Elastic anomalies and orientational glass transition in Na(CN) \(\)Cl \(\) mixed crystals. A Brillouin spectroscopic study
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High performance Brillouin spectroscopy (BS) has been used to study the elastic properties (static and dynamic) of the orientational glassy state of Na(CN)xCl1-x samples \(\)). The temperature behaviour of the elastic properties reveals a more complex scenario for the orientational glass transition than generally believed. The shear elastic constant shows the well-known c 44 (T) anomaly, indicated by a minimum, found in other cyanide mixed crystals. The results obtained for the hypersonic attenuation are in clear contradiction with the dynamic character of the c 44 (T)-minimum. The temperature behaviour of the longitudinal elastic constant c11 of very dilute \(\)Na(CN)xCl1-x samples shows two striking features: i) Similar to the anomalous temperature behaviour of c 44 (T), lowering the temperature c 11 (T) first decreases, goes through a minimum and then rises again. The minimum takes place at a temperature above the temperature, \(\), where c 44 (T) reaches its minimum value. ii) A kink-like anomaly of c 11 (T) is observed at lower temperatures. This second anomaly is similar to the classical one observed in canonical glasses at their glass transition temperature \(\).
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