Abstract
► The effect of ball milling time on the dispersion of glucose in MgB
2 was systematically studied using XRD, SEM and TEM. ► Establish the ball milling time for the substitution of C in MgB
2 using glucose and quantify its amount. ► Uniform dispersion of the glucose in MgB
2 is necessary to get the optimum benefit of the C substitution.
The effect of the ball milling time (BMT) on the substitution of the carbon in the glucose doped MgB
2 samples is investigated here. Using in situ solid state reaction, four different doped samples of Mg(B
.98C
.02)
2 were prepared by mixing powders of Mg, boron and glucose for 2
h, 4
h, 8
h and 12
h using planetary ball milling. A reference sample of un-doped MgB
2 was also prepared under same conditions. The particle size distribution of the un-reacted samples show a decrease in the particle size as the BMT is increased. Both the average particle size as well as the standard deviation show a substantial decrease with the increase in the milling time up to 8
h. After 8
h, the size reduction is rather insignificant. From the XRD data, the crystallite size of the doped MgB
2 computed using the Scherrer formula was found to decrease with the increasing BMT, showing a saturation level after 8
h of the milling time. TEM images also confirm the crystallite size obtained from the XRD data. The substitution of the C in the MgB
2 lattice, measured from the change in the
c/a ratio, increases with increasing BMT. The maximum carbon substitution is achieved at approximately 8
h of BMT. Moreover, a systematic enhancement of the residual resistivity and a decrease in
T
C with an increasing BMT further confirms a progressive substitution of the carbon in the MgB
2. These results suggest that a minimum ball milling time is necessary to disperse the glucose uniformly for a maximum substitution of nano C in the B plane of MgB
2 lattice. The optimum BMT is found to be 8
h. Thus, the decrease in the particle size due to the ball milling enhances the dispersion of the constituent materials thereby favoring a greater substitution of the dopant in the MgB
2 during the solid-state reaction.