高压非弹性中子散射揭示立方ZrW₂O₈中负热膨胀的起源

Origin of negative thermal expansion in cubic ZrW2O8 revealed by high pressure inelastic neutron scattering.

作者信息

Mittal R, Chaplot S L, Schober H, Mary T A

机构信息

Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India.

出版信息

Phys Rev Lett. 2001 May 14;86(20):4692-5. doi: 10.1103/PhysRevLett.86.4692.

DOI:10.1103/PhysRevLett.86.4692

PMID:11384316

Abstract

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.

摘要

据报道，立方ZrW₂O₈在很宽的温度范围（0 - 1050 K）内具有各向同性负热膨胀特性。在此，我们通过高压非弹性中子散射测量，报告了在整个布里渊区平均的声子模式的格林艾森参数随其能量的直接实验测定结果。我们观察到，与常压相比，在1.7 kbar压力下，能量低于8 meV的声子的声子谱明显软化，软化程度约为0.1 - 0.2 meV。这种压缩时异常的声子软化，对应着大的负格林艾森参数，能够解释所观察到的大的负热膨胀现象。