Ferro and piezo electric materials
Ferroelectricity :
The dielectric materials having spontaneous polarization in the absence of electric field called "Ferroelectric materials" and the phenomenon is called "Ferroelectricity"
Examples are Barium Titanate, Potassium Di Hydrogen Phosphate, Ammonium Di Hydrogen Phosphate, PZT, PLZT.
Properties of Ferroelectric materials:
The dielectric materials having spontaneous polarization in the absence of electric field called "Ferroelectric materials" and the phenomenon is called "Ferroelectricity"
Examples are Barium Titanate, Potassium Di Hydrogen Phosphate, Ammonium Di Hydrogen Phosphate, PZT, PLZT.
Properties of Ferroelectric materials:
- Ferroelectrics exhibit spontaneous polarization.
- Ferroelectrics have high value of dielectric constant (K).
- Ferroelectrics exhibit piezoelectricity and pyroelectricity. Its spontaneous polarization vanishes above a perticular Tc called Curie temperature.
- According to Curie-Weiss law,
- The most important property of ferro electrics is that they exhibit hysteresis behaviour.
- When a Ferroelectric material is subjected to an electric field, the graph between polarization (P) and Electric field (E) results a closed loop called Hysteresis loop.
- As the field increases, the polarization will raise and reaches its saturation at certain value at A.
- The polarization at A will not be changed even if the applied electric field is increased further.
- If the field is decreased, curve follows the path A to B, at that point field is zero but some polarization retains in that material called Residual polarization.
- If you further increase the field in reverse direction, curve follows the path B to C where the polarization is zero and field is Coercive field.
- These materials are used to manufacture small size capacitors.
- These are used in memory devices of computer.
- Ferroelectrics exhibits pyroelectricity and hence they are used to detect the infrared radiation. They are used in Microphones.
Materials which are polarized when they are subjected to mechanical stress, are called Piezoelectric materials and the phenomenon is called Piezoelectricity.
All the ferroelectrics are piezoelectrics, but all the piezoelectrics are not ferroelectrics.
Examples are Barium Titanate exhibits both the the properties, Quartz exhibits piezoelectricity but not ferroelectricity.
Applications:
- These materials are widely used in transducers and strain guage. Strain guage is used to determine strain in the sample.
- Piezoelectric crystals are used for production of ultrasonic waves.
- Direct piezoelectric effect is used in microphones.
- Inverse piezoelectric effect is used in quartz watches.