**2.1. Synthesis**

**1. Introduction**

114 Ferroelectrics and Their Applications

[BKT], KNbO<sup>3</sup>

Barium titanate, BaTiO<sup>3</sup>

perovskite-structured ferroelectrics such as BaTiO<sup>3</sup>

piezoceramics such as lower Curie temperatures (*Tc*

ity, poor densification, and phase stability; b) BaTiO<sup>3</sup>

free ferroelectric ceramic with perovskite ABO<sup>3</sup>

have suffered from its poor sinterability and hence densification.

[KN], (K,Na)NbO<sup>3</sup>

Currently, most of the electronic devices and naval departments use the materials that are based on interconversion of mechanical and electrical energies i.e. piezoelectric effect for actuator/ transducer/energy harvester applications. The examples of these devices include ink-jet printers, fuel injection actuators in cars, transducers for ultrasonic imaging and therapy in medicine, sensors and actuators for vibration control, and sonars. In many of devices, (PbZr1 <sup>−</sup> <sup>x</sup>

PZT) based piezoelectric materials are mainly employed due to its excellent piezoelectric properties viz. piezoelectric charge coefficient (*d33 ~ 250–600 pC/N*), electromechanical coupling factor (*Kp ~ > 0.50*), mechanical quality factor (Qm ~ 10–1000), high dielectric constant (*ε<sup>r</sup>* ~ > 700), low dielectric loss (t*anδ ~ < 1%*) and high Curie temperatures (Tc ~ > 300°C). However, lead oxide (PbO), main component of PZT, is highly toxic and its toxicity is further enhanced due to its volatilization at higher temperature, particularly during calcination/ sintering and thus causing environmental pollution. Today, with increasing level of electronic equipments being manufactured, used and discarded, it has been well recognized that the level of hazardous substances (in the environment) has been rising day- to- day life. Further, Pb causes severe chronic poisoning and pain with long-term exposure (years-to-decades), even when accumulated in small traces. Therefore, to reduce environmental damage during the waste disposal of piezoelectric products as well as health hazard issues, many countries have adopted the waste from electrical and electronic equipment (WEEE), restriction of hazardous substances (RoHS) and end-of life vehicles (ELV) legislations coined by the European Union and banned the use of Pb/ PbO based materials for electronic and automobile industries. Thus, there is an open challenge to search and invent the lead-free piezoelectric ceramics and transfer them into applications in place of PZT ceramics [1]. Among the lead-free piezoelectric ceramics,

est of researchers. However, there are some general problems associated with these lead-free

difficulties in poling treatments, low relative densities. For example, a) The processing of KNN ceramic has some critical issues such as volatility of alkali-oxides, compositional inhomogene-

lower coercive field which results in more temperature dependent properties and less polarization stability as well as difficulties in poling treatments; c) BNT and BKT based ceramics

its the stable piezoelectric and dielectric properties; hence considered as a promising lead-

ferroelectric materials specifically known for its wide range of applications from dielectric capacitor to non-linear optic devices. For BT ceramic, below Curie temperature (120°C), the vector of the spontaneous polarization points in the [001] direction (tetragonal phase), below 5°C it reorients in the [011] (orthorhombic phase), and below −90°C in [111] direction (rhombohedral phase) [3–5]. The present scenario of BT based electroceramics is to

piezoelectric properties, but the main issue is of lower Curie temperature (T<sup>c</sup>

[BT], (Bi1/2Na1/2)TiO3

(BT) is the first polycrystalline ceramic ever discovered that exhib-

[KNN], and their solid solutions have drawn great inter-

), or low depolarization temperatures (*Td*

structure [2]. BT is one of the promising

(BT) based piezoelectric shows stable

Tix O3 ,

[BNT], (Bi1/2K1/2)TiO3

) ~ < 100°C and

),

#### *2.1.1. BaTiO<sup>3</sup> (BT) synthesis*

Barium titanate, BaTiO<sup>3</sup> polycrystalline electroceramic was synthesized by conventional solidstate reaction method. Staring raw materials barium carbonate (BaCO3 , ≥ 99%) and titanium dioxide (TiO2 , ≥ 99%) (from Sigma Aldrich) were weighted and mixed in stoichiometric proportions and ball-milled for 15 h in the ethanol medium. After ball milling slurry were dried at 100°C overnight and dried powder grounded well. Then the powder pressed into pellets of 2 cm in diameter and 4–5 mm in thickness and calcined at 1260°C for 5 h. The calcined pellets were crushed and grounded well to form the fine powder. Thereafter, pellets with 10 mm diameter and 0.6–1 mm in thickness were prepared from calcined powder by using poly vinyl alcohol (PVA) as a binder. Finally, the prepared pellets were sintered at 1300°C for 5 h.

#### *2.1.2. Ba0.7Ca0.3Ti1−xSn<sup>x</sup> O3 (BCST) synthesis*

Ba0.7Ca0.3Ti1−xSnx O3 (BCST) ceramics with *x* = 0.00, 0.025, 0.050, 0.075, 0.1 were prepared by solid state reaction method. Stoichiometric amounts of AR grade raw materials of BaCO3 (99%), CaCO<sup>3</sup> (99%), TiO<sup>2</sup> (99%) and SnO2 (99.9%) (all are from Sigma Aldrich) were mixed 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 homogenization and avoid the phase segregation of CaTiO3 .

of the dielectric permittivity (ε<sup>r</sup>

applications with larger *Pr*

paraelectric was observed at Curie temperature (Tc

shows the polarization-electric field (P-E) hysteresis loops for BaTiO<sup>3</sup>

ceramic. The saturation and remnant polarization, Psat = 24.13 μC/cm2

and *P<sup>s</sup>*

loop (d) J-E loop, (e) S-E loop, (f) S-P curve, of BaTiO<sup>3</sup>

AIP publishing.).

for BT is 0.6689 × 10−27 C.cm by using Pr and lattice constant values.

having low E<sup>c</sup>

**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

) in the range of 25–160°C at fixed frequencies viz. 1, 25, 50,

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

~ 125°C) with ε<sup>r</sup> = 5617 [23]. **Figure 1(c)**

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

. The estimated value of electric dipole moment

ceramics. (reprinted figure from ref. 23. Copyright (2016) by the

ceramic measured at

117

and Pr = 10.42 μC/cm2

75 and100 kHz for BT ceramic sintered at 1300°C. The phase transition from ferroelectric to

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

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

#### *2.1.3. (1−x) Ba0.95Ca0.05Ti0.92Sn0.08O<sup>3</sup> -xBa0.95Ca0.05Ti0.92Zr0.08O<sup>3</sup> [(1−x)BCST-xBCZT] synthesis*

The (1−x) Ba0.95Ca0.05Ti0.92Sn0.08O3 -xBa0.95Ca0.05Ti0.92Zr0.08O3 [(1−x)BCST-xBCZT] lead-free piezoelectric ceramics with x = 0, 0.25, 0.50, 0.75, 1 were prepared by mixed oxide solid state reaction. High purity analytical grade BaCO3 , CaCO<sup>3</sup> , TiO<sup>2</sup> , SnO<sup>2</sup> , and ZrO<sup>2</sup> (Hi Media; purity ≥99%) chemicals were 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 University.

## **2.2. Characterizations**

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 any measurements. Dielectric constant (ε<sup>r</sup> ) and loss tangent (tanδ) were measured as a function of 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).
