zr0.02)O3
lead-free ceramics with relative high Curie temperature, Mater. Lett.,
64 (2010) 2325-2337. (4) D. Xue, Y. Zhou, H. Bao, C. Zhou, J. Gao, X. Ren, Elastic, piezoelectric, and dielectric properties of 50Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 Pb-free ceramic at the morphotropic
RI PT
phase boundary, J. Appl. Phys., 109 (2011) 054110. (5) H. Maiwa, Electromechanical properties of BaTiO3 ceramics prepared by spark plasma sintering and other methods, Jpn. J. Appl. Phys., 48 (2009) 09KD04-1-4.
(6) A. Dixit, S. B. Majumder, A. Savvinov, R. S.Katiyar, R. Guo, A.S. Bhalla, Investigations on
SC
the sol-gel-derived barium zirconium titanate thin films, Mater. Lett., 56 (2002) 933- 940. (7) P. S. Dobal, A. Dixit, R. S. Katiyar, Z. Yu, R. Guo, A. S. Bhalla, Micro-Raman scattering
Appl. Phys., 89 (2001) 8085–8091.
M AN U
and dielectric investigations of phase transition behavior in the BaTiO3–BaZrO3 system, J. (8) M. Aparna, T. Bhimasankaram, S. V. Suryanarayana, G. Prasad, G. S. Kumar, Effect of lanthanum doping on electrical and electromechanical properties of Ba1-xLaxTiO3, Bull. Mater. Sci., 24 (2000) 497–504.
(9) Li W., Xu Z., Chu R., Fu P., Zang G., Piezoelectric and dielectric properties of (Ba1lead-free ceramics, J. Am. Ceram. Soc., 93 (2010) 2942–2944.
TE D
xCax)(Ti0.95Zr0.05)O3
(10) B. Jaffe, W. R. Cook, H. Jaffe, Piezoelectric ceramics, Academic Press, London, U. K, 3 (1971) chapter-7.
(11) S. J. Zhang, R. Xia, T. R. Shrout, Modified (K0.5Na0.5)NbO3 based lead-free piezoelectrics
EP
with broad temperature usage range, Appl. Phys. Lett., 91 (2007) 132913. (12) Z. Yu, R. Guo, A.S. Bhalla, Piezoelectric and strain properties of Ba(Ti1-xZrx)O3 ceramics,
AC C
J. Appl. Phys., 92 (2002) 1489-1493 (13) H. Bao, C. Zhou, D. Xue, J. Gao, X. Ren, A modified lead-free piezoelectric BZT–xBCT system with higher TC, J. Phys. D: Appl. Phys., 43 (2010) 465401. (14) S. Mahajan, O. P. Thakur, D. K. Bhattacharya, K. Sreenivas, A comparative study of Ba0.09Ca0.05Zr0.025Ti0.75O3 relaxor ceramics prepared by conventional and microwave technique, Mater. Chem. Phys., 112 (2008) 858–862. (15) V. Sreenivas Puli., A. Kumar, B. Chrisey Douglas, M. Tomozawa, J. F. Scott, R. S. Katiyar, Barium zirconate-titanate/barium calcium-titanate ceramics via sol-gel process: novel highenergy-density capacitors, J. Phys. D: Appl. Phys., 44 (2011) 395403-395412.
ACCEPTED MANUSCRIPT (16) I. Coondoo, N. Pamwar, H. Amorin, M. Algucro, A. Kholkin, Synthesis and characterization of lead free 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 ceramic, J. Appl. Phy., 113 (2013) 214107-214113. (17) V. Pal, R. K. Dwivedi, O. P. Thakur, Effect of neodymium substitution on structural and ferroelectric properties of BNT ceramics, Mater. Res. Bull., 51 (2014) 189-196. Pal, O. P. Thakur, R. K. Dwivedi, Effect of La/Li on structure, microstructure,
RI PT
(18) V.
dielectric and piezoelectric behavior of BNT ceramics, Indian J. Phys., 89 (2015) 123–130. (19) V. Pal, O. P. Thakur, R. K. Dwivedi, Investigation of MPB region in lead free BLNT-BCT system through XRD and Raman spectroscopy, J. Phys. D: Appl. Phys., 48 (2015) 055301-
SC
1-055301-8.
(20) J. Rodrigues-Carvajal, FULLPROF A Rietveld refinement and pattern matching analysis program, laboratoire leon Brillouin (CEA-CNRS), France, (2000).
M AN U
(21) S. J. Zhang, E.F. Alberta, R.E. Eitel, C.A. Randall, T.R. Shrout, Elastic piezoelectric and dielectric characterization of modified BiScO3–PbTiO3 ceramics, IEEE Trans Utrason. Ferroelectr. Freq. Control, 52 (2005) 2131-2139.
(22) Joint committee on powder diffraction standards (JCPDS) card no 05-0626. (23) R. E. Venkata, A. Mahajan, M.P.F. Graca, S.K. Mendiratta, J.M. Monteiro, M. Valente, A
TE D
Structure and ferroelectric studies of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 piezoelectric ceramics, Mater. Res. Bull., 48 (2013) 4395-4401.
(24) R. D. Shannon, Revised effective ionic radii and systematic studies of inter-atomic distances in halides and chalcogenides, Acta Crystallogr. A., 32 (1976) 751-761.
EP
(25) F. Benabdullah, A. Simon, H. Khemakhem, C. Elissalde, M. Maglione, Linking large piezoelectric coefficients to highly flexible polarization of lead free BaTiO3-CaTiO3-
AC C
BaZrO3 ceramics, J. Appl. Phys., 109 (2011) 124116. (26) D. M. J. Domenico, S. H. Wemple, S. P. Porto, R. P. Bauman, Raman spectrum of singledomain BaTiO3, Phys. Rev. 174 (1968) 522–530. (27) U. D. Ventkateswaran, V. M. Naik, R. Naik, High-pressure Raman studies of polycrystalline BaTiO3, Phys. Rev. B., 58 (1998) 14256-14260. (28) U. M. Pasha, H. Zheng, O. P. Thakur, A. Feteira, K. R. Whittle, D. C. Sinclair, I. M. Reaney, In situ Raman spectroscopy of A-site doped barium titanate, Appl. Phys. Lett., 91 (2007) 062908-062911. (29) J. D. Freire, R. S. Katiyar, Lattice dynamics of crystals with tetragonal BaTiO3 structure, Phys. Rev. B, 37 (1988) 2074.
ACCEPTED MANUSCRIPT (30) J. A. Sanjurjo, E. Lopez-Cruz, G. Burns,High-pressure Raman study of zone-center phonons in PbTiO3, Phys. Rev. B, 28 (1983) 7260–7283. (31) P. Bharathi, K. B. R. Varma, Grain and the concomitant ferroelectric domain size dependent physical properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics fabricated using powders derived from oxalate precursor route, J. Appl. Phys., 116 (2014) 164107-1- 164107-10.
RI PT
(32) V. Pal, A. Kumar, O.P. Thakur, R.K. Dwivedi, N Eswara Prasad, Preparation, microstructure and relaxor ferroelectric characteristics of BLNT–BCT lead-free Piezoceramics, J. Alloys Comp., 714 (2017) 725–735.
(33) N. Binhayeeniyi, P. Sukvisut, C. Thanachayanont, M. Supasarote, Physical and
temperature, Mater. Lett., 64 (2010) 305–308.
SC
electromechanical properties of barium zirconium titanate synthesized at low-sintering
(34) W. Jiagang, X. Dingquan, W. Wenjuan, Z. Jianguo, W. John, Effect of dwell time during
M AN U
sintering on piezoelectric properties of (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 lead-free ceramics, J. Alloys Comp., 509 (2011) L359– L361.
(35) A. Kumar, S. K. Misra, Dielectric, piezoelectric, and ferroelectric properties of lanthanummodified PZTFN ceramics, International Journal of Minerals, Metallurgy and Materials, 21
TE D
(2014) 595-603.
List of figure captions
Figure 1: Flow Chart of Semi-wet Technique for Ba1-xCaxTi1-yZryO3 based ceramics. Figure 2: Variation of relative densities (ρrel.) of BCTZ ceramics with y ≤ 0.15; Inset shows
EP
bulk density (ρbulk).
Figure 3: X-ray diffraction patterns of BCTZ ceramics (x = 0.13, y ≤ 0.15) at room
AC C
temperature.
Figure 4: Rietveld refined X-ray diffraction patterns of all BCTZ ceramics. Figure 5: Room temperature de-convoluted Raman spectrum of all the specimens of BCTZ ceramics.
Figure 6: Microstructures of all the compositions of BCTZ ceramics with y ≤ 0.15. Figure 7: EDX spectra of BCTZ ceramics for y = 0, 0.10 and 0.15. Figure 8: εr vs. T (a) and tan δ vs. T (b) of BCTZ ceramics y ≤ 0.15 in the range from RT to 250 º C at 10 kHz. Inset of Fig.8 (a) shows the variations of εr and tan δ at RT and (b) shows the variations of Tc. Figure 9: Variation of piezoelectric charge coefficient (d33) and planar electromechanical coupling factor (kp) of BCTZ ceramics with y ≤ 0.15.
ACCEPTED MANUSCRIPT
List of table captions
grain size of all BCTZ ceramics with y ≤ 0.15.
RI PT
Table 1: Lattice parameters, volume and Rietveld refined agreement R-factors and average
AC C
EP
TE D
M AN U
SC
Table 2: Fundamental frequencies (cm-1) of BCTZ system with their symmetry modes.
ACCEPTED MANUSCRIPT
Structural investigation of Ca/Zr co-substituted BaTiO3 through XRD and Raman spectroscopy Source Files
AC C
EP
TE D
M AN U
SC
RI PT
Figure 1
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Figure 2
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Figure 3
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
Figure 4 (a)
AC C
EP
TE D
Figure 4 (b)
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
Figure 5
AC C
EP
TE D
Figure 6
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Figure 7
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Figure 8 (a)
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
Figure 8 (b)
AC C
EP
TE D
Figure 9
ACCEPTED MANUSCRIPT Table 1.
y = 0.10
y = 0.12
a = b = 3.9737(2) c = 4.0149(2) α = β = γ = 90 a = b = 3.9745(2) c = 4.0154(2) α = β = γ = 90 a = b = 3.9825(2) c = 4.0159(2) α = β = γ = 90
AC C
EP
y = 0.15
a = b = 3.9739(2) c = 4.0143(2) α = β = γ = 90
R-factors
Average grain size (Dav) (µm)
63.2609(1)
Rwp = 6.14; Rexp= 5.04 χ2 = 1.48
28.57
1.0099
63.3890(1)
1.0101
63.3916(1)
RI PT
y = 0.08
a = b = 3.9741(2) c = 4.0138(2) α = β = γ = 90
1.0077
V (Å3)
1.0104
63.3969 (1)
1.0102
63.3978 (1)
1.0083
Rwp = 7.56; Rexp= 4.88 χ2 = 1.40
Rwp = 8.15; Rexp= 5.00 χ2 = 1.66
SC
y = 0.04
a = b = 3.9743(2) c = 4.0052(2) α = β = γ = 90
c/a
M AN U
y=0
Lattice constants (Å)
TE D
BCTZ x = 0.13; y ≤ 0.15
63.4061 (1)
Rwp = 7.39; Rexp= 5.40 χ2 = 1.87 Rwp = 7.01; Rexp= 5.08 χ2 = 1.90
Rwp=5.94;Rex p= 5.05 χ2 = 1.39
25.08
20.86
18.74
12.49
8.28
ACCEPTED MANUSCRIPT Table 2.
E(TO1)
39
This work BCTZ system x = 0.13 & y ≤ 0.15 -
Experiment
A1(TO1)/E(LO1)
155/182
~176-183
178/180
A1(LO1)/E(TO2)
193/196
-
189/180
B1
282
~252
308
E(LO2)/E(TO3)
308/320
308/308
E(LO3)/A1(LO2)
462/466
~297302/347 ~443
E(TO4)/A1(TO3)
514/554
E(LO4)
Ref. 23
Ref. 27
Ref. 28
Ref. 29
38
<50
-
-
RI PT
Theory (Ref. 29) J. D. Freire et al.
178/180
185
148
185/180
185
182/182
307
303
275
305/305
303
275/300
SC
Mode
463/475
463
-
489/512
486,518/520
520
519
699
~516523/561 ~629
722
-
720
723
A1(LO3)
729
~723-725
740
720
720
723
A1g
-
~820*
-
-
-
816
M AN U
466/473
AC C
EP
TE D
*refers that modes which appears for higher concentration of y i.e. y = 0.15
ACCEPTED MANUSCRIPT Highlights First time, we synthesized BCTZ piezoceramics by semi-wet method. XRD and Raman spectroscopy revealed the phase formation with tetragonal structure. Grain size reduced with additives (x/y), leading to inhibit the grain growth.
RI PT
Specimen (x/y = 0.13/0.10) exhibits excellent piezoelectric/eletromechanical
AC C
EP
TE D
M AN U
SC
properties.