**2.3 Barium strontium titanate (BST)**

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 Curie temperature depend upon the ratio of Ba:Sr. If the ratio decreases the curie temperature decreases. The dielectric constant at the Curie temperature of BST is more than BTO. BST is simply ferroelectric with spontaneous polarization below the Curie temperature. Nearly Tc the tenability of BST has extremely high in the FE phase. So in this phase find application for non volatile application. Above the Curie temperature the pyroelectric BST finds its applications in tunable microwave device associate with low dielectric loss and high dielectric constant. It also finds application in phase shifters, tunable filters and tunable antennas due to its composition dependent curie temperature with permittivity depends electric field.

Due to its high value of capacitance make it useful to construct high capacitance capacitor. It has uses in tunable microwave devices tunable capacitor, phase shifters, tunable transformers. BST varactors are a good replacement of the presently used semiconductor varactor and mechanical tuners. It is not only the drawback of large size with small tuning speed of mechanical tunners, but also small power handling capability of semiconductor varactor. BST also used in band pass and low pass tunable filter.

Semiconductor based phase shifter are used in fighter aircraft radar and cellular telephone base stations are associated with high loss at microwave frequencies with low power use ability. BST is the best replacement of these semiconductor based phase shifter associate with small loss, inexpensive and with better power handling properties. It is used in micro strip antenna. In tunable microwave application thin film of BST is used. The reduced size with small weight makes it compatible with microwave circuit. Dielectric constant not decreases sharply with the variation of the thickness of the film [47–49]. When it's used in metal–insulator–metal capacitor shows high dielectric constant, low dielectric loss, high leakage current density, high charge storage density makes it's used in dynamic random access memory (DRAM).

## **2.4 Lead titanate (PbTiO3)**

Another member of perovskite family is the inorganic lead salt of titanic acid compound, i.e. Lead titanate (PbTiO3). Yellow powder of lead titanate is water insoluble. It shows a high Curie point of 490°C. It shows second order phase transition due to which it changes from cubic pyroelectric phase to ferroelectric tetragonal phase. At room temperature it shows the tetragonal structure belongs to *P*4 mm space group. It undergoes large volume change when cooled below the Curie temperature. It is not easy to formulate it in the bulk form. There is formation of crack during manufacture due to strain. To reduce this strain various dopants are used to modify the lead titanate. Ferroelctric lead titanate find its uses in, resonators, actuators, IR sensors, ultrasonic transducers and MLCs etc. [50–52]. Various process such as melting, Co precipitation, decomposition, hydrothermal, sol–gel, chemical vapor deposition, molecular beam epitaxy (MBE), molten salt methods, solid state method and sputtering is used to prepare thin films, single crystals and ceramic powders of PbTiO3 [53–74]. For advance electromechanical devices, it is the capable building blocks. It can be prepared in micro tube, Nano sized powder and nanowire by the use of hydrothermal method [68, 75–79]. It is one of the most used materials for the fabrication of sensors, memory capacitors, optoelectronics devices etc. [76, 79].

#### **2.5 Lead zirconate titanate (PZT)**

Lead zirconate titanate with perovskite structures is an inorganic intermetallic compound. It is a solid solution of lead zirconate and lead titanate represented as [Pb (ZrxTi1−x) O3, 0≤x≤1]. PZT has Pb2+ ions at A site with random occupation of B

**37**

*Perovskite Ferroelectric*

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

either by the use of Al3+, Fe3+ at B site and Na+

and used for generation of energy in alternating loads [89, 90].

leads to the diffuse phase transition in the relaxor ferroelectric.

zero with the increasing in temperature [103–106].

**2.7 Potassium niobate (KNbO3)**

**2.6 Lead magnesium niobate (PMN)**

site by Ti4+ and Zr4+ ions. It undergoes phase change with composition, but also with temperature. Above its Curie temperature it shows the pyroelectric effect with cubic structure. It undergoes a structural change from PE cubic phase either to FE rhombohedral phase or tetragonal phase. The spontaneous polarization in these structures is oriented in< 100⟩ and ⟨111⟩ set of directions for tetragonal and rhombohedral phase respectively. The morphotropic phase boundary is around at 52/48 of Zr/Ti ratio separating FE tetragonal and orthorhombic phases. At this boundary PZT has shown maximum dielectric and piezoelectric constants. Rhombohedral phase with 8 possible domains and tetragonal phase with 6 domains with total 14 domains are equally favorable at this composition. Piezoelectric PZT ceramics can be tailored according to application with ions having valence diverse from the host ions in the lattice. Especially PZT at MPB is modified to form soft and hard PZT. Acceptor ions are used

produce oxygen vacancies in the lattice [80, 81]. Donor ions PZT produced domains wall motion fromed by Nd3+, La3+ at A site where as Nb5+, Sb5+ at B site in the lattice [82–85]. Hard PZT formed by donor doping shows low dielectric constant, small electrical losses, small piezoelectric co-efficient with high coercive field. So it is difficult to pole and dipole the sample and make them useful for rough applications. Whereas soft PZT has shown larger losses, high dielectric constant and piezoelectric co-efficient. So they can easily dope and dipole. They are used in FeRAM, actuator of STM/AFM type, ultrasound transducer, capacitor with high dielectric constant, IR sensor, etc. High value of piezoelectric coefficient of FE PZT make them useful for micro sensor, micro actuator used micro electromechanical system (MEMS) devices [86–88]. Nano rods, wire and hollow tube of PZT are now used for different application [89–98]. PZT Nanogenerator are used for piezoelectric effect to produce piezoelectric energy in the microscale. The intrinsic polar crystal structure of PZT nanofibers shows high piezoelectric voltage constant. High aspect ratio of nanostructure PZT overcomes extremely brittle nature observed in bulk PZT and its thin films

Single crystal of Pb (Mg1/3Nb2/3) O3 (PMN) materials belongs to the FE relaxor materials and are used in [99], and the work in the electrostrictive actuators with high-strain and capacitor with high dielectric constant [100–102]. The Perovskite type structure of Pb (B1, B2) O3 formula with lower valence B1 such as Zn2+, Mg2+, Fe3+ and Ni2+ and higher valency B2 is such as Ta5+, Nb5+ and W5+. On cooling below the Curie temperature relaxor PMN ferroelectrics shows a wide dispersive and the diffused phase transition. Heterogeneity in composition on a microscopic scale

In micoregion the stoichiometry is not obeyed by disorder B-site leads to change in FE transition temperatures leads to broadening dielectric peak. Strong frequency dependent dielectric constant has been observed in the relaxor ferroelectric. Curie temperature changes linearly with frequency with high dielectric loss below this temperature. Some relaxor shows second order phase transition. This relaxor remnant polarization is starting to decrease from Curie temperature and becomes

KN (KNbO3) is also exhibited perovskite structure. It shows interesting ferroelectric properties at low temperature. It shows three phase transitions simple displacive type at low temperature with different symmetry and PE phase at

and K+

at A site of the perovskite to

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

*Multifunctional Ferroelectric Materials*

memory (DRAM).

**2.4 Lead titanate (PbTiO3)**

Curie temperature depend upon the ratio of Ba:Sr. If the ratio decreases the curie temperature decreases. The dielectric constant at the Curie temperature of BST is more than BTO. BST is simply ferroelectric with spontaneous polarization below the Curie temperature. Nearly Tc the tenability of BST has extremely high in the FE phase. So in this phase find application for non volatile application. Above the Curie temperature the pyroelectric BST finds its applications in tunable microwave device associate with low dielectric loss and high dielectric constant. It also finds application in phase shifters, tunable filters and tunable antennas due to its composition

Due to its high value of capacitance make it useful to construct high capacitance capacitor. It has uses in tunable microwave devices tunable capacitor, phase shifters, tunable transformers. BST varactors are a good replacement of the presently used semiconductor varactor and mechanical tuners. It is not only the drawback of large size with small tuning speed of mechanical tunners, but also small power handling capability of

Semiconductor based phase shifter are used in fighter aircraft radar and cellular telephone base stations are associated with high loss at microwave frequencies with low power use ability. BST is the best replacement of these semiconductor based phase shifter associate with small loss, inexpensive and with better power handling properties. It is used in micro strip antenna. In tunable microwave application thin film of BST is used. The reduced size with small weight makes it compatible with microwave circuit. Dielectric constant not decreases sharply with the variation of the thickness of the film [47–49]. When it's used in metal–insulator–metal capacitor shows high dielectric constant, low dielectric loss, high leakage current density, high charge storage density makes it's used in dynamic random access

Another member of perovskite family is the inorganic lead salt of titanic acid compound, i.e. Lead titanate (PbTiO3). Yellow powder of lead titanate is water insoluble. It shows a high Curie point of 490°C. It shows second order phase transition due to which it changes from cubic pyroelectric phase to ferroelectric tetragonal phase. At room temperature it shows the tetragonal structure belongs to *P*4 mm space group. It undergoes large volume change when cooled below the Curie temperature. It is not easy to formulate it in the bulk form. There is formation of crack during manufacture due to strain. To reduce this strain various dopants are used to modify the lead titanate. Ferroelctric lead titanate find its uses in, resonators, actuators, IR sensors, ultrasonic transducers and MLCs etc. [50–52]. Various process such as melting, Co precipitation, decomposition, hydrothermal, sol–gel, chemical vapor deposition, molecular beam epitaxy (MBE), molten salt methods, solid state method and sputtering is used to prepare thin films, single crystals and ceramic powders of PbTiO3 [53–74]. For advance electromechanical devices, it is the capable building blocks. It can be prepared in micro tube, Nano sized powder and nanowire by the use of hydrothermal method [68, 75–79]. It is one of the most used materials for the fabrication of sensors, memory capacitors, optoelectronics devices

Lead zirconate titanate with perovskite structures is an inorganic intermetallic compound. It is a solid solution of lead zirconate and lead titanate represented as [Pb (ZrxTi1−x) O3, 0≤x≤1]. PZT has Pb2+ ions at A site with random occupation of B

dependent curie temperature with permittivity depends electric field.

semiconductor varactor. BST also used in band pass and low pass tunable filter.

**36**

etc. [76, 79].

**2.5 Lead zirconate titanate (PZT)**

site by Ti4+ and Zr4+ ions. It undergoes phase change with composition, but also with temperature. Above its Curie temperature it shows the pyroelectric effect with cubic structure. It undergoes a structural change from PE cubic phase either to FE rhombohedral phase or tetragonal phase. The spontaneous polarization in these structures is oriented in< 100⟩ and ⟨111⟩ set of directions for tetragonal and rhombohedral phase respectively. The morphotropic phase boundary is around at 52/48 of Zr/Ti ratio separating FE tetragonal and orthorhombic phases. At this boundary PZT has shown maximum dielectric and piezoelectric constants. Rhombohedral phase with 8 possible domains and tetragonal phase with 6 domains with total 14 domains are equally favorable at this composition. Piezoelectric PZT ceramics can be tailored according to application with ions having valence diverse from the host ions in the lattice. Especially PZT at MPB is modified to form soft and hard PZT. Acceptor ions are used either by the use of Al3+, Fe3+ at B site and Na+ and K+ at A site of the perovskite to produce oxygen vacancies in the lattice [80, 81]. Donor ions PZT produced domains wall motion fromed by Nd3+, La3+ at A site where as Nb5+, Sb5+ at B site in the lattice [82–85]. Hard PZT formed by donor doping shows low dielectric constant, small electrical losses, small piezoelectric co-efficient with high coercive field. So it is difficult to pole and dipole the sample and make them useful for rough applications. Whereas soft PZT has shown larger losses, high dielectric constant and piezoelectric co-efficient. So they can easily dope and dipole. They are used in FeRAM, actuator of STM/AFM type, ultrasound transducer, capacitor with high dielectric constant, IR sensor, etc. High value of piezoelectric coefficient of FE PZT make them useful for micro sensor, micro actuator used micro electromechanical system (MEMS) devices [86–88]. Nano rods, wire and hollow tube of PZT are now used for different application [89–98]. PZT Nanogenerator are used for piezoelectric effect to produce piezoelectric energy in the microscale. The intrinsic polar crystal structure of PZT nanofibers shows high piezoelectric voltage constant. High aspect ratio of nanostructure PZT overcomes extremely brittle nature observed in bulk PZT and its thin films and used for generation of energy in alternating loads [89, 90].
