Influence of the OH group position in the molecule on solid state polymorphism was found. Dynamics in solid phases of two dimethyl butanols were studied by inelastic incoherent neutron scattering. In glass of plastic crystal the boson peak was detected.

The Quasi-elastic Neutron scattering (QENS) spectra of polycrystalline hexamethylbenzene (HMB) were measured for temperatures from 10 K to room temperature (phase III and phase II) for momentum transfer 1.9 Å−1. The Inelastic Neutron scattering (INS) and QENS spectra for momentum transfer 0.5–2.9 Å−1 were measured at T=20, 100 and 130 K for energy transfer up to 200 meV. The low-resolution diffraction patterns, used as the phase indicator, were also obtained. In the phase III (below 117 K), we see practically no quasi-elastic broadening. In phase II, the broadening changes with the temperature are in good agreement with the Arrhenius law. The estimated activation barrier to reorientation is 6 kJ/mol. The fitted mean time between instantaneous 120° jumps of CH3 groups changes from 10−11 s at T=130K to 2×10−13 s at room temperature. On the basis of EISF versus momentum transfer dependency it is hardly possible to decide what is the geometry of the reorientation. Both reorientation of the CH3 groups around the three-fold symmetry axis and reorientation of the whole molecule around the six-fold symmetry axis of the benzene ring could describe our results, the former being more probable. The measured INS spectra are compared with the quantum chemical ab initio calculations performed for an isolated HMB molecule.

The results of inelastic incoherent neutron-scattering measurements of solid phases of isopentyl cyanobiphenyl (5*CB), isooctyloxy cyanobiphenyl (8*OCB), cyclooctanol and glycerol are presented. Low-energy excitations in glassy phases were observed both as a boson peak in direct geometry measurements and as an excess density of states in inverted geometry experiments. The mechanism of the phenomenon is suggested.

As a part of a project for glass-formers having various values of fragility, molecular dynamics of a glass-forming material 3,3-dimethyl-1-butanol has been presented on the basis of the dielectric relaxation studies. Three characteristic relaxations were observed. To provide thermodynamic aspects of this material, adiabatic heat-capacity calorimetry has also been performed in the (13 to 302) K temperature range. The stable crystal of this material melts at Tm=235.7 K. When the material is rapidly cooled at a rate greater than 5 Kmin−1, the liquid is easily super-cooled and eventually transformed to a glassy state. Standard thermodynamic quantities are evaluated for both the stable crystalline and the glassy states. Structural relaxation processes are discussed in relation to the phase behaviour revealed by the calorimetry.

The low-energy excitations in crystalline and glassy triphenyl phosphite were studied by inelastic incoherent neutron scattering with two different instruments. The results – the incoherent dynamic structure factor S(2θ,ω) and the density of states G(ω) – were obtained using direct and inverted geometry time-of-flight spectrometers, respectively. The probable origin of the excess density of states in the glass (boson peak) is discussed.

Abstract DSC measurements performed at 95 -290 K have shown that [Mn(H 2 O) 6 ](CIO 4) 2 possesses, besides a high-temperature phase, existing above 323 K, four low-temperature solid phases. The inelastic incoherent neutron scattering (IINS) spectra and neutron powder diffraction (NPD) pat-terns registered at 20 -290 K have supported the DSC results and provided evidence that the investigated substance possesses even more than five solid phases. The IINS spectra have shown that in the room-temperature phase, water molecules perform fast stochastic reorientation at the picosecond scale. The orientational disorder characteristic for the room-temperature phase can be easily overcooled and frozen. Even by relatively slow cooling at ca. 40 K/hour a metastable, orientational (protonic) glass phase is formed below ca. 160 K. Below ca. 100 K, a structural phase transition was observed by the NPD, however the IINS spectra indicate existence of the pure ordered low-temperature phase only after annealing the sample for a few hours at 100 K. On heating, a structural phase transition takes place at ca. 120 K, and at ca. 225 K water molecules begin fast reorientation.

The paper presents adiabatic calorimetry investigations of slow relaxation processes (enthalpy relaxation) in isopentylcyanobiphenyl (right handed (s) 4–(2-methylbutyl) 4′–cyanobiphenyl) in a vicinity of the glass transition. The preliminary neutron scattering results concerning the fast relaxation processes and low-energy excitation detected as “boson peak” are also presented. The general behaviour observed in the experiments seems to correspond to the typical picture for the molecular glasses.

Basing on the results of polarizing microscopy, differential scanning calorimetry (DSC) and infrared spectroscopy (in the range 70 -700 cm(-1)) in the temperature range from 100 K to 320 K the phase diagram of right handed (S) 4-(2-methylbutyl)-4'-cyanobiphenyl was established. On cooling an isotropic phase transforms at 246 Ii into a cholesteric phase which can be easily supercooled to a glass at ca, 210 Ii, On heating this sequence of transitions reverses. Further heating of the sample leads to crystallization of supercooled isotropic phase at about 250 ii. The crystal phase melts at 276 Ii. It was clarified that process of nucleation starts on cooling below 240 Ii, The shape of the far infrared bands (lattice vibration range) suggests that the crystal phase is highly disordered.

We present measurements made by DSC and polarizing microscopy techniques used for identification of phases and phase transitions in right handed (S) 4-(2-methylbutyl) 4/-cyanobiphenyl. The observed phase transitions are illustrated by chosen dielectric relaxation data. Analysis of the results has given detailed information concerning the phase diagram. This substance forms a monotropic system of phases, namely the stable phase sequence: crystal 276 K isotropic phase. metastable phases: glass 213 K cholesteric 246 K supercooled isotropic liquid. This modifies our understanding of the phase behaviour reported previously by Gray and McDonnell and by us.

Rotation of (CH3NH3)+ cations in crystalline (CH3NH3)5Bi2Cl11, (CD3NH3)5Bi2Cl11 and (CH3NH3)5Bi2Br11 was studied by QNS. The model of instantaneous 120° jumps of whole cations around their C–N axes was fitted to the experimental data. The parameters describing reorientation obtained for two types of cations agree well with the results of NMR experiments.

The results of DSC measurements in the temperature range 140–370 K on nine crystalline compounds of the type [M(H 2 O) 6 ](ClO 4 ) 2 , where M=Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd and Hg, are discussed. Anomalies detected in the DSC curves are related to the existence of solid-solid phase transitions and/or to the melting points of these compounds. In consequence of two different hypothetical structural modifications of [Fe(H 2 O) 6 ](ClO 4 ) 2 , two DSC curves are obtained. For the compounds with M=Fe, Cd and Hg, new phase transitions have been discovered. The transition temperatures of the other phase transitions are in good agreement with literature data obtained by adiabatic calorimetry. For the compounds with M=Mg, Ni and Cd, DTA measurements were also carried out and the melting points of theses compounds were established.

DSC measurements were carried out for four crystalline compounds of the type: [Me(H2O)(6)](ClO4)2, where Me=Zn, Cd, Hg and Cu, in the temperature range 140-370 K. For [Zn(H2O)(6)](ClO4)(2) and [Cd(H2O)(6)](ClO4)(2) three anomalies (at 348 K, 290 K, 226 K and at 363 K, 271 K, 239 K, respectively) on the DSC curves were detected and interpreted as connected with the existence of the solid-solid phase transitions in these compounds. The phase transition at 363 K has not yet been described in the literature. The rest transition temperatures are in a good agreement with results obtained previously by other authors using adiabatic calorimetry method. For [Cd(H2O)(6)](ClO4)2 the comparison with the DTA results was made. For [Hg(H2O)(6)](ClO4)(2) three anomalies (at 340 K, 306 K and 208 K) were detected. The crystals at 306 K partially and at 340 K fully melt. For [Cu(H2O)(6)](ClO4)(2) only one anomaly (at 353 K) connected with the melting of the substance was detected. The phase transitions for the two last compounds have not yet been described in the literature.

This paper presents a search for tunnel transitions of NH3 groups in Co(NH3)6I2 above the phase transition at which classical rotation, i.e. hopping over barrier to rotation, starts. It was possible to detect two broad satellites of the elastic line in the neutron scattering pattern, which provided the tunnel transition energy. This energy decreases when approaching the phase transition on cooling, thus showing a soft-mode type of behaviour.

DTA, DSC, NMR and dielectric studies have been performed for pyridinium chlorochromate over a wide temperature range. A sequence of four solid-solid phase transitions was discovered. The in-plane complex reorientation of the cation is described by a three-well potential model with two correlation times. At higher temperatures one observes simultaneous cation tumbling and diffusion. Thus existence of a new ionic plastic phase is revealed. The domain structure observed suggests ferroelastic properties of the compound.

Ethoxybenzylidene-propylaniline (EBPA) was studied using polarizing microscopy and differential scanning calorimetry (DSC) in the temperarure range 100 K - 380 K with various heating and cooling rates (from 0.1 deg/min to 200 deg//min). The metastable solid crystal phase was discovered. It is formed rapidly on cooling of nematic phase and transforms spontaneously to stable crystal phase. But can be also frozen or separately melted. The rich polymorphism of isomeric to EBPA MBBA compound is also discussed proving the importance of terminal groups in the formation of different polymorphs.

Incoherent quasielastic neutron scattering spectra were measured for nematic para-azoxyanisole (PAA) and para-azoxyphenetole (PAP) with the energy resolution of ca. 30 mu eV, at Dubna IBR-2 reactor. Data processing contained a careful background subtraction and the multiple scattering correction. The corrected spectra were subjected to a reorientational model fitting procedure. For PAA, a model of two convoluted reorientations - that of benzene rings coupled with the terminals and that of the whole molecule around the long molecular axis - gave a fairly good description of the quasielastic neutron scattering spectrum. For PAP, introducing a third motion - interconformational jumps in the ethoxy terminals - in addition to motions suggested for PAA, gave a good agreement with the measured quasielastic neutron scattering spectrum.

(CH3NH3)(+)-cation rotation in crystalline (CH3NH3)(5)Bi2Cl11 was studied by the QNS. The following (no doubt simplified) models were considered:1. All cations are equivalent and rotate as a whole around C-N axes2. Majority of cations behave as in point (1) and the remaining ones do not move (for the neutron observation window).3. All CH3 groups rotate, whereas all NH3 groups do not move.The QNS measurements exclude the possibilities (1) and (3). A transition at ca. 160-170 K was confirmed in the measurements, as connected with an increase of the quasielastic component intensity observed via a dip of the EISF. (C) 1998 Elsevier Science B.V. All rights reserved.

DSC measurements were carried out for three compounds of the type: [Me(H2O)(6)](ClO4)(2), where Me = Mn, Fe and Co, in the temperature range of 130-350 K. For [Mn(H2O)(6)](ClO4)(2) and [Fe(H2O)(6)] (ClO4)(2) two anomalies (at 323 K, 247 K and at 338 K, 247 K, respectively) on the DSC curves were detected and interpreted as connected with the existence of phase transitions in these compounds. These phase transitions have not yet been described in the literature. For [Co(H2O)(6)](ClO4)(2) three anomalies (at 348 K, 243 K and 153 K) were detected. These transition temperatures are in a good agreement with the results obtained previously by other authors using various methods. The comparison with the literature data for other isomorphic compounds of the type: [Me(H2O)(6)](ClO4)(2) where Me = Mg, Ni and Zn, have also beeen made.

Specific heat measurements by adiabatic calorimetry are presented in the range 80-300 K. A discussion of the phase transitions between different solid modifications of cyclooctanol is given. Special attention is paid to the transition between the plastic phases. An attempt to obtain a low-temperature ordered phase under ambient pressure failed. Evidence for two glassy states is presented.