The thermodynamic properties and phase diagram of icosahedral Alsub x Li sub 3 Cu.

Thermodynamic and x-ray diffraction studies of Al sub x Li sub 3 Cu alloys reveal that in the composition range 4.8=x=6. 1, an icosahedral (i) Al sub (5.1) Li sub 3 Cu phase forms peritectically from liquid and a cubic R-Al sub (4.8) Li sub 3 Cu phase at T sub m ~ 884K, while the R-Al sub (4.8) Li sub 3 Cu precipitates at T sub (l,R) >= T sub m. The heat, DELTA H sub m, and entropy, DELTA S sub m, of melting for the R- and i-phases are similar, and equal to 3.2 kcal/mol and 3.5 cal/mol-K, respectively. The high values of DELTA H sub m and DELTA S sub m are responsible for the observed faceting of R- and i-grains.