  The glass-formation range of bulk metallic glasses (BMGs) based on lanthanum
and cerium was pinpointed in La-Al-Co, Ce-Al-Co and pseudo-ternary
(La-Ce)-Al-Co system respectively by copper mold casting. Through the stepwise
substitution of La for solvent Ce in (LaxCe1-x)65Al10Co25 alloys (0<x<1), the
fully glassy rods of the (La0.7Ce0.3)65Al10Co25 alloy can be successfully
produced up to 25 mm in diameter by tilt-pour casting. Comparing with the
glass-forming ability (GFA) of single-lanthanide based alloys, La65Al10Co25 and
Ce65Al10Co25, the coexistence of La and Ce with similar atomic size and various
valence electronic structure can obviously improve the GFA of
(LaxCe1-x)65Al10Co25 BMGs, which can't be explained by the former GFA criteria
for BMGs, e.g. atomic size mismatch and negative heats of mixing. A
thermodynamic model was proposed to evaluate this substitution effect, which
gives a reasonable explanation for the obvious improvement of GFA induced by
the coexistence of similar atoms.
