Critical pretransitional dynamics within crystallographic superspaces
The goal of this proposal is to study the critical dynamics around a phase transition involving high dimensional spaces in an aperiodic material. Recently, we reported a quite original phase transition in the composite crystal, n-nonadecane/urea, revealing an incresase of the dimension of the crystallographic superspace at Tc1=149K, from 4 (phase I : hexagonal superspace group P6122(00gamma)) to 5 (phase II: orthorhombic superspace group C2221(00gamma) (10delta)). Afterwards, a very high resolution study of the static aspect of the critical phenomena revealed quite anomalous long correlation lengths along the incommensurate direction. This could be tentitatively interpreted in terms of a soft phason at a critical wave vector qs characterized by five independent vectors. Only inelastic measurements can prove this assessment and only a coupled four circles, triple axis spectrometer permits this study at such a complex qs location.
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TOUDIC Bertrand; Bourges; ECOLIVET Claude; GUERIN Laurent; LEMEE Marie Helene; MARIETTE Celine; OLLIVIER Jacques; OULADDIAF Bachir; RABILLER Philippe and VEREZHAK Mariana. (2013). Critical pretransitional dynamics within crystallographic superspaces. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.7-02-143
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