Fifty years of Rietveld refinement: Methodology and guidelines in superconductors and functional magnetic nanoadsorbents

The Rietveld refinement method has taken high relevance since its creation. Nowadays, it is an useful tool in many fields of industry, materials science, and technology. For these reasons, it becomes a need for scientists and engineers whom pretend to use it for proper analysis of their materials. However, the initiation in the method can be slow, taking into account the accelerated rhythm of the research and economic demands. Thus, this work is an intend to fulfill this hole, providing the basic foundations and methodology of the Rietveld refinement in a brief way, this along with the results of its application in superconducting samples of Yttrium Barium Copper Oxide and magnesium diboride, and functional magnetic nanoadsorbents of maghemite and a multiphasic composite (iron oxide, hydroxyapatite and secondary phases). In the process, an in-detail protocol was designed and provided. It was concluded that the samples were successfully refined and that this work represents a fast introduction to the Rietveld method for which beginners can obtain good results while making correct interpretations ofthe whole refinement process.

Bio-dielectric based on superconductors yttrium calcium barium copper oxide (YCaBa2Cu3O7−x ) from eggshell as calcium oxide source via sol-gel process

Eggshell is a rich source of calcium that is a dielectric material used for doping in a superconductor. Yttrium calcium barium copper oxide (Y x Ca1−x Ba2Cu3O7) was prepared using the sol-gel process and fired at 900 °C or 1,000 °C. The stoichiometric ratio of the raw materials Y2O3:BaCl2:CuO:CaO was 1:2:3:1 based on the molar mass. The obtained YCaBCO had an orthorhombic crystal structure composed of distorted oxygen-deficient perovskite. The orthorhombic structure was unsymmetrical, providing a substantial increase in the physical electromagnetic properties of the superconductor. The YBCO-900-reference analyzed using an impedance analyzer in the range from 500 Hz to (1 × 106) Hz and at room temperature (27 °C) had the following values for capacitance, electrical conductivity, and dielectric constant ± standard error: 8,286.70 ± 28.49 pF, (3.60 ± 0.01) × 107 S/m, and 1,874.794 ± 6.446, respectively. The YCaBCO-900-eggshell (Y x Ca1−x Ba2Cu3O7) analyzed at 500 Hz at room temperature (27 °C) had high values for capacitance, electrical conductivity, and dielectric constant, namely, 8,540.10 ± 2.00 pF, (1.32 ± 0.00) × 108 S/m, and 1,988.540 ± 0.500, respectively. Furthermore, the YCaBCO-900-eggshell had electrical properties (capacitance, conductivity, and dielectric constant values) higher than those of YCaBCO-900-commercial grade measured under the same conditions. The YCaBCO-900-com grade had capacitance of 8,225.75 ± 0.73 pF, electrical conductivity of (1.40 ± 0.01) × 108 S/m, and dielectric constant of 1,874.59 ± 0.17, respectively. Therefore, eggshell is an alternative dielectric material useful for doping in yttrium barium copper oxide (YBCO) to form YCaBCO, thus causing an increase in its electrical properties. The obtained superconductor is a candidate that could be applied in many industries.

Optimized Omnidirectional High-Reflectance Using Octonacci Photonic Crystal for Thermographic Sensing Applications

The transmittance of waves through one-dimensional periodic and Octonacci photonic structures was studied using the theoretical transfer matrix method for both wave-polarization-modes. The first structures were made up of the SiO2 and TiO2 materials. The objective here was to obtain a broad omnidirectional high reflector covering the infrared spectrum of a thermographic camera [1–14µm] and, especially, to prevent the transmission of emitted human body peak radiation λmax = 9.341 µm. By comparing the periodic and Octonacci structures, we found that the last structure presented a main and wide photonic band gap near this human radiation. For that, we kept only the Octonacci structure for the rest of the study. The first structure did not give the aspired objective; thus, we replaced the TiO2 layers with yttrium barium copper oxide material, and a significant enhancement of the omnidirectional photonic band gap was found for both TE and TM polarization modes. It was shown that the width of this band was sensitive to the Octonacci iteration number and the optical thickness (by changing the reference wavelength), but it was not affected by the ambient temperature. The number of layers and the thickness of the structure was optimized while improving the omnidirectional high reflector properties.

Nanosized Pinning Centers in the Rare Earth-Barium-Copper-Oxide Thin-Film Superconductors

Since the discovery of high-temperature superconductivity, significant progress in the fabrication of REBCO-based (Rare Earth Barium Copper mixed Oxides) thin-films superconductors has been achieved. In our review, we described the approaches and possibilities of the improvement of superconducting properties by the introduction of nanosized pinning centers. We focused on the synthesis and viability of the material for artificial pinning centers and methods used for the introduction of the pinning centers into superconducting REBCO-based thin-films. This article summarizes available materials and procedures regardless of the financial cost of the individual method. According to available literature, the most significant superconducting REBCO tapes can be obtained when a combination of 1D and 0D nanoparticles are used for nanoscale pinning.