Pressure Induced Pseudomelting Implied By Negative Clapeyron Slope for Silicon

Abstract

We have studied pressure induced pseudomelting implied by the negative clapeyron  slope for Silicon. Pressure induced amorphization was based primarily on Raman  measurements. This does not rule out the possibility of a transformation to a phase  which may not have a Raman-active mode such as the primitive hexagonal. Energy  dispersive x-ray diffraction measurements on the sample had shown pressure  induced annealing of nanocrystalline regions. Since this would have resulted in an  increase of the particle size and reduced surface effects, the high pressure behavior  should have been similar to that of surface terminated nanoparticles. We have  observed that the cubic nano π-silicon undergoes a crystalline-crystalline phase  transition to the primitive hexagonal phase under high pressure at ~20Gpa and the  amorphous phase arised only on release of pressure. This observation is consistent  with the transformation seen earlier in the case of surface terminated nanocrystalline  silicon. Nanoamorphous phase thus obtained transforms reversibly to the Ph phase  under further pressure cycles. The role of particle size in this reversible behavior. Our  results showed that the reversible inter conversion also takes place in bulk amorphous  Silicon, provided the pressure release is fast, unlike in the case of nanoamorphous  Silicon. Our studies showed that irrespective of the method of preparation or size of  the amorphous Silicon particles, it always transforms to primitive hexagonal phase  under compression. The obtained results were found in good agreement with  previously obtained results.