6533b860fe1ef96bd12c3885

RESEARCH PRODUCT

Inelastic neutron scattering study of the rotational excitations in(KBr)1−x(KCN)xin the paraelastic and structural glass state

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The coupled rotational-translational excitations in ${(\mathrm{KBr})}_{1\ensuremath{-}x}{(\mathrm{KCN})}_{x}$ were studied by inelastic neutron scattering for concentrations $0.008\ensuremath{\le}x\ensuremath{\le}0.20$. We followed the ${A}_{1g}\ensuremath{-}{T}_{2g}$ tunneling transition and the ${A}_{1g}\ensuremath{-}{E}_{g}$ librational excitation through the transition from the paraelastic to the structural glass state. We found that these two excitations and their coupling to the lattice strains exhibit a very different temperature dependence in the glass state. While the tunneling transition, which triggers reorientations of the ${\mathrm{CN}}^{\ensuremath{-}}$ ions, shows a drastic reduction of the ${T}_{2g}$ rotation-translation coupling, the librational excitations conserving the CN alignment are less influenced. These results suggest that for $T\ensuremath{\le}{T}_{F}$ the CN system is gradually blocked in clusters, thereby reducing the density of free-ion tunneling states in favor of cluster-reorientation modes effectively decoupled from the lattice. This leads to a metastable low-temperature state with extremely long relaxation times.