High-pressure low-symmetry phases of cesium halides

Marco Buongiorno Nardelli, Stefano Baroni, and Paolo Giannozzi
Phys. Rev. B 51, 8060 – Published 1 April 1995
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Abstract

The relative stability of different high-pressure phases of various cesium halides is studied from first principles and analyzed using the Landau theory of phase transitions. We present results for CsI, CsBr, and CsCl up to pressures of ≊100 GPa. A cubic-to-orthorhombic transition, driven by the softening of an acoustic phonon at the M point of the Brillouin zone, is competing with the cubic-to-tetragonal martensitic transition typical of these compounds. The phonon softening takes place only in CsI and CsBr at a residual volume of V/V0=0.64, 0.52, respectively. A cubic-to-tetragonal instability is found instead to occur at V/V0≊0.54 for all the compounds considered here. The orthorhombic phase is stable only in CsI, whereas it is taken over by the tetragonal one in the case of CsBr. Our analysis reveals the essential role played by the phonon-strain coupling in stabilizing the orthorhombic phase and in making the corresponding transition first order.

  • Received 5 August 1994

DOI:https://doi.org/10.1103/PhysRevB.51.8060

©1995 American Physical Society

Authors & Affiliations

Marco Buongiorno Nardelli

  • Laboratorio Istituto Nazionale di Fisica Nucleare-TASC and BULL-Unix Competence Center, AREA di Ricerca di Trieste, Padriciano 99, I-34012 Trieste, Italy

Stefano Baroni

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

Paolo Giannozzi

  • Scuola Normale Superiore (SNS), Piazza dei Cavalieri 7, I-56126 Pisa, Italy

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Issue

Vol. 51, Iss. 13 — 1 April 1995

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