Most ceramics are insulators that block electricity. However, advanced ceramics have unique properties that enable them to conduct electricity under certain conditions. They are called electroceramics and include materials such as ferroelectrics – capacitors, nonvolatile memories; piezoelectrics – sonar; and semiconducting oxides – power generation, storage, conversion, and electronics. The global $4.5 trillion electronics industry would not exist without these special types of ceramic.
The electrical properties of ceramics are related to their bonding and crystal structures. Two different bonding mechanisms occur in ceramics: ionic and covalent. Ionic bonds connect atoms that have different electronegativities. The atoms in these structures can transfer electrons to other atoms or to vacancies (holes) in the crystal lattice. The free electrons are called ions, and they can move with great speed. Ionic conduction is fast at low temperatures, but slow at higher ones.
Semi-metallic ceramics are the best electronic conductors of all ceramic materials. These have overlapping electron energy bands that allow them to conduct electricity like metals. Examples of these are lead oxide, ruthenium dioxide, and bismuth ruthenate. They are also used as “inks” for screen-printing resistors into thick-film microcircuits.
Most ceramics are insulators, and their insulation properties are very important for many applications. For example, they make excellent dinnerware, which is dishwasher safe and can withstand a variety of chemicals, including acids and salts. They are also good thermal insulators and can maintain stable temperatures. The insulating properties of ceramics are also very useful in spark plugs, hermetic packages, and tubing for electric power lines.