Origin of negative thermal expansion in cubic ZrW2O8 revealed by high pressure inelastic neutron scattering.
Isotropic negative thermal expansion has been reported in cubic ZrW2O8 over a wide range of temperatures (0-1050 K). Here we report the direct experimental determination of the Grüneisen parameters of phonon modes as a function of their energy, averaged over the whole Brillouin zone, by means of high pressure inelastic neutron scattering measurements. We observe a pronounced softening of the phonon spectrum at P = 1.7 kbar compared to that at ambient pressure by about 0.1-0.2 meV for phonons of energy below 8 meV. This unusual phonon softening on compression, corresponding to large negative Grüneisen parameters, is able to account for the observed large negative thermal expansion.
Mittal
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Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India.
Chaplot
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Schober
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Mary
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