Phonon instabilities in rocksalt AgCl and AgBr under pressure studied within density functional theory

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DOIResolve DOI: http://doi.org/10.1103/PhysRevB.74.054102
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TypeArticle
Journal titlePhys. Rev. B
Physical Review B (Condensed Matter and Materials Physics)
Volume74
Issue5
Pages0541026; # of pages: 54097
SubjectAPW calculations; density functional theory; elastic constants; high-pressure solid-state phase transformations; phonons; shear modulus; silver compounds; soft modes
AbstractThe phonons and elastic constants of rocksalt AgCl and AgBr under pressure are extensively studied by using the pseudopotential plane-wave method within density functional theory. A pressure-induced soft transverse acoustic (TA) phonon mode is identified for both compounds. Interestingly, each compound shows a different phonon softening behavior. A TA phonon branch softens to zero pressure at 6.5 GPa along [xi00] direction in AgCl, resulting in the phase transition from the rocksalt structure to the monoclinic structure. A softening TA phonon mode at the zone boundary X point in AgBr is predicted and the deduced transition pressure of ~9.8 GPa is found to be 24% larger than the experimental measurement of ~7.9 GPa. The predicted larger transition pressure indicated that the TA softening phonon mode at the zone boundary X point in AgBr may not independently induce the phase transition. Moreover, a pressure-induced softening of shear modulus in C44 is also verified for both compounds. However, it is suggested that the phonon instability, instead of C44 instability, dominates the pressure-induced structural phase transition.
Publication date
AffiliationNational Research Council Canada; NRC Steacie Institute for Molecular Sciences
Peer reviewedNo
NPARC number12326997
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Record identifier85b9ec78-483f-4a2c-a3b7-52b789681a02
Record created2009-09-10
Record modified2016-05-09
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