Electrification of an ionic crystal upon plastic deformation and fracture

Three independent electrification effects have been found and studied in crystals of lithium fluoride. Upon cleavage, the parts of the crystal become charged with charges equal in magnitude and opposite in sign. As a result of plastic deformation, the crystal becomes a sort of pyroelectric, and an intrinsic electric field appears in it. When the deformed crystal contacts a conductor, the crystal becomes charged with a sign opposite to that of the intrinsic field at the point of contact. An interpretation of the cited effects is given.