Electron paramagnetic resonance and Raman spectroscopy studies on carbon-doped MgB2 superconductor nanomaterials

Abstract

Articles you may be interested inThe critical parameters in in-situ MgB2 wires and tapes with ex-situ MgB2 barrier after hot isostatic pressure, cold drawing, cold rolling and doping Doping effect of nano-Ho2O3 and naphthalene in MgB2 superconductor prepared by powder-in-sealed-tube method A new scaling relation for n-AlN doped superconducting MgB2 Effect of thermal strain on Jc and Tc in high density nano-SiC doped MgB2 J. Appl. Phys. 109, 07E108 (2011); 10.1063/1.3549590 Superconductivity and the disorder effect in Ag and Al double doped Mg B 2Undoped and carbon-doped magnesium diboride (MgB 2 ) samples were synthesized using two sets of mixtures prepared from the precursors, amorphous nanoboron, and as-received amorphous carbon-doped nanoboron. The microscopic defect structures of carbon-doped MgB 2 samples were systematically investigated using X-ray powder diffraction, Raman and electron paramagnetic resonance spectroscopy. Mg vacancies and C-related dangling-bond active centers could be distinguished, and sp 3 -hybridized carbon radicals were detected. A strong reduction in the critical temperature T c was observed due to defects and crystal distortion. The symmetry effect of the latter is also reflected on the vibrational modes in the Raman spectra. V C 2015 AIP Publishing LLC.

Al-doped MgB2 materials studied using electron paramagnetic resonance and Raman spectroscopy

“…As the Raman-active soft mode (E 2g ) is related to inter-plane vibrations of boron atoms, 27 this mode in MgB 2 around 600 cm À1 can be easily affected either by changes in defect concentration or elemental doping. 28 In this study, a reduction in defect concentration by doping with Al can be deduced from the spectra shown in Fig. 2.…”

“…Our EPR data reveal that doping triggers the quenching of Mg vacancies via trapping of Al ions. In a previous study, 28 we have shown that in C-doped MgB 2 defects still play a significant role in conductivity. In Al-doped MgB 2 , however, the role of defects smears out above a certain level of Al content, and Al reduces the conductivity of MgB 2 .…”

“…However, just above T c , before the paramagnetic defects smear out, both paramagnetic defects (here, V Mg ) still interact with the magnetic field and phonons, and thus cause quite "instable" EPR spectra. 28 This can be clearly seen in Fig. 4(a) that by approaching the T c value the signal-to-noise ratio of the EPR spectra strongly decreases as compared with higher temperatures.…”

“…Note, that the low-temperature EPR results of undoped MgB 2 have been published elsewhere and a decrease in T c has been reported. 28 superconducting quantum interference device (SQUID) measurements 38 but also directly using EPR for undoped and C-doped MgB 2 . 28 However, it is not possible to determine quantitatively the dependency of the superconducting fraction from EPR.…”

Theoretical study of hydrogen adsorption on Ca-decorated C48B12 clusters

“…[30][31][32][33][34][35] On the other hand, it was suggested to enhance the structural stability of metal decorated complexes by introducing structural or chemical defects. [36][37][38][39][40][41][42] For instance, substitutional doping of boron at the carbon site in carbon nanomaterials improves dramatically the binding strength of metal atoms. 41,42 B-C mixed nanostructures have been a research focus, which are also lightweight and porous.…”