Electroceramics are ceramic materials that have been specially formulated for specific electrical, electro-magnetic, or optical properties. They include dielectric ceramics, electrostrictive ceramics, ferrite ceramics, garnets (ferromagnets), and piezoelectric ceramics. The properties of electroceramics can be tailored for their use as insulators, ferroelectric materials, highly-conductive ceramics, electrodes, sensors and actuators. The development of electroceramics depends upon the presence of ionic-covalent bonding; microstructures that comprise inorganic crystal compounds and/or amorphous glass in varying proportion; and thermal processing conducted at elevated temperatures.
Types of Electroceramics
Dielectric ceramics and electrostrictive ceramics are common types of electroceramics. Dielectric ceramics have high electrical resistivity (low electrical conductivity) and high dielectric strength. Electrostrictive ceramics are relaxor ferroelectric ceramics. Strain varies quadratically with electric field for an electrostrictor, rather than linearly as in a piezoelectric ceramics. Relaxors exhibit very high dielectric constants (K > 20,000), diffuse ferroelectric-to-paraelectric phase transitions, and electrostrictive strain vs. electric field behavior. Electrostrictors excel at high frequencies and very-low driving fields. Often, these electrostrictive ceramics are applied in specialized microactuators.
Electroceramics include ferrite ceramics (ferrites) and garnets (ferrogarnets). Ferrites are ferrimagnetic oxides with dielectric and magnetic properties that are useful for RF and microwave applications. Spinel ferrites typically have a general formula of AB2O4. Iron-based ferrites have the general formula MO-Fe2O3 where M is a divalent ion such as Fe, Ni, Cu, Mg, Mn, Co, Zn, or Li. Hexagonal ferrites, hexaferrites, or materials in the magnetoplumbites group have the general formula AB12O19 and include barium ferrite and strontium ferrites. Garnets are electroceramics that have a fairly complex structure with the general formula of (3M2O3)C(2Fe2O3)A(3Fe2O3)D where M is yttria or rare earth ion and (A,C,D) are lattice site.
Piezoelectric ceramics are electroceramics that include quartz and ferroelectric or perovskite materials. Ferroelectric materials include lead titanates, lead zirconates, lead zirconate titanates (PZT), barium titanates, barium tantalate and lead magnesium niobates. Ferroelectric materials and have the general formula ABO3 . Piezoelectric materials produce an electrical charge when a load is applied and deformation occurs. These properties make piezoelectric materials useful for pressure or load sensors. Inversely, piezoelectric materials produce force or deformation when a load is an electrical charge applied. These properties make such electroceramics useful for microactuators, nanoactuators or piezoelectric motors.
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Piezoelectric ceramics produce an electrical charge when a load is applied and deformation occurs. Piezoelectric ceramics can also produce force or deformation when an electrical charge is applied.