What is Ferro-electricity
Ferro-electricity is the process in which certain materials could exhibit a spontaneous dipole movement. Ferro-electricity results from relative shifts of positive and negative ions that induce surface charges. It can also be described as the sudden electric polarization of certain materials. Ferroelectric materials could be used to make capacitors with high dielectric constant, transducers and actuators. They are also used for many industrial applications such as sensors, read heads. The direction of polarization in this material can be switched to equivalent states by the application of an external electric field. In ferroelectric materials, the sudden polarization will occur at temperatures below the curie-temperature.
What is spontaneous polarization
In a ferromagnetic material, spontaneous polarization occurs at a temperature below the curie-temperature. The direction of the polarization can be reversed by application of an electric field which exceeds the coercive field. Ferroelectric material demonstrates a spontaneous non-zero polarization when the applied field is zero. Ferro-electricity is the result of polarization, polarization can be described as the electric dipole movement.
What is the difference between a dielectric and Ferro-electric
Dielectric is an electrical insulator that can be polarized by applying an electric field. Dielectrics can store electrical energy, if an electric field is applied to the dielectric then the negative and positive charged particles are separated in different directions and that will produce electric dipole in the material. Ferroelectrics are mostly crystalline substances that have permanent spontaneous electric polarization.
What is para-electricity
Para-electricity can be defined as the ability of the materials to become polarized under an applied electric field and mostly the materials will be ceramic. It is different from ferroelectricity because, ferroelectricity occurs if there is a permanent electric dipole, but in the case of para-electricity it doesn’t need that. Para-electricity is caused by the distortion of ions and polarization of molecules.
What is Ferro-electric crystal
A ferroelectric crystal can be described as a crystal which has ferroelectric property. All ferroelectric materials will exhibit sudden dipole movement and there will be relative shifts of positive and negative ions.
What is a ferroelectric capacitor
Ferroelectric capacitors can be created by placing a ferroelectric material between two conductive plates. These capacitors exhibit nonlinear properties and have very high dielectric constant. The internal electric dipoles can be forced to change their direction by the application of an external voltage and that will give rise to hysteresis in the polarization vs voltage property of the capacitor. Ferroelectric capacitors have the combined properties of memory, piezoelectricity, and pyro-electricity and that makes the ferroelectric capacitors the most useful technological device. Ferroelectric capacitors are used in medical ultrasound machines, high-quality infrared cameras, fire sensors, sonar and vibration sensors.
What are the properties of ferroelectric material
Curie point and phase transition
Most of the ferroelectric materials go through a phase transition from a high-temperature non-ferroelectric phase into a low-temperature ferroelectric phase. The para-electric phase may be piezoelectric or non-piezoelectric and is rarely polar. The symmetry of the ferroelectric phase is always lower than the symmetry of the para-electric phase. The temperature of the phase transition is called the curie point and above the curie point the dielectric permittivity falls off with temperature. All the ferroelectric materials have a transition temperature called the curie-point. While decreasing the temperature through the curie point, ferroelectric crystal undergoes a phase transition from a non-ferroelectric phase to a ferroelectric phase. If there are more than one ferroelectric phases then the temperature at which the crystal transforms from one phase to another is called the transition temperature.
Domain and domain boundary
Ferroelectric materials are divided into a number of ferroelectric domains each domain has a large number of the dipole that has the same direction and these domains are separated by domain boundary domains will only differ in the polarization direction.
The domain walls have a higher length when compared to the dimensions of the domain. So while applying an electric field to the ferroelectric crystal, polarization takes place into processes. So for the weak field, the volume of the domains that have polarization in the direction of the applied field will grow in the size on the expense of other domains and for strong fields, the domain prefers to orient themselves in the direction of the applied field.
The reversal of the polarization can be seen by measuring the ferroelectric hysteresis when the electric field strength is increased then the domains will start to align in the positive direction which will give rise to a sudden increase of the polarization. At high field levels, the polarization reaches a saturation value and the polarization does not fall to zero when the external field is removed. The domains will remain in a positive direction when there is no external field, the crystal will only show a small polarization. In order to depolarize the crystal, a magnetic field must be applied in a negative direction. The external field which is required to reduce the polarization to zero is called the coercive field strength. The direction of the polarization flips when the field is increased to a more negative value and a hysteresis loop will be obtained.
What are the types of ferroelectric materials
Corner sharing octahedra
A major part of ferroelectric crystals are made up of mixed oxides containing corner-sharing octahedra of O2- ions inside each octahedron is a cation Bb+, the space between the octahedral are occupied by Aa+ ions. When polarized the A and B ions are displaced from their geometric centers with respect to the O2- ions, to give a net polarity to the lattice. This displacement occurs due to the changes in the lattice structure when the phase transition takes place as the temperature is changed
Perovskite is the family name of a group of materials and the mineral name of calcium titanate having a structure of the type ABO3. Many piezoelectric ceramics such as barium titanate, lead titanate, lead magnesium niobate, potassium niobate have a perovskite-type structure.
What are the applications of ferroelectric materials
- Ferroelectric materials are used for the capacitor manufacturing and the capacitors are generally formed by the barium titanate.
- It can be used as storage memory, FRAM ferroelectric random access memory is non-volatile and they are cheaper and reliable
- Ferroelectric materials are used in waveguides, waveguides are devices which can control the propagation of light within the device
- Ferroelectric materials are used in an optical memory display