Li-substitution effect and ferroelectric properties in piezoelectric semiconductor ZnO

Ferroelectric properties and the effects of Lj-substitution were studied in hot-pressed ceramics and single crystals of semiconducting ZnO. The transition temperature (T-c) of Zn0.9Li0.1O ceramic samples synthesized by the spark plasma sintering method increases to 470 K, while it was 330 K in previous cold-pressed ceramics. Single crystals of ZnO, the T-c of which is 430 K, were grown by the hydrothermal method and annealed in an atmosphere of Li at 920 K for 24 hours. Although the dielectric and thermal behaviors are almost the same as those reported in previous works, T-c increases by 140 K. The ferroelectric transition temperature is strongly influenced by the procedures of sample preparation: annealing in an atmosphere of Li was found to be effective for introducing Li into single crystals.