Pyroelectric properties of sol-gel processed lanthanum modified lead titanate ferroelectric thin films

Abstract
Textured lanthanum modified lead titanate ferroelectric thin films have been prepared on Pt/Si substrates by a diol-based sol-gel procedure. Precursor solutions including a growing excess of PbO, and crystallization with a heating rate higher than 500°C min^-1, are used. Pb/Ti ratio in films is measured by EDXS, and is found to increase systematically with the excess of PbO included in solutions. Such increase inPb/Ti is likely related to the disappearance of a Pb deficient second phase, reaching the nominal value of the perovskite in those films prepared from solutions including a 20% excess of PbO. Films dieletric constant, ε, remanent polarization, P_R, and pyroelectric coefficient, γ, measured in poled samples, increase as the Pb/Ti ratio, reaching values of~730, ~25 µC cm^-2 and ~1.4x10^-2 µC cm^-2K^-1 in those with the nominal ratio of the perovskite. Infrared sensor figures of merit for voltage responsivity, F_v α γ/ε, and specific detectivity, F_m α γ/(ε)^1/2, are calculated. The possibility of using films containing small amounts of second phase, with a smaller pyroelectric coefficient, but with a smaller dielectric constant, is discussed.