Synthesis and Characterization of Sol-Gel-Derived (Pb_1-xLa_x)Ti_1-x/4O₃ Thin Films

Ferroelectric lead lanthanum titanate (Pb1-xLaxTi1-x/4O3) (PLTx) thin films (x = 0.04, 0.08 and 0.12) have been prepared by sol-gel spin-coating process on ITO- coated 7059 Corning glass substrates. Investigations have been made on the crystal structure, surface morphology, dielectric and ferroelectric properties of the thin films. Characterization of these films by X-ray diffraction shows that the films annealed at 650degreesC exhibit tetragonal structure with perovskite phase. Replacement of lanthanum in lead titanate results in reduction of the tetragonal ratio (c/a), thereby resulting in better mechanical stability. Microstructural analyses of the films are carried out by obtaining atomic force microscope (AFM) images. AFM images are characterized by slight surface roughness with a uniform crack-free, densely packed structure. Dielectric, pyroelectric and ferroelectric studies carried out on these films have been reported. The dielectric constant increases with La concentration. The Curie temperature is found to decrease with the addition of lanthanum. The pyroelectric coefficient increases from 17 nC/ cm 2 K to 31 nC/cm(2) K as La content increases from 4 to 12%. The pyroelectric figures of merit of the films have been calculated from these studies. These studies indicate that 8% lanthanum is the material best suited for infrared detectors owing to its high pyroelectric coefficient (similar to29 nC/cm(2) K), high voltage responsivity (similar to420 Vcm(2)/J), high detectivity (similar to 1.04 x 10(-5) Pa-1/2) and low variation of pyrocoefficient with temperature.