The Synthesis of A15-Type Materials at High Pressures: Comments and Critiques
Materials with the A15 structure are of interest principally because a number of them are superconductors. Nb3Ge, which has the highest known superconducting transition temperature To, 23.2 K, has this A15 structure . Of 65 known A15 Compounds 41 are superconducting. Figure 1 shows the structure of an A15 unit cell. The B atoms, hatched here, form a body-centered cubic network. Woven through this network are three mutually orthogonal chains of A atoms, shown as stippled here. There is evidence that the integrity of these A chains is important to superconductivity . Figure 2 shows the location of the A and B atoms in the Periodic Table. The A atoms (stippled) are from the Ta, V, and Cr groups, with V and Nb forming 30 of these A15 Compounds. Technetium has been reported acting as the A element in one Compound . The B atoms (hatched) are from the groups of transition metals from Mn through Zn, and the groups of non-transition metals A1, Si and P. Beryllium is included because Mo3Be has been reported to form with the Al5 structure . Nb3Te has been formed by high pressure, high temperature techniques .
KeywordsBoron Nitride Elemental Powder Nitride Reaction Molybdenum Sheet High Temperature Technique
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