Abstract
To clarify the inconsistency between calculated and existing experimental X-ray diffraction (XRD) pattern for dicopper magnesium (MgCu
2) and to identify the impurity phase in Cu-sheathed MgB
2 superconductors, polycrystalline MgCu
2 samples were synthesized and studied by XRD measurement. The XRD result shows that the (2
2
0), (4
2
2), (6
2
0), and (6
4
2) reflection lines, which are missing from the standard pattern of MgCu
2 in the current Powder Diffraction File (PDF) database with file #01-1226, are all present in the XRD patterns of our MgCu
2 samples. This result reveals that the long-time widely used XRD pattern in the PDF file #01-1226 is in fact an incomplete one and should be replaced by a more complete pattern. By comparison with our measured XRD pattern for MgCu
2 samples, the reflection line located at 2
θ
≈
36° for Cu-sheathed MgB
2 wires has been unambiguously identified as the (2
2
0) line of the MgCu
2 impurity phase. This line was previously unidentifiable due to its absence in current PDF database. The calculated XRD pattern for MgCu
2 was found to match well with the measured pattern in terms of both line position and intensity. Thus, this study has provided a more complete powder XRD pattern of MgCu
2 than that in the current PDF database for future phase determination and crystal structure study on alloys and compounds containing MgCu
2 phase.