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Abstract:
We report on the inelastic response of AV(2)Al(20) (with A - Sc, La and
Ce) probed by high-resolution inelastic neutron scattering experiments.
Intense signals associated with the dynamics of Sc, La and Ce are
identified in the low-energy range at 6-14 meV in ScV2Al20 and at 8-16
meV in LaV2Al20 and CeV2Al20. Their response to temperature changes
between 2 and 300 K reveals a very weak softening of the modes upon
heating in LaV2Al20 and CeV2Al20 and a distinguished blue shift by about
2 meV in ScV2Al20. By means of density functional theory (DFT) and
lattice dynamics calculations (LDC) we show that the unusual
anharmonicity of the Sc-dominated modes is due to the local potential of
Sc featured by a strong quartic term. The vibrational dynamics of
ScV2Al20 as well as of LaV2Al20 and CeV2Al20 is reproduced by a set of
eigenmodes. To screen the validity of the DFT and LDC results they are
confronted with data from X-ray diffraction measurements. The effect of
the strong phonon renormalization in ScV2Al20 on thermodynamic
observables is computed on grounds of the LDC derived inelastic
response. To set the data in a general context of AV(2)Al(20) compounds
and their physical properties we report in addition computer and
experimental results of the binary V2Al20 compound.
