Acoustic phonon anomaly at small wavevectors in Nb-H

Abstract
The hydrogen-induced phonon-frequency shift in the system Nb-H0.15 has been investigated by high resolution triple-axis spectrometry. The transverse mode propagating in the ( zeta zeta 0) direction displays a dispersion step of 5.5% in the low-wavevector regime ( zeta -1 dependence of the step amplitude has not been found by ultrasonic and pendulum methods.