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Contribution of Optical Phonons to the Elastic Moduli of PdHX and PdDX

  • B. M. Geerken
  • R. Griessen
  • L. M. Huisman
  • E. Walker
Part of the NATO Conference Series book series (NATOCS, volume 6)

Abstract

Sound velocity measurements carried out between 10 and 300K on α’-phase PdHx and PdDx show that the temperature coefficients dCij/dT of the elastic moduli Cij are significantly more negative in PdDx than in PdHx. This isotope effect is well described by a quasiharmonic model in which the transverse and longitudinal optical phonons are treated as Einstein oscillators with different Grüneisen parameters γt and γ. The Einstein temperatures are θ t H = 650K, θ H = 910K in PdH0.66, θ t D = 450K and θ D = 640K in PdD0.652. Our analysis implies that |γ−γt| is large compared to the average optical phonon Grüneisen parameter γ̅ = (γ + 2γt)/3 determined from thermal expansion measurements. For CL, C’ and C44 a maximum in ultrasonic absorption is found around 220K. It is interpreted as arising from a reorientation of pairs (or clusters) of vacancies in the hydrogen sublattice under uniaxial or shear strains.

Keywords

Elastic Modulus Optical Phonon Phonon Dispersion Curve Longitudinal Optical Phonon Ultrasonic Absorption 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Plenum Press, New York 1983

Authors and Affiliations

  • B. M. Geerken
    • 1
  • R. Griessen
    • 1
  • L. M. Huisman
    • 1
  • E. Walker
    • 2
  1. 1.Vrije Universiteit AmsterdamThe Netherlands
  2. 2.Université de GenèveSwitzerland

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