Correlation of the optical gap of (Ba,Sr)(y)TiO2+y thin films with film composition

A series of 26 (Ba1-xSrx)(y)TiO2+y thin films with 0.22 less than or equal to y less than or equal to 1.01 and x < 0.07 were grown by metalorganic che mical vapor deposition. Most of the films with 0.22 less than or equal to y less than or equal to 0.37 were fully amorphous, whereas the films with 0. 43 less than or equal to y < 1 were composed of crystalline (Ba,Sr)-TiO3 an d a Ti-rich amorphous phase. Transmission spectra were measured and analyze d to determine the optical constants of the films, including the optical ga p, which was found to decrease as y increased. An effective medium model wa s used to estimate the volume fraction of amorphous material in the two-pha se films from the transmission spectra, by assuming that the two phases eac h had a fixed optical gap. (C) 2000 Elsevier Science S.A. All rights reserv ed.