**1. Introduction**

Like ferromagnetic materials, the functional properties of ferroelectric materials find wide range of applications, ranging from actuators and sensors to memory or optical devices. A ferroelctric class of materials cannot define in a single sentence. So before we define the ferroelectric materials, we should classify dielectric materials. Dielectric is belonging to a class of insulating materials that on the application of an electric field shows dielectric polarization [1]. Here the center of symmetry plays a significant role for their properties. Crystal structure with a center of symmetry have such an arrangement of atoms around a point or center that by the inversion, we can get the same arrangement of atoms in the crystal. Dielectric materials belong to a group of non Centro symmetric crystal structure. In 432 point group the entire non Centro symmetric point group shows piezoelectric properties [2]. The properties due to which voltage obtains form charge a separation in the face due to the mechanical stress and vice versa. Both direct and inverse piezoelectric effects have a wide range of application in electronic devices [3]. Barium titanate is an example of non-centrosymmetric piezoelectric material used in microphone and transducer [2–4]. In non centrosymmetric crystals there is an axis of symmetry, called polarity. These piezoelectric polar crystals are shown pyroelectricity. With changes in temperature there is a charge separation. The cells of polar structure have efficient dielectric polarization, so often called a spontaneous polarization. Either by stress or by a change in temperature the dipole moment of these polar

structures is change. The is a charge separation in the surface, results in the spontaneous polarization. So the polar dielectric spontaneous polarization direction and magnitude can be modified with the applied stress. Zinc oxide, which belongs to family of polar dielectric shows wurtzitecrystal structure [5]. In this structure, between hexagonally packed oxygen ions layer, Zn2+ions are at the tetrahedral site.

Between these layers dielectric, whose spontaneous polarization depends on the direction and magnitude of the applied stress. Adequate amount of stress can change the direction of spontaneous polarization. But the exclusion of the stress does not bring back the original magnitude and direction of the spontaneous polarization. These families of polar dielectric are called ferroelectric. **Figure 1** shows the way the Centro symmetric, acentric, polar and ferroelectric, dielectrics are related to each other. Many review articles shown the history of ferroelectric [6–12]. Many great scientist open the path of discovery of the ferroelectric.

Pyroelctricity was studied by Brewster. Piezoelectricity was discovered by J. P. Curie. Debye, Boltzmann, Pockelsetc helps in conceptualizing the polarization in the dielectric. It was E. Schoridgener, who coined the term ferroelectricity, but JoesphValasek known for the discovery of ferroelectric. In 1920 the Rochelle salt (sodium potassium tartrate) shows spontaneous polarization which can be switch with the magnitude and direction of the applied field. This is the first manifestation of the ferroelectricity in a crystal. That is the trademark of ferroelectricity. Logically effectively the term ferroelectricity is defined as the switchable polarization between two or more stable state by the application of electric field. There exist some exceptions. Some semiconductor materials show ferroelectric properties. They do not posses electric polarization. In some ferroelectrics materials the spontaneous polarization cannot be switched with the electric field. This is either due to they are too conducting or reach the electrical break down first. This ferroelectric property first observed in Rochelle salt. But later it is observed in oxides, polymer, ceramics, and liquid crystal. When it is about ferroelectric property, the perovskite structure materials have a special importance. So in this chapter, we will discuss some perovskite ferroelectrics which are used in various electronics devices. According to the structure, there are five types of structure. (i) Organicpolymer (ii) Charge ordered ferroelectrics (iii) Magnetic order ferroelectric (iv) Corner-sharing oxygen octahedral (v) Hydrogen bonded radical compound (v) Ceramic polymer composites [11]. Among these ferroelectricgroup a mostly used ferroelectrics are the corner sharing oxygen octahedral oxides.

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*Perovskite Ferroelectric*

**Figure 2.**

*DOI: http://dx.doi.org/10.5772/intechopen.98382*

Basically, the corner sharing oxygen octahedral oxide structures is represented as Aa+Bb+O3 [12]. **Figure 2** shows the schematic figure of O2− ions corner sharing oxygen octahedral. The Bb+ cation is seated within every octahedron. The b of the cation has the value lies in between 3 to 6. Aa+ ions lie in the gap among the octahedral with its value of *a* is in between 1 to 3. A nonpolar lattice has been observed in prototype forms by the overlap of Aa+, Bb+, and O2− ions geometric center. The total polarity of the lattice is obtained by displacement of A and B ions with respect to the O2− ions. Due to change in temperature, phase transition takes place. This will result in displacement of ion results in a change in lattice structure. Spontaneous polarization will produce due to the displacement of ions in the arrangement of

It is a family of a subgroup of corner sharing oxygen octahedral material's exhibiting ABO3 structure. This family contains some mostly used piezoelectric and ferroelectric ceramics. Some member which is used in different field of Technology are strontium titanate (STO), barium titanate (BaTiO3), (SrTiO3), lead titanate (PbTiO3), barium strontium titanate (BST), PZT, potassium niobate (KN) (KNbO3)

Barium titanate which a member of perovskite family exhibit good piezoelectric, ferroelectric and high dielectric constant. This FE ceramics are used in first piezoelectric transducer. But now it is mostly used in multilayer capacitors (MLCs) due to having a high dielectric constant. It is also used in positive temperature coefficient

dipoles if there is no recompense pattern in the diploe.

etc. Some of these perovskite are discussed in detail as follows.

**2. Perovskite ferroelectrics**

*Shows the schematic diagram of perovskite structure.*

**2.1 Barium titanate ceramics**

**Figure 1.** *Ven diagram of ferroelectric fit into different materials.*

*Multifunctional Ferroelectric Materials*

structures is change. The is a charge separation in the surface, results in the spontaneous polarization. So the polar dielectric spontaneous polarization direction and magnitude can be modified with the applied stress. Zinc oxide, which belongs to family of polar dielectric shows wurtzitecrystal structure [5]. In this structure, between hexagonally packed oxygen ions layer, Zn2+ions are at the tetrahedral site. Between these layers dielectric, whose spontaneous polarization depends on the direction and magnitude of the applied stress. Adequate amount of stress can change the direction of spontaneous polarization. But the exclusion of the stress does not bring back the original magnitude and direction of the spontaneous polarization. These families of polar dielectric are called ferroelectric. **Figure 1** shows the way the Centro symmetric, acentric, polar and ferroelectric, dielectrics are related to each other. Many review articles shown the history of ferroelectric [6–12]. Many

Pyroelctricity was studied by Brewster. Piezoelectricity was discovered by J. P. Curie. Debye, Boltzmann, Pockelsetc helps in conceptualizing the polarization in the dielectric. It was E. Schoridgener, who coined the term ferroelectricity, but JoesphValasek known for the discovery of ferroelectric. In 1920 the Rochelle salt (sodium potassium tartrate) shows spontaneous polarization which can be switch with the magnitude and direction of the applied field. This is the first manifestation of the ferroelectricity in a crystal. That is the trademark of ferroelectricity. Logically effectively the term ferroelectricity is defined as the switchable polarization between two or more stable state by the application of electric field. There exist some exceptions. Some semiconductor materials show ferroelectric properties. They do not posses electric polarization. In some ferroelectrics materials the spontaneous polarization cannot be switched with the electric field. This is either due to they are too conducting or reach the electrical break down first. This ferroelectric property first observed in Rochelle salt. But later it is observed in oxides, polymer, ceramics, and liquid crystal. When it is about ferroelectric property, the perovskite structure materials have a special importance. So in this chapter, we will discuss some perovskite ferroelectrics which are used in various electronics devices. According to the structure, there are five types of structure. (i) Organicpolymer (ii) Charge ordered ferroelectrics (iii) Magnetic order ferroelectric (iv) Corner-sharing oxygen octahedral (v) Hydrogen bonded radical compound (v) Ceramic polymer composites [11]. Among these ferroelectricgroup a mostly used ferroelectrics are

great scientist open the path of discovery of the ferroelectric.

the corner sharing oxygen octahedral oxides.

*Ven diagram of ferroelectric fit into different materials.*

**32**

**Figure 1.**

**Figure 2.** *Shows the schematic diagram of perovskite structure.*

Basically, the corner sharing oxygen octahedral oxide structures is represented as Aa+Bb+O3 [12]. **Figure 2** shows the schematic figure of O2− ions corner sharing oxygen octahedral. The Bb+ cation is seated within every octahedron. The b of the cation has the value lies in between 3 to 6. Aa+ ions lie in the gap among the octahedral with its value of *a* is in between 1 to 3. A nonpolar lattice has been observed in prototype forms by the overlap of Aa+, Bb+, and O2− ions geometric center. The total polarity of the lattice is obtained by displacement of A and B ions with respect to the O2− ions. Due to change in temperature, phase transition takes place. This will result in displacement of ion results in a change in lattice structure. Spontaneous polarization will produce due to the displacement of ions in the arrangement of dipoles if there is no recompense pattern in the diploe.
