1. 7. OTHER FAMILIES OF GLASSES AND DISORDERED CRYSTALS: PLASTIC CRYSTALS AND ORIENTATIONALLY DISORDERED CRYSTALS Comparative study of translational and orientational disorder in a model, polymorphic material: ETHANOL

2. ORIENTATIONALLY DISORDERED CRYSTALS (“ORIENTATIONAL GLASSES”) “Mixed crystals” “Glassy crystals” <

3. MIXED CRYSTALS (orientational glasses) KCl:OH KCl:Li K 1-x Li x TaO 3 (NaCN) 1-x (KCN) x..... U.T. Höchli, K. Knorr and A. Loidl, Advances in Physics 39, 405 (1990).

4. De Yoreo, Knaak, Meissner and Pohl (1986)

5. ”Glassy crystals” (another special kind of orientationally-disordered crystals/orientational glasses) they can be obtained by supercooling a high-symmetry crystalline phase where molecules are rotating (PLASTIC CRYSTAL or ROTATOR PHASE) cyclohexanol, cycloheptanol... cyclohexene, cicloheptane... SnCl 2 ·2H 2 O cyanoadamantane ethanol H. Suga and S. Seki, J. Non-Cryst. Solids 16, 171 (1974). stoichiometrically homogeneous materials a 1st order transition to a lower symmetry (more stable) crystalline state usually should be by-passed through supercooling the PC they exhibit  C p (T g ) ! they also exhibit “universal glassy properties” at low temperatures

6. Liquid / Glass Liquid crystal Orientationally- Disordered Crystal “orientational glass” Crystal

7. ETHANOL (CH 3 CH 2 OH)

8. W. Kauzmann, Chem. Rev. 43, 219 (1948) KAUZMANN PARADOX

9. O. Haida, H. Suga, and S. Seki, J. Chem. Thermodynamics 9, 1133 (1977) glass “glassy crystal” (orientational glass) crystal ETHANOL

11. A. Srinivasan et al., Phys. Rev. B53, 8172 (1996) X-ray diffraction P.G. Jönsson, Acta Cryst. B32, 232 (1976) monoclinic crystal: Pc, Z = 4 T = 87 K : a=5.377 b=6.882 c=8.255 Å  =102.2º V=298.6 Å 3

12. W. Kauzmann, Chem. Rev. 43, 219 (1948)

13. Thermal and vibrational properties at low temperatures / low frequencies

14. Specific heat Thermal conductivity

15. U. Buchenau et al., Phys.Rev. B34, 5665 (1986)

16. M.A.R. et al., Phys. Rev. Lett. 78, 82 (1997) ETHANOL

17. M.A.R. et al., Phys. Rev. Lett. 78, 82 (1997) Vibrational density of states from inelastic neutron scattering

19. SL = Supercooled Liquid OG = Orientational Glass RP = Rotator Phase C. Talón et al., Phys. Rev. B 58, 745 (1998)

20. C. Talón et al., Phys. Rev. B 66, 012201 (2002)

22. M.A.R. et al., J. Phys.: Condens. Matter 15, S1007 (2003)

24. A. Krivchikov et al., Phys. Rev. B 74, 060201 (R) (2006). crystal ODC glass Thermal conductivity

25. M.A.R. et al., J. Non-Cryst. Solids 352, 4769 (2006) Polymorphism of ethanol: how many crystalline phases?

26. 4 different varieties ( , , ,  ) of monoclinic crystal ! M.A.R. et al., J. Non-Cryst. Solids 352, 4769 (2006) B. Kabtoul et al., Philos. Mag. 88, 4197 (2008)

27.     X-ray diffraction M.A.R. et al., J. Non-Cryst. Solids 352, 4769 (2006)

28. SUMMARY on ethanol “critical” aspect ratio of the molecule + OH bonding  competition between crystallization and vitrification  very rich POLYMORPHISM! :  SCL  (amorphous) Glass  PC  (bcc) Orientationally-Disordered Crystal … with full glassy properties both at T g and at low temperatures !!!  4 different (monoclinic) fully-ordered crystals  Excellent benchmark to discriminate the roles played by translational, rotational and orientational disorder

29. CONCLUSIONS Very similar glass transitions (T g and  C p ) observed in ethanol for glass--SCL and ODC--plastic crystal transitions. Very similar “glassy features” at low temperatures observed for the conventional (amorphous) glass and for the OG/ODC (= orientationally- disordered crystal) : * two-level systems * boson peak The GLASS TRANSITION event (the freezing of an ergodic state into a non-ergodic one) is more general than the kinetic arrest of a SCL into a non-crystalline solid. The low-temperature universal properties of glasses are NOT related to the lack of long-range crystalline order (topological disorder), but rather to a softening of the rigid vibrational spectrum of a crystalline lattice. * Predominance of transverse / orientational degrees of freedom in the glass state !

30. FIN GLASSES YES, THANKS !