Influence ofin situandex situZrO2addition on the properties of MgB2

The effect of ZrO 2 addition on the properties of MgB 2 has been studied using in situ and ex situ processes. The in situ process was performed by introducing ZrO 2 from the milling tools into MgB 2 throughout the planetary ball milling, whereas the ex situ process was accomplished by mixing ZrO 2 from the milling tools with MgB 2 by hand grinding in a mortar. A detectable amount of ZrO 2 was present in MgB 2 after 4 h of milling during the in situ process and its content increased with milling time as expected. The 400 h milled powder was partially amorphized and showed the formation of a minority ZrB 2 phase. For milling up to 100 h, diamagnetism of MgB 2 was significantly reduced while T c remained unchanged. Superconductivity was totally destroyed after 148 h of milling. The loss of superconductivity is attributed to the effect of disordering induced by mechanical milling. As a result of in situ ZrO 2 addition, the initial T c and crystal structure of MgB 2 could not be restored upon annealing. With increasing milling time, the expansion of lattice parameters in both the a- axis and c- axis may be due to possible substitution of Mg or B by Zr. The result from the magnetic measurement shows that J c of MgB 2 is deteriorated by in situ ZrO 2 addition. On the other hand, ex situ ZrO 2 addition with annealing did not degrade the T c of MgB 2 .