RESUMEN

This paper describes the properties of a lead-free ceramic material based on barium titanate, designed for the construction of ultracapacitors and sensors used in mechatronic systems. The admixture of lanthanum (La3+) served as a modifier. The ceramic powders were obtained by the solid phase reaction method (conventional method-mixed oxides method-MOM). Technological conditions of the synthesis process were determined on the basis of thermal analysis. The obtained samples are characterized, at room temperature (Tr < TC), by a single-phase tetragonal structure and a P4mm space group. Properly developed large grains (d = 5 µm) contributed to the increase in electric permittivity, the maximum value of which is at the level of εm ≈ 112,000, as well as to a strong decrease in specific resistance in the ferroelectric phase, whereas above the Curie temperature, by creating a potential barrier at their boundaries, there was a a rapid increase in resistivity. The temperature coefficient of resistance of the obtained posistor is 10.53%/K. The electrical properties of the obtained ceramics were examined using impedance spectroscopy. In order to analyze the obtained results, a method of comparing the behavior of the real object and its replacement system in a specific frequency region was used, whereas the Kramer--Kroning (K-K) test was used to determine the consistency of the measured data. The proper selection of the stoichiometry and synthesis conditions resulted in the creation of an appropriate concentration of donor levels and oxygen gaps, which in turn resulted in a significant increase in the value of electrical permittivity, with small values of the angle of dielectric loss tangent. This fact predisposes the discussed material for certain applications (in the construction of ultracapacitors, among others).

RESUMEN

Correlation between structure and optical properties of rare earth ions in lead borate glasses and glass-ceramics was evidenced by X-ray-diffraction, Raman, FT-IR and luminescence spectroscopy. The rare earths were limited to Eu(3+) and Er(3+) ions. The observed BO(3)↔BO(4) conversion strongly depends on the relative PbO/B(2)O(3) ratios in glass composition, giving important contribution to the luminescence intensities associated to (5)D(0)-(7)F(2) and (5)D(0)-(7)F(1) transitions of Eu(3+). The near-infrared luminescence and up-conversion spectra for Er(3+) ions in lead borate glasses before and after heat treatment were measured. The more intense and narrowing luminescence lines suggest partial incorporation of Er(3+) ions into the orthorhombic PbF(2) crystalline phase, which was identified using X-ray diffraction analysis.

Asunto(s)

Boratos/química , Cerámica/química , Plomo/química , Metales de Tierras Raras/química , Luminiscencia , Espectrofotometría Infrarroja , Espectroscopía Infrarroja Corta , Espectrometría Raman , Relación Estructura-Actividad , Temperatura , Elementos de Transición/química

RESUMEN

The electron back scattered diffraction method was applied for carrying out detailed surface studies of the ternary Ni-Ti-Co alloy produced using melt-spinning and twin roll casting techniques. The samples were studied in the as-cast state without grinding or polishing. It was found that in the melt-spun ribbon apart from fine narrow columnar grains, that extended along the ribbon thickness, wider columnar grains parallel to the ribbon surface were also observed. These grains were textured along the {100}011 orientation. The twin roll cast strip revealed more complex and inhomogeneous morphology of its surface. Mainly, the axes of the grains were oriented along two textural components: 100 for the fine grains and {100}011 for the columnar grains parallel to the surface. In addition to the results obtained from the X-ray diffraction, the electron back scattered diffraction technique revealed the 111 fibre texture in the sample.

RESUMEN

TiN and TiO(2) coatings, which are known from their low chemical reactivity, high hardness and wear and corrosion resistance, are used for protecting the NiTi surface. In the present work, nearly equiatomic NiTi (50.6 at.%) shape memory alloy was covered with the layers obtained by nitriding under glow discharge at 1073 K. Additionally, at the end of the process some amount of oxygen was added. Characterization of the nitrided/oxided layers structure was carried out using transmission and scanning electron microscopy. The investigations were focused on the structure of the multilayer nitrided/oxided NiTi surface. The surface is formed from nanocrystalline and columnar grains of the TiN phase. Between the top layer and beta-NiTi substrate the interface Ti(2)Ni layer was formed. Addition of oxygen at the end of the process created a thin layer of TiO(2) phase nanograins at the surface of the TiN phase. In the same areas, small amount of amorphous phase was identified. The combination of nitriding and oxidation formed layers that reveal relatively high corrosion resistance.