Scholarly article on topic 'Strong and anisotropic magnetoelectricity in composites of magnetostrictive Ni and solid-state grown lead-free piezoelectric BZT–BCT single crystals'

Strong and anisotropic magnetoelectricity in composites of magnetostrictive Ni and solid-state grown lead-free piezoelectric BZT–BCT single crystals Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — Haribabu Palneedi, Venkateswarlu Annapureddy, Ho-Yong Lee, Jong-Jin Choi, Si-Young Choi, et al.

Abstract Aimed at developing lead-free magnetoelectric (ME) composites with performances as good as lead (Pb)-based ones, this study employed (001) and (011) oriented 82BaTiO3-10BaZrO3-8CaTiO3 (BZT–BCT) piezoelectric single crystals, fabricated by the cost-effective solid-state single crystal growth (SSCG) method, in combination with inexpensive, magnetostrictive base metal Nickel (Ni). The off-resonance, direct ME coupling in the prepared Ni/BZT–BCT/Ni laminate composites was found to be strongly dependent on the crystallographic orientation of the BZT–BCT single crystals, as well as the applied magnetic field direction. Larger and anisotropic ME voltage coefficients were observed for the composite made using the (011) oriented BZT–BCT single crystal. The optimized ME coupling of 1V/cmOe was obtained from the Ni/(011) BZT–BCT single crystal/Ni composite, in the d32 mode of the single crystal, when a magnetic field was applied along its [100] direction. This performance is similar to that reported for the Ni/Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 (PMN–PZT) single crystal/Ni, but larger than that obtained from the Ni/Pb(Zr,Ti)O3 ceramic/Ni composites. The results of this work demonstrate that the use of lead-free piezoelectric single crystals with special orientations permits the selection of desired anisotropic properties, enabling the realization of customized ME effects in composites.

Academic research paper on topic "Strong and anisotropic magnetoelectricity in composites of magnetostrictive Ni and solid-state grown lead-free piezoelectric BZT–BCT single crystals"

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Full Length Article

Strong and anisotropic magnetoelectricity in composites of magnetostrictive Ni and solid-state grown lead-free piezoelectric BZT-BCT single crystals

Haribabu Palneedia b, Venkateswarlu Annapureddyb, Ho-Yong Leec, jong-jin Choib, Si-Young Choib, Sung-Yoon Chunga, Suk-joong L. Kangad, jungho Ryub *

a Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea b Korea Institute of Materials Science (KIMS), Changwon 51508, Republic of Korea c Sunmoon University, Asan 31460, Republic of Korea

d Korea Institute of Ceramic Engineering and Technology (KICET), Jinju 52851, Republic of Korea

ARTICLE INFO

ABSTRACT

Article history:

Received 23 July 2016

Received in revised form 3 November 2016

Accepted 26 December 2016

Available online xxx

Keywords:

Lead-free

Magnetoelectric

Composites

Anisotropic

Piezoelectric

Single crystal

Aimed at developing lead-free magnetoelectric (ME) composites with performances as good as lead (Pb)-based ones, this study employed (001) and (011) oriented 82BaTiO3-10BaZrO3-8CaTiO3 (BZT-BCT) piezoelectric single crystals, fabricated by the cost-effective solid-state single crystal growth (SSCG) method, in combination with inexpensive, magnetostrictive base metal Nickel (Ni). The off-resonance, direct ME coupling in the prepared Ni/BZT-BCT/Ni laminate composites was found to be strongly dependent on the crystallographic orientation of the BZT-BCT single crystals, as well as the applied magnetic field direction. Larger and anisotropic ME voltage coefficients were observed for the composite made using the (011) oriented BZT-BCT single crystal. The optimized ME coupling of 1 V/cm Oe was obtained from the Ni/(011) BZT-BCT single crystal/Ni composite, in the d32 mode of the single crystal, when a magnetic field was applied along its [100] direction. This performance is similar to that reported for the Ni/Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 (PMN-PZT) single crystal/Ni, but larger than that obtained from the Ni/Pb(Zr,Ti)O3 ceramic/Ni composites. The results of this work demonstrate that the use of lead-free piezoelectric single crystals with special orientations permits the selection of desired anisotropic properties, enabling the realization of customized ME effects in composites.

© 2017 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

1. Introduction

Magnetoelectric (ME) materials continue to draw a lot of attention due to their wide spectrum of possible applications, including sensing, transduction, memory, and energy harvesting systems [1-4]. Compared to other heterostructures, laminate structured ME composites consisting of magnetostrictive and piezoelectric layers are easier to fabricate and have been found to exhibit superior ME responses [5]. Lead (Pb)-based ferroelectrics such as Pb(Zr,Ti)O3 (PZT), Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT), and Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 (PMN-PZT) are often employed in ME composites due to their large piezoelectric coefficients (dy, gy ) and electromechanical coupling factors

* Corresponding author. Fax: +82 55 280 3392. E-mail address: jhryu@kims.re.kr (j. Ryu).

(kjj) [6]. Although these ceramics have been found to show good ME performance when combined with magnetostrictive metallic alloys (Terfenol-D, Metglas), because of environmental concerns over the use of toxic and hazardous Pb containing materials, it is now necessary to develop eco-friendly ME composites with lead-free piezoelectric materials. In addition, replacing expensive magnetic alloys with the widely available base metals such as Nickel (Ni) is of interest for the economical production of ME composites.

Most of the investigated lead-free ME composites have been based on (K,Na)NbO3 (KNN), Nao.5Bio.5TiO3 (NBT), and BaTiO3 (BT). But, due to the low piezoelectricity (d33 <300pC/N, in most cases) of these lead-free ceramics, the corresponding ME composites have been found to exhibit weaker ME responses (on the order of a few hundred mV/cmOe) than those of the Pb-based ME composites [6]. Recently, a new lead-free ceramic system based on a Ba(Zr0.8Ti0.2)O3-(Ba0.7Ca0.3)TiO3 solid solution was reported to

http://dx.doi.org/10.1016/jyascer.2016.12.005

2187-0764/© 2017 The Ceramic Society of japan and the Korean Ceramic Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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exhibit an elevated piezoelectric coefficient (d33 ~620pC/N) at optimal composition, which is comparable to that of high-end PZT (d33 -5 00-600 pC/N for PZT-5H) [7,8]. Hence, ME composites prepared using BZT-BCT ceramics are expected to exhibit good ME performance. Nevertheless, there are hardly any reports available on the BZT-BCT ceramic based ME composites [9].

In comparison, single crystal piezoelectric materials demonstrate better piezoelectric performance than their polycrystalline counterparts due to their uniform dipole alignment [10]. Relaxor-based ferroelectric single crystals (PMN-PT, PZN-PT, and PMN-PZT), when cut and poled along specific crystallographic directions, are known to offer excellent strain responses and piezoelectric properties. These rhombohedral structured, domain engineered single crystals display greatly enhanced piezoelectric coefficients and electromechanical coupling factors along the [001] and [011] non-polar orientations, as compared to the [111] spontaneous polarization direction [11]. Results have shown that designing ME composites with special oriented single crystals is an efficient approach to optimizing the ME coupling [12-14]. Interesting relations have been identified between the directional ME coupling and the material constants of the differently oriented piezoelectric single crystals. Although the processing of polycrys-talline BZT-BCT ceramics has been considerably well reported, the synthesis of BZT-BCT single crystals has rarely been attempted, since it is expensive as well as challenging to grow lead-free single crystals of usable sizes with uniform composition [15,16]. Recently, single crystals of BZT-BCT with good chemical homogeneity and better piezoelectric properties have been produced via the solid-state conversion of polycrystals into single crystals, using an innovative technique developed by Ceracomp Co., Ltd., Korea [17].

Bulk ME composites are usually developed as trilayered laminates, in which the piezoelectric layer is arranged between two magnetostrictive ones. They are normally operated in the transversely (in-plane direction) magnetized and perpendicularly (thickness direction) polarized mode. This configuration intensifies the strain along the planar direction and minimizes the influence of demagnetizing fields from thickness direction, contributing to a better ME output in low magnetic bias ranges. For a direct ME effect in this mode, because the magnetostrictive phase deforms in the in-plane direction, the piezoelectric phase, due to the interfacial coupling, also has to deform synchronously along the planar direction and induce an electric voltage along the thickness direction [12-14]. This requires the piezoelectric phase to possess a large inplane strain response (i.e., transverse piezoelectric coefficients, d31 and d32) in order to generate a maximized ME output. To exploit this idea further in the case of lead-free piezoelectric single crystals in combination with inexpensive Ni, (001) and (011) oriented 82BaTiO3 -10BaZr03 -8CaTiO3 (BZT-BCT) single crystals with high transverse piezoelectric coefficients (d31 or d32) were chosen for this study. Herein, the off-resonance, direct ME responses of tri-layered composites of Ni/(001) BZT-BCT single crystal/Ni, Ni/(011) BZT-BCT single crystal/Ni, Ni/polycrystalline PZT/Ni are compared. The effects of the different orientations of the BZT-BCT single crystals on the ME output was also investigated. The present work is an attempt to develop eco-friendly ME composites with desired sensitivity by replacing the Pb-based piezoelectric ceramics with lead-free ones.

Fig. 1. (a) Photograph of the as-received BZT-BCT single crystals (SCs), (b) and (c) schematic diagrams of the Ni/(001) BZT-BCT/Ni and Ni/(011) BZT-BCT/Ni ME composites, respectively. Here, the arrows on the Ni and BZT-BCT SCs indicate the magnetization and poling directions, respectively.

2. Experimental procedure

ME trilayered composites of Ni/BZT-BCT/Ni and Ni/PZT/Ni were prepared using square (10mm x 10mm) plates of Ni (0.25 mm thick), BZT-BCT (0.5 mm thick), and PZT (0.5 mm thick). A photograph of the (001) and (011) oriented BZT-BCT single crystals and the schematics of the Ni/BZT-BCT/Ni laminates are presented in Fig. 1. The properties of the differently oriented BZT-BCT single crystals and the PZT ceramic are summarized in Table 1. High quality single crystals of BZT-BCT which were prepared by the SSCG technique and cut to make their plane vectors parallel to the [001] and [011] directions, were commercially obtained from Ceracomp Co., Ltd., Korea (LTExyi, LTExy2). The polycrystalline PZT plate was machined and wire cut from a PZT pellet, which was prepared by pressing and sintering (1250°C, 2h) commercially available PZT granules intended for use in high performance piezoelectric sensors and transducers. The X-ray diffraction (XRD, D/Max 2200, Rigaku Corporation, Japan) patterns of the (001) and (011) oriented, rhombohedral 82BaTi03-10BaZr03-8CaTi03 single crystals and the polyscrystalline PZT used in this study are shown in Fig. 2. The BZT-BCT single crystals were thickness poled by applying a dc electric field of 1.4 kV/mm at room temperature for 10 min. The PZT plate was poled under 4 kV/mm at 120 °C for 20 min, in its thickness direction.

To form the trilayer laminates, magnetostrictive Ni plates (Alfa Aesar, 99.5% metals basis) were bonded to the top and bottom surfaces of the piezoelectric layer using epoxy adhesive (3 M Scotch-WeldTM, DP-460) and cured at 80 °C for 4 h. For the Ni plate, the saturated in-plane magnetostriction (^11) was measured to be -40ppm [18]. The in-plane strain-electric field (S-E) behavior of the BZT-BCT and PZT samples was studied using a strain measurement method, which involves a microstrain gauge with Wheatstone bridge. A strain gauge of 5 mm gauge length and 350 ^ nominal gauge resistance (MFLA-5-350-11-1LS, Tokyo Sokki Kenkyujo Co., Ltd, Japan) was mounted on the sample surface with M-bond 200 adhesive. A unipolar electric field (<3 kV/mm) of trian-

Table 1

Dielectric and piezoelectric properties of the BZT-BCT single crystals and the PZT ceramic used in this study.

Material

dai (pC/N)

d32(pC/N)

Sli (pm2/N)

SE2 (pm2/N)

gai (10-3 mV/N)

g32(10-3mV/N)

(001)BZT-BCT

(oii)bzt-bct

0.41 0.55 0.36

-19 17.4

-13.67

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(a) o o Au (002)

(b) —-, o, (N Au f

(c) o o JL S* XI O O CM Ol r- ^ 1 i CS A

->-1 ' I ' I-'-

20 30 40 50 26 (degree)

Fig. 2. XRD patterns of the (a) (001) oriented and (b) (011) oriented BZT-BCT single crystals and (c) polycrystalline PZT.

gular wave shape formed by a function generator and amplified by a high voltage power amplifier was applied to the sample at a frequency of 0.1 Hz. The change in resistance of the sample, under the applied field, was recorded using a digital data acquisition system (USB-2404-U1, Tracer DAQ, Measurement Computing Corporation, USA) interfaced to a computer and the data gathered was further converted into a S-E loop. The polarization vs electric field (P-E) hysteresis was characterized by a ferroelectric testing system (Precision LC 11, Radiant Technologies Inc., USA) at room temperature. The ME output voltage generated from the composite samples, in response to a superimposed ac and dc magnetic field applied at an off-resonance frequency of f=1 kHz, was measured using a lock-in amplifier (SR-850, Stanford Research Systems, USA). The value of the ME voltage coefficient (aME) was calculated by dividing the

measured output voltage by the thickness of the piezoelectric layer and the applied ac magnetic field (Hac = 1 Oe).

3. Results and discussion

As listed in Table 1, the (001) oriented BZT-BCT single crystal possesses isotropic transverse piezoelectric properties, while the (011) oriented BZT-BCT single crystal displays anisotropic piezoelectric properties. The crystallographic orientations of BZT-BCT single crystals and the configurations of the d31 and d32 modes in them are depicted in Fig. 3. Here the voltage generated along the 3-axes per the unit force applied either along the 1- or 2-axes is the same (d31 =d32) for the (001) oriented BZT-BCT single crystal (Fig. 3(a)) and is different (d31 = d32) in the case of the (011) oriented BZT-BCT single crystal (Fig. 3(b) and (c)). Such isotropy or anisotropy in the properties of these crystals can be attributed to the differences in the number of degenerate states of their multidomain structures, produced upon poling [19,20]. Analogous to the Pb-based rhombohedral ferroelectric single crystals such as PMN-PT, PZN-PT, and PMN-PZT, the spontaneous polarization lies along the [111] direction, with eight possible dipole orientations for the BZT-BCT single crystals in rhombohedral symmetry. An electric poling field applied to the crystals along a non-polar direction ([001] or [011]) creates a macrosymmetric multidomain structure in them.

The engineered domain configurations for the BZT-BCT single crystals oriented and poled along [001] and [011] directions are schematically shown in Fig. 4. Here the dashed arrows represent the domain states induced by poling and their switching upon reversal of applied electric field. The (001) oriented and poled BZT-BCT crystal presents a multidomain configuration, with each domain

having one of the four dipole orientations ([111], [111], [111], and

[111]). When the poling field is reversed, the polarization switches

to the [111], [111], [111], and [111] domain variants (Fig. 4(a)). Thus, the components of all four polarization vectors lying along the body diagonals of the pseudocubicunit cell of the (001) oriented BZT-BCT are equal, so that the domain walls have no incentive to move under an external electric field along [001], giving rise to an isotropic piezoelectric response in the plane (i.e., d31 =d32) [21,22]. Once the isotropic BZT-BCT single crystal is combined with the magnetostrictive phase to form a laminate composite, the resultant transverse ME response is supposed to be isotropic. When the BZT-BCT single crystal is oriented and poled along the [011] direction, all the polarizations are aligned to the [111] and [111] dipole

orientations, which switch to the [111] and [111] domain variants upon reversal of the poling field (Fig. 4(b)). These two dipole orientations lying along the diagonals of the (011) and (011) planes tend to rotate toward the [011] direction upon the application of a positive electric field. Such a move simultaneously induces compressive

stress along the [100] direction and tensile stress along the [011] direction, resulting in different signs and magnitudes of the planar

Fig. 3. Schematic representation of the d31 and d32 modes in (001) and (011) oriented BZT-BCT single crystals.

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Fig. 4. Schematic illustration of the domain configurations for the (a) (001) and (b) (011) oriented and poled BZT-BCT single crystals.

exhibits largest electric field induced strain (0.2%) while the PZT shows least strain response (0.076%). The (001) oriented BZT-BCT displayed the same magnitude of strain (0.12%) along both the [010] and [100] directions (the S-E curve is shown for the [010] direction only). This indicates that the (011) oriented BZT-BCT single crystal, in d32 mode, would generate a higher strain induced electric voltage and contribute to better transverse ME output than those of the (001) oriented BZT-BCT single crystal and the PZT, from the respective ME composites. The anisotropic strain behavior of the (011) oriented BZT-BCT single crystal can be understood to be the result of its anisotropic piezoelectricity. This further suggests the possibility of isotropic and anisotropic ME coupling in the Ni/(001) BZT-BCT/Ni and Ni/(011) BZT-BCT/Ni composites, respectively.

The variations in the transverse aME with an applied bias field (Hdc), for the trilayer composites made using the BZT-BCT single crystals and the PZT plate are shown in Fig. 7(a) and (b), respectively. It can be seen that, among all the composite samples, aME exhibited a typical Hdc dependence, showing a sign change with respect to the reversal of the Hdc direction. Moreover, the bias field position of the maximum aME, which is directly related to the piezomagnetic coefficient (qy) of the magnetostrictive phase (Ni, in this study), remains the same for all the samples. In the case of the Ni/BZT-BCT/Ni laminates, aME was measured by applying a magnetic field along different planar directions i.e., H//[010]

and H//[100] for (001) BZT-BCT, and H//[100] and H//[011] for (011) BZT-BCT.The Ni/(001) BZT-BCT/Ni composite showed almost identical aME curves with approximately the same magnitude of maximum aME (0.3V/cm0e) irrespective of the magnetic field direction (H//[100] and H//[010]). This similarity in magnetoele-cricity can be attributed to the isotropic transverse piezoelectricity (d31 =d32) of the (001) oriented BZT-BCT single crystal (Table 1). In contrast, the Ni/(011) BZT-BCT/Ni laminate displayed strongly anisotropic ME coupling characteristics, with opposite signs of the aME curves, and different maximum aME values of 1 V/cmOe

and 0.6V/cm0e, obtained for the H//[100] and H//[0H] configurations, respectively. Such direction dependent ME responses can be a consequence of the anisotropy in the transverse piezoelectric properties of the (011) oriented BZT-BCT single crystal, i.e., d32 ^ -3 d31 (Table 1 ). It has been demonstrated in earlier studies by Patil et al.

Fig. 5. Electrical polarization hysteresis behavior of (001) and (011) oriented BZT-BCT single crystals.

piezoelectric coefficients (i.e., d31 == d32 ) [23,24].These anisotropic transverse piezoelectric properties of the (011) oriented BZT-BCT single crystal would enable the realization of anisotropic ME properties in combination with Ni.

Fig. 5 shows the P-E hysteresis loops of the (001) and (011) oriented BZT-BCT single crystals. Although the coercive fields of both the single crystals are found to be similar, the higher remanent polarization displayed by the (011) oriented BZT-BCT reflects the better ferroelectric nature of it. This leads to enhanced electromechanical response from the (011) oriented BZT-BCT as well as efficient conversion of magnetic field induced strain into electrical output from the corresponding ME composite. For further understanding, the S-E behavior of the BZT-BCT single crystals and the PZT ceramic was investigated. The schematic of the strain measurement set-up and the unipolar strain responses of the BZT-BCT and the PZT samples are shown in Fig. 6. The in-plane strains were

measured along the [100] and [011] directions for the (011) oriented BZT-BCT and along the [010] and [100] directions for the (001) oriented BZT-BCT. It is clear from the S-E curves of the samples that the (011) oriented BZT-BCT, along the [100] direction,

G Model

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Fig. 6. (a) Schematic of the in-plane strain measurement set up and (b) Strain vs E-field (unipolar) behavior for the Au-electroded, differently oriented BZT-BCT single crystals and PZT ceramic samples.

Magnetic field (Oe) Magnetic field (Oe)

Fig. 7. Magnetoelectric responses of the (a) Ni/BZT-BCT/Ni laminates with different BZT-BCT single crystal orientations and (b) Ni/PZT/Ni laminate.

[25] that different theoretical expressions are applicable for each

of the transverse ME coefficients (aE31 = IE3/IH1 (H//[0l1]) and aE32 = IE3/IH2 (H//[100])) of the ME laminate with an anisotropic piezoelectric crystal, giving rise to a different sign and magnitude of the magnetoelectricity, consistent with the experimental data. For the Ni/PZT/Ni composite, a lower value of aME, 0.2V/cmOe, was obtained, which is much lower than those measured for the Ni/BZT-BCT/Ni composites. The ME response of the Ni/PZT/Ni composite prepared in this study was similar to the range of reported ME outputs (0.2-0.4V/cmOe) forthe same trilayer composites fabricated by different methods [26,27].

It is noteworthy here that the value of aME obtained for the Ni/(011) BZT-BCT/Ni (when H//[100]) was 5 times larger than that of the Ni/PZT/Ni and more than 3 times greater than that of the Ni/(001) BZT-BCT/Ni. These results are justified by the smaller transverse piezoelectric coefficient of PZT (d31 or d32) and the larger transverse piezoelectric coefficient (d32) of (011) BZT-BCT (Table 1). The differences in the elastic compliances (s^ or s^2) and electro mechanical coupling factors of the PZT (k31 =k32 =0.36), (001) BZT-BCT (k31 =k32 =0.41) and (011) BZT-BCT (k31=0.55, k32 = 0.77) crystals are also likely to contribute to the varied ME performances of the respective composites. The strain-mediated ME coupling follows the relation, aME ady. qy where dy is the piezoelectric constant, qy (=d^y/dH) is the piezomagnetic coefficient, and ^¡j is the magnetostriction. Due to the negative in-plane magnetostriction of Ni, it contracts in the applied magnetic field direction and expands in its thickness direction. Since the Ni plate is square-shaped and its transverse dimensions are larger than its thickness, its planar magnetostriction will be isotropic but more

dominant than its out-of-plane magnetostriction. The isotropic in-plane magnetostriction behavior of Ni results in a constant transverse piezomagnetic coefficient. So, the quantity of magnetostrictive strain transferred from Ni to the BZT-BCT will be the same in all directions, but its effect on the resultant electric voltage and the ME behavior of Ni/BZT-BCT/Ni shall be mainly influenced by the signs and magnitudes of the transverse piezoelectric coefficients (d31 or d32), the elastic compliances (s^ or sj;2), and the electromechanical coupling factor (k31 or k32).

The ME responses of Ni/BZT-BCT/Ni show similar trends to those in other studies [3,22,23,28]. The greater value of aME (1 V/cmOe) displayed by the lead-free Ni/(011) BZT-BCT/Ni composite is comparable to those obtained for the Pb-based Ni/(011) PMN-PZT single crystal/Ni (1 V/cm Oe) and Ni/(011) PMN-PT single crystal/Ni (2.5V/cmOe) composites with similar geometry and dimensions [22,23]. The aME value of Ni/(011) BZT-BCT/Ni is also similar to the best reported one (1.32 V/cm Oe) for the Pb-free ME composite of Terfenol-D/(001) NBT-BT single crystal/Terfenol-D [28]. It should be reiterated here that Ni is much cheaper than the frequently employed magnetostrictive alloys Terfenol-D and Metglas and thus, it is more economical to develop Ni-based ME composites. Based on the above results, it can be emphasized that optimal cut BZT-BCT single crystals are potential candidates to replace Pb-based ceramics as piezoelectric constituents in ME composites.

4. Conclusions

In summary, lead-free magnetoelectric laminate composites were prepared using magnetostrictive Ni and (001) and (011) ori-

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ented BZT-BCT piezoelectric single crystals. The differences in the transverse piezoelectric properties of these single crystals, due to the differences in number of allowed domain states or dipole orientations under polarization, significantly influenced the ME output of the trilayer composites. The Ni/BZT-BCT/Ni composite made using the (011) oriented BZT-BCT single crystal with anisotropic transverse piezoelectric properties showed a large ME coefficient of 1 V/cm Oe, outperforming the ME response of composites formed using the (001) oriented BZT-BCT single crystal with isotropic transverse properties, and polycrystalline PZT. It can be suggested that using high performance, anisotropic lead-free piezoelectric single crystals along with magnetostrictive base metals such as Ni, will allow the development of eco-friendly and cost-effective ME composites with good output as alternatives to Pb-based ones.

Acknowledgments

This research work was supported by the Global Frontier R&D Program (Grant No. 2016M3A6B1925390) on Center for Hybrid Interface Materials (HIM) funded by the Ministry of Science, ICT & Future Planning, Korea; Korea Institute of Materials Science (KIMS) internal R&D program (Grant No. PNK4991); and the U.S. Office of Naval Research Global (Grant No. N62909-16-1-2135).

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