Negative thermal expansion (NTE) is known in Cu 2 O below 300 K and in Ag 2 O up to its
decomposition temperature of about 500 K. Inelastic neutron scattering measurements in Cu
2 O and lattice dynamics calculations of NTE in both Cu 2 O and Ag 2 O are reported. The
phonon density of states from a polycrystalline sample of Cu 2 O is measured using the triple-
axis spectrometer at Trombay. A lattice dynamical model is used for the calculations of
phonon frequencies and their pressure dependence in the entire Brillouin zone. The …

The compounds ZrW 2 O 8 and HfW 2 O 8 undergo large isotropic negative thermal
expansion (NTE) over a wide range of temperatures up to 1443 K and 1050 K, respectively.
We have showed previously that large softening of low-energy phonons in ZrW 2 O 8 is
responsible for its anomalous thermal expansion behavior. In order to understand the effect
of replacing Zr by Hf on NTE behavior we report lattice dynamical calculations and neutron
time-of-flight spectroscopic measurements of the phonon density of states for cubic HfW 2 O …