Interpretation of X-Ray Line Profile of Polycrystalline ${\hbox {MgB}}_{2}$

XRD peak profile analysis was performed on polycrystalline MgB₂ bulks and tapes manufactured by various heat treatment conditions in order to investigate statistical value of crystallite size. Volume-weighted and area-weighted mean diameter of a bulk sample heated at 600degC for 6 h were estimated to be approximately 90 nm and 20 nm, respectively. These suggest that crystallite size distribution of MgB₂ is very wide, although a lot of very small crystallites exist. Similar tendencies were observed for other samples. On the other hand J _c values were found to be rather low compared to the expected values considering its small D _a . This indicates that a small portion of crystallite interfaces act as effective pinning centers.