The pressure-induced phase transition in amorphous silicon ~a-Si! is studied using ab initio constantpressure molecular-dynamic simulations. Crystalline silicon ~c-Si! shows a phase transformation from diamond-to-simple hexagonal at 29.5 GPa, whereas a-Si presents an irreversible sharp transition to an amorphous metallic phase at 16.25 GPa. The transition pressure of a-Si is also calculated fro...

Pressure-induced structural changes in di-iron nonacarbonyl [Fe2(CO)9] were examined by in situ Raman spectroscopy with the aid of a diamond anvil cell. Our results indicate that Fe2(CO)9 undergoes a pressure-induced phase transformation at about 0.9 GPa. Upon further compression, another structural transformation is identified at 7 GPa. In the low-pressure phase below 0.9 GPa, the π back-bondi...

An investigation was initiated to examine the effect of rotation speed on the allotropic α to ω-phase transformation in titanium. A grade 2 commercial purity titanium was processed by high-pressure torsion (HPT) at room temperature up to a maximum of 10 turns using a pressure of 5.0 GPa and different rotation speeds from 0.5 to 2 rpm. It is shown that the allotropic phase transformation occurs ...

Structural inhomogeneity is ubiquitous in solid crystals and plays critical roles in phase nucleation and propagation. Here, we develop a heterogeneous solid-solid phase transition theory for predicting the prevailing heterophase junctions, the metastable states governing microstructure evolution in solids. Using this theory and first-principles pathway sampling simulation, we determine two typ...

[1] High-pressure Raman and X-ray diffraction data on single crystals of hydrous layer-structure minerals, dickite and gibbsite, reveal structural phase transitions occurring between 2.0 and 2.5 GPa. In the case of dickite, this is the first documented occurrence of a pressure-induced phase transformation in a 1:1 phyllosilicate. Above the transition the structure of individual 1:1 layers remai...

In situ synchrotron powder diffraction has been used to probe the pressure-dependent structural properties of the magnetic molecular framework material Co(dca)2 [dca = dicyanamide or N(CN)2(-)]. An orthorhombic (Pmnn) to monoclinic (P2₁/n) transformation to a high-pressure phase, namely γ-Co(dca)2, occurs at 1.1 GPa. Structural determination of γ-Co(dca)2 shows that the rutile-like topology of ...