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(-3) Angstrom, 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 Mg2+ (ionic radius 0.65 Angstrom, 1s(2)2s(2)2p(6) ) instead of Li+ (ionic radius 0.6 Angstrom, 1s(2) ) suppresses T-c, while Be2+ (ionic radius 0.3 Angstrom, 1s(2) ) shows almost the same T-c. The Mg2+ plays a different role from the isoelectronic Li+ and Be2+ .