BaxK1-xFe2As2 (BaK-122) iron-based superconductors (IBSs) have been considered to be promising for high-field applications. The transport J
c performance of BaK-122 wires and tapes is continuously enhanced by introducing advanced fabricating methods. The mass density of BaK-122 superconducting core in wires and tapes is important to the transport J
c performance and related to the mechanical behavior during preparation. In this work, the mechanical property parameters including Poisson's ratio-density, yield strength-density, and elastic modulus-density of BaK-122 IBS powder were examined via uniaxial compression experiments. The density-dependent mechanical constitutive of BaK-122 was obtained for the first time. The relationship function between density and Vickers hardness of BaK-122 was established as HV0.05=0.0249ρ5.332 based on the numerical simulation of hardness testing, and a method for characterizing the BaK-122 core density was developed. It had been found the sheath materials and preparation method have great influences on the stress state of the BaK-122 core, and then affect the density. The densification mechanism and corresponding improvement method were revealed to provide guidance for preparing high-density BaK-122 wires and tapes. Finally, the generalized relationship between density and the superconducting transport J
c was established according to lots of experimental data from multiple BaK-122 samples, which has confirmed the positive correlation of ρcore and J
c. We comparatively discussed the various cold-work and heat-treatment processes used in our team for preparing the BaK-122 wires and tapes, and the critical factors affecting the transport performance were summarized.
The phononic crystal band calculation and control method were studied. We used the finite element software COMSOL to analyze the modulation law of band gap width. The material parameters, structure parameters and phononic crystal plate thickness were the main factors affecting the band gap. It was found that the larger the density ratio of the scattering body was, the greater the density of the matrix would be; the wider the band gap was, the greater the influence of the scattering body on the band gap appeared. In the aspect of structure parameters, it was found that the higher the symmetry was, the wider the bandgap width of the crystal lattice would be. In terms of filling rate, the forbidden band width became wider when the filling rate was increased, and the forbidden band width narrowed to a certain extent. In the aspect of phononic crystal plate thickness: twodimensional component phononic crystal plate thickness had an impact on the band gap. As the thickness of the plate increased, the band gap became wider. The results were of guiding significance for the design and fabrication of novel acoustic devices.
The effect of temperature on the structural evolution and physical properties of nanocrystalline BiFeO3 compound has been studied systematically. The results show that the compound crystallizes in the hexagonal LiNbO3 type-structure (space group R3c) and the structural characterization was a=b=5.5979 Å, c=13.9163 Å and V=387.43 Å3. The average crystallite size was about 32.5 nm. The Neel temperature was the same in the vacuum and air conditions, but the decomposition temperature in the air condition was higher 190°C than that of the vacuum condition.
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