Interface-Driven Phase Transition of Phase-Change Material

In order to be able to control the phase transition of engineered phase-change materials, the specific understanding of phase transition processes is essential. To understand the effect of dopant on phase transition, the phase transition processes of Bi _5.5 (In ₃ SbTe ₂ ) _94.5 (Bi-IST) are quantitatively investigated with regard to the interfacial, bulk, entropy, and Gibbs free energies involved in the intermediate InSb and InTe phases and the crystallized Bi-IST. In the first step, InSb is crystallized; InTe and Bi are present in the amorphous phase. In the second step, heterogeneous nucleation of crystalline InTe occurs on the InSb. The energy barrier calculated for this nucleation of crystalline InTe is reduced by 1.5 times owing to the interfacial reaction of 5.5 atom % of Bi atoms compared to the case without Bi. In the third step, crystalline InSb and InTe are crystallized to Bi-IST since Bi atoms substitute Sb sites with a higher interfacial energy. The difference in the Gibbs free energy of the Bi-IST is -1.4 × 10 ⁵ eV, which is lower than the -1.1 × 10 ⁵ eV of the IST; this is because the differences in entropy with an increase in temperature and the interfacial energy are increased owing to the added Bi atoms. This lower Gibbs free energy becomes a driving force for the stable phase transition of Bi-IST at a lower transition temperature compared with that of the IST. With these phase transition processes, the contribution shares of enthalpy, entropy with temperature change, and interfacial energy are quantitatively analyzed; moreover, we recommend one of the various methods to design a novel phase-change material.