Institutional Research Information Service
UCL Logo
Please report any queries concerning the funding data shown on the profile page to:

Please report any queries concerning the student data shown on the profile page to:

Email: portico-services@ucl.ac.uk

Help Desk: http://www.ucl.ac.uk/ras/portico/helpdesk
Publication Detail
Equilibrium and metastable phase transitions in silicon nitride at high pressure: A first-principles and experimental study
We have combined first-principles calculations and high-pressure experiments to study pressure-induced phase transitions in silicon nitride (SiN). Within the quasi-harmonic approximation, we predict that the α phase is always metastable relative to the β phase over a wide pressure-temperature range. Our lattice vibration calculations indicate that there are two significant and competing phonon-softening mechanisms in the β-SiN, while phonon softening in the α-SiN is rather moderate. When the previously observed equilibrium high-pressure and high-temperature β → γ transition is bypassed at room temperature (RT) due to kinetic reasons, the β phase is predicted to undergo a first-order structural transformation to a denser P6̄ phase above 39 GPa. The estimated enthalpy barrier height is less than 70 meV/atom, which suggests that the transition is kinetically possible around RT. This predicted new high-pressure metastable phase should be classified as a "postphenacite" phase. Our high-pressure x-ray diffraction experiment confirms this predicted RT phase transition around 34 GPa. No similar RT phase transition is predicted for α-Si N. Furthermore, we discuss the differences in the pressure dependencies of phonon modes among the α, β, and γ phases and the consequences on their thermal properties. We attribute the phonon modes with negative Grüneisen ratios in the α and β phases as the cause of the predicted negative thermal expansion coefficients (TECs) at low temperatures in these two phases, and predict no negative TECs in the γ phase. © 2011 American Physical Society.
Publication data is maintained in RPS. Visit https://rps.ucl.ac.uk
 More search options
UCL Authors
University College London - Gower Street - London - WC1E 6BT Tel:+44 (0)20 7679 2000

© UCL 1999–2011

Search by