Studies on the structural, microstructural and optical properties of sol-gel derived lead lanthanum titanate thin films

The La modified lead titanate Pb1-xLaxTi1-x,O-4(3) (PLT) (x = 0.0, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) thin films were deposited on sapphire (0001) substrates by the sol-gel process. The X-ray diffraction data and micro-Raman analysis show that with the increase in La content the crystal quality of the PLT films undergoes a tetragonal-to-cubic transformation. X-ray photoelectron spectroscopy analysis shows an excellent surface stoichiometry for all compositions under study. The optical properties of these films were investigated using both transmission and reflection spectra in the wavelength range of 200-900 nm. The appearance of interference fringes is an indication of the thickness uniformity of the film, The low value of extinction coefficient (in the order of 10(-2)) as observed in our films is a qualitative indication of excellent surface smoothness of the films. Absorption coefficient (alpha) and the band-gap energy (E-g) are obtained for undoped and La doped films with varying La concentrations. It has been found that the refractive index and packing fraction values decrease with La doping. Lanthanum. doping was found to decrease the grain size of the films and improve the densification of individual grains. Increased La content lead to clusterification of smaller grains. The observed variation of band-gap energy with La doping has been correlated with the observed microstructure of these films. (C) 2001 Published by Elsevier Science B.V.