J. Ricote

Size effect in morphotropic phase boundary Pb(Mg1∕3Nb2∕3)O3–PbTiO3

Phases, domain configuration, and properties of 0.65Pb(Mg1∕3Nb2∕3)O3–0.35PbTiO3 ceramics with grain sizes of 4 and 0.15μm have been studied. The average phase is monoclinic Pm in coexistence with tetragonal. An evolution from micron-sized lamellar domains towards submicron/nanometer sized crosshatched domains is found with the decrease in size, which results in electrical relaxor type behavior and hindered switching. This is proposed to be associated with the slowing down of the relaxor to ferroelectric transition that causes the long time presence of an intermediate domain configuration. Nevertheless, a high sensitivity piezoelectric submicron-structured material is obtained under tailored poling (d33∼300pCN−1).

Room temperature stabilisation of γ-Bi2VO5.5 and synthesis of the new fluorite phase f-Bi2VO5 by a mechanochemical activation method

Mechanochemical activation followed by annealing at moderate temperatures results in the stabilisation at room temperature of the high ionic conductor oxide γ-Bi2VO5.5 belonging to the Bi–VV–O2 system, while in the Bi–VIV–O2 system a non-previously reported fluorite-type f-Bi2VO5 phase is isolated. All α-, β- and γ-Bi2VO5.5 and f-, α- and β-Bi2VO5, as well as amorphous powders with 2Bi2O3∶V2O5 and Bi2O3∶VO2 compositions, are studied by X-ray powder diffraction at ambient and high temperatures, thermal analysis and scanning electron microscopy.

Microstructure-properties relationships in samarium modified lead titanate piezoceramics—I. Quantitative study of the microstructure

Samarium modified lead titanate piezoceramics prepared from hydrothermally synthesized powder are microstructurally characterized. The evolution of the ceramic microstructure of the ceramics during sintering and Hot Isostatic Pressing (HIP) as a post-sintering treatment is studied by a combination of optical and scanning electron microscopies with computerized image analysis. The obtained grain size and pore area distributions are studied through the use of probability plots. The analysis of the grain size distributions indicates that a process of normal grain growth takes place during sintering. The pore area distributions of some of the studied ceramics are bimodal, revealing a degradation of the microstructure, with the appearance of large area pores as sintering time or temperature increases. The post-sintering HIP process reduces drastically the ceramic porosity and acts mainly on the pores of large area, thus restoring the degraded microstructures.

Monoclinic morphotropic phase and grain size-induced polarization rotation in Pb(Mg1∕3Nb2∕3)O3–PbTiO3

A detailed Rietveld analysis of x-ray data, collected at room temperature, was done on ceramics with controlled grain size between 100nm and 4μm for (PbMg1∕3Nb2∕3O3)0.80–(PbTiO3)0.20 (PMN-PT20), i.e., a compound at the border of the so-called morphotropic phase boundary. With size reduction the polarization rotates within the monoclinic plane from MB, i.e., Px=Py>Pz to MA, i.e., Px=Py<Pz, and finally reaches a rhombohedral phase, i.e., Px=Py=Pz, below a critical value of ∼200nm without diminishing the amplitude of the polarization. This study provides an easy way to tailor the direction of polarization of these materials.

Apparent vanishing of ferroelectricity in nanostructured BiScO3–PbTiO3

Nanostructured ceramics of high-temperature piezoelectric 0.375BiScO3?0.625PbTiO3 were prepared by spark plasma sintering of nanocrystalline powders obtained by mechanosynthesis. The macroscopic electrical properties were characterized on dense ceramics with decreasing average grain size down to 28?nm. Results indicate that the electric field is screened by the electrically insulating grain boundaries at the nanoscale, which needs to be considered when discussing size effects in ferroelectric polycrystalline materials. Moreover, the requirement of increasingly large electric fields to achieve a given polarization with the decrease in the grain size, together with the depletion of the dielectric anomaly associated with the ferroelectric transition until its disappearance, seems to be the result of grain boundary effects.

Microcharacterisation of grain-oriented ceramics based on Bi3TiNbO9 obtained from mechanochemically activated precursors

Abstract Hot pressing was applied to a novel powder, synthesised by the mechanochemical activation of starting oxides, in order to obtain dense ceramics of Bi 3 TiNbO 9 for use as piezoelectric material at high temperatures. Since these compositions belong to the family of layered perovskites, hot pressing produces a preferential orientation of the grains. An assessment of the degree of orientation achieved was carried out by quantitative texture analysis using experimental X-ray pole figures. Although texture could be considered as the most influential factor on the final properties, other microstructural features were studied by transmission electron microscopy including grain boundaries and ferroelectric domains. The results of the microcharacterisation of these ceramics are discussed in order to understand the process involved in the development of preferential orientation in these ceramics.

Stress-induced depolarization of (Pb, La)TiO3 ferroelectric thin films by nanoindentation

Electrical depolarization has been observed in lanthanum-modified lead titanate ferroelectric thin films stressed by nanoindentation. A spherical metallic indenter was used as a top electrode to locally pole the films and then to measure the depolarization current intensity. The current intensity had distinctive maxima at given indentation forces. These are related to the stress thresholds for the depolarization mechanism, which is probably 90° domain wall movements. Knowledge of the depolarization stresses is necessary for the design of microelectromechanical systems that include a ferroelectric layer.

Aqueous Solutions for Low-Temperature Photoannealing of Functional Oxide Films: Reaching the 400 °C Si-Technology Integration Barrier

Functional oxide films were obtained at low temperature by combination of aqueous precursors and a UV-assisted annealing process (aqueous photochemical solution deposition). For a PbTiO(3) model system, functional ferroelectric perovskite films were prepared at only 400 °C, a temperature compatible with the current Si-technology demands. Intrinsically photosensitive and environmentally friendly aqueous precursors can be prepared for most of the functional multimetal oxides, as additionally demonstrated here for multiferroic BiFeO(3), yielding virtually unlimited possibilities for this low-temperature fabrication technology.

Quantitative analysis of preferential orientation components of ferroelectric thin films

Abstract A quantitative study of the preferred orientation of lanthanum and calcium modified lead titanate thin films, including the measurement of pole figures and calculation of orientation distribution function (OD), is presented. The main preferential orientation components are identified as <001> and <100> perpendicular to the film surface. Variations of the texture strength and the contribution of these components to the final texture are observed with changes in the film thickness or the substrate used. These variations are correlated to the ferroelectric properties of these films. This information can be used to optimise the preparation process to obtain improved thin films for pyroelectric and piezoelectric applications.

Low‐Temperature Liquid Precursors of Crystalline Metal Oxides Assisted by Heterogeneous Photocatalysis

The photocatalytically assisted decomposition of liquid precursors of metal oxides incorporating TiO2 particles enables the preparation of functional layers from the ferroelectric Pb(Zr,Ti)O3 and multiferroic BiFeO3 perovskite systems at temperatures not exceeding 350 ºC. This enables direct deposition on flexible plastic, where the multifunctionality provided by these complex-oxide materials guarantees their potential use in next-generation flexible electronics.