Nuclear magnetic resonance contribution to the understanding of the structure, the dynamics and the phase transitions of aperiodic crystals

Christophe Odin (1) , Bertrand Toudic (1) , An-Pang Tsai (2)

1 IPR - Institut de Physique de Rennes
2 Tohoku University [Sendai]

Nuclear magnetic resonance is a local technique since it mostly probes a self-correlation function. Nevertheless, it appears to be one of the most sensitive technique to probe collective critical phenomena around phase transitions and dynamics and structural order within incommensurate phases. A major contribution to this field was done by Prof. Robert Blinc and his team. These results took long time to be understood and accepted by the strong neutron scattering community. The fundamental concept introduced by Blinc et al. was that a local property is the result of a weighted sum of all the critical and non critical fluctuations, as described in terms of normal modes within the Brillouin zone of the reciprocal space. They demonstrated that for a second order phase transition, the spin lattice relaxation rate T1-1 diverges on approaching the transition temperature Tc (within the fast motion limit), even if it is a local property! In the case of a phase transition towards an incommensurate phase, due to this property, T1-1 N.M.R. and N.Q.R. measurements were the most efficient way to observe the famous original dynamical fluctuations there, the phason. Even more striking, these techniques were also the most efficient to find incommensurate phases since Blinc et al. showed that the shape of the resonance lines was a direct measure of the density of the atoms displaced along the incommensurate static modulation. A short review of these historical results will be given in the first part of the talk. The application of N.M.R. for the study of the structure and the dynamics of quasicrystals appeared to be much more difficult, for many reasons. In the second part of the talk, we will present a recent Zn and Sc N.M.R. study of the icosahedral ZnAgSc Tsai-type quasi-crystal and its 1:1 Zn6Sc approximant. Results concerning the structural organization and the dynamics of these atoms and on the structural instabilities will be discussed.

Mots clés: Quasicrystal; Quasicrystal approximant; Solid state NMR spectroscopy

Domaines: Autre [cond-mat.other]; Science des matériaux [cond-mat.mtrl-sci]

Christophe Odin, Bertrand Toudic, An-Pang Tsai. Nuclear magnetic resonance contribution to the understanding of the structure, the dynamics and the phase transitions of aperiodic crystals. 14th International Conference on Quasicrystals (ICQ14), May 2019, Kranjska Gora, Slovenia. ⟨hal-02408439⟩