Study of the temperature dependence of the localized vibrations of H and D in niobium

The second harmonic of the local deuterium vibration in NbD0.85 has been observed for the first time. Its energy ω=170 meV is 7 meV below the harmonic value of twice the lower local-mode energy, 2ω₁. The measured isotope effect for the lowest local-mode energy is ω₁Hω₁D=1.365±0.005 which differs from the harmonic value of (MDMH)1/2=√2. The temperature dependence of the local modes for both the deuteride and hydride system exhibit pronounced precursor effects prior to the β→α^' order-disorder phase transition.