THE EFFECT OF STOICHIOMETRY ON THE MICROSTRUCTURE AND PROPERTIES OF LEAD LANTHANUM TITANATE THIN-FILMS

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 t he 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 w as studied for 0% to 20% excess PbO. The x-ray diffraction patterns of all films at room temperature indicated a cubic structure with a latt ice constant of 3.92 Angstrom. Optical and electrical measurements sho wed 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 assumin g the formation of B-site vacancies, PLT showed improved electrical pr operties only up to 5-10% excess PbO, while higher PbO additions had a deleterious effect. The films had a high resistivity, good relative p ermittivity, low loss, very low leakage current density, and high char ge storage density. A type-B film with 10% excess Pb had a relative pe rmittivity of 1340 at 100 kHz and a charge storage density of around 1 6.1 mu C/cm(2) at a field of 200 kV/cm at room temperature.