We report on the metal-insulator transition of La0.5Sr0.5CoO3 thin films deposited by pulsed laser ablation on LaAlO3 substrates. The films were cooled in oxygen partial pressures between 760 and 10−5 Torr and electrical resistivity of the films was measured as a function of cooling oxygen pressure. La0.5Sr0.5CoO3 films changed from metallic to insulating behavior depending on their oxygen content. A defect model has been proposed to explain this transition and the change in conductivity is related to the change in the oxidation state of the cobalt ions. The model explains the relationship between oxygen partial pressure and electrical conductivity in La0.5Sr0.5CoO3, which describes the experimental dependence reasonably well. Positron annihilation studies were also done on the same set of samples and the S parameter was seen to increase by 8% from a fully oxygenated sample to a sample cooled in 10−5 Torr.

Effects of WO 3 dopant on the structure and electrical properties of Pb 0.97 La 0.03 ( Zr 0.52 Ti 0.48 ) O 3 thin films Appl. Phys. Lett. 86, 092901 (2005); 10.1063/1.1870125 Competition between ferroelectric and semiconductor properties in Pb ( Zr 0.65 Ti 0.35 ) O 3 thin films deposited by sol-gel J. Appl. Phys. 93, 4776 (2003); 10.1063/1.1562009 Dielectric and ferroelectric properties of compositionally graded (Pb,La)TiO 3 thin films on Pt/Ti/SiO 2 /Si substrates Appl. Structural, dielectric, and ferroelectric properties of compositionally graded ( Pb,La ) TiO 3 thin films with conductive LaNiO 3 bottom electrodes

We report results of high-speed polarization relaxation measurements in ferroelectric thin film capacitors. Polarization relaxation has been reported to occur in two distinct time regimes, one for relaxation times in the range of a few milliseconds and a second for longer relaxation times. We find that the polarization relaxation in the first regime is governed by at least two different physical processes, namely depoling fields and the activation field for switching. Using prototypical epitaxial PbZr0.2Ti0.8O3 and Pb0.9La0.1Zr0.2Ti0.8O3 test capacitors, we demonstrate the effect of film microstructure and switching speed on the relaxation dynamics in the first regime.

A study of vacancy-related defects in ferroelectric capacitors was performed using a variable energy positron beam (VEPB). Heterostructures of (Pb0.9La0.1)(Zr0.2Ti0.8)O3 (PLZT) ferroelectric with La0.5Sr0.5CoO3 (LSCO) electrodes were deposited by pulsed laser deposition and the effects of oxygen deficiency studied using structures grown with 760 and 1×10−5 Torr oxygen. The VEPB depth profile showed an increase in vacancy-related defects with increased oxygen nonstoichiometry. A study of LSCO and PLZT thin films was also performed. The formation of vacancy clusters in the LSCO top electrode, and VPb−VO defects in the PLZT layer, with increased oxygen deficiency is inferred.

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