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. 2020 Aug 31;5(36):22800–22807. doi: 10.1021/acsomega.0c01845

Tetragonal Distortion of a BaTiO3/Bi0.5Na0.5TiO3 Nanocomposite Responsible for Anomalous Piezoelectric and Ferroelectric Behaviors

Wenxiong Zhang †, Qi Feng ‡, Eiji Hosono §,∥,⊥,*, Daisuke Asakura ∥,⊥, Jun Miyawaki †, Yoshihisa Harada †,⊥,*
PMCID: PMC7495457  PMID: 32954128

Abstract

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Ferroelectric mesocrystalline nanocomposites are functional materials with improved ferroelectricity via lattice strain engineering. In this study, X-ray diffraction (XRD) and soft X-ray absorption spectroscopy (XAS) are performed to determine the tetragonal distortion of Bi0.5Na0.5TiO3 (BNT) in a ferroelectric mesocrystalline BaTiO3 (BT)/BNT nanocomposite. The XRD results demonstrate the expansion of the BNT lattice in the BT/BNT nanocomposite. Using Williamson–Hall analysis, the tensile strain of BNT in BT/BNT-700 is confirmed. Shift and splitting of the eg orbital are observed for BNT in the BT/BNT nanocomposite in Ti L3-edge XAS, suggesting the lower symmetry of the TiO6 octahedron in BNT, which is ascribed to a significant tetragonal distortion of BNT in the BT/BNT nanocomposite caused by the lattice mismatch between BNT and BT. It is found that the tetragonally distorted BNT in BT/BNT is responsible for the anomalous ferroelectric response of the mesocrystalline BT/BNT nanocomposite.

1. Introduction

Ferroelectric materials are commonly used in sensors, actuators, and transducer technologies due to their unique ability to couple electrical- and mechanical-energy transformations.1 In recent years, lead-free piezoelectric materials have drawn significant attention due to their eco-friendly nature.2 Up to now, the lead-free piezoelectric materials have been competitive for some specific properties but still not good enough to replace the lead-based one (Pb(Zr1–xTix)O3, PZT). In the lead-free piezoelectric families, Bi0.5Na0.5TiO3 (BNT) is a promising candidate for the replacement of PZT materials because of its high Curie temperature (Tc) of 320 °C and relatively large remanent polarization (Pr) of 38 μC/cm2.3 However, difficulty in poling limits its application as a basic material for device manufacture. On the other hand, BaTiO3 (BT) exhibits a much higher piezoelectric response (d33) than commercialized PZT, while its low Tc (120 °C) still restrains its application range.4,5 The formation of solid solutions for perovskite ferroelectric materials has frequently been utilized to improve their dielectric, piezoelectric, and ferroelectric properties.3,6−8 Specifically, (1 – x)BNT–xBT solid solution with formation of the morphotropic phase boundary (MPB) at x = 0.07 exhibited a highly elevated d33 of ∼322 pC/N compared with ∼78 pC/N of BNT, but it showed a lower Tc.6,9

To solve the problem, strain engineering has been applied to 2D ferroelectric materials to improve the Tc by using the lattice mismatch between the thin film and its substrate with different lattice constants, which creates the 2D heteroepitaxial interface.10−12 The Tc of BT has been dramatically increased to over 540 °C,10 while the improvement of d33 has not yet been reported. Researchers have concentrated more on making use of the lattice mismatch between two different ferroelectric materials with different lattice constants, such as BT/SrTiO3,13 BT/KNbO3,14 and BT/BiFeO3.15 Recently, both the d33 and Tc of mesocrystalline BT/BNT nanocomposite have been successfully improved by introducing strain engineering with a 3D heteroepitaxial interface.16,17 The increase in the Tc of BT/BNT nanocomposite could be attributed to the highly tetragonal distortion of BT or BNT that originated from the lattice strain. However, it has not been definitively confirmed.

Here, we applied soft X-ray absorption spectroscopy (XAS) to 3d transition metal compounds, which is sensitive to the valence state, orbital occupation, and spin arrangement in response to the change in the local coordination of the targeted metal site. Therefore, XAS is very useful in shedding light on how the interface influences the electronic structure and the consequent superior piezoelectric response of mixed perovskite compounds.18−23 Paul et al. reported the induced ferromagnetic moment of the interfacial Ti atoms in ferroelectric–ferromagnetic Fe/BT bilayers by XAS measurement. Jan et al. and Mastelaro et al. used XAS to detect the change of tetragonality in PbTiO3 compounds with the replacement of Pb by Ca and La, respectively.19,23 Herein, to better understand the tetragonal distortion of a ferroelectric perovskite BT/BNT nanocomposite, X-ray diffraction (XRD) and Ti L2,3 edge XAS analyses were employed to verify the role of the heteroepitaxial interface in the anomalous ferroelectric behavior of mesocrystalline ferroelectric BT/BNT nanocomposites.

2. Results and Discussion

Figure 1 shows the XRD patterns of perovskite BT obtained from the hydrothermal treatment of HTO and Ba(OH)2 at 200 °C for 12 h and BT samples obtained after heating treatment at different temperatures for 3 h. It can be clearly seen that the pure BT phase was obtained after the hydrothermal reaction, which seems to show the cubic structure (a = b = c = 4.006 Å, c/a = 1.000) with the plate-like morphology (Figure 2a). The plate-like morphology of BT is inherited from HTO by the topotactic hydrothermal process.16,17 The cubic structure has a centrosymmetric TiO6 octahedron without Ti off-center displacement, as shown in the left ball model of Figure 1f, which exhibits paraelectric behavior.24 To increase the crystalline size and the crystallinity of the BT sample, the heating treatment was applied. By increasing the heating temperature, the crystalline size increased to 100, 200, and 400 nm for BT-700, 1000, and 1200, respectively (Figure 2b–d). In addition, the plate-like morphology of BT was maintained until 1000 °C. By further increasing the heating temperature up to 1200 °C, the splitting of the (200) peak into (002) and (200) peaks appeared (Figure 1e), indicating the formation of the tetragonal structure of the BT sample (a′ = b′ = 3.994 Å, c = 4.038, c/a = 1.011).25 The Ti off-center displacement of TiO6 formed the dipoles, where all the cations moved slightly toward the [001] direction, and the two oxygen anions along [001] moved toward the opposite direction, as shown in the right ball model of Figure 1f.26 It shows a macroscopic Ps along the [001] direction, namely, ferroelectricity. It is well known that ferroelectric perovskite oxides with giant tetragonality (c/a) have large polarization values and high Tc as a result of the large dipolar moment.12

Figure 1.

Figure 1

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XRD patterns of (a) BT obtained from hydrothermal treatment of H1.07Ti1.73O4·H2O (HTO) and Ba(OH)2 and BT samples obtained after heating treatment at (b) 500, (c) 700, (d) 1000, and (e) 1200 °C for 3 h. (f) Cubic structure of BT and tetragonal structure of BT with spontaneous polarization (Ps) along [001].

Figure 2.

Figure 2

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Field emission scanning electron microscopy (FE-SEM) images of (a) BT, (b) BT-700, (c) BT-1000, (d) BT-1200, (e) BNT-700, and (f) BT/BNT-700 samples.

For comparison, the BNT sample was also successfully fabricated. The same amount of BNT and the aforementioned BT powders obtained at 700 °C were physically mixed for the XRD measurement (Figure 3a). Based on the XRD analysis, both individual BT-700 and BNT-700 samples seemed to exhibit the cubic structure with lattice parameters of a = 4.006 and 3.890 Å, respectively. In addition, they are both mesocrystals constructed from corresponding nanocrystals with the same orientation direction along [110] with plate-like morphology as shown in Figures 2b,e and 3d9,27 and single-crystal-like selected area electron diffraction patterns.16,27 Mesocrystals are polycrystals constructed from the uniform distribution of nanocrystals, and each nanocrystal shows the same orientation direction and single-crystal-like selected area electron diffraction (SAED) pattern.9,16,27 For the formation of the plate-like BT/BNT nanocomposite, a two-step reaction process was employed. In the first step, the plate-like HTO crystals were solvothermally reacted with Ba(OH)2 (Ba/Ti = 0.5) to obtain a BT/HTO nanocomposite.16,17,28 In the second step, a mixture of BT/HTO, 20% excess Bi2O3, and 40% excess Na2CO3 was calcined to obtain the BT/BNT nanocomposite. The excess of Bi2O3 and Na2CO3 not only guarantees the complete reaction with residual HTO in BT/HTO but also avoids their evaporation loss during the heating treatment.16 After the heating treatment at 700 °C, a mixture of BT and BNT phases was seen, as shown in Figure 3b. In the meantime, the plate-like morphology of BT/BNT-700 was seen from the FE-SEM image (Figure 2f). Moreover, the plate-like particle was the polycrystalline particle constructed from nanocrystals, which was confirmed by the transmission electron microscope (TEM) image (Figure 4a). Moreover, two sets of SAED patterns corresponding to the BT phase and the BNT phase were observed simultaneously in one plate-like particle (Figure 4b). The SAED result also revealed that the BT and BNT nanocrystals in the mesocrystalline BT/BNT-700 had the same crystal-axis orientation direction in the [110]-zone axis, and the lattice constant of the BT phase was slightly larger than that of the BNT phase, which also agrees well with the XRD result in Figure 3. The chemical composition distributions in the plate-like particle were investigated using energy dispersive X-ray spectroscopy (EDS) analysis (Figure 4c).28,29 Three positions (labeled “①”, “②”, and “③” in Figure 4a) in the BT/BNT-700 particle presented almost the same EDS spectra, suggesting a homogeneous chemical composition distribution in the plate-like particle. The C and Cu elements were from the copper grid used for the sample holder, but all the remaining elements corresponded to BT/BNT-700, suggesting no impurities.

Figure 3.

Figure 3

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XRD patterns of (a) physically mixed BT and BNT powder samples with the same weight and the (b) BT/BNT-700 sample. Panel (c) is from the range (31o to 33o) of (a) and (b). (d) Schematic images of BT-700, BNT-700, and BT/BNT-700 mesocrystals and heteroepitaxial interfaces in the BT/BNT-700 mesocrystal. (e) Polarization–electric field (P–E) hysteresis loops of pellet samples of BT-700, BNT-700, and BT/BNT-700. Adapted with permission from ref (16). Copyright 2018 Royal Chemical Society.

Figure 4.

Figure 4

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(a) TEM image, (b) SAED pattern, and (c) EDS spectra of the BT/BNT-700 mesocrystal.

BT in the BT/BNT-700 mesocrystal exhibited the same cubic structure as the individual BT-700 mesocrystal based on the XRD analysis in Figure 3. However, the structure of BNT in the BT/BNT-700 mesocrystal could not be confirmed from the XRD analysis.16 It can be clearly seen from Figure 3c (scanning range of 31–33°) that the (110) peak of BNT in BT/BNT-700 shifted to a lower diffraction angle compared with the individual BNT-700, indicating the increase in the lattice constant due to the tensile strains from the larger lattice constant of neighboring BT. However, the (110) peak of BT in BT/BNT-700 showed no peak shifting toward a higher angle, which can be explained by the fact that the BT nanocrystals in the BT/BNT-700 mesocrystal formed in the first step of the solvothermal reaction and the BNT nanocrystals formed and coherently grew on the BT nanocrystals during the second step of the heating treatment. Furthermore, the continuous area between BT and BNT was the heteroepitaxial interface area of BNT growth on BT, which is schematically described in Figure 3d. Subsequently, the tensile force to BNT caused the transition formation of BNT by gradually decreasing the lattice constant, as shown in Figure 3d, suggesting the expansion of the (110) plane of BNT according to the crystallographic relationship.

To determine the crystalline sizes of the BT and BNT nanocrystals in the BT/BNT-700 mesocrystal and further confirm its strains, the Williamson–Hall equation was utilized, which is simply expressed as follows:30,31

2. 1

where βhkl is the full width at half maximum (FWHM) value for each diffraction peak, K is the shape factor (0.89), λ is the wavelength of Cu Kα (0.154 nm) radiation, D is the crystalline size, and ε is the integral breadth related to the strain. Hence, by plotting the graph of βhklcosθ against 4sinθ, the crystalline size and the lattice strain of samples can be estimated from the intercept and slope of the Williamson–Hall plot, respectively. Figure 5 shows the Williamson–Hall plots of BT and BNT in the BT/BNT-700 mesocrystal. The instrumental broadening was determined by the SrTiO3 standard. The crystalline size of SrTiO3 was 80 nm by the calculation and was obviously independent of the d-spacing (4sinθ), which suggests that the instrumental broadening and strain in the sample were negligible.32,33 The crystalline sizes of BT and BNT in BT/BNT-700 were calculated to be 39 and 46 nm, respectively. The positive slope value for BNT in BT/BNT-700 confirmed the existence of tensile strain. On the other hand, BT in BT/BNT-700 showed a very small negative value within the error bars, making it difficult to confirm the strain type.

Figure 5.

Figure 5

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Williamson–Hall plots of BT/BNT-700 samples (BT in BT/BNT-700 and BNT in BT/BNT-700); SrTiO3 standard was analyzed for instrumental calibration.

In order to obtain convincing evidence to identify the intrinsic ferroelectric properties of the materials, we measured their P–E hysteresis.34Figure 3e shows the P–E hysteresis loops of the pellet samples of BT-700, BNT-700, and BT/BNT-700. The BT/BNT-700 nanocomposite showed ferroelectric behavior with a large Pr value of 2.4 μC/cm2, whereas the BT-700 and BNT-700 samples showed very weak ferroelectric but not paraelectric responses, suggesting that they were not cubic structures, which contradicted the XRD results. Moreover, the converse piezoelectric responses of BT-700, BNT-700, and BT/BNT-700 were measured by the piezoresponse force microscopy (PFM) technique, where BT/BNT-700 showed a large piezoelectric response of 408 pm/V, suggesting its ferroelectricity. In the meantime, BT-700 and BNT-700 showed weak piezoelectric responses, revealing their weak ferroelectricity.16 Actually, it is well known that BT and BNT perovskites prepared by low-temperature processes, such as hydrothermal, solvothermal, and sol–gel processes, have pseudo-cubic structures, which are almost cubic with very little distortion at the crystal plane angle and are difficult to distinguish from XRD results. The lattice defects, low crystallinity, and small crystal sizes are responsible for the formation of the pseudo-cubic BT and BNT phases.28,35 The results demonstrated that both the BT-700 and BNT-700 samples showed pseudo-cubic structures (c/a = 1.000).

The strain induced by the lattice mismatch between BT and BNT can generally lower the crystal symmetry from cubic (Oh) to tetragonal (D4h). Therefore, Ti L-edge XAS can be employed to determine the actual symmetry of the TiO6 octahedron of BNT in the BT/BNT nanocomposite and elucidate the anomalous ferroelectric behavior.19,36,37

Figure 6 shows Ti L-edge XAS spectra for the BT-500, BT-700, and BT-1200 samples. These spectra have L3 and L2 regions created by the spin–orbit interaction, and each region contains t2g and eg peaks separated by approximately 2.10 eV by crystal-field splitting (ΔL3). The L3 eg state, which consists of 3dz2 and 3dx2 – y2 orbitals, is directed toward ligand anions and is therefore more sensitive to deviations from the Ti octahedral symmetry, which means the eg orbital is expected to split and shift to lower energy for tetragonal distortion in the symmetry of the TiO6 octahedron.36 By increasing the heating temperature, the area intensity of the spectra was increased. Based on the XRD results (Figure 1), BT-500 and BT-700 showed pseudo-cubic structures with nearly centrosymmetric TiO6 octahedra, resulting in no decrease in ΔL3 or splitting of the eg orbital. The BT-1200 sample showed a tetragonal structure (c/a = 1.011) with a non-centrosymmetric TiO6 octahedron. However, there was no peak splitting or shifting of the eg orbital, suggesting that the tetragonal distortion of the TiO6 octahedron was not obvious. Similar behavior has also been found when Ba atoms are substituted by Sr atoms in the Ba1–xSrxTiO3 ceramic system.23 Torres-Pardo et al. demonstrated that significant Ti off-centering is only observed once the tetragonality exceeds c/a = 1.020 for SrTiO3, confirming the paraelectric state c/a = 1.000 as the predicted ground state by local density approximation (LDA) calculations.38 It is similar to the case of PbTiO3 where the bulk phase with a tetragonal structure (c/a = 1.030) exhibited L3 eg peak splitting with a ΔL3 of 1.80 eV, and a PbTiO3 thin film (c/a = 1.063) deposited on the SrTiO3 substrate exhibited L3 eg peak splitting with an even smaller ΔL3 of 1.65 eV.19,38

Figure 6.

Figure 6

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Ti L2,3-edge XAS spectra for BT-500, BT-700, and BT-1200 samples.

Figure 7a shows the Ti L-edge XAS spectra for BT-700, BNT-700, and BT/BNT-700. The L3-edge eg orbital centered at 460 eV for BT-700 reveals the centrosymmetry of the TiO6 octahedron; that is, the structure of BT-700 is pseudo-cubic. Similarly, the TiO6 octahedron in BNT-700 also keeps the pseudo-cubic centrosymmetric structure.23,40 They are all consistent with the XRD results in Figure 3a.

Figure 7.

Figure 7

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(a) Ti L2,3-edge XAS spectra and (b–d) their peak fitting of Ti L3 edge by Gaussian after background subtraction with two arctangent functions in the form of y = atan–1(x + x0) + y0 shown as dashed lines for BT-700, BNT-700, and BT/BNT-700.23,39 (e) Peak fitting of the L3 eg peak by Gaussians after same background subtraction. (f) Symmetry transformation of a TiO6 octahedron from cubic to tetragonal by (110) plane tensile strains.

For the BT/BNT-700 sample, on the other hand, the L3-edge eg peak has an asymmetric profile tailing toward high energy and peaking at lower energy than BT-700 and BNT-700 (Figure 7a). The asymmetric profile of the eg peak directly indicates the tetragonal distortion of the TiO6 octahedron of BNT in BT/BNT-700, as revealed by the XRD result. We investigated the tetragonal distortion in detail by a Gaussian fitting of the eg peak. The BT/BNT-700 sample should have had the BT-700 region without tetragonal distortion as well as the BNT region with tetragonal distortion. Then, we assumed a fixed Gaussian (peak 3 in Figure 7e) peaking at the same energy as BT-700, and two Gaussians (peaks 1 and 2) representing the split eg peaks originated from the distorted BNT-700. Figure 7e shows the three Gaussian fittings of the eg peak of BT/BNT-700. The relatively higher intensity of peak 1 than peak 2 is consistent with previous results on Fe implanted SrTiO341 and TiO2 anatase.42 A recent Ti 2p XAS calculation for rutile and anatase TiO2 using a sizable supercell and the Bethe–Salpeter equation43 reproduced not only the splitting of the eg peak (peaks 1 and 2) distributed across the single peak 3 but also the enhancement of peak 1 for anatase and peak 2 for rutile TiO2. The different eg peak profiles between anatase and rutile TiO2 can be explained largely by differences in the binding energies of the excitons for the corresponding eg peaks. The enhancement of peak 1 in the present case may have a connection with the localized character of the eg state for the highly defective structure typical for anatase, which constructs the asymmetric profile peaking at a lower energy than that of BT-700 and BNT-700. This also leads to the observed reduction in ΔL3 from 2.00 eV (e.g., BNT-700) to 1.85 eV. The Gaussian fitting of the eg peak also allowed us to estimate the volume ratio of BT-700 and BNT-700 by comparing the area intensity ratio of the sum of peaks 1 and 2 with that of peak 3. The obtained value of 1.18 is close to the expected volume ratio (1.23) of BNT and BT in BT/BNT-700.16 The slightly lower than expected value may be due to the less heteroepitaxial interface depicted in Figure 3d.

As shown in Figure 7b–d, the ratio of the area intensity of the eg and t2g peaks (Aeg/t2g) for BT-700, BNT-700, and BT/BNT-700 were estimated to be 2.71, 2.83, and 3.24 by simply fitting the L3-edge using two Gaussians and background subtractions. According to the configuration interaction (CI) cluster model calculations by Wu et al., simulated eg peaks in Ti 2p XAS spectra for tetragonally distorted SrTiO3-based thin films by the strain from the substrate shift to lower energy (corresponding to the smaller ΔL3) and the increased Aeg/t2g.44 Thus, it can be concluded that the BNT phase subjected to tensile strain in a (110) plane from the BT phase caused a tetragonal distortion with the expansion of the [001]-axis Ti–O bond length, as shown in Figure 7f. Ootsuki et al.45 reported the ΔL3 and the tetragonal distortion (c/a) of a TiO6 octahedron by employing different strains, where the c/a ratio was estimated to be 1.020 in BNT of BT/BNT-700. On the other hand, the lattice mismatch between BT and BNT in BT/BNT-700 was calculated to be 2.14% from the XRD result, suggesting that the tensile strains almost contribute to the tetragonal distortion of BNT in BT/BNT-700. Tensile strains often lead to the improvement of the ferroelectricity of the ferroelectric material or turn paraelectric behavior into ferroelectric behavior.10−12 The present result explains how the tensile strain causes the tetragonal distortion only in the BNT phase, which is responsible for the anomalous ferroelectric properties of the BT/BNT nanocomposite. Now, we know that the tetragonal distortion can be well confirmed, and its c/a ratio can be estimated using XAS. The increasing shifts and split of the Ti L3 eg peak for the BT/BNT nanocomposite indicate larger tetragonal distortion at the BNT site. Ferroelectricity with larger tetragonality (c/a) exhibits improved ferroelectric and piezoelectric behaviors of materials.46 In this paper, we identified the connection between the tetragonal distortion and the corresponding modification in the electronic structure only at the BNT site that is responsible for the change of ferroelectricity in the BT/BNT nanocomposite.

3. Conclusions

BT-700, BNT-700, and BT/BNT-700 mesocrystal samples were successfully synthesized, and their structures were confirmed by XRD measurement. Both BT-700 and BNT-700 showed weak-ferroelectric pseudo-cubic structures (c/a = 1.000). BT with a tetragonal structure (c/a = 1.011) was obtained after heating treatment up to 1200 °C. In the BT/BNT-700 nanocomposite, the BT phase did not suffer strain from the neighboring BNT phase, while the BNT phase was highly tetragonally distorted, which was also confirmed by the Williamson–Hall method. The electronic structure of the corresponding samples was also confirmed by Ti 2p XAS. The Ti 3d(eg) peak shift and splitting of the BT sample heated at 1200 °C could not be detected due to insignificant tetragonal distortion. Ti 3d(eg) peak shift and splitting were observed for the BT/BNT-700 nanocomposite, which is ascribed to a significant tetragonal deformation (c/a = 1.020) of the TiO6 octahedron of BNT in the BT/BNT nanocomposite caused by the lattice mismatch between BT and BNT. That is, the tetragonally distorted BNT in BT/BNT should be responsible for the improved ferroelectric behavior of the mesocrystalline BT/BNT nanocomposite.

4. Experimental Section

4.1. Fabrication of Perovskite Mesocrystals

The mesocrystalline BT/BNT nanocomposite was prepared from an HTO powder sample as reported in our previous study.16 For the synthesis of the plate-like mesocrystal samples of BT and BNT for comparison, the plate-like HTO crystals (0.4 g) and Ba(OH)2·8H2O (mole ratio of Ba/Ti = 1.2) were hydrothermally treated in 30 mL of distilled water under stirring conditions at 200 °C for 12 h. Then, the obtained samples were washed with distilled water and dried at 60 °C. Finally, the obtained BT samples were heat treated at different temperatures for 3 h at a heating rate of 10 °C/min. The BNT was prepared according to the reference.47 The samples obtained by heat treatment were designated as BT/BNT-X, BT-X, and BNT-X, where X represents the heating temperature.

4.2. Characterization

The structures of powder samples were investigated using a powder X-ray diffractometer (Shimadzu, XRD-6100) with Cu Kα (λ = 0.154 nm) radiation. The particle size and morphology of the samples were observed using FE-SEM (Hitachi, S-900).

The P–E loops of the pellet samples were measured using a ferroelectric testing system (Toyo Corporation, FCE3-4KVSYS) at room temperature. XAS measurement was carried out at BL07LSU of SPring-8. The Ti L2,3-edge XAS spectra for the samples fabricated in this research were obtained in the total-electron-yield detection mode. Note that XAS in the total-electron-yield mode is not as surface sensitive as photoelectrons, and although all the samples in this study have a mesocrystalline structure with uniform distribution of nanocrystals, it is safe to say that we can mostly probe the characteristics of the entire particle using XAS in the total-electron-yield mode.

Acknowledgments

We wish to acknowledge Fangyi Yao for XRD, FE-SEM, and P–E hysteresis measurements and Masaki Kobayashi for valuable hints and discussions during the preparation of the manuscript.

Author Contributions

E.H. and Y.H. conceived, designed, and coordinated the study. Q.F. prepared the concerning materials. W.Z. and J.M. conducted the XAS measurement. W.Z., E.H., D.A., J.M., and Y.H. analyzed the data from XAS measurement. All authors discussed the results and wrote the manuscript.

The authors declare no competing financial interest.

References

  1. Guo R.; Cross L. E.; Park S.-E.; Noheda B.; Cox D. E.; Shirane G. Origin of the High Piezoelectric Response in PbZr1–xTixO3. Phys. Rev. Lett. 2000, 84, 5423. 10.1103/PhysRevLett.84.5423. [DOI] [PubMed] [Google Scholar]
  2. Saito Y.; Takao H.; Tani T.; Nonoyama T.; Takatori K.; Homma T.; Nagaya T.; Nakamura M. Lead-free Piezoceramics. Nature 2004, 432, 84–87. 10.1038/nature03028. [DOI] [PubMed] [Google Scholar]
  3. Hajra S.; Tripathy A.; Panigrahi B. K.; Choudhary R. N. P. Development and Excitation Performance of Lead Free Electronic Material: Eu and Fe Doped Bi0. 5Na0. 5TiO3 for Filter Application. Mater. Res. Express 2019, 6, 076304 10.1088/2053-1591/ab149b. [DOI] [Google Scholar]
  4. Wada S.; Takeda K.; Muraishi T.; Kakemoto H.; Tsurumi T.; Kimura T. Preparation of [110] Grain Oriented Barium Titanate Ceramics by Templated Grain Growth Method and Their Piezoelectric Properties. Jpn. J. Appl. Phys. 2007, 46, 7039. 10.1143/JJAP.46.7039. [DOI] [Google Scholar]
  5. Shrout T. R.; Zhang S. J. Lead-free Piezoelectric Ceramics: Alternatives for PZT?. J. Electroceram. 2007, 19, 113–126. 10.1007/s10832-007-9047-0. [DOI] [Google Scholar]
  6. Maurya D.; Zhou Y.; Yan Y.; Priya S. Synthesis Mechanism of Grain-oriented Lead-free Piezoelectric Na0.5Bi0.5TiO3-BaTiO3 Ceramics with Giant Piezoelectric Response. J. Mater. Chem. C 2013, 1, 2102. 10.1039/c3tc00619k. [DOI] [Google Scholar]
  7. Hajra S.; Sahoo S.; Das R.; Choudhary R. N. P. Structural, Dielectric and Impedance Characteristics of (Bi0.5Na0.5)TiO3-BaTiO3 Electronic System. J. Alloys Compd. 2018, 750, 507–514. 10.1016/j.jallcom.2018.04.010. [DOI] [Google Scholar]
  8. Hajra S.; Sahu M.; Purohit V.; Choudhary R. N. P. Dielectric, Conductivity and Ferroelectric Properties of Lead-free Electronic Ceramic: 0.6Bi(Fe0.98Ga0.02)O3-0.4BaTiO3. Heliyon 2019, 5, e01654 10.1016/j.heliyon.2019.e01654. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Hu D.; Kong X.; Mori K.; Tanaka Y.; Shinagawa K.; Feng Q. Ferroelectric Mesocrystals of Bismuth Sodium Titanate: Formation Mechanism, Nanostructure, and Application to Piezoelectric Materials. Inorg. Chem. 2013, 52, 10542–10551. 10.1021/ic4015256. [DOI] [PubMed] [Google Scholar]
  10. Choi K. J.; Biegalski M.; Li Y. L.; Sharan A.; Schubert J.; Uecker R.; Reiche P.; Chen Y. B.; Pan X. Q.; Gopalan V.; Chen L.-Q.; Schlom D. G.; Eom C. B. Enhancement of Ferroelectricity in Strained BaTiO3 Thin Films. Science 2004, 306, 1005–1009. 10.1126/science.1103218. [DOI] [PubMed] [Google Scholar]
  11. Haeni J. H.; Irvin P.; Chang W.; Uecker R.; Reiche P.; Li Y. L.; Choudhury S.; Tian W.; Hawley M. E.; Craigo B.; Tagantsev A. K.; Pan X. Q.; Streiffer S. K.; Chen L. Q.; Kirchoefer S. W.; Levy J.; Schlom D. G. Room-temperature Ferroelectricity in Strained SrTiO3. Nature 2004, 430, 758–761. 10.1038/nature02773. [DOI] [PubMed] [Google Scholar]
  12. Zhang L.; Chen J.; Fan L.; Diéguez O.; Cao J.; Pan Z.; Wang Y.; Wang J.; Kim M.; Deng S.; Wang J.; Wang H.; Deng J.; Yu R.; Scott J. F.; Xing X. Giant Polarization in Super-tetragonal Thin Films Through Interphase Strain. Science 2018, 361, 494–497. 10.1126/science.aan2433. [DOI] [PubMed] [Google Scholar]
  13. Harigai T.; Tanaka D.; Kakemoto H.; Wada S.; Tsurumi T. Dielectric Properties of BaTiO3/SrTiO3 Superlattices Measured with Interdigital Electrodes and Electromagnetic Field Analysis. J. Appl. Phys. 2003, 94, 7923. 10.1063/1.1625780. [DOI] [Google Scholar]
  14. Fujii I.; Shimizu S.; Yamashita K.; Nakashima K.; Kumada N.; Moriyoshi C.; Kuroiwa Y.; Fujikawa Y.; Tanaka D.; Furukawa M.; Wada S. Enhanced Piezoelectric Response of BaTiO3-KNbO3 Composites. Appl. Phys. Lett. 2011, 99, 202902. 10.1063/1.3662397. [DOI] [Google Scholar]
  15. Lorenz M.; Lazenka V.; Schwinkendorf P.; Bern F.; Ziese M.; Modarresi H.; Volodin A.; Van Bael M. J.; Temst K.; Vantomme A.; Grundmann M. Multiferroic BaTiO3-BiFeO3 Composite Thin Films and Multilayers: Strain Engineering and Magnetoelectric Coupling. J. Phys. D: Appl. Phys. 2014, 47, 135303. 10.1088/0022-3727/47/13/135303. [DOI] [Google Scholar]
  16. Zhang W.; Ma H.; Li S.; Hu D.; Kong X.; Uemura S.; Kusunose T.; Feng Q. Anomalous Piezoelectric Response of Ferroelectric Mesocrystalline BaTiO3/Bi0.5Na0.5TiO3 Nanocomposites Designed by Strain Engineering. Nanoscale 2018, 10, 8196–8206. 10.1039/C7NR09135D. [DOI] [PubMed] [Google Scholar]
  17. Zhang W.; Li S.; Ma H.; Hu D.; Kong X.; Uemura S.; Kusunose T.; Feng Q. Ferroelectric Mesocrystalline BaTiO3/BaBi4Ti4O15 Nanocomposite: Formation Mechanism, Nanostructure, and Anomalous Ferroelectric Response. Nanoscale 2019, 11, 3837–3846. 10.1039/C8NR07587E. [DOI] [PubMed] [Google Scholar]
  18. Asokan K.; Jan J. C.; Chiou J. W.; Pong W. F.; Tsai M.-H.; Shih H. L.; Chen H. Y.; Hsueh H. C.; Chuang C. C.; Chang Y. K. Electronic Structures of Ba1-xCaxTiO3 Studied by X-ray Absorption Spectroscopy and Theoretical Calculation. J. Phys.: Condens. Matter 2001, 13, 11087. 10.1088/0953-8984/13/48/332. [DOI] [Google Scholar]
  19. Mastelaro V. R.; Neves P. P.; De Lazaro S. R.; Longo E.; Michalowicz A.; Eiras J. A. Electronic Structure of Pb1-xLaxTiO3 Ferroelectric Materials from Ti 2p and O 1s Soft X-Ray Absorption Spectroscopy. J. Appl. Phys. 2006, 99, 044104 10.1063/1.2173683. [DOI] [Google Scholar]
  20. Mesquita A.; Michalowicz A.; Mastelaro V. R. Local Order and Electronic Structure of Pb1-xLaxZr0.40Ti0.60O3 Materials and Its Relation with Ferroelectric Properties. J. Appl. Phys. 2012, 111, 104110. 10.1063/1.4720472. [DOI] [Google Scholar]
  21. Jan J. C.; Kumar K. P. K.; Chiou J. W.; Tsai H. M.; Shih H. L.; Hsueh H. C.; Ray S. C.; Asokan K.; Pong W. F.; Tsai M.-H.; Kuo S. Y.; Hsieh W. F. Effect of the Ca Content on the Electronic Structure of Pb1-xCaxTiO3 Perovskites. Appl. Phys. Lett. 2003, 83, 3311–3313. 10.1063/1.1618375. [DOI] [Google Scholar]
  22. Paul A.; Zheng J.-G.; Aoki T. Titanium Magnetic Polarization at the Fe/BaTiO3 Interfaces: An Effect of Ferroelectric Polarization Discontinuity. J. Appl. Phys. 2017, 122, 154302. 10.1063/1.4998531. [DOI] [Google Scholar]
  23. Jan J. C.; Tsai H. M.; Pao C. W.; Chiou J. W.; Asokan K.; Kumar K. P. K.; Pong W. F.; Tang Y. H.; Tsai M.-H.; Kuo S. Y.; Hsieh W. F. Direct Experimental Evidence of Hybridization of Pb States with O 2p States in Ferroelectric Perovskite Oxides. Appl. Phys. Lett. 2005, 87, 012103 10.1063/1.1988984. [DOI] [Google Scholar]
  24. Feng Q.; Hirasawa M.; Yanagisawa K. Synthesis of Crystal-Axis-Oriented BaTiO3 and Anatase Platelike Particles by a Hydrothermal Soft Chemical Process. Chem. Mater. 2001, 13, 290–296. 10.1021/cm000411e. [DOI] [Google Scholar]
  25. Zhong W.; Zhang P.; Wang Y.; Ren T. Size Effect on the Dielectric Properties of BaTiO3. Ferroelectrics 1994, 160, 55–59. 10.1080/00150199408007694. [DOI] [Google Scholar]
  26. Zhang J.; Visinoiu A.; Heyroth F.; Syrowatka F.; Alexe M.; Hesse D.; Leipner H. S. High-resolution Electron Energy-Loss Spectroscopy of BaTiO3/SrTiO3 Multilayers. Phys. Rev. B 2005, 71, 064108 10.1103/PhysRevB.71.064108. [DOI] [Google Scholar]
  27. Song R. Q.; Cölfen H. Mesocrystals—Ordered Nanoparticle Superstructures. Adv. Mater. 2010, 22, 1301–1330. 10.1002/adma.200901365. [DOI] [PubMed] [Google Scholar]
  28. Hu D.; Ma H.; Tanaka Y.; Zhao L.; Feng Q. Ferroelectric Mesocrystalline BaTiO3/SrTiO3 Nanocomposites with Enhanced Dielectric and Piezoelectric Responses. Chem. Mater. 2015, 27, 4983–4994. 10.1021/acs.chemmater.5b01368. [DOI] [Google Scholar]
  29. Kong X.; Hu D.; Ishikawa Y.; Tanaka Y.; Feng Q. Solvothermal Soft Chemical Synthesis and Characterization of Nanostructured Ba1–x(Bi0.5K0.5)xTiO3 Platelike Particles with Crystal-Axis Orientation. Chem. Mater. 2011, 23, 3978–3986. 10.1021/cm2015252. [DOI] [Google Scholar]
  30. Mote V. D.; Purushotham Y.; Dole B. N. Williamson-Hall Analysis in Estimation of Lattice Strain in Nanometer-sized ZnO Particles. J. Theor. Appl. Phys. 2012, 6, 6. 10.1186/2251-7235-6-6. [DOI] [Google Scholar]
  31. Ilyas S.; Heryanto; Abdullah B.; Tahir D. X-ray Diffraction Analysis of Nanocomposite Fe3O4/activated carbon by Williamson-Hall and Size-strain Plot Methods. Nano-Struct. Nano-Objects 2019, 20, 100396. 10.1016/j.nanoso.2019.100396. [DOI] [Google Scholar]
  32. Zhang H.; Liu S.; Scofield M. E.; Wong S. S.; Hong X.; Prakapenka V. B.; Greenberg E.; Tyson T. A. Structural Phase Transitions in SrTiO3 Nanoparticles. Appl. Phys. Lett. 2017, 111, 052904 10.1063/1.4997332. [DOI] [Google Scholar]
  33. Yabuuchi N.; Sugano M.; Yamakawa Y.; Nakai I.; Sakamoto K.; Muramatsu H.; Komaba S. Effect of Heat-treatment Process on FeF3 Nanocomposite Electrodes for Rechargeable Li Batteries. J. Mater. Chem. 2011, 21, 10035–10041. 10.1039/c0jm04231e. [DOI] [Google Scholar]
  34. Haertling G. H. Ferroelectric Ceramics: History and Technology. J. Am. Ceram. Soc. 1999, 82, 797–818. 10.1111/j.1151-2916.1999.tb01840.x. [DOI] [Google Scholar]
  35. Smith M. B.; Page K.; Siegrist T.; Redmond P. L.; Walter E. C.; Seshadri R.; Brus L. E.; Steigerwald M. L. Crystal Structure and the Paraelectric-to-ferroelectric Phase Transition of Nanoscale BaTiO3. J. Am. Chem. Soc. 2008, 130, 6955–6963. 10.1021/ja0758436. [DOI] [PubMed] [Google Scholar]
  36. Mastelaro V. R.; Neves P. P.; Michalowicz A.; Eiras J. A. Electronic Structure of Pb1- xBaxZr0.65Ti0.35O3 Ferroelectric Compounds Probed by Soft X-Ray Absorption Spectroscopy. J. Phys.: Condens. Matter 2007, 19, 226212. 10.1088/0953-8984/19/22/226212. [DOI] [Google Scholar]
  37. Arenholz E.; Van der Laan G.; Fraile-Rodríguez A.; Yu P.; He Q.; Ramesh R. Probing Ferroelectricity in PbZr0.2Ti0.8O3 with Polarized Soft X-rays. Phys. Rev. B 2010, 82, 140103. 10.1103/PhysRevB.82.140103. [DOI] [Google Scholar]
  38. Torres-Pardo A.; Gloter A.; Zubko P.; Jecklin N.; Lichtensteiger C.; Colliex C.; Triscone J.-M.; Stéphan O. Spectroscopic Mapping of Local Structural Distortions in Ferroelectric PbTiO3/SrTiO3 Superlattices at the Unit-cell Scale. Phys. Rev. B 2011, 84, 220102. 10.1103/PhysRevB.84.220102. [DOI] [Google Scholar]
  39. Stöhr J.NEXAFS spectroscopy; Springer Science & Business Media: 2013; Vol. 25. [Google Scholar]
  40. Sargent W.Table of periodic properties of the elements; Sargent-Welch Scientific: Skokie, IL,1980. [Google Scholar]
  41. Lobacheva O.; Chavarha M.; Yiu Y. M.; Sham T. K.; Goncharova L. V. The Local Structure and Ferromagnetism in Fe-implanted SrTiO3 Single Crystals. J. Appl. Phys. 2014, 116, 013901 10.1063/1.4886875. [DOI] [Google Scholar]
  42. Krüger P. Multichannel Multiple Scattering Calculation of L2,3-edge Spectra of TiO2 and SrTiO3: Importance of Multiplet Coupling and Band Structure. Phys. Rev. B 2010, 81, 125121. 10.1103/PhysRevB.81.125121. [DOI] [Google Scholar]
  43. Laskowski R.; Blaha P. Understanding the L2,3 X-ray Absorption Spectra of Early 3d Transition Elements. Phys. Rev. B 2010, 82, 205104. 10.1103/PhysRevB.82.205104. [DOI] [Google Scholar]
  44. Wu M.; Xin H. L.; Wang J. O.; Li X. J.; Yuan X. B.; Zeng H.; Zheng J.-C.; Wang H.-Q. Investigation of the Multiplet Features of SrTiO3 in X-ray Absorption Spectra Based on Configuration Interaction Calculations. J. Synchrotron Radiat. 2018, 25, 777–784. 10.1107/S160057751800423X. [DOI] [PubMed] [Google Scholar]
  45. Ootsuki S.; Ikeno H.; Umeda Y.; Yonezawa Y.; Moriwake H.; Kuwabara A.; Kido O.; Ueda S.; Tanaka I.; Fujikawa Y.; Mizoguchi T. Impact of local Strain on Ti-L2,3 Electron Energy-loss Near-edge Structures of BaTiO3: A first-principles Multiplet Study. Microscopy 2014, 63, 249–254. 10.1093/jmicro/dfu011. [DOI] [PubMed] [Google Scholar]
  46. Woicik J.; Shirley E. L.; Hellberg C. S.; Andersen K. E.; Sambasivan S.; Fischer D. A.; Chapman B. D.; Stern E. A.; Ryan P.; Ederer D. L.; Li H. Ferroelectric Distortion in SrTiO3 Thin Films on Si (001) by X-ray Absorption Fine Structure Spectroscopy: Experiment and First-principles Calculations. Phys. Rev. B 2007, 75, 140103. 10.1103/PhysRevB.75.140103. [DOI] [Google Scholar]
  47. Hu D.; Mori K.; Kong X.; Shinagawa K.; Wada S.; Feng Q. Fabrication of [100]-oriented Bismuth Sodium Titanate Ceramics with Small Grain Size and High Density for Piezoelectric Materials. J. Eur. Ceram. Soc. 2014, 34, 1169–1180. 10.1016/j.jeurceramsoc.2013.11.031. [DOI] [Google Scholar]

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