BUILDING ALKALI-LEAD INTERMETALLIC COMPOUNDS FROM CLUSTERS

Ab initio total energy calculations are used to investigate the struct ural trends of equiatomic solid APb alloys (A = Li, Na, K). The NaPb b ulk structure was assembled starting from a greatly expanded array of eight Na4Pb4 clusters per unit cell. The clusters were drawn together by shrinking the unit cell in stages and allowing full atomic relaxati on at each stage. Charged Pb-4 tetrahedral units dominate the structur al and electronic properties and these units are remarkably robust and insensitive to their alkali environment. The stability of the Pb4 uni ts diminishes as we progress from K to Li and leads to their absence i n the LiPb alloy in accordance with experiment. The distance between P b4 units seems to be the critical factor responsible for the structura l trends and the atomic size of the alkali determines this. (C) 1998 E lsevier Science Ltd. All rights reserved.