Ferroelectric properties in KNbO_3 thin films probed by optical second harmonic generation

摘要

Ferroelectric phase transitions and the structure of KNbO_3 nanometer-thick films deposited by Metal-organic chemical-vapor deposition technique on a MgO(100) substrate are studied. Thin KNbO_3 films of the average thickness from 20 to 150 nm possess a grainlike structure with a lateral grain size of about 250 nm. Such films reveal ferroelectric properties similar to KNbO_3 single crystal. Temperature dependencies of optical second harmonic generation intensity show that the Curie temperature T_C of the nanometer-thick KNbO_3 films is about 30℃ lower than the T_C of KNbO_3 single crystal, which is attributed to size effects in KNbO_3 nanograins.