Electrical properties of La-graded heterostructure of Pb_1-xLa_xTiO₃ thin films

Abstract

La-graded heterostructure films were prepared by sol-gel technique on platinum substrates and electrical properties of these films were compared with those of conventional thin films of similar compositions. X-ray diffraction results indicate the pure perovskite polycrystalline structure of these films. Atomic Force Microscopy analysis revealed a finer grain size and relatively lower surface roughness. Relatively higher values of P_m and P_r (69 and 38 μC cm^-2, respectively) and excellent dielectric properties with lower loss (K=1900, tan δ =0.035 at 100 kHz) were observed for La-graded heterostructure films. Also lower leakage current density (~2.5 nA cm^-2) and a higher onset field (~50 kV cm^-1) of space charge conduction indicated higher breakdown strength and good leakage current characteristics. The ac electric field dependence of the permittivity at sub-switching fields was analyzed in the framework of the Rayleigh dynamics of domain walls. The estimated irreversible domain wall displacement contribution to the total dielectric permittivity was 17 and 9% for conventional 15 at.% La doped PbTiO₃ and La-graded heterostructure films, respectively. The improved dielectric and polarization behavior of La-graded heterostructure films may be attributed to homogenous dopant distribution compared to the conventional 15 at.% La doped PbTiO₃ films.