Crystal structure of the Mg1−xAlxB2 superconductors near x≈0.5

Serena Margadonna; Kosmas Prassides; Ioannis Arvanitidis; Michael Pissas; Georgios Papavassiliou; Andrew N. Fitch

doi:10.1103/PhysRevB.66.014518

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Crystal structure of the Mg1−xAlxB2 superconductors near x≈0.5

Serena Margadonna, Kosmas Prassides, Ioannis Arvanitidis, Michael Pissas, Georgios Papavassiliou, Andrew N. Fitch

DOI 10.1103/PhysRevB.66.014518 · Physical Review B

T1

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Abstract

Precise structural information on the Mg1−xAlxB2 superconductors in the vicinity of x≈0.5 is derived from high-resolution synchrotron x-ray powder diffraction measurements. We find that a hexagonal superstructure, accompanied by doubling of the c axis, ordering of Mg and Al in alternating layers, and a shift of the B layers towards Al by ∼0.12 Å, is formed. The unusually large width of the (0012) superlattice peak implies the presence of microstrain broadening, arising from anisotropic stacking of Al and Mg layers and/or structural modulations within the ab plane. The ordered phase survives only over a limited range of compositions away from the optimum x=0.5 doping level.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	39	Pressure not reported	unknown
Mg0.55Al0.45B2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	6	Pressure not reported	onset
Mg0.5Al0.5B2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	3	Pressure not reported	onset
Mg0.45Al0.55B2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	4	Pressure not reported	onset