Most ceramics have good electrical insulation, so they are widely used to make insulation devices of various voltages (1kV ~ 110kV). Ferroelectric ceramics have a high dielectric constant and can be used to make capacitors. Ferroelectric ceramics can also change their shape under the action of an external electric field and convert electrical energy into mechanical energy (with the characteristics of piezoelectric materials). , Ultrasonic instrument, sonar, medical spectrometer, etc. A few ceramics also have semiconductor characteristics and can be used as rectifiers.