Phonon softening and high-pressure low-symmetry phases of cesium iodide

Marco Buongiorno Nardelli, Stefano Baroni, and Paolo Giannozzi
Phys. Rev. Lett. 69, 1069 – Published 17 August 1992
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Abstract

The relative stability of various high-pressure phases of CsI is studied from first principles and analyzed using the Landau theory of phase transitions. We demonstrate that the cubic-to-orthorhombic transition recently observed to occur slightly below 20 GPa is driven by the softening of an acoustic phonon at the M point of the Brillouin zone. The coupling between this mode and anisotropic strain makes the transition slightly first order (with a volume variation of the order of 0.1%), and stabilizes the experimentally observed orthorhombic phase with respect to other competing symmetry-allowed structures.

  • Received 15 April 1992

DOI:https://doi.org/10.1103/PhysRevLett.69.1069

©1992 American Physical Society

Authors & Affiliations

Marco Buongiorno Nardelli and Stefano Baroni

  • Scuola Internazionale Superiore di Studî Avanzati (SISSA), via Beirut 2/4, I-34014 Trieste, Italy

Paolo Giannozzi

  • Scuola Normale Superiore (SNS), piazza dei Cavalieri 7, I-56100 Pisa, Italy

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Issue

Vol. 69, Iss. 7 — 17 August 1992

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