Novel Ferroelectricity in II-VI Semiconductor ZnO

Novel ferroelectricity was discovered in semiconducting ZnO by partial substitution of Li for Zn. Introduction of 6% Li induces a ferroelectric phase transition at 330 K. The T c increases with the increasing Li concentration. Structural changes due to Li-substitution are only on the order of 10 m 3 Å, while 3 d electrons around Zn cannot be detected. The mechanism of ferroelectricity was studied based on two models, the size-mismatch model and electronic model. Dielectric measurements indicate that the introduction of Mg 2+ (ionic radius 0.65 Å, 1s 2 2s 2 2p 6 ) instead of Li + (ionic radius 0.6 Å, 1s 2 ) suppresses T c , while Be 2+ (ionic radius 0.3 Å, 1s 2 ) shows almost the same T c . The Mg 2+ plays a different role from the isoelectronic Li + and Be 2+ .