HIGH-PRESSURE SYNTHESIS AND CRYSTAL-STRUCTURE OF PD8AL21, PD8AL17SI4 AND PT8AL21

The intermetallic phases Pd//8Al//2//1, Pd//8Al//1//7Si//4, Pt//8Al//2//1 were synthesized from the elements by high pressure-high temperature synthesis in a modified belt-type apparatus. The isotypic compounds crystallize in a tetragonal structure. In the complicated crystal structure, the transition metal atoms are 10-fold coordinated by aluminium (or silicon); the aluminium atoms (except at atomic positions Al(1) and Al(5) are surrounded by four heavy metal atoms. Pd//8Al//2//1 and Pd//8Al//1//7Si//4 are true high-pressure phases, being only metastable under normal conditions.