  While phase-change materials (PCMs) composed of chalcogenide have different
crystallization mechanisms (CM), such as nucleation-dominated Ge2Sb2Te5 (GST)
and growth-dominated GeTe (GT), revealing the essential reason of CM as well as
the tuned properties is still a long-standing issue. Here, we remarkably find
the distinct stability of Te-terminated (111) boundaries (TTB) in different
systems, which provides a path to understand the difference in CM. It stems
from the quantum effect of molecular orbital theory: the optimal local chemical
composition results in the formation of TTB without dangling bonds (DB) in GST
but with DB in GT, where DB destabilizes boundary due to its distorted local
environment mismatching Oh symmetry of p orbitals. Moreover, the inner vacancy
concentration in GST is alterable and controlled by TTB, manifested by the
absence of cubic-to-hexagonal transition in carbon-doped GST of small grains
and minimized inner vacancy. Finally, the charge transport property (CTP) is
controlled by boundary via changing the density of charge or hole nearby as
well as vacancy. These findings open the door to tune CTP by CM, which is
necessary for achieving low-power and ultrafast devices.
