The MgB2 was prepared by mixing B with excess Mg, compressing them into pellets, heating at 950C for 4h and sublimating off the excess Mg at 700C in vacuum. The resultant MgB2 was heated to 800 to 1300C in an inert atmosphere. At up to 800C, the compound was stable. It then lost Mg slowly, with the formation of 3 consecutive Mg-poor compounds.

Magnesium Boride: its Thermal Reactions. A.Chretien, P.Duhart: Comptes Rendus, 1962, 254, 1439-41

Figure 9

Interstitial O Atom Seen along [100]