M. G. Stachiotti

Synthesis and Characterization of PMN-PT Thin Films Prepared by a New Chemical Route

Thin films of lead magnesium niobate-lead titanate (PMN-PT) have been synthesized by a new and simple chemical solution deposition route, using Acetoin (3-Hydroxy 2-butanone) as chelating agent and methanol as solvent. The starting materials were Niobium ethoxide, Titanium butoxide, Magnesium ethoxide and Lead acetate. The films were deposited on Pt/Ti/SiO2/Si substrates by spin-coating. By a multilayer process, homogenous and crack-free films with thickness up to 1 μ m were obtained. The microstructure and surface morphology of the films were characterized by X-ray diffraction and atomic force microscopy (AFM) techniques. Films with a predominant perovskite phase and average grain size of ∼ 200 nm were obtained. The dielectric and ferroelectric properties are reported.

Effects of the Chelating Agent on the Fabrication of SBT Thin Films: Part I. Stoichiometry and Crystallization Behavior

The effects of the chelating agent on the thermal evolution of SrBi 2 Ta 2 O 9 precursor powders were investigated. The precursor solutions were prepared from non-hydrolyzing precursors of bismuth and strontium and a tantalum alkoxide. The utilization of alkanolamines as chelating agent was found to produce the segregation of metallic bismuth in the as-prepared powders, which led to the formation of a multiphase system. On the other hand, acetoin, one of the Hydroxyketones, showed outstanding characteristics for the low-temperature synthesis of SrBi 2 Ta 2 O 9 : elimination of residual organics at low temperature, an earlier onset of crystallization, and no segregation of secondary phases during the whole crystallization process.

Effect of Li- and Ta-doping on the ferroelectric properties of Na0.5K0.5NbO3 thin films prepared by a chelate route

The effects of lithium and tantalum doping on the properties of Na0.5K0.5NbO3 (NKN) thin films were investigated. The films were fabricated by an optimized chelate route which offers the advantage of a simple and rapid solution synthesis. The optimization was achieved by investigating the effects of alkaline volatilization loss on film properties. In this way, undoped NKN thin films fabricated by this conventional method exhibited good ferroelectric properties (Prxa0~xa08xa0μC/cm2, and Ecxa0~xa055xa0kV/cm for films annealed at 650xa0°C). The developed chelate route was then used to grow Li (5xa0%) and Ta (10xa0%) substituted thin films. Such structures allowed us to compare the effect of these dopant cations on phase formation, microstructure and ferroelectric properties. We show that both modifications produced a remarkable improvement on the ferroelectricity of the films. While the undoped material exhibited large leakage components in films annealed at 600xa0°C, films modified with Li or Ta presented well saturated ferroelectric hysteresis loops, indicating that those ions have a significant influence on the conducting process. The remnant polarizations of the Ta-doped films are greater than those of the Li-doped samples. This feature is however reversed for films annealed at low temperature (600xa0°C) due to the presence of a non-ferroelectric secondary phase in the Ta-doped composition.

Effects of the Chelating Agent on the Fabrication of SBT Thin Films: Part II. Microstructural Properties

The effects of the chelating agent on the micro structural properties of SBT thin films annealed at different temperatures are investigated. The films were prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition technique. Strontium acetate, bismuth nitrate and tantalum ethoxide were used as precursor materials, with methanol and glacial acetic as solvents. We make a comparative investigation of the surface microstructure, grain size distribution, crystallinity, and degree of crystal orientation for films prepared using acetoin and alkanolamines as chelating agent.

Oxygen ion implantation in Strontium Bismuth Tantalate thin films

Strontium Bismuth Tantalate (SBT) ferroelectric thin films have attracted considerable attention for the development of non-volatile ferroelectric random access memories (NV-FRAMs). These films, however, have a critical problem: a high processing temperature ( > 700oC) is required for the crystallization of the perovskite phase. The thermal evolution of the SBT films prepared by Chemical Solution Deposition (CSD) techniques showed the formation of an intermediate oxygen-deficient fluorite phase at ~ 550oC. The SBT perovskite phase crystallizes at higher temperatures. To favor an earlier perovskite crystallization, SBT thin films were implanted with oxygen ions pulses produced by a Plasma Focus (1 kJ). The samples were annealed at different temperatures in oxygen atmosphere and characterized by GI-XRD and Atomic Force Microscopy techniques. It was found that oxygen addition into the SBT structure promotes a better crystallization of the perovskite phase.

Preparation and Characterization of Mn-Doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramics

MnO2-doped lead free 0.5[Ba(Zr0.2Ti0.8)O3]-0.5[(Ba0.7Ca0.3)TiO3] ceramics were synthesized by a high-energy ball milling process. We studied the phase formation process along different steps of the mechanical milling. We show that the addition of a small amount of MnO2 (x < 0.5 mol.%) improves the dielectric and ferroelectric properties of the ceramics. It is found that the doping with manganese increases the dielectric constant and reduces the loss, which decreases considerably as the Mn content increases. The remnant polarization of the doped ceramics is increased by 10%.

Simple and rapid fabrication of Na0.5K0.5NbO3 thin films by a chelate route

Na0.5K0.5NbO3 (NKN) thin films were prepared by a chelate route which offers the advantage of a simple and rapid solution synthesis. The route is based on the use of acetoin as a chelating agent. The process was optimized by investigating the effects of alkaline volatilization on film properties. While we observed no evidence of stoichiometry problems due to potassium volatilization loss during the heat treatments, thin films synthesized with insufficient sodium excess presented a potassium-rich secondary phase, which has a significant influence on the ferroelectric properties. We show that the amount of spurious phase decreases with increasing Na

Influence of Tungsten Doping on the Ferroelectric Behavior of Sr0.8Bi2.3Ta2O9 Thin Films

The substitution effect of W+6 at Ta+5 site on the structural, dielectric and ferroelectric properties of Bi-rich Sr0.8Bi2.3Ta2O9 (SBT) thin films is reported. Samples of compositions Sr0.8-x/2Bi2.3Ta2-xWxO9 (SBTW) with x ranging from 0.0 to 0.2 were synthesized by a chemical solution deposition technique using non-hydrolyzing precursors. The microstructure and ferroelectricity of SBTW films as functions of dopant concentration and annealing temperature were studied. Well-defined hysteresis loops were obtained for the doped films annealed between 650°C and 750°C. The ferroelectric properties, however, were not improved compared to those of undoped SBT films due to the appearance of a non-ferroelectric secondary phase.