Fixable complementary gratings in photorefractive BaTiO_3

A complementary photorefractive grating was created and stored in BaTiO(3). For a grating wave vector oriented along the crystal's c axis, the grating first appeared above 80 degrees C and would remain indefinitely after the crystal was cooled to room temperature. If the grating wave vector was aligned perpendicular to the c axis, the complementary grating could be created at room temperature but would last only a few hours. We attribute the formation of the complementary grating to the movement of ions in the crystal.