The effect of stoichiometry on the microstructure and properties of lead lanthanum titanate thin films

Abstract

Thin films of Lead Lanthanum Titanate (PLT) corresponding to 28 at. % of La were prepared by the metal-organic decomposition (MOD) process. The films were fabricated from two solutions of different composition. The composition of the first solution was determined, assuming that the incorporation of La3+ in the PbTiO3 structure gives rise to A-site or Pb vacancies, whereas for the composition of the other solution the creation of B-site or Ti vacancies was assumed. The effect of excess lead on the microstructure and the optical and electrical properties was studied for 0% to 20% excess PbO. The x-ray diffraction patterns of all films at room temperature indicated a cubic structure with a lattice constant of 3.92 Å. Optical and electrical measurements showed the films made assuming B-site vacancies had better properties. In general, excess PbO was found to improve the optical transmittance as well as the electrical properties of films. However, in films assuming the formation of B-site vacancies, PLT showed improved electrical properties only up to 5–10% excess PbO, while higher PbO additions had a deleterious effect. The films had a high resistivity, good relative permittivity, low loss, very low leakage current density, and high charge storage density. A type-B film with 10% excess Pb had a relative permittivity of 1340 at 100 kHz and a charge storage density of around 16.1 μC/cm2 at a field of 200 kV/cm at room temperature.