Phase Identification for Cu-sheathed MgB$_{2}$ Superconducting wires

X-ray diffraction (XRD) and SEM measurements have been performed for Cu-sheathed MgB$_{2 }$wires fabricated using ultra-fine Mg and B precursor and powder-in-tube method. Thirteen samples sintered at temperatures ranging from 450 \r{ }C to 875 \r{ }C, each for 5 minutes, were measured. It is found that MgB$_{2}$ phase can be formed in all these samples. From 400 \r{ }C to 550 \r{ }C, the fraction of the Mg$_{2}$Cu phase increases with sintering temperature while the Mg-phase decreases. Between 550 \r{ }C and 725 \r{ }C, the Mg$_{2}$Cu phase disappears, only MgB$_{2}$ and MgCu$_{2}$ phase co-exist. At or above 725 \r{ }C , MgB$_{2}$, MgB$_{4}$, and Mg$_{1+y}$Cu$_{32+\delta }$ phase coexist, and the fraction of the Mg$_{1+y}$Cu$_{32+\delta }$ phase increases with sintering temperature while the other two phases decrease. With the help of the measured XRD pattern for standard compound MgCu$_{2}$, the MgCu$_{2}$ phase in the Cu-sheathed MgB$_{2}$ wire samples can be clearly identified. We also for the first time identify a new phase, the Mg$_{1+y}$Cu$_{32+\delta }$ phase, in Cu-sheathed MgB$_{2}$ wires. The XRD results are analyzed together with SEM and current density ($J_{c})$ measurement results.