A unique type of polycrystalline ceramic having properties that make possible the production of reliable, high-density optical memories for computers that are more efficient than conventional types. Lead zirconate titanate, heated and pressed into thin plates, is one of the compounds used. As a result of its ferroelectric properties, an applied voltage aligns the electric charges in the molecules of ceramic in the direction of the field and the polarization so induced remains indefinitely. Thus, the material accommodates itself to the requirements of the digital system, namely, binary 0 and binary 1.See Ferroelectric.