271 research outputs found
Measurement of anharmonicity of phonons in negative thermal expansion compound Zn(CN)2 by high pressure inelastic neutron scattering
Zn(CN)2 is known to have an isotropic negative thermal expansion (NTE)
coefficient (about -51 x 10-6 K-1) over 10-370 K that is twice as large as that
of ZrW2O8. We have measured the pressure dependence of the phonon spectra up to
30 meV from a polycrystalline sample of Zn(CN)2 at pressures of 0, 0.3, 1.9 and
2.8 kbar at temperatures of 165 and 225 K. The measurements enabled us to
estimate the energy dependence of the ratios Gamma/B (Gamma are Gruneisen
parameters as a function of phonon energy Ei at ambient pressure and B is the
bulk modulus), which reflect the anharmonicity of phonons. We conclude that the
phonon modes of low energy below 15 meV play an important role in the
understanding of the NTE behavior in Zn(CN)2 and the measured anharmonicity can
quantitatively explain the NTE.Comment: 5 pages, 4 figure
Collective dynamics in crystalline polymorphs of ZnCl: potential modelling and inelastic neutron scattering study
We report a phonon density of states measurement of -ZnCl using
the coherent inelastic neutron scattering technique and a lattice dynamical
calculation in four crystalline phases of ZnCl using a transferable
interatomic potential. The model calculations agree reasonably well with the
available experimental data on the structures, specific heat, Raman frequencies
and their pressure variation in various crystalline phases. The calculated
results have been able to provide a fair description of the vibrational as well
as the thermodynamic properties of ZnCl in all its four phases.Comment: Accepted in J. Phys.: Condens. Matte
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