M. T. Escote

Characterization of BaTi1−xZrxO3 thin films obtained by a soft chemical spin-coating technique

Single-phase perovskite structure BaZrxTi1−xO3 (BZT) (0.05⩽x⩽0.25) thin films were deposited on Pt–Ti–SiO2–Si substrates by the spin-coating technique. The structural modifications in the thin films were studied using x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate an increase in lattice (a axis) with the increasing content of zirconium in these films. Such Zr substitution also result in variations of the phonon mode wave numbers, especially those of lower wave numbers, for BaZrxTi1−xO3 thin films, corroborate to the structural change caused by the zirconium doping. On the other hand, Raman modes persist above structural phase transition, although all optical modes should be Raman inactive in the cubic phase. The origin of these modes must be interpreted as a function of a local breakdown of the cubic symmetry, which could be a result of some kind of disorder. The BZT thin films exhibited a satisfactory dielectric constant close to 181–138, a...

Room-temperature photoluminescence in structurally disordered SrWO4

Intense and broad visible photoluminescent (PL) band in structurally disordered SrWO4 compounds was observed at room temperature. The polycrystalline scheelite strontium tungstate (SrWO4) samples prepared by the polymeric precursor method at different temperatures of annealing were structurally characterized by x-ray diffraction and Fourier transform Raman spectroscopy measurements. Quantum-mechanical calculations showed that the local disorder in the cluster of the network modifiers Sr has a very important role in the charge transfer. The experimental and theoretical results are in good agreement, indicating that the generation of the intense visible PL band can be related to short-range order-disorder degree in the scheelite structure.

Structural, microstructural, and transport properties of highly oriented LaNiO3 thin films deposited on SrTiO3 (100) single crystal

Electrical conductive textured LaNiO3/SrTiO3 (100) thin films were successfully produced by the polymeric precursor method. A comparison between features of these films of LaNiO3 (LNO) when heat treated in a conventional furnace (CF) and in a domestic microwave (MW) oven is presented. The x-ray diffraction data indicated good crystallinity and a structural orientation along the (h00) direction for both films. The surface images obtained by atomic force microscopy revealed similar roughness values, whereas films LNO-MW present slightly smaller average grain size (∼80 nm) than those observed for LNO-CF (60–150 nm). These grain size values were in good agreement with those evaluated from the x-ray data. The transport properties have been studied by temperature dependence of the electrical resistivity ρ(T) which revealed for both films a metallic behavior in the entire temperature range studied. The behavior of ρ(T) was investigated, allowing to a discussion of the transport mechanisms in these films.

Metal-insulator transition in Nd1−x Eux NiO3 probed by specific heat and anelastic measurements

Oxides RNiO3 (R = rare-earth, R ≠ La) exhibit a metal-insulator (MI) transition at a temperature TMI and an antiferromagnetic (AF) transition at TN. Specific heat (CP) and anelastic spectroscopy measurements were performed in samples of Nd1−xEuxNiO3, 0 ≤ x ≤ 0.35. For x = 0, a peak in CP is observed upon cooling and warming at essentially the same temperature TMI = TN ∼ 195 K, although the cooling peak is much smaller. For x ≥ 0.25, differences between the cooling and warming curves are negligible, and two well defined peaks are clearly observed: one at lower temperatures that define TN, and the other one at TMI. An external magnetic field of 9 T had no significant effect on these results. The elastic compliance (s) and the reciprocal of the mechanical quality factor (Q−1) of NdNiO3, measured upon warming, showed a very sharp peak at essentially the same temperature obtained from CP, and no peak is observed upon cooling. The elastic modulus hardens below TMI much more sharply upon warming, while the cooli...

High oxygen-pressure annealing effects on the ferroelectric and structural properties of PbZr0.3Ti0.7O3 thin films

We report on the synthesis of polycrystalline thin films of PbZr0.3Ti0.7O3 (PZT) by the so-called chemical solution deposition technique. The thin films were deposited on Pt∕Ti∕SiO2∕Si substrates by the spin-coating method, and were heat treateded at 700°C in air and under several oxygen pressures (10<PO2<60bars). The structural, morphological, and ferroelectric properties were characterized by x-ray diffraction (XRD), infrared and Raman spectroscopy, atomic force microscopy (AFM), and polarization-electric-field hysteresis loop measurements. The XRD and the Raman spectroscopy results revealed that the films heat treated in air and at low oxygen pressures (PO2<40bars) are single phase. However, analysis of the data indicated a clear decreasing of the crystallization degree of the films with increasing oxygen pressure. AFM results showed the PZT films display a rosette structure embedded in a matrix, which comprises grains with an average grain size ranging from 60 to 120nm. Ferroelectric hysteresis loops’...

Very large dielectric constant of highly oriented Pb1-xBaxTiO3 thin films prepared by chemical deposition

Highly (100) oriented Pb0.8Ba0.2TiO3/LaNiO3 structures were grown on LaAlO3(100) substrates by using a wet, soft chemical method and crystallized by the microwave oven technique. The Au/PBT/LaNiO3/LaAlO3 capacitor shows a hysteresis loop with remnant polarization, Pr, of 15 μC/cm2, and coercive field, Ec, of 47 kV/cm at an applied voltage of 3 V, along with a dielectric constant over 1800. Atomic force microscopy showed that Pb0.8Ba0.2TiO3 is composed of large grains about 300 nm. The experimental results demonstrated that the microwave preparation is rapid, clean, and energy efficient. Therefore, we demonstrated that the combination of the soft chemical method with the microwave process is a promising technique to grow highly oriented thin films with excellent dielectric and ferroelectric properties, which can be used in various integrated device applications.

Development of artificial muscles based on electroactive ionomeric polymer-metal composites.

This work contextualizes the research of materials that can be applied as artificial muscles. The main motivation of this research is the importance of the development of mechatronic systems for the replacement of traditional devices of actuation and motion based on rotational electrical motors by other devices that reproduce biological muscle movements. Electroactive polymers (EAPs) are materials that respond to electric stimuli with shape and/or dimension changes, and accomplish movements that are smooth enough to mimic biological muscles. Among EAPs, the ionomeric polymer-metal composites (IPMCs) are an interesting alternative to biomimetic devices due to large displacements when submitted to low applied voltage. This article presents a brief review of IPMCs, a sample preparation procedure, and some electromechanical experimental results. We also discuss the applicability of this technology in medical devices and as artificial muscles.

Electrical characterization of SnO2:Sb ultrathin films obtained by controlled thickness deposition

A representative study is reported on the electrical properties of SnO2:Sb ultrathin films (thickness of 40–70 nm) produced by a deposition method based on aqueous colloidal suspensions of 3–5 nm crystalline oxides. The results revealed the films’ electrical behavior in a range of 10–300 K, showing a strong dependence on dopant incorporation, with minimum resistivity values in 10 mol % of Sb content. All the samples displayed semiconductor behavior, but the transport mechanism showed a strong dependence on thickness, making it difficult to fit it to well-known models. In thicker films, the mechanism proved to be an intermediary system, with thermally activated and hopping features. Electron hopping was estimated in the range of 0.4–1.9 nm, i.e., in the same order as the particle size.

FOTOLUMINESCÊNCIA E ADSORÇÃO DE CO 2 EM NANOPARTÍCULAS DE CaTiO 3 DOPADAS COM LANTÂNIO

Ca1-xLaxTiO3 powders were prepared by the polymeric precursor method. X-ray diffraction (XRD), FT-Raman spectroscopy, transmission electron microscopy (TEM), and N2 and CO2 adsorption were used for the microstructural and surface characterization of the powders. Room temperature photoluminescence (PL) was observed in Ca1-xLaxTiO3 amorphous particles. The PL intensity of these powders was found to be dependent on the lanthanum molar concentration.

Textured PbZr0.3Ti0.7O3 thin films produced by polymeric precursor method using microwave oven

PbZr 0.3 Ti 0.7 O 3 (PZT) films were produced by polymeric precursor route and deposited by spin-coater technique on Pt(111)/Ti/SiO 2 /Si(100) substrates. The films were heat-treated using different furnaces: (a) a conventional furnace, at 700°C; and (b) a domestic microwave oven, at 600°C. The X-ray patterns revealed that both films are single phase and reflections were identified as belongs to the PZT phase. The intensity of these reflections showed a (111), (001) and (100) preferred orientation. Morphological and electrical characterizations showed that all samples present a rather different microstructure and both with high spontaneous polarization.