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.

High-pressure low-symmetry phases of cesium halides / Buongiorno Nardelli, M.; Baroni, S.; Giannozzi, Paolo. - In: PHYSICAL REVIEW. B, CONDENSED MATTER. - ISSN 0163-1829. - 51:13(1995), pp. 8060-8068. [10.1103/PhysRevB.51.8060]

High-pressure low-symmetry phases of cesium halides

Baroni, S.;Giannozzi, Paolo
1995-01-01

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.
1995
51
13
8060
8068
Buongiorno Nardelli, M.; Baroni, S.; Giannozzi, Paolo
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11767/12903
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