Negative thermal expansion in cubic ZrMo2O8:: Inelastic neutron scattering and lattice dynamical studies -: art. no. 214303

Disordered cubic ZrMo2O8(Pa(3) over bar, Z=4) is known to display isotropic negative thermal expansion (NTE) below 600 K. We report high-pressure inelastic neutron scattering experiments up to 2.5 kbar in this material using the IN6 spectrometer at Institut Laue-Langevin. The observed phonon softening of about 0.1-0.3 meV for phonons below 8 meV is able to account for the NTE below 100 K. The phonon spectrum in the entire energy range up to 150 meV has been measured using the HRMECS spectrometer at Argonne National Laboratory. The ordered phase (space group P2(1)3) of cubic ZrMo2O8 has not yet been synthesized. However, we have calculated the phonon spectrum and thermal expansion in this phase for comparison with the known ordered phase of cubic ZrW2O8.