**1. Introduction**

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> Tix O3 , 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, perovskite-structured ferroelectrics such as BaTiO<sup>3</sup> [BT], (Bi1/2Na1/2)TiO3 [BNT], (Bi1/2K1/2)TiO3 [BKT], KNbO<sup>3</sup> [KN], (K,Na)NbO<sup>3</sup> [KNN], and their solid solutions have drawn great interest of researchers. However, there are some general problems associated with these lead-free piezoceramics such as lower Curie temperatures (*Tc* ), or low depolarization temperatures (*Td* ), 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 inhomogeneity, poor densification, and phase stability; b) BaTiO<sup>3</sup> (BT) based piezoelectric shows stable piezoelectric properties, but the main issue is of lower Curie temperature (T<sup>c</sup> ) ~ < 100°C and 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 have suffered from its poor sinterability and hence densification.

bring the polymorphic phase transition (PPT) i.e. Rhombohedral to orthorhombic (TR-O) and Orthorhombic to Tetragonal (TO-T) close to room temperature to achieve the phase coexistence at 300 K and hence shows the enhanced piezoelectric properties [6]. For Zr4+, Sn4+, and

(0°C and −90°C) to room temperature [6]. Recently, high performance BT-based ceramics

Ca2+ at A-site and Zr4+/Sn4+ at B-site showed the properties comparable to that of soft PZT

and on the other hand suppresses the orthorhombic to tetragonal (TO-T) transition temperature. This is one of the important considerations in developing the temperature stability of piezoelectric properties for various practical applications [13]. Many research groups have reported the dielectric, diffused phase transition, ferroelectric and piezoelectric properties of BCZT and BCST ceramics [6, 7, 13–22]. However, there is a need of detailed investigation of electrostrictive properties of BT based lead free electroceramics which are correlated with the structure–property-composition having the phase coexistence of orthorhombictetragonal (O-T), Rhombohedral-Orthorhombic (R-O) and Rhombohedral-Tetragonal (R-T) lattice symmetries, at room temperature. Thus, in view of the above, we have investigated the ferroelectric, piezoelectric and electrostrictive properties of Ca2+, Sn4+ and Zr4+ modified

ceramics and tried to correlate the observed results with the phase coexistence of

polycrystalline electroceramic was synthesized by conventional solid-

, ≥ 99%) (from Sigma Aldrich) were weighted and mixed in stoichiometric pro-

(BCST) ceramics with *x* = 0.00, 0.025, 0.050, 0.075, 0.1 were prepared by

(99.9%) (all are from Sigma Aldrich) were mixed

portions 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.

solid state reaction method. Stoichiometric amounts of AR grade raw materials of BaCO3

(BCT) ceramics) results in a slight increase in the Curie temperature (TC)

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

(BCZT) and (Ba,Ca)(Ti,Sn)O<sup>3</sup>

materials [7–12]. Furthermore, the substitution of Ca2+at Ba2+ in BaTiO3

noncentrosymmetric lattice symmetries achieved at room temperature.

state reaction method. Staring raw materials barium carbonate (BaCO3

 *(BCST) synthesis*

(99%) and SnO2

increases PPT temperatures from low temperatures

(BCST) prepared by substitution of

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


system (i.e. to

115

, ≥ 99%) and titanium

Hf4+ substitution at Ti4+ site in BaTiO3

such as (Ba,Ca)(Ti,Zr)O<sup>3</sup>

TiO3

**2. Experimental details**

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

*2.1.2. Ba0.7Ca0.3Ti1−xSn<sup>x</sup>*

Ba0.7Ca0.3Ti1−xSnx

(99%), CaCO<sup>3</sup>

 *(BT) synthesis*

*O3*

O3

(99%), TiO<sup>2</sup>

form Ba1−xCax

BaTiO3

**2.1. Synthesis**

*2.1.1. BaTiO<sup>3</sup>*

dioxide (TiO2

Barium titanate, BaTiO<sup>3</sup> (BT) is the first polycrystalline ceramic ever discovered that exhibits the stable piezoelectric and dielectric properties; hence considered as a promising leadfree ferroelectric ceramic with perovskite ABO<sup>3</sup> structure [2]. BT is one of the promising 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 bring the polymorphic phase transition (PPT) i.e. Rhombohedral to orthorhombic (TR-O) and Orthorhombic to Tetragonal (TO-T) close to room temperature to achieve the phase coexistence at 300 K and hence shows the enhanced piezoelectric properties [6]. For Zr4+, Sn4+, and Hf4+ substitution at Ti4+ site in BaTiO3 increases PPT temperatures from low temperatures (0°C and −90°C) to room temperature [6]. Recently, high performance BT-based ceramics such as (Ba,Ca)(Ti,Zr)O<sup>3</sup> (BCZT) and (Ba,Ca)(Ti,Sn)O<sup>3</sup> (BCST) prepared by substitution of Ca2+ at A-site and Zr4+/Sn4+ at B-site showed the properties comparable to that of soft PZT materials [7–12]. Furthermore, the substitution of Ca2+at Ba2+ in BaTiO3 -CaTiO3 system (i.e. to form Ba1−xCax TiO3 (BCT) ceramics) results in a slight increase in the Curie temperature (TC) and on the other hand suppresses the orthorhombic to tetragonal (TO-T) transition temperature. This is one of the important considerations in developing the temperature stability of piezoelectric properties for various practical applications [13]. Many research groups have reported the dielectric, diffused phase transition, ferroelectric and piezoelectric properties of BCZT and BCST ceramics [6, 7, 13–22]. However, there is a need of detailed investigation of electrostrictive properties of BT based lead free electroceramics which are correlated with the structure–property-composition having the phase coexistence of orthorhombictetragonal (O-T), Rhombohedral-Orthorhombic (R-O) and Rhombohedral-Tetragonal (R-T) lattice symmetries, at room temperature. Thus, in view of the above, we have investigated the ferroelectric, piezoelectric and electrostrictive properties of Ca2+, Sn4+ and Zr4+ modified BaTiO3 ceramics and tried to correlate the observed results with the phase coexistence of noncentrosymmetric lattice symmetries achieved at room temperature.
