**2.1 Barium titanate ceramics**

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

Resistance (PTCR), sensor, PTC Thermistors, IR detectors, RAM, sonars and in electro optic devices. By doping Barium titanate which is insulator in pure form can be changed into a semiconductor. Barium titanate basically white powder of inorganic compound. With a decrease in temperature the octahedral TiO6 undergoes distortion gives rise to five structural phase transition from hexagonal, cubic, tetragonal, orthorhombic, and rhombohedra. Very large spontaneous polarization and high dielectric constant are observed in this phase due to the distorted octahedral. At Curie point, i.e. above 120°C the distorted octahedral of TiO6 comes to equilibrium result in an isotropic cubic structure [13, 14] so only this phase does not exhibit FE properties.

Capacitor, MLC etc. used first BaTiO3 as the dielectric ceramic with large dielectric constant and dielectric loss for manufacturing. The factor that affects the dielectric properties of the materials is not only its structure but also its synthesis route which will reflect in its size of the grain, density, purity etc. [15]. The Applied frequency of the electric field, temperature and do pants also affects the dielectric properties of the materials [16–23].

The dielectric constant of Barium titanate prepared by any method increase depends on the grain size and distribution of grains [17, 24]. At room temperature the frequency dependent dielectric constant decreases at low frequency and then increases slightly and become constant at high frequency. Temperature dependent dielectric constant decreases at higher temperature [25]. Ions of different size can be can be added to the perovskite structure. So doping at both A and B site of this perovskite structure is used to tolerate its electrical properties [26]. At A site mono, die and trivalent acceptor do pants are substituted to produce P-type semiconductor, whereas N type semiconductor are obtained by donor dopant of tri, tetra and pentavalent ions at the B site of the perovskite. The concentration of the dopants also affects the electrical properties of Barium titanate. Increase in concentration of Donor dopant makes the semiconducting ceramics to an insulating one. Barium titanate ceramics have application in various engineering fields.

#### *2.1.1 Multilayer capacitor (MLCs)*

Mostly BaTiO3 is used in capacitor due to having a high dielectric constant. In thin dielectric form packed in a minimum space not only with high capacitance but also mechanically tough [27]. It is used as passive component in the circuit for large scale integration (LSI). It is also cost effective one with the use of internal electrode made of, nickel (Ni) and copper (Cu) [28].

#### *2.1.2 (s2) PTC thermistor*

The high resistivity of BaTiO3 makes it as good candidates for PTC thermistor. Doping at A and B site of BaTiO3 convert them as a semiconducting material. Below the Curie temperature these semiconductor materials have low resistance. Above crystal particle boarder barrier layer persuades by the surface state. So FE characteristics with high dielectric constant exhibit by this crystal boundary of high resistance. So below Curie temperature the potential barrier is small. Low resistivity has been exhibited in these materials due to effortlessly penetration of electron. The height of potential barrier increases above the Curie temperature makes electron difficult to pass through it results in increasing the resistivity of the material. In various electronics circuits this semiconducting BaTiO3 materials are used as constant temperature heaters or switching devices. For temperature or parameter related to temperature can be detected, measured and control of temperature with

**35**

*Perovskite Ferroelectric*

*2.1.3 Nanogenerator (NG)*

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

energy without an external energy source.

**2.2 Strontium titanate (SrTiO3)**

the highest temperature coefficient of resistance.

the use of this PTC thermistor. Among all the available sensor materials PTC has

High piezoelectric effect with biocompatibility make them use as Nanogenerator. Piezoelectric potential is induced in between the two electrodes of NG, this is due to mechanical stress. Commercial devices can be work using this generated electrical

Another member of perovskite family is strontium ferrite STO (SrTiO3) is a complex oxide. It exhibits cubic structure at room temperature. O2− ions are bonded with six folded coordinate to Ti4+ ions and with twelve folded coordinate to Sr2+ ion. Each Sr2+ ion lies in between four TiO6 octahedral. To decrease in temperature, it undergoes a phase transition. The first transition below room occur at −168°C. The opposite rotation of adjacent oxygen octahedral at this term turns the cubic structure to tetragonal structure. To further decrease in temperature at −236°C the changeable phonon modes turns the tetragonal structure to orthorhombic structure. The orthorhombic structure is change to rhombohedra structure at −263°C [29]. As Curie–Weiss law suggests the dielectric constant increases with the phase transition below room temperature. At this temperature due to quantum fluctuations leads to the quantum PE [30]. The charge storage capacity is high, chemical stability, optical transparency in the visible region with good insulating properties makes it use in modern electronics applications such as phase shifters, high-voltage capacitors, delay lines, filters, tunable oscillators etc. [31–33]. It is used in cancer treatment and in thermo – electric generators due to they have insolubility and high melting point properties [34, 35]. It shows photoconductivity when exposed to light due to having an direct gap and indirect band gap of 3.75 eV and 3.25 eV respectively [36]. Its conductivity increases with the contact of light to the crystal.

Its conductivity persists for several days, with small decay [37, 38].

memories, soft phonon devices, oxygen sensors [45, 46].

**2.3 Barium strontium titanate (BST)**

The first oxide, which is superconducting below 0.35 K is the strontium oxide (STO) [39]. It can be used as a tremendous substrate for superconductors with a high operating temperature and for oxide-based thin films. It is used as single-crystal substrate due to the enhanced electrical conductivity of niobium doped STO for the growth of perovskite oxides. It is also used for other ferroelectric and magnetic oxide substrate due to its large lattice parameter. Variation of temperature and pressure parameter can lead to increase oxygen vacancies in both crystal and thin films of SrTiO3. So it becomes more conducting due to stimulate free electrons in the conduction band and also opaque. This used as gate-dielectric material due to the growth of high quality growth of epitaxial SrTiO3 layers on silicon without forming silicon oxide Furthermore, it allow the incorporation of other perovskite oxides based thin-film on top of silicon [40]. It is also used for its piezoelectricity, ferroelectricity and Pyro electricity application in nanoscale [41–44]. It is used for various technological applications such as in super capacitor, nonvolatile memory, tunable microwave capacitors, ultralow-temperature scanning microscopies, high-density dynamic random access

The model of BaTiO3 (BTO) has been used to develop Barium strontium titanate (BaxSr1−*x*TiO3 perovskite. This perovskite also undergoes phase change at it the use of this PTC thermistor. Among all the available sensor materials PTC has the highest temperature coefficient of resistance.
