Effects on transition temperature and Raman spectra of substitution of Cr and Al for Mg in MgB₂

Abstract

Mg 1-x M x B 2 (M = Cr, Al) polycrystalline bulk samples with 0 ≤ x ≤ 5% have been synthesized by a solid state reaction and studied by X-ray diffraction, SEM and Raman spectroscopy. By comparing with the results of Sc-substituted MgB 2 , it is found that all these atomic substitutions for Mg depress T c , and Cr and Sc substitutions depress T c even more quickly than the one of Al doping. It is suggested that the T c changes of the M-substituted MgB 2 can be understood by the competing/cooperating effects of the holefilling and the disorder. The Raman peak linewidth decreases for Al-substituted MgB 2 , which represents an opposite trend to the linewidth change of Mg 1-x Cr x B 2 and shows an evidence of the disorder caused by the atomic substitution and the different arrangement of the substituted atoms in the lattice. Meanwhile, different frequency changes of the Raman peak for the Cr-and Al-substitute MgB 2 are discovered and understood by the competing/cooperating effects of the electron-phonon coupling, the grain size, and the lattice contraction.

Promotion of Acid–Water Oxidation by Lattice Distortion and Orbital Hybridization Induced by Ionic Dopant in Pyrochlore Y2Ru2O7

“…In fact, the partial replacement of Ru x >4 with M 2+ cations at the B-sites should induce the lattice distortion due to the lattice mismatch caused by their different ionic radii or the statistical variance σ 2 (= ∑ i y i r i 2 – ⟨ r i ⟩ 2 ; here y i is the fractional occupancy of the i th ion at the B-site, ∑ i y i = 1, r i is the radius of the i th ion). − It can be found that the calculated value of σ 2 grows with the radius of the doped ions (Figure S16 and Table ). From Table , it is clearly indicated that the grain size decreases with the increase of σ 2 , or the lattice distortion ε, suggesting that the lattice distortion hinders the grain from growing up, which is related to the replacement of Ru x >4 with larger M 2+ cations in the pyrochlore structure.…”

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

“…With this finding we disentangle the effect of Al on the Raman spectrum, which has already been mentioned in various reports. 24,30,31 In most of these studies, 30,31 Al was investigated in combination with other co-doping ions so that the effect of Al, based solely on the Raman spectra, was not easy to interpret. Our Raman spectroscopic findings shed some light on previously reported Raman data 11,24 regarding MgB 2 , AlB 2 , and Aldoped MgB 2 .…”