Tailoring of the functional properties of sol-gel films on Pt/TiO2/SiO2/(100)Si substrates:: (Pb, La)TiO3/(Pb, Ca)TiO3 multilayer heterostructures

Preferentially oriented sol-gel (Pb, Ca)TiO3/ (Pb, La)TiO3/(Pb, Ca)TiO3 and (Pb, La)TiO3/(Pb, Ca)TiO3/ (Pb, La)TiO3 multilayer heterostructure thin films deposited on silicon-based substrates have been studied and compared with identically prepared (Pb, La)TiO3 (PTL) and (Pb, Ca)TiO3 (PTC) films. The existence in their texture of two components that contribute to the net polarization in the direction normal to the plane of the film, (001) and (111), results in significant ferroelectric and pyroelectric properties. P-r = 26 muC cm(-2) and gamma = 28.5 x 10(-9) C cm(-2) K-1, and P-r = 17 muC cm(-2) and gamma = 22.8 x 10(-9) C cm(-2) K-1, have been achieved, respectively, in the PTL/PTC/PTL and PTC/PTL/PTC heterostructures. The surface roughness of these films provides a high specific surface that can be interesting for infrared detectivity. An increase of the dielectric permittivity in the whole temperature interval up to the transition temperature has been observed for both heterostructures with respect to the PTL and PTC films. This effect is due to a release of stress in the heterostructures that is revealed by the increase of the tetragonal distortion, c/a, of these films.