Can high pressure I-II transitions in semiconductors be affected by plastic flow and nanocrystal precipitation in phase I?

Pressure-Raman spectroscopy in ZnSe and ZnTe single crystals reveals that Se and Te nano-crystals (NCs) precipitate in these II-VI hosts for pressures far below their I-II phase transitions.[1] The inclusions are evident from the appearance and negative pressure-shift of the A1 Raman peaks of Se and Te (trigonal phase). The Se and Te NCs nucleate at dislocations and grain boundaries that arise from pressure-induced plastic flow. This produces chemical and structural inhomogeneities in the zincblende phase of the host. At substantially higher pressures, the I-II transition proceeds in the presence of these inhomogenities. This can affect the transition's onset pressure P$_{t}$ and width $\Delta $P$_{t}$, and the occurrence of metastable phases along the transition path. Precipitation models in metals show that nucleation of inclusions depends on the Peierls stress $\tau _{p}$ and a parameter $\alpha $ related to the net free energy gained on nucleation. For favorable values of $\tau_{p}$ and $\alpha $, NC precipitation at pressures below the I-II transition could occur in other compounds. We propose criteria to judge whether this is likely based on the observed ranges of $\tau_{p}$ in the hosts, and estimates of $\alpha $ derived from the cohesive energy densities of the NC materials. One finds trends that can serve as a useful guide, both to test the proposed criteria, and to decide when closer scrutiny of phase transition experiments is warranted, e.g., in powders where high dislocation densities are initially created. [1] G. P. Lindberg, et. al., Phys. Status Solidi B 250, 711 (2013)