Shock-induced phase transition ofβ−Si3N4toc−Si3N4

Abstract

Hugoniot curve (shock velocity vs particle velocity and pressure vs density) of $\ensuremath{\beta}\ensuremath{-}{\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ has been measured up to 150 GPa by a two-stage light gas gun and an inclined-mirror method. The Hugoniot elastic limit is detected to be about 16 GPa. Above \ensuremath{\sim}36 GPa, a phase transition from $\ensuremath{\beta}\ensuremath{-}{\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ to $c\ensuremath{-}{\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ is discovered. The kinetics is very sluggish. This phase transition does not seem to complete at the highest pressure achieved in this work, but an extrapolation gives a pressure of \ensuremath{\sim}180 GPa for the completion. Isentrope of $c\ensuremath{-}{\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ has been determined from the Hugoniot data by fitting the Birch-Murnaghan equation of state. The zero-pressure bulk modulus and its first pressure derivative are found to be $300\ifmmode\pm\else\textpm\fi{}10\mathrm{GPa}$ and $3.0\ifmmode\pm\else\textpm\fi{}0.1,$ respectively. These values are in agreement with the first-principles calculations, and therefore strongly support that $c\ensuremath{-}{\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ is a low compressibility phase.