**3. Results and discussion**

#### **3.1. High dense BaTiO3 ceramic with their ferroelectric and piezoelectric properties**

X-ray diffraction study confirmed the tetragonal crystal structure having c/a ~ 1.0144. The dense microstructure was evidenced from morphological studies with an average grain size ~ 7.8 μm as shown in **Figure 1(a)**. **Figure 1(b)** shows the temperature dependent variation of the dielectric permittivity (ε<sup>r</sup> ) in the range of 25–160°C at fixed frequencies viz. 1, 25, 50, 75 and100 kHz for BT ceramic sintered at 1300°C. The phase transition from ferroelectric to paraelectric was observed at Curie temperature (Tc ~ 125°C) with ε<sup>r</sup> = 5617 [23]. **Figure 1(c)** shows the polarization-electric field (P-E) hysteresis loops for BaTiO<sup>3</sup> ceramic measured at 0.1 Hz and room temperature. Typical hysteresis loop confirms the ferroelectric nature of the sample at room temperature. The hysteresis loop is well saturated and fully developed, indicate that external field has enough energy to switch and rotate the ferroelectric domain of BT ceramic. The saturation and remnant polarization, Psat = 24.13 μC/cm2 and Pr = 10.42 μC/cm2 was observed at the electric field strength of 57.14 kV/cm having lower coercive field of E<sup>c</sup> = 2.047 kV/cm. The reason for achieving improved ferroelectric properties in the present work may be attributed to the high value of c/a ratio ~1.014 and dense microstructure with average grain size 7.8 μm. The lower Ec indicate that low energy loss during electric field sweep having low energy barriers for polarization rotation i.e. soft ferroelectric nature. Low energy barrier can greatly promote the polarization rotation and effectively enhance the piezoelectric properties [3]. **Figure 1(d)** shows variation of polarization current density with respect to applied electric field. Current density exhibits the peaking behavior for both positive and negative cycle of applied electric field. The peaking behavior is a characteristic feature of the good ferroelectric ceramic having saturation polarization. Therefore, in present work we are successful to obtain the high-quality BT ceramic having saturated polarization states [23]. Thus, the observed ferroelectric properties are promising for ferroelectric memory device applications with larger *Pr* and *P<sup>s</sup>* having low E<sup>c</sup> . The estimated value of electric dipole moment for BT is 0.6689 × 10−27 C.cm by using Pr and lattice constant values.

with the addition of ethanol, and dried, then calcined at 1130°C for 10 h. Thereafter, they were remixed and pressed into pellets having 10 mm diameter and 0.6–1 mm in thickness and sintered for two times first at 1260°C for 10 h and secondly at 1400°C for 5 h in an air atmosphere. The post-calcination at 1260°C for 10 h was carried out to achieve proper diffusion to assist the

*-xBa0.95Ca0.05Ti0.92Zr0.08O<sup>3</sup>*

ceramics with x = 0, 0.25, 0.50, 0.75, 1 were prepared by mixed oxide solid state reaction. High purity

, and ZrO<sup>2</sup>

mixed in stoichiometric proportion and ball milled for 24 h using ethanol medium. Thereafter solutions were dried and calcined at 1200°C for 10 h in air. Calcined powders were grounded well and pressed into pellets of 1 cm in diameter and ~ 0.7–0.8 mm in thickness using 5 wt% polyvinyl alcohol (PVA) as a binder. After burning out PVA at 600°C the samples were sintered at 1350°C for 10 h. All ferroelectric materials system investigated in this book chapter was prepared and characterized for structural information at functional ceramics laboratory, Savitribai Phule Pune

The phase formation, crystal lattice symmetry and microstructural features of the samples were examined using the X-ray diffraction (XRD) with a CuKα radiation (λ = 1.5406 Å; D8 Advance, Bruker Inc., Germany) and the scanning electron microscopy (JEOL-JSM 6306A, Japan). The relative density of sintered pellets was estimated from the ratio of the apparent density measured by Archimedes' principle and the theoretical density calculated using crystal cell parameters. For electrical property measurements, silver paste was applied on both sides of the polished surfaces of pellet and then the sample was cured at 200°C for overnight to dry out the moisture prior to

temperature from −100 to 150°C at 100 kHz using inductance-capacitance-resistance (LCR) meter (HIOKI- 3532-50, Japan), connected to a computer-controlled furnace. Polarization (*P*) versus electric field (*E*) i.e. *P-E* hysteresis loops and the electric field induced strain i.e. *S-E* curves for ceramics were recorded at Ceramics and Composites Group, DMRL, Hyderabad on virgin (unpoled) samples at an applied electric field of ~ 50–60 kV/cm at 0.1 Hz, using a ferroelectric test system (TF Analyzer 2000 of M/s. aixAcct Systems, GmbH, Germany). The piezoelectric constant d33 for poled ceramics was measured using piezoelectric coefficient *d33* meter (YE2730A *d33* meter, USA).

X-ray diffraction study confirmed the tetragonal crystal structure having c/a ~ 1.0144. The dense microstructure was evidenced from morphological studies with an average grain size ~ 7.8 μm as shown in **Figure 1(a)**. **Figure 1(b)** shows the temperature dependent variation

 **ceramic with their ferroelectric and piezoelectric properties**


, SnO<sup>2</sup>

.

 *[(1−x)BCST-xBCZT] synthesis*

) and loss tangent (tanδ) were measured as a function of

[(1−x)BCST-xBCZT] lead-free piezoelectric

(Hi Media; purity ≥99%) chemicals were

homogenization and avoid the phase segregation of CaTiO3

, CaCO<sup>3</sup>

, TiO<sup>2</sup>

*2.1.3. (1−x) Ba0.95Ca0.05Ti0.92Sn0.08O<sup>3</sup>*

The (1−x) Ba0.95Ca0.05Ti0.92Sn0.08O3

analytical grade BaCO3

116 Ferroelectrics and Their Applications

**2.2. Characterizations**

any measurements. Dielectric constant (ε<sup>r</sup>

**3. Results and discussion**

**3.1. High dense BaTiO3**

University.

**Figure 1(e)** shows the bipolar electric field induced strain curves measured for BT sample at frequency of 0.1 Hz with respect to bipolar electric fields. Sample revealed the "sprout"

**Figure 1.** (a-f). (a) X- ray diffraction pattern, inset SEM, (b) relative permittivity verses temperature, (c) P-E hysteresis loop (d) J-E loop, (e) S-E loop, (f) S-P curve, of BaTiO<sup>3</sup> ceramics. (reprinted figure from ref. 23. Copyright (2016) by the AIP publishing.).

shape loop instead of "butterfly" loop which confirms the improved piezoelectric behavior [4]. Which indicates that the BT ceramic is not showing negative strain behavior, therefore here we should note that the enhancement of strain (S) is due to the sprout shape of bipolar electric field induced strain curve [4]. For electric field E = 57.14 kV/cm, better value of remnant strain 0.212% and higher value of the converse piezoelectric coefficient d\*<sup>33</sup> = 376 pm/V were observed. Unfortunately, practical implementations of BT-based ceramics for commercial actuator applications are still limited by their inferior electromechanical properties as compare to those of their conventional PZT counterparts. In the present study, it is worth pointing out that the strain reaches 0.212% at E = 57.14 kV/cm which is a promising value for lead-free piezoelectric ceramic. Large value of strain output of BaTiO<sup>3</sup> is accompanied by small strain hysteresis which enabling the materials to be a promising potential for actuator applications. It is well known that domain switching and domain wall motion of BaTiO<sup>3</sup> ceramic could contribute to field-induced strain as an extrinsic effect. Since the extrinsic contribution is sensitive to external excitation, the large electric field in strain measurement may be responsible for a larger d\*<sup>33</sup> = 376 pm/V [23]. Here for BaTiO3 ceramic the strain-electric field hysteresis loop, which resembles the "sprout" shape loop, is may be due to the three types of effects; one is the normal converse piezoelectric effect of the lattice and other two are due to switching and movement of domain walls of BaTiO3 [24]. The electrostriction coefficients Q is a four-rank tensor property that describes the relationship between polarization-induced strain (S) which proportional to the square of polarization (P) and is given by *S = QP2* [25]. **Figure 1(f)** shows the variation of strain with respect to polarization for BaTiO3 ceramic; using this graph of strain vs. polarization we can find value of electrostriction coefficient. The relationship between field-induced strain S and polarization P satisfied equation; Q<sup>33</sup> = (S3 )/(P3 ) 2 , where Q33 is electrostrictive coefficient, S3 is the strain and P3 is the polarization [4]. In our case for BaTiO<sup>3</sup> the observed value of the electrostrictive coefficient was Q<sup>33</sup> = 0.035 m<sup>4</sup> /C2 this is larger than that of PZT (0.018–0.025 m<sup>4</sup> / C2 ) based ceramic [4]. The high Q33 of the BT ceramic is an important factor accounting for their high piezoelectric constant [4]. The high Q33 of the present BT ceramic means that it would be valuable to investigate the possible electrostrictive applications of BT ceramic.

to Ti4+. Thus, incorporation of Sn4+ inhibits the grain growth of BaTiO3

) and remnant polarization (*Pr*

), maximum polarization (*Pmax*) and coercive electric field (*Ec*

in **Figure 3(f)**. For *x* = 0.00 the observed values of *Pr*

that, most of the time, the reported values of *Pr*

temperature range.

of coercive field (*Ec*

ferroelectric materials.

sponds to the coercive field *Ec*

(*Pr*

ics. To evident the phase coexistence of noncentrosymmetric lattice symmetries near room temperature the temperature dependent dielectric constant measurements were performed in the range of −150 to 150°C . Based on the dielectric anomaly observed at different temperatures with Sn4+ content in BCST ceramics, a phase diagram has been constructed and is shown in **Figure 2**. Thus, the observed dielectric results support the XRD results about the phase coexistence of orthorhombic-tetragonal lattice symmetry for x = 0.075 of BCST ceramics. All the BCST ceramics exhibits low dielectric loss (tanδ) < 4% in the measured

BaTiO3-Based Lead-Free Electroceramics with Their Ferroelectric and Piezoelectric Properties…

**Figure 3 (a-e)**, shows the polarization-electric field (*P-E*) hysteresis loop and displacement current density - electric field (*J-E*) curves measured with an applied electric field up to 50–60 kV/cm at 0.1 Hz. Both the P-E and J-E measurements were performed on virgin (unpoled) composition. All BCST ceramics exhibit a typical electric-field induced ferroelectric polarization hysteresis loop, which confirms the ferroelectric nature of investigated samples. In the present work, the compositions with *x* = 0.00 and 0.1 do not show the well-saturated P-E hysteresis loops. Because to achieve the saturation state of polarization in electroceramics is rather quite difficult due to the dielectric strength of the electroceramics which limits the electric field value. Moreover, the saturation state of polarization as well as the proper values

field induced displacement current density that reveals the sharp peaking behavior during

a field responsible for domain switching for a saturated loop [27–29]. It is important to note

P-E hysteresis loop which is not well saturated; thus, in principles they are not proper values as they are measured from the pre-saturated P-E loops [27, 28]. Therefore, the peak value of displacement current density (*J*) shown in **Figure 3(a-e)** for the forward and reverse cycles indicate the presence of a cyclic and uniform in both the directions, a typical characteristic of

An observation made from **Figure 3(a-e)** reveals that the compositions with *x* = 0.00 and 0.1 does not exhibit the sharp peaking behavior hence they are said to be not the completely saturated, whereas the compositions with *x* = 0.025, 0.05 and 0.075 show the sharp peaking behavior of displacement current density. Thus, the compositions with *x* = 0.025, 0.05 and 0.075 are said to be completely saturated with respect to an applied electric field. Another important observation is made from **Figure 3** that for compositions with *x* = 0.025, 0.05 and 0.075, both the P-E and J-E curves are intersecting at a value of electric field which is approximately corre-

not show any intersection of P-E and J-E plots. Furthermore, the compositions with x = 0.025, 0.05 and 0.075 exhibit the symmetric nature during positive and negative cycle of an applied electric field i.e. there is no imprint behavior of polarization state. This means that the compositions with *x* = 0.025, 0.05 and 0.075 may be useful for piezoelectric Ac device i.e. vibrational energy harvesting applications. The ferroelectric parameters namely remnant polarization

. On the other hand, the compositions with *x* = 0.00 and 0.1 does

, *Pmax* and *Ec*

and *Ec*

positive and negative cycles [27, 28]. The presence of J-E peak corresponds to the *Ec*

based electroceram-

119

http://dx.doi.org/10.5772/intechopen.77388

) can be reported by measuring the electric

values are estimated from the observed

), with Sn4+ content is presented

, 12.70 μC/cm<sup>2</sup>

are 5.75 μC/cm<sup>2</sup>

value i.e.

#### **3.2. Tune the ferroelectric and piezoelectric properties of BaTiO3 by Ca2+ and Sn4+ substitution**

The phase formation, microstructural aspects and dielectric properties for Ba0.7Ca0.3Ti1− x Snx O3 (BCST) ceramics with *x* = 0.00, 0.025, 0.05, 0.075 and 0.1 compositions are investigated and concluded that the compositions with x = 0.00, 0.025 and 0.05 reveals the tetragonal lattice symmetry *P4mm*, while the composition x = 0.075 shows the phase coexistence of tetragonal and orthorhombic lattice symmetries i.e. *P4mm + Amm2*. However, the composition x = 0.10 shows the combination *P4mm* (60%) and cubic *Pm*¯ 3*m* (40%) (ICSD# 99736) lattice symmetries which is called the pseudo-cubic (PC) lattice symmetry [26]. Thus, to invoke the improved ferroelectric and piezoelectric behavior of the material system an attempt to be made to achieve phase coexistence of noncentrosymmetric lattice symmetries near room temperature. The average grain size of BCST ceramics is found to be decreased from 8.56 to 2.36 μm with increasing Sn4+ content from x = 0.00 to 0.1 [26]. This is due to the lower grain-growth rates of slowly diffusing Sn4+ due to its higher ionic radii compared to Ti4+. Thus, incorporation of Sn4+ inhibits the grain growth of BaTiO3 based electroceramics. To evident the phase coexistence of noncentrosymmetric lattice symmetries near room temperature the temperature dependent dielectric constant measurements were performed in the range of −150 to 150°C . Based on the dielectric anomaly observed at different temperatures with Sn4+ content in BCST ceramics, a phase diagram has been constructed and is shown in **Figure 2**. Thus, the observed dielectric results support the XRD results about the phase coexistence of orthorhombic-tetragonal lattice symmetry for x = 0.075 of BCST ceramics. All the BCST ceramics exhibits low dielectric loss (tanδ) < 4% in the measured temperature range.

shape loop instead of "butterfly" loop which confirms the improved piezoelectric behavior [4]. Which indicates that the BT ceramic is not showing negative strain behavior, therefore here we should note that the enhancement of strain (S) is due to the sprout shape of bipolar electric field induced strain curve [4]. For electric field E = 57.14 kV/cm, better value of remnant strain 0.212% and higher value of the converse piezoelectric coefficient d\*<sup>33</sup> = 376 pm/V were observed. Unfortunately, practical implementations of BT-based ceramics for commercial actuator applications are still limited by their inferior electromechanical properties as compare to those of their conventional PZT counterparts. In the present study, it is worth pointing out that the strain reaches 0.212% at E = 57.14 kV/cm which is a promising value for lead-free piezo-

esis which enabling the materials to be a promising potential for actuator applications. It is well

field-induced strain as an extrinsic effect. Since the extrinsic contribution is sensitive to external excitation, the large electric field in strain measurement may be responsible for a larger d\*<sup>33</sup> = 376 pm/V [23]. Here for BaTiO3 ceramic the strain-electric field hysteresis loop, which resembles the "sprout" shape loop, is may be due to the three types of effects; one is the normal converse piezoelectric effect of the lattice and other two are due to switching and movement of

that describes the relationship between polarization-induced strain (S) which proportional to

we can find value of electrostriction coefficient. The relationship between field-induced strain

is the polarization [4]. In our case for BaTiO<sup>3</sup>

valuable to investigate the possible electrostrictive applications of BT ceramic.

**3.2. Tune the ferroelectric and piezoelectric properties of BaTiO3**

sition x = 0.10 shows the combination *P4mm* (60%) and cubic *Pm*¯

/C2

) based ceramic [4]. The high Q33 of the BT ceramic is an important factor accounting for their high piezoelectric constant [4]. The high Q33 of the present BT ceramic means that it would be

The phase formation, microstructural aspects and dielectric properties for Ba0.7Ca0.3Ti1−

lattice symmetries which is called the pseudo-cubic (PC) lattice symmetry [26]. Thus, to invoke the improved ferroelectric and piezoelectric behavior of the material system an attempt to be made to achieve phase coexistence of noncentrosymmetric lattice symmetries near room temperature. The average grain size of BCST ceramics is found to be decreased from 8.56 to 2.36 μm with increasing Sn4+ content from x = 0.00 to 0.1 [26]. This is due to the lower grain-growth rates of slowly diffusing Sn4+ due to its higher ionic radii compared

 (BCST) ceramics with *x* = 0.00, 0.025, 0.05, 0.075 and 0.1 compositions are investigated and concluded that the compositions with x = 0.00, 0.025 and 0.05 reveals the tetragonal lattice symmetry *P4mm*, while the composition x = 0.075 shows the phase coexistence of tetragonal and orthorhombic lattice symmetries i.e. *P4mm + Amm2*. However, the compo-

)/(P3 ) 2

[24]. The electrostriction coefficients Q is a four-rank tensor property

is accompanied by small strain hyster-

[25]. **Figure 1(f)** shows the variation of

, where Q33 is electrostrictive coefficient,

 **by Ca2+ and Sn4+**

the observed value of the

3*m* (40%) (ICSD# 99736)

/

ceramic; using this graph of strain vs. polarization

this is larger than that of PZT (0.018–0.025 m<sup>4</sup>

ceramic could contribute to

electric ceramic. Large value of strain output of BaTiO<sup>3</sup>

the square of polarization (P) and is given by *S = QP2*

strain with respect to polarization for BaTiO3

electrostrictive coefficient was Q<sup>33</sup> = 0.035 m<sup>4</sup>

S and polarization P satisfied equation; Q<sup>33</sup> = (S3

domain walls of BaTiO3

118 Ferroelectrics and Their Applications

is the strain and P3

S3

C2

x Snx O3

**substitution**

known that domain switching and domain wall motion of BaTiO<sup>3</sup>

**Figure 3 (a-e)**, shows the polarization-electric field (*P-E*) hysteresis loop and displacement current density - electric field (*J-E*) curves measured with an applied electric field up to 50–60 kV/cm at 0.1 Hz. Both the P-E and J-E measurements were performed on virgin (unpoled) composition. All BCST ceramics exhibit a typical electric-field induced ferroelectric polarization hysteresis loop, which confirms the ferroelectric nature of investigated samples. In the present work, the compositions with *x* = 0.00 and 0.1 do not show the well-saturated P-E hysteresis loops. Because to achieve the saturation state of polarization in electroceramics is rather quite difficult due to the dielectric strength of the electroceramics which limits the electric field value. Moreover, the saturation state of polarization as well as the proper values of coercive field (*Ec* ) and remnant polarization (*Pr* ) can be reported by measuring the electric field induced displacement current density that reveals the sharp peaking behavior during positive and negative cycles [27, 28]. The presence of J-E peak corresponds to the *Ec* value i.e. a field responsible for domain switching for a saturated loop [27–29]. It is important to note that, most of the time, the reported values of *Pr* and *Ec* values are estimated from the observed P-E hysteresis loop which is not well saturated; thus, in principles they are not proper values as they are measured from the pre-saturated P-E loops [27, 28]. Therefore, the peak value of displacement current density (*J*) shown in **Figure 3(a-e)** for the forward and reverse cycles indicate the presence of a cyclic and uniform in both the directions, a typical characteristic of ferroelectric materials.

An observation made from **Figure 3(a-e)** reveals that the compositions with *x* = 0.00 and 0.1 does not exhibit the sharp peaking behavior hence they are said to be not the completely saturated, whereas the compositions with *x* = 0.025, 0.05 and 0.075 show the sharp peaking behavior of displacement current density. Thus, the compositions with *x* = 0.025, 0.05 and 0.075 are said to be completely saturated with respect to an applied electric field. Another important observation is made from **Figure 3** that for compositions with *x* = 0.025, 0.05 and 0.075, both the P-E and J-E curves are intersecting at a value of electric field which is approximately corresponds to the coercive field *Ec* . On the other hand, the compositions with *x* = 0.00 and 0.1 does not show any intersection of P-E and J-E plots. Furthermore, the compositions with x = 0.025, 0.05 and 0.075 exhibit the symmetric nature during positive and negative cycle of an applied electric field i.e. there is no imprint behavior of polarization state. This means that the compositions with *x* = 0.025, 0.05 and 0.075 may be useful for piezoelectric Ac device i.e. vibrational energy harvesting applications. The ferroelectric parameters namely remnant polarization (*Pr* ), maximum polarization (*Pmax*) and coercive electric field (*Ec* ), with Sn4+ content is presented in **Figure 3(f)**. For *x* = 0.00 the observed values of *Pr* , *Pmax* and *Ec* are 5.75 μC/cm<sup>2</sup> , 12.70 μC/cm<sup>2</sup>

and 7.12 kV/cm, respectively. Here, the BCT showed high value of *Ec*

increases up to 7.05 μC/cm2

The possible reason for decrease of *Ec*

Thus, the incorporation of Sn4+ into BaTiO3

of ferroelectric domain and thus the *Pr*

electric/electrostrictive properties. The increase in *Pr*

for x = 0.00, 0.025,0.050,0.075 and 0.1 respectively.

symmetric butterfly loop with as small as deviation in *d*<sup>33</sup>

butterfly loop for *x* = 0.1 having small deviations in *d*<sup>33</sup>

<sup>∗</sup> i.e. (*d*<sup>33</sup>

reported values for Sn4+ modified BaTiO<sup>3</sup>

decreases to 185 pm/V (for *x* = 0.1). The observed values of (*d*<sup>33</sup>

for *x* = 0.1. This increase of *Pr*

increases, the *Pr*

increasing trend of *Pr*

is defined as *d*<sup>33</sup>

The average value of *d*<sup>33</sup>

ferroelectric domains are stabilized and thus the larger electric field is required to reverse the

in the range, 5.77–4.34 kV/cm, which indicates that these ceramics are relatively easy to pole and hence it may be possible to achieve better piezoelectric and electrostrictive properties.

content, because the stress resulted from the domain switching gets reduced with decrease of *c/a* ratio; hence the domain switches easily under a lower electric field [30]. With Sn4+ content

known that the Sn4+ are not ferroelectric active whereas Ti4+ are ferroelectric active [16, 17, 19].

piezoelectric/electrostrictive properties. However, in the present study, we have noticed the

to the tetragonal crystal lattice symmetry retained in the composition. However, the compositions *x* = 0.075 and 0.1 exhibit the crystallographic phase coexistence of orthorhombictetragonal and pseudo-cubic lattice symmetries respectively which gives rise to the instability

polarization and lattice constant values we have estimated the electric dipole moment for BCST ceramics and are found to be (0.3618, 0.4119, 0.4460, 0.3542, 0.2464) x 10−27 C.cm namely

The bipolar strain (S) versus electric field (E) behavior was investigated for all the BCST samples and is shown in **Figure 4(a-e)**. They exhibit a typical butterfly loop, which is a feature of piezoelectric system for biaxial field. It is well-known that the butterfly loop is observed due to the normal converse piezoelectric effect of the lattice along with the switching and movement of domain walls. Here, all the BCST ceramics show the hysteretic strain behavior which may be associated with the domain reorientation. The converse piezoelectric constant

accordingly, it is calculated and shown in **Figure 4(f)**. A careful observation made on S-E plots reveals that the butterfly shape for *x* = 0.00 is not symmetric for positive and negative electric field cycle. This type of asymmetric strain behavior is not suitable for AC applications where the electric field cycles get continuously changed and hence will not work properly as desired. Therefore, an effort should be made to tailor the materials composition to get the

cycles. Interestingly, in the present work, we have observed that, with Sn4+ content increases, the asymmetric butterfly observed for *x* = 0.00, tends to transform towards the symmetric

BCST ceramics as shown in **Figure 4(f)**. It is observed that, as Sn4+ content increases the *(d*<sup>33</sup>


value increases linearly from 133 pm/V (for *x* = 0.00) to 199 pm/V (for *x* = 0.075) and thereafter

<sup>∗</sup> = *Smax/Emax*, where *Smax* is the maximum strain at maximum electric field (*Emax*);

domains [13]. Further, as Sn4+ content increases from *x* = 0.025 to 0.1, the observed *Ec*

which indicates that the

http://dx.doi.org/10.5772/intechopen.77388

with Sn4+ is ascribed to the decrease of *c/a* ratio with Sn4+

values with increasing Sn4+ content is quite reliable, as it is

with Sn4+ content up to *x* = 0.05 which could show the promising piezo-

BaTiO3-Based Lead-Free Electroceramics with Their Ferroelectric and Piezoelectric Properties…

(for *x* = 0.05) and then decreases to 3.97 μC/cm2

may dilute the ferroelectricity and suppresses the

and *Pmax* decreases [31]. Furthermore, by using remnant

and *Pmax* for *x* = 0.05 may be attributed

<sup>∗</sup> values for positive and negative

<sup>∗</sup> )*ave* are lower compared to the

ceramics [10, 16–19, 32–34] but

<sup>∗</sup> *)ave*

<sup>∗</sup> values for positive and negative cycles.

<sup>∗</sup> )*ave*, is calculated and plotted as a function of Sn4+ content for

and BaTiO3

values are

,

121

**Figure 2.** Phase diagram for Ba0.7Ca0.3Ti1−xSnx O3 ceramics. (reprinted figure from ref. 26. Copyright (2017) by the American ceramic society.).

**Figure 3.** (a-f) (a-e) variation of polarization and displacement current density with applied electric field at 0.1 Hz for BCST ceramics, (f) variation of coercive field (E<sup>c</sup> ), remnant polarization (P<sup>r</sup> ) and maximum polarization (Pmax) with Sn4+ content in BCST ceramics. (reprinted figure from ref. 26. Copyright (2017) by the American ceramic society.).

and 7.12 kV/cm, respectively. Here, the BCT showed high value of *Ec* which indicates that the ferroelectric domains are stabilized and thus the larger electric field is required to reverse the domains [13]. Further, as Sn4+ content increases from *x* = 0.025 to 0.1, the observed *Ec* values are in the range, 5.77–4.34 kV/cm, which indicates that these ceramics are relatively easy to pole and hence it may be possible to achieve better piezoelectric and electrostrictive properties. The possible reason for decrease of *Ec* with Sn4+ is ascribed to the decrease of *c/a* ratio with Sn4+ content, because the stress resulted from the domain switching gets reduced with decrease of *c/a* ratio; hence the domain switches easily under a lower electric field [30]. With Sn4+ content increases, the *Pr* increases up to 7.05 μC/cm2 (for *x* = 0.05) and then decreases to 3.97 μC/cm2 , for *x* = 0.1. This increase of *Pr* values with increasing Sn4+ content is quite reliable, as it is known that the Sn4+ are not ferroelectric active whereas Ti4+ are ferroelectric active [16, 17, 19]. Thus, the incorporation of Sn4+ into BaTiO3 may dilute the ferroelectricity and suppresses the piezoelectric/electrostrictive properties. However, in the present study, we have noticed the increasing trend of *Pr* with Sn4+ content up to *x* = 0.05 which could show the promising piezoelectric/electrostrictive properties. The increase in *Pr* and *Pmax* for *x* = 0.05 may be attributed to the tetragonal crystal lattice symmetry retained in the composition. However, the compositions *x* = 0.075 and 0.1 exhibit the crystallographic phase coexistence of orthorhombictetragonal and pseudo-cubic lattice symmetries respectively which gives rise to the instability of ferroelectric domain and thus the *Pr* and *Pmax* decreases [31]. Furthermore, by using remnant polarization and lattice constant values we have estimated the electric dipole moment for BCST ceramics and are found to be (0.3618, 0.4119, 0.4460, 0.3542, 0.2464) x 10−27 C.cm namely for x = 0.00, 0.025,0.050,0.075 and 0.1 respectively.

**Figure 2.** Phase diagram for Ba0.7Ca0.3Ti1−xSnx

120 Ferroelectrics and Their Applications

BCST ceramics, (f) variation of coercive field (E<sup>c</sup>

ceramic society.).

O3

**Figure 3.** (a-f) (a-e) variation of polarization and displacement current density with applied electric field at 0.1 Hz for

content in BCST ceramics. (reprinted figure from ref. 26. Copyright (2017) by the American ceramic society.).

), remnant polarization (P<sup>r</sup>

ceramics. (reprinted figure from ref. 26. Copyright (2017) by the American

) and maximum polarization (Pmax) with Sn4+

The bipolar strain (S) versus electric field (E) behavior was investigated for all the BCST samples and is shown in **Figure 4(a-e)**. They exhibit a typical butterfly loop, which is a feature of piezoelectric system for biaxial field. It is well-known that the butterfly loop is observed due to the normal converse piezoelectric effect of the lattice along with the switching and movement of domain walls. Here, all the BCST ceramics show the hysteretic strain behavior which may be associated with the domain reorientation. The converse piezoelectric constant is defined as *d*<sup>33</sup> <sup>∗</sup> = *Smax/Emax*, where *Smax* is the maximum strain at maximum electric field (*Emax*); accordingly, it is calculated and shown in **Figure 4(f)**. A careful observation made on S-E plots reveals that the butterfly shape for *x* = 0.00 is not symmetric for positive and negative electric field cycle. This type of asymmetric strain behavior is not suitable for AC applications where the electric field cycles get continuously changed and hence will not work properly as desired. Therefore, an effort should be made to tailor the materials composition to get the symmetric butterfly loop with as small as deviation in *d*<sup>33</sup> <sup>∗</sup> values for positive and negative cycles. Interestingly, in the present work, we have observed that, with Sn4+ content increases, the asymmetric butterfly observed for *x* = 0.00, tends to transform towards the symmetric butterfly loop for *x* = 0.1 having small deviations in *d*<sup>33</sup> <sup>∗</sup> values for positive and negative cycles.

The average value of *d*<sup>33</sup> <sup>∗</sup> i.e. (*d*<sup>33</sup> <sup>∗</sup> )*ave*, is calculated and plotted as a function of Sn4+ content for BCST ceramics as shown in **Figure 4(f)**. It is observed that, as Sn4+ content increases the *(d*<sup>33</sup> <sup>∗</sup> *)ave* value increases linearly from 133 pm/V (for *x* = 0.00) to 199 pm/V (for *x* = 0.075) and thereafter decreases to 185 pm/V (for *x* = 0.1). The observed values of (*d*<sup>33</sup> <sup>∗</sup> )*ave* are lower compared to the reported values for Sn4+ modified BaTiO<sup>3</sup> -CaTiO3 and BaTiO3 ceramics [10, 16–19, 32–34] but

values of BCST materials are notably larger than that of the lead-based and other known lead-free electrostrictors [38–40]. Thus, the Sn4+ modified BCT ceramics with *x* = 0.05, 0.075

ear strain-polarization relation, can be registered as a promising candidate for electrostrictive

and 1 measured at room temperature. All the ceramics possess the single-phase perovskite structure, and no secondary phases are detected, showing the formation of a stable solid solution between BCST and BCZT. The standard diffraction peaks cited from the tetragonal (T)

**Figure 5.** (a-f) (a-e) strain-polarization loops measured at 0.1 Hz for BCST ceramics (f) variation of electrostrictive

*ave* with Sn4+ content in BCST ceramics. (reprinted figure from ref. 26. Copyright (2017) by the American

 (PDF#81-2205), the orthorhombic (O) (PDF#81–2200) and rhombohedral (R) (PDF#85– 0368) are indicated by vertical lines for comparison. Sample with x = 0.00, shows the phase coexistence of O and T phases [34]. The diffraction peaks for 0.25 ≤ x ≥ 0.5 well matches with PDF#81–2200, suggesting that the crystalline structure of samples is of orthorhombic symmetry. The composition x = 1 reveals the rhombohedral phase according to PDF#85–0368. The composition x = 0.75 showed the phase coexistence of orthorhombic and rhombohedral lattice

/C2

BaTiO3-Based Lead-Free Electroceramics with Their Ferroelectric and Piezoelectric Properties…

(BCZT) i.e. (1−x) BCST-xBCZT ceramics with x = 0.00, 0.25, 0.50, 0.75,

, respectively, exhibiting the non-lin-

http://dx.doi.org/10.5772/intechopen.77388

 **by Ca2+, Sn4+ and** 

(BCST) – (X)

123

and 0.1 having (*Q33*)*ave* ~ 0.0469, 0.0667 and 0.0543 m<sup>4</sup>

**3.3. Tune the ferroelectric and piezoelectric properties of BaTiO3**

**Figure 6(a)** shows the XRD patterns of the (1−x) Ba0.95Ca0.05Ti0.92Sn0.08O3

actuator applications.

Ba0.95Ca0.05Ti0.92Zr0.08O3

**Zr4+ substitution**

BaTiO3

coefficient*(Q33)*

ceramic society.).

**Figure 4.** (a-f) (a-e) variation of bipolar electric field induced strain hysteresis loops measured at 0.1 Hz for BCST ceramics (f) variation of effective piezoelectric coefficient*(d\* <sup>33</sup>)ave.* with respect to Sn4+ content in BCST ceramics. (reprinted figure from ref. 26. Copyright (2017) by the American ceramic society.).

it is remarkable to understand the observed symmetric and asymmetric nature of S-E butterfly loop having smaller hysteresis area. Furthermore, it can be seen from **Figure 4(a-e)** that the bipolar strain level increases from 0.097 at −56 kV/cm, 0.052% at +56 kV/cm (for *x* = 0.00) to 0.12 at −56 kV/cm, 0.105% at +56 kV/cm (for x = 0.075). The observed values of strain 0.115 at 56 kV/cm and 0.1% at 56 kV/cm for *x* = 0.075 and *x* = 0.05, respectively, are quite remarkable and comparable to the lead-based piezoelectric materials [35]. Thus, the present BCST ceramics with *x* = 0.05 and 0.075 possess the reasonably high strain level ~ 0.10 (with sprout shape rather than the usual butterfly loop) and consistently smaller area of hysteresis loop, suitable candidate for piezoelectric Ac devices [36]. The higher value of strain observed for *x* = 0.075 may be attributed to the ferroelectric orthorhombic-tetragonal phase coexistence at room temperature as evidenced from XRD and dielectric measurements. The strain as well as (*d*<sup>33</sup> <sup>∗</sup> )*ave* values observed to be decreases for *x* = 0.1 and this may be because at this composition, the system gets transformed from non-centrosymmetric to less symmetric crystal structure i.e. pseudo-cubic structure as confirmed from XRD data. The results of electromechanical investigations for BCST ceramics obtained at an applied electric field up to 50–60 kV/cm at a frequency of 0.1 Hz. The strain curves follow the square of the polarization i.e. *S-P2* as shown in **Figure 5(a-e)**, and the corresponding averaged (*Q33*)*ave* value was calculated and shown in **Figure 5(f)**. The observed *S-P2* hysteresis loop suggests that the strain and polarization are not in phase. The (*Q33*)*ave* value of lead-based electrostrictive material, such as Pb(Mg1/3Nb2/3) O3 -PbTiO3 (PMN-PT), is reported to be about 0.017 m<sup>4</sup> /C2 [37]. This means that the (*Q33*)*ave*

values of BCST materials are notably larger than that of the lead-based and other known lead-free electrostrictors [38–40]. Thus, the Sn4+ modified BCT ceramics with *x* = 0.05, 0.075 and 0.1 having (*Q33*)*ave* ~ 0.0469, 0.0667 and 0.0543 m<sup>4</sup> /C2 , respectively, exhibiting the non-linear strain-polarization relation, can be registered as a promising candidate for electrostrictive actuator applications.

#### **3.3. Tune the ferroelectric and piezoelectric properties of BaTiO3 by Ca2+, Sn4+ and Zr4+ substitution**

**Figure 6(a)** shows the XRD patterns of the (1−x) Ba0.95Ca0.05Ti0.92Sn0.08O3 (BCST) – (X) Ba0.95Ca0.05Ti0.92Zr0.08O3 (BCZT) i.e. (1−x) BCST-xBCZT ceramics with x = 0.00, 0.25, 0.50, 0.75, and 1 measured at room temperature. All the ceramics possess the single-phase perovskite structure, and no secondary phases are detected, showing the formation of a stable solid solution between BCST and BCZT. The standard diffraction peaks cited from the tetragonal (T) BaTiO3 (PDF#81-2205), the orthorhombic (O) (PDF#81–2200) and rhombohedral (R) (PDF#85– 0368) are indicated by vertical lines for comparison. Sample with x = 0.00, shows the phase coexistence of O and T phases [34]. The diffraction peaks for 0.25 ≤ x ≥ 0.5 well matches with PDF#81–2200, suggesting that the crystalline structure of samples is of orthorhombic symmetry. The composition x = 1 reveals the rhombohedral phase according to PDF#85–0368. The composition x = 0.75 showed the phase coexistence of orthorhombic and rhombohedral lattice

it is remarkable to understand the observed symmetric and asymmetric nature of S-E butterfly loop having smaller hysteresis area. Furthermore, it can be seen from **Figure 4(a-e)** that the bipolar strain level increases from 0.097 at −56 kV/cm, 0.052% at +56 kV/cm (for *x* = 0.00) to 0.12 at −56 kV/cm, 0.105% at +56 kV/cm (for x = 0.075). The observed values of strain 0.115 at 56 kV/cm and 0.1% at 56 kV/cm for *x* = 0.075 and *x* = 0.05, respectively, are quite remarkable and comparable to the lead-based piezoelectric materials [35]. Thus, the present BCST ceramics with *x* = 0.05 and 0.075 possess the reasonably high strain level ~ 0.10 (with sprout shape rather than the usual butterfly loop) and consistently smaller area of hysteresis loop, suitable candidate for piezoelectric Ac devices [36]. The higher value of strain observed for *x* = 0.075 may be attributed to the ferroelectric orthorhombic-tetragonal phase coexistence at room temperature as evidenced from XRD and dielectric measurements. The strain as well as (*d*<sup>33</sup>

**Figure 4.** (a-f) (a-e) variation of bipolar electric field induced strain hysteresis loops measured at 0.1 Hz for BCST ceramics

values observed to be decreases for *x* = 0.1 and this may be because at this composition, the system gets transformed from non-centrosymmetric to less symmetric crystal structure i.e. pseudo-cubic structure as confirmed from XRD data. The results of electromechanical investigations for BCST ceramics obtained at an applied electric field up to 50–60 kV/cm at a

in **Figure 5(a-e)**, and the corresponding averaged (*Q33*)*ave* value was calculated and shown in

not in phase. The (*Q33*)*ave* value of lead-based electrostrictive material, such as Pb(Mg1/3Nb2/3)

hysteresis loop suggests that the strain and polarization are

*<sup>33</sup>)ave.* with respect to Sn4+ content in BCST ceramics. (reprinted figure

/C2

frequency of 0.1 Hz. The strain curves follow the square of the polarization i.e. *S-P2*

(PMN-PT), is reported to be about 0.017 m<sup>4</sup>

**Figure 5(f)**. The observed *S-P2*

(f) variation of effective piezoelectric coefficient*(d\**

122 Ferroelectrics and Their Applications

from ref. 26. Copyright (2017) by the American ceramic society.).

O3


<sup>∗</sup> )*ave*

as shown

[37]. This means that the (*Q33*)*ave*

**Figure 5.** (a-f) (a-e) strain-polarization loops measured at 0.1 Hz for BCST ceramics (f) variation of electrostrictive coefficient*(Q33)ave* with Sn4+ content in BCST ceramics. (reprinted figure from ref. 26. Copyright (2017) by the American ceramic society.).

symmetries. The change in diffraction peak around 45° as shown in **Figure 6(b)** the gradual transitions from orthorhombic to mixed phase to rhombohedral symmetry of the unit cell at room temperature, due to the increase of x content that can be favorable to enhance the piezoelectric properties. **Figure 7** shows the temperature dependence of dielectric constant (*εr* ) and dielectric loss (*tanδ*) of (1−x) BCST-xBCZT ceramics with different x, which measured at 100 kHz between −100 and 180°C. Effect of change of composition on the ferroelectric phase transitions are observed. As can be seen, (1−x) BCST-xBCZT ceramics exhibits three obvious polymorphic phase transitions corresponding to the rhombohedral to orthorhombic (TR-O), orthorhombic to tetragonal (TO-T) and tetragonal to cubic (Tc ) respectively. The Curie temperature (Tc ) is about 74°C for x = 0.00 and displays linear increasing trend up to 106°C for x = 1.00 with increasing x. This observation indicates that the Curie temperature is higher for the substitution of Ti4+ with Zr4+ than the substitution of Ti4+ with Sn4+. It is observed that all three transitions TR-O, TO-T and Tc shift to higher temperature with increase in BCZT content. Interestingly this improves Curie temperature as well as at x = 0.75 the TR-O observed at room temperature, provides the phase coexistence. The multiphase coexistence boundary, which has hardly any energy barrier for polarization rotation between different ferroelectric phases, is in favor of both polarization rotation and extension contributing to enhancement of piezoelectricity [41]. The observed results are in analogues to the structural analysis of (1−x) BCSTxBCZT ceramics. The dielectric constants are found in the order of 8269–9877 with lower dielectric loss in the range of 0.033–0.046, also the room temperature dielectric constant values are observed in the range of 1300–2700.

The micrograph images for (1−x) BCST-xBCZT system is shown in **Figure 8**, well densified and pore-free microstructure, consisting of irregular grains in which the large one is approximately 35 μm and the small is only about 6 μm with well-defined grain boundaries were observed. Clear grain boundary observed for ceramics samples could enhance the density

obtained ceramics are well sintered and acquires the relative densities in the range of 93–95% with average grain size 19.4–25 μm. **Figure 9** shows the polarization versus electric field hysteresis loops of (1−x) BCST-xBCZT ceramics with different x content measured with an applied electric field up to 30–40 kV/cm at 0.1 Hz. All samples possess a typical ferroelectric polariza-

increase in BCZT content. Sample with x = 0.75 shows superior value of remnant polarization

of the compositions near the R-O phase coexistence being able to reorient dipoles more com-

[10, 44]. The sample of "soft" indicates that the free energy profile for polarization rotation is anisotropically flattened at the two phases and multiphase coexistence [10]. However, Lower value of Ec indicates that the lower energy barriers are needed for polarization rotation. This lower energy barrier can greatly facilitate the polarization rotation and effectively enhance the piezoelectric properties [10, 44]. **Figure 9** shows displacement current density-electric field (J-E) curves measured for (1−x) BCST-xBCZT ceramics with an applied electric field up to 30–40 kV/cm at 0.1 Hz. All samples show sharp-peaking behavior which reveals that

with lower value of Ec = 2.9 kV/cm this can be attributed to the dipole moments

based ceramics [42, 43]. All the

) and dielectric loss (*tanδ*) of (1−x) BCST-xBCZT ceramics

http://dx.doi.org/10.5772/intechopen.77388

125

) and coercive

are observed in the

), saturation polarization (P<sup>s</sup>

and the coercive field E<sup>c</sup>

reveals that, the sample become "softer" with increase of *x*

and 2.6–3.6 kV/cm respectively. Remnant polarization increases with

BaTiO3-Based Lead-Free Electroceramics with Their Ferroelectric and Piezoelectric Properties…

and helps to improve the electrical properties of the BaTiO3

tion hysteresis loop with remnant polarization (Pr

**Figure 7.** Temperature dependence of dielectric constant (*ε<sup>r</sup>*

). The ferroelectric properties, i.e. the P<sup>r</sup>

field (E<sup>c</sup>

6.3 μC/cm<sup>2</sup>

range of 4.7–6.6 μC/cm<sup>2</sup>

with x = 0.00, 0.25, 0.50, 0.75, and 1.

pletely [34]. The decrease of *Ec*

**Figure 6.** (a-b) (a) combined x- ray diffraction pattern between 2θ = 20 to 80° and (b) enlarged x-ray diffraction pattern between 2θ = 42 to 48°.

BaTiO3-Based Lead-Free Electroceramics with Their Ferroelectric and Piezoelectric Properties… http://dx.doi.org/10.5772/intechopen.77388 125

symmetries. The change in diffraction peak around 45° as shown in **Figure 6(b)** the gradual transitions from orthorhombic to mixed phase to rhombohedral symmetry of the unit cell at room temperature, due to the increase of x content that can be favorable to enhance the piezoelectric properties. **Figure 7** shows the temperature dependence of dielectric constant

) and dielectric loss (*tanδ*) of (1−x) BCST-xBCZT ceramics with different x, which measured at 100 kHz between −100 and 180°C. Effect of change of composition on the ferroelectric phase transitions are observed. As can be seen, (1−x) BCST-xBCZT ceramics exhibits three obvious polymorphic phase transitions corresponding to the rhombohedral to orthorhombic (TR-O),

x = 1.00 with increasing x. This observation indicates that the Curie temperature is higher for the substitution of Ti4+ with Zr4+ than the substitution of Ti4+ with Sn4+. It is observed that all

Interestingly this improves Curie temperature as well as at x = 0.75 the TR-O observed at room temperature, provides the phase coexistence. The multiphase coexistence boundary, which has hardly any energy barrier for polarization rotation between different ferroelectric phases, is in favor of both polarization rotation and extension contributing to enhancement of piezoelectricity [41]. The observed results are in analogues to the structural analysis of (1−x) BCSTxBCZT ceramics. The dielectric constants are found in the order of 8269–9877 with lower dielectric loss in the range of 0.033–0.046, also the room temperature dielectric constant values

**Figure 6.** (a-b) (a) combined x- ray diffraction pattern between 2θ = 20 to 80° and (b) enlarged x-ray diffraction pattern

) is about 74°C for x = 0.00 and displays linear increasing trend up to 106°C for

shift to higher temperature with increase in BCZT content.

) respectively. The Curie tem-

orthorhombic to tetragonal (TO-T) and tetragonal to cubic (Tc

(*εr*

perature (Tc

124 Ferroelectrics and Their Applications

between 2θ = 42 to 48°.

three transitions TR-O, TO-T and Tc

are observed in the range of 1300–2700.

**Figure 7.** Temperature dependence of dielectric constant (*ε<sup>r</sup>* ) and dielectric loss (*tanδ*) of (1−x) BCST-xBCZT ceramics with x = 0.00, 0.25, 0.50, 0.75, and 1.

The micrograph images for (1−x) BCST-xBCZT system is shown in **Figure 8**, well densified and pore-free microstructure, consisting of irregular grains in which the large one is approximately 35 μm and the small is only about 6 μm with well-defined grain boundaries were observed. Clear grain boundary observed for ceramics samples could enhance the density and helps to improve the electrical properties of the BaTiO3 based ceramics [42, 43]. All the obtained ceramics are well sintered and acquires the relative densities in the range of 93–95% with average grain size 19.4–25 μm. **Figure 9** shows the polarization versus electric field hysteresis loops of (1−x) BCST-xBCZT ceramics with different x content measured with an applied electric field up to 30–40 kV/cm at 0.1 Hz. All samples possess a typical ferroelectric polarization hysteresis loop with remnant polarization (Pr ), saturation polarization (P<sup>s</sup> ) and coercive field (E<sup>c</sup> ). The ferroelectric properties, i.e. the P<sup>r</sup> and the coercive field E<sup>c</sup> are observed in the range of 4.7–6.6 μC/cm<sup>2</sup> and 2.6–3.6 kV/cm respectively. Remnant polarization increases with increase in BCZT content. Sample with x = 0.75 shows superior value of remnant polarization 6.3 μC/cm<sup>2</sup> with lower value of Ec = 2.9 kV/cm this can be attributed to the dipole moments of the compositions near the R-O phase coexistence being able to reorient dipoles more completely [34]. The decrease of *Ec* reveals that, the sample become "softer" with increase of *x* [10, 44]. The sample of "soft" indicates that the free energy profile for polarization rotation is anisotropically flattened at the two phases and multiphase coexistence [10]. However, Lower value of Ec indicates that the lower energy barriers are needed for polarization rotation. This lower energy barrier can greatly facilitate the polarization rotation and effectively enhance the piezoelectric properties [10, 44]. **Figure 9** shows displacement current density-electric field (J-E) curves measured for (1−x) BCST-xBCZT ceramics with an applied electric field up to 30–40 kV/cm at 0.1 Hz. All samples show sharp-peaking behavior which reveals that

**Figure 8.** (a-e) SEM micrographs of (1−x)BCST-xBCZT ceramic pellets sintered at 1350°C for 10 h (f) variation of average grain size with respect to BCZT content.

samples are completely saturated with respect to applied electric field [26]. Furthermore, by using remnant polarization and lattice constant values we have estimated the electric dipole moment for (1−x) BCST-xBCZT ceramics and are found to be (0.3045, 0.3500, 0.3505, 0.4090, 0.4132) × 10−27 C.cm namely for x = 0.00, 0.25,0.50,0.75 and 1.0 respectively.

**Figure 10** shows the bipolar field-induced strain (S-E) curves for (1−x) BCST-xBCZT ceramics measured with an applied electric field up to 30–40 kV/cm at 0.1 Hz. All samples reveal the butterfly shaped S-E loops that are typical feature of ferroelectric materials. A prominent enhancement in the maximum positive strain response from 0.086% at x = 0.00 to 0.122% at x = 0.75 is observed. In ferroelectric, electric field induced butterfly like hysteresis strain loops are occurs fundamentally due to the intrinsic and extrinsic contribution [41]. By modifying the chemical composition of BaTiO3 based masteries one can achieve phase coexistence that facilitated the polarization rotation and enhance the intrinsic contribution (lattice strain) [10, 34, 41]. In ferroelectric materials the domain switching provides the extrinsic contribution, it happens when ferroelectric materials change the spontaneous polarized state along the applied electric field direction. Therefore, the higher strain S = 0.122 observed for x = 0.75 is attributed to the R-O phase coexistence. However, the extrinsic contribution is attributed to the lower value of E<sup>c</sup> which supports to easy domain switching and contributes to achieve the superior piezoelectric properties. **Figure 10** shows variation of direct piezoelectric coefficient *(d33)ave* and converse piezoelectric coefficient *(d\* <sup>33</sup>)ave* for (1−x)BCST-xBCZT ceramics as a function of BCZT content. It can be observed that both of *d33* and *d ⃰ <sup>33</sup>* curves possess a peak with increasing BCZT content. At x = 0.75, the

higher *d33* and *d\**

xBCZT ceramics.

tively with *Q33* of 0.089 m4

piezoelectric materials.

/C2

piezoelectric coefficient *(d33)ave.* and converse piezoelectric coefficient *(d\**

*<sup>33</sup>* of the (1−x) BCST-xBCZT ceramics are 310 pC/N and 385 pm/V respec-

should be ascribed to the phase coexistence. The O-T phase coexistence causes instability of the polarization state; therefore, the polarization direction can be easily rotated by external stress or electric field, resulting in a high piezoelectricity [10, 34, 41]. Therefore, to achieve high piezoelectric properties for lead free ceramics one has prepare samples having PPT or MPB phase compositions. The 0.25BCST-0.75BCZT ceramic sample shows the superior piezoelectric properties having moderate Curie temperature ~ 100°C can be a potential lead-free piezoelectric material to further study to replace the toxic lead based

**Figure 10.** Variation of bipolar electric field induced strain hysteresis loops measured at 0.1 Hz, variation of direct

**Figure 9.** Variation of polarization and displacement current density with applied electric field at 0.1 Hz for (1−x)BCST-

BaTiO3-Based Lead-Free Electroceramics with Their Ferroelectric and Piezoelectric Properties…

http://dx.doi.org/10.5772/intechopen.77388

127

. It is believed that the observed high piezoelectric properties

*<sup>33</sup>)ave.* for (1−x)BCST-xBCZT ceramics.

BaTiO3-Based Lead-Free Electroceramics with Their Ferroelectric and Piezoelectric Properties… http://dx.doi.org/10.5772/intechopen.77388 127

**Figure 9.** Variation of polarization and displacement current density with applied electric field at 0.1 Hz for (1−x)BCSTxBCZT ceramics.

samples are completely saturated with respect to applied electric field [26]. Furthermore, by using remnant polarization and lattice constant values we have estimated the electric dipole moment for (1−x) BCST-xBCZT ceramics and are found to be (0.3045, 0.3500, 0.3505, 0.4090,

**Figure 8.** (a-e) SEM micrographs of (1−x)BCST-xBCZT ceramic pellets sintered at 1350°C for 10 h (f) variation of average

**Figure 10** shows the bipolar field-induced strain (S-E) curves for (1−x) BCST-xBCZT ceramics measured with an applied electric field up to 30–40 kV/cm at 0.1 Hz. All samples reveal the butterfly shaped S-E loops that are typical feature of ferroelectric materials. A prominent enhancement in the maximum positive strain response from 0.086% at x = 0.00 to 0.122% at x = 0.75 is observed. In ferroelectric, electric field induced butterfly like hysteresis strain loops are occurs fundamentally due to the intrinsic and extrinsic contribution [41].

coexistence that facilitated the polarization rotation and enhance the intrinsic contribution (lattice strain) [10, 34, 41]. In ferroelectric materials the domain switching provides the extrinsic contribution, it happens when ferroelectric materials change the spontaneous polarized state along the applied electric field direction. Therefore, the higher strain S = 0.122 observed for x = 0.75 is attributed to the R-O phase coexistence. However, the

switching and contributes to achieve the superior piezoelectric properties. **Figure 10** shows variation of direct piezoelectric coefficient *(d33)ave* and converse piezoelectric coefficient

*<sup>33</sup>)ave* for (1−x)BCST-xBCZT ceramics as a function of BCZT content. It can be observed

*<sup>33</sup>* curves possess a peak with increasing BCZT content. At x = 0.75, the

based masteries one can achieve phase

which supports to easy domain

0.4132) × 10−27 C.cm namely for x = 0.00, 0.25,0.50,0.75 and 1.0 respectively.

By modifying the chemical composition of BaTiO3

grain size with respect to BCZT content.

126 Ferroelectrics and Their Applications

*(d\**

that both of *d33* and *d ⃰*

extrinsic contribution is attributed to the lower value of E<sup>c</sup>

**Figure 10.** Variation of bipolar electric field induced strain hysteresis loops measured at 0.1 Hz, variation of direct piezoelectric coefficient *(d33)ave.* and converse piezoelectric coefficient *(d\* <sup>33</sup>)ave.* for (1−x)BCST-xBCZT ceramics.

higher *d33* and *d\* <sup>33</sup>* of the (1−x) BCST-xBCZT ceramics are 310 pC/N and 385 pm/V respectively with *Q33* of 0.089 m4 /C2 . It is believed that the observed high piezoelectric properties should be ascribed to the phase coexistence. The O-T phase coexistence causes instability of the polarization state; therefore, the polarization direction can be easily rotated by external stress or electric field, resulting in a high piezoelectricity [10, 34, 41]. Therefore, to achieve high piezoelectric properties for lead free ceramics one has prepare samples having PPT or MPB phase compositions. The 0.25BCST-0.75BCZT ceramic sample shows the superior piezoelectric properties having moderate Curie temperature ~ 100°C can be a potential lead-free piezoelectric material to further study to replace the toxic lead based piezoelectric materials.
