Introduction to Piezoelectrics and Ferroelectrics
“Piezo” is a greek word pronounced for “pressure” whereas we define “electricity as motion of electrons”. Therefore, piezoelectricity is the property of material to produce electricity under the applications of pressure. In a border sense, piezoelectricity is defined as the electric charge that accumulates in response to applied mechanical stress in materials with non centrosymmetric crystal structures ( certain ceramics and biological matter such as bone, DNA and various proteins). Application of pressure results in charge separation within the crystals resulting in piezoelectric effect.
Before we understand ferroelectricity we must know what dielectrics is? Well, dielectrics is defined as non conducting material which can be polarized by applied electric field. Now we can relate ferroelectricity which is defined as the property of dielectrics exhibiting spontaneous electric polarization that can be reversed in direction by the application of an appropriate electric field. The reason for ferroelectricity is permanent dipole moment(natural dipole).
Short History
In 1880, piezoelectric effect was discovered by Jacques and Pierre Curie.While working on quartz crystal, electric charge was created in the quartz during application of pressure and they named this incredible phenomena as piezoelectric effect. Ferroelectricity carries a beautiful history where Debye proposed, critical temperature is analogous to the curie temperature of ferromagnet. Below this temperature permanent dielectric polarisation ought to be expected in absence of an electric field in Rochelle salt.This theory of Debye was further studied by Erwin Schrodinger where he extended Debye’s simple model to solids proposing ferroelectricity.
Applications of Piezoelectrics and Ferroelectrics
Direct piezoelectricity of some substances like quartz can generate potential differences of thousands volts which are used as a high power and voltage sources like that in piezoelectric transformers. The piezoelectric properties of quartz are useful as a standard of frequency like that in crystal oscillators. Piezoelectric sensors coupled with high frequency sound in ultrasonic transducers are used for medical imaging and also for industrial non destructive testing.The important discovery led by piezoelectricity is improvement in fertilization outcomes where activation of oocytes piezoelectrically is carried out together with intracytoplasmic sperm injection resulting improved fertilization in people with total fertility failures. Piezoelectric ceramic fiber technology is being used as an electronic damping system to reduce vibrations and noises.
Basically, materials demonstrate ferroelectricity below Curie temperature and are paraelectric above this temperature i.e the spontaneous polarization vanishes and ferroelectric materials get transformed to paraelectric. This anomalous property is used to make tunable capacitors( able to be adjusted to the frequency of the required signals) These kinds of capacitors are used to make ferroelectric RAM for computers and RFID cards.Furthermore, their use in Sensor applications is also wide.Ferroelectric polarisation can be used in energy harvesting which are more pronounced in wearable electronics and wireless sensors networks.Catalytic properties are also considered while we discuss the application of ferroelectric materials.
Limitations
Despite a lot of advantages piezoelectric materials have constraints as well.Piezoelectric crystals are water soluble hence these get dissolved in a highly humid environment. They are highly temperature sensitive and are used for dynamic measurements only.Multidomain ferroelectricity imposes a severe limit to the maximum step up of the surface potential obtainable in devices.
In a nutshell
Ferroelectrics are considered to be the subset of piezoelectrics in a sense that ferroelectrics undergo spontaneous polarization and this polarization can be changed under the application of stress, implying all ferroelectric materials to be piezoelectric but all piezoelectric materials are not ferroelectrics. These materials produce no waste and pollution and can be used repetitively. As long as there is power there is electricity, so it’s a clean renewable energy. Its power generating efficiency in comparison to traditional fossil fuels has been a key factor for future.
