Acoustic phonon anomalies and superstructure of two NbZr alloys

The anomalous dispersion of the [001] transverse phonon branch of Nb_0.9Zr_0.1 and Nb_0.8Zr_0.2 has been measured by neutron inelastic scattering. The anomaly is found to become less pronounced as the Zr content of the alloy is increased. Although the anomaly is strongly temperature-dependent it is not obviously affected by the superconducting transition. Diffraction measurements with the Nb_0.9Zr_0.1 sample show the diffuse scattering which Wakabayashi has recently reported to occur at wave-vectors around [$\text{3}\text{4}$,$\text{3}\text{4}$,$\text{3}\text{4}$] in a 12% alloy. The Nb_0.8Zr_0.2 crystal however displays unbroadened superlattice peaks at wavevectors [$\text{3}\text{4}$,$\text{3}\text{4}$,$\text{3}\text{4}$ in some Brillouin zones.