Structural correlations in disordered matter: An experimental separation of orientational and positional contributions

Abstract

The structures of the liquid, glass ͑i.e., amorphous͒, rotator-phase ͑RP͒ crystal, orientational glass ͑OG͒, and the stable ͑monoclinic͒ crystal phases of ethanol are investigated by means of neutron and x-ray diffraction. The RP crystal and OG phases show an intermediate kind of disorder between that of the fully disordered glass and liquid phases and that of the stable crystal. The Bragg pattern of the RP and OG crystals provides information about the time-averaged distribution of single-molecule orientations, and a contribution comprising intermolecular correlations is isolated from the diffuse intensity. Finally, the RP→OG rotational freezing transition is analyzed in detail and shown to constitute a physical realization of the glass transition found in hard-needle models. ͓S0163-1829͑97͒05441-6͔

On the phase diagram of polymorphic ethanol: Thermodynamic and structural studies

“…Nevertheless, there seems to be some confusion in the literature concerning this point. In our previous low-temperature experiments [8,10], we observed and reported a critical cooling rate around À20 K/min, in the light-scattering experiments by Surovtsev et al [20] a quench of À10 K/min was enough to avoid crystallization, and in other experiments À6 K/min has been reported [6,7,21]. Of course, some discrepancies from one experimental set-up to another, including different thermal arrangements and thermometry for these rapid variations of temperature, could be expected, but the found discrepancies seem excessive.…”

Experimental assessment of the extent of orientational short-range order in liquids

“…Here we will follow steps similar to those employed in the pioneering work of Dolling et al on the plastic phases of SF 6 and CBr 4 . The static structure factor S͑Q͒, for a disordered polycrystal, can be represented by a sum of Bragg and diffuse components 24,25 …”

Structural and phase transitions in nanocluster ethanol samples at low temperatures

“…The stable orientational ordered crystal of monoclinic phase was produced via very slow growth of the sample at a temperature close to the melting point. There are a lot of measurements of different type with ethanol samples: x-ray diffraction [1][2][3][4], Raman spectroscopy [2], specific heat [3,[5][6][7][8][9][10], complex dielectric susceptibility [11], neutron scattering [3,5,12], thermal conductivity [13], light and infrared reflection [14,15]. In fact, the most evident experimental result is the existence of the stable monoclinic crystalline phase at the temperature close to melting [1] (fully ordered structure) and the amorphous state (glass like state, supercooled liquid and so on) in a completely disordered phase, which was formed by quenching faster than 30 K/min [16].…”