However, as this accessible window is chemistry dependent, an alternative descriptor has been proposed based on the amorphous limit. Here, only crystalline phases of lower energy than the amorphous 'polymorph' of the relevant composition is considered accessible, as the barrier for transformation to an amorphous state must be low. Figure illustrates this stability window. Here, two phases are thermodynamically stable at different conditions, one phase is metastable, and potentially synthesisable, since it is of lower energy than the amorphous phase, while the last phase is inaccessible, since it should spontaneously decompose into the amorphous phase.