Structural, Dielectric and Pyroelectric properties of Lanthanum modified Lead Titanate Thin Films

摘要

Ferroelectric lead lanthanum titanate (Pb_(1-x)La_xTi_(1-x/4)O_3) (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. For a better understanding of the crystallization mechanism, the structural investigations were carried out at various annealing temperatures (350℃, 450℃, 550℃ and 650℃). Characterization of these films by X-ray diffraction shows that the films annealed at 650℃ exhibit tetragonal structure with perovskite phase. Replacement of lanthanum in lead titanate results in reduction of tetragonal ratio (c/a), resulting in better mechanical stability. Microstructural analysis of the firms are carried out by taking the Atomic Force Microscope (AFM) pictures. 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. Dielectric constant and pyroelectric coefficient increase while Curie temperature decreases with increase in La content. The pyroelectric figures of merit of the films have also been calculated which suggest that 8% lanthanum is best suited material for pyroelectric detectors owing to its high pyroelectric coefficient (～ 29nC/cm~2K), high voltage responsivity (～420Vcm~2/J), high detectivity (～1.04x10~(-5) Pa~(-1/2)) and low variation of pyrocoefficient with temperature.