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Electrical measurements were carried out on nanocrystals Yb2-xVxO3+x (YbVO) (where x=0.10, 0.15, 0.20, 0.30, and 0.40) obtained in the high-energy ball milling process, which crystallite size increased from 23.3 to 42.4 nm with increasing vanadium content. Electrical conductivity and thermoelectric power studies showed insulating properties in the extrinsic region (77-300 K) and n-type semiconductivity in the intrinsic one (350-400 K) with an activation energy of 1.3 eV. Broadband dielectric spectroscopy studies showed a low relative dielectric permittivity (εr<16) and loss tangent (tan(δ)<0.05) weakly dependent on temperature and frequency with the exception of a wide maximum between 200 and 300 K, suggesting an antiferroelectric-paraelectric phase transition. The most interesting result is the observation of a strong increase in the thermoelectric power factor with an increase in unit cell volume and nanograin size in a highly thermally activated Arrhenius region. [ABSTRACT FROM AUTHOR]

In this work, we examined the effect of the length of alkyl chain attached to the benzene ring on the self-assembling phenomena for a series of phenyl alcohol (PhA) derivatives, from phenylmethanol (benzyl alcohol) to 7-phenyl-1-heptanol, by means of X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR) spectroscopy, and Broadband Dielectric Spectroscopy (BDS) methods. XRD data in the reciprocal and real spaces showed a gradual increase in the local order with the elongation of the alkyl chain. However, the position and full width at half maximum of the main diffraction peak exhibited a non-systematic behavior. To better understand this fact, PhAs were subjected to FTIR spectroscopic studies. These investigations revealed that the association degree and the activation energy of dissociation increase as the alkyl chain length grows. On the other hand, BDS data showed a non-monotonic variation in the Kirkwood correlation factor with increasing length of the alkyl chain, indicating a competition between interactions of the non-polar and polar parts of the molecules in the studied PhAs. Finally, it was also found that the molar surface entropy for PhAs increases with the number of methylene groups, approaching values reported for alkanes, which indicates suppression of the surface order for PhAs with a long alkyl chain. This variability of the various parameters as a function of the length of the side chain shows that the interplay between soft interactions has a strong impact on the local structure and intra and intermolecular dynamics of the studied PhAs. [ABSTRACT FROM AUTHOR]

Three-dimensional organic-inorganic perovskites are rapidly evolving materials with diverse applications. This study focuses on their two representatives - acetamidinium manganese(II) formate (AceMn) and formamidinium manganese(II) formate (FMDMn) - subjected to varying temperature and pressure. We show that AceMn undergoes atypical pressure-induced structural transformations at room temperature, increasing the symmetry from ambient-pressure P2 1 /n phase II to the high-pressure Pbca phase III. In turn, FMDMn in its C2/c phase II displays temperature- and pressure-induced ordering of cage cations that proceeds without changing the phase symmetry or energy barriers. The FMD + cations do not order under constant volume across the pressure-temperature plane, despite similar pressure and temperature evolution of the unit-cell parameters. Temperature and pressure affect the cage cations differently, which is particularly pronounced in their relaxation dynamics seen by dielectric spectroscopy. Their motion require a rearrangement of the metal-formate framework, resulting in the energy and volumetric barriers defined by temperature-independent activation energy and activation volume parameters. As this process is phonon-assisted, the relaxation time is strongly temperature-dependent. Consequently, relaxation times do not scale with unit-cell volume nor H-bond lengths in formates, offering the possibility of tuning their electronic properties by external stimuli (like temperature or pressure) even without any structural changes., (© 2024. The Author(s).)

Molecular dynamics and transport coefficients change significantly around the so-called Arrhenius crossover in glass-forming systems. In this article, we revisit the dynamic processes occurring in a glass-forming macrocyclic crown thiaether MeBzS 2 O above its glass transition, revealing two crossover temperatures: T B at 309 and T A at 333 K. We identify the second one as the Arrhenius crossover that is closely related to the normal-to-supercooled liquid transition in this compound. We show that the transformation occurring at this point goes far beyond molecular dynamics (where the temperature dependence of structural relaxation times changes its character from activation-like to super-Arrhenius), being reflected also in the internal structure and diffraction pattern. In this respect, we found a twofold local organization of the nearest-neighbor molecules via weak van der Waals forces, without the formation of any medium-range order or mesophases. The nearest surrounding of each molecule evolves structurally in time due to the ongoing fast conformational changes. We identify several conformers of MeBzS 2 O , demonstrating that its lowest-energy conformation is preferred mainly at lower temperatures, i.e., in the supercooled liquid state. Its increased prevalence modifies locally the short-range intermolecular order and promotes vitrification. Consequently, we indicate that the Arrhenius transition is fuelled rather by conformational changes in this glass-forming macrocyclic crown thiaether, which is a different scenario from the so-far existing concepts. Our studies combine broadband dielectric spectroscopy (BDS), X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, molecular dynamics (MD) simulations, and density functional theory (DFT) calculations.

This study examined the clustering behavior of monohydroxy alcohols, where hydrogen-bonded clusters of up to a hundred molecules on the nanoscale can form. By performing X-ray diffraction experiments at different temperatures and under high pressure, we investigated how these conditions affect the ability of alcohols to form clusters. The pioneering high-pressure experiment performed on liquid alcohols contributes to the emerging knowledge in this field. Implementation of molecular dynamics simulations yielded excellent agreement with the experimental results, enabling the analysis of theoretical models. Here we show that at the same global density achieved either by alteration of pressure or temperature, the local aggregation of molecules at the nanoscale may significantly differ. Surprisingly, high pressure not only promotes the formation of hydrogen-bonded clusters but also induces the serious reorganization of molecules. This research represents a milestone in understanding association under extreme thermodynamic conditions in other hydrogen bonding systems such as water.

Despite decades of studies, a clear understanding of near- T g phenomena remains challenging for glass-forming systems. This review delves into the intricate molecular dynamics of the small, heterocyclic thioether, 6-methyl-2,3-dihydro-1,4-benzodithiine (MeBzS 2 ), with a particular focus on its near- T g cold crystallization and relaxation mechanisms. Investigating isothermal crystallization kinetics at various temperatures reveals a significant interplay between its molecular dynamics and recrystallization from a supercooled liquid. We also identify two independent interconversion paths between energetically privileged conformers, characterized by strained transition states. We demonstrate that these spatial transformations induce substantial alterations in the dipole moment orientation and magnitude. Our investigation also extends to the complex salt PdCl 2 (MeBzS 2 ), where we observe the transient conformers directly, revealing a direct relationship between their abundance and the local or macroscopic electric field. The initially energetically privileged isomers in an undisturbed system become less favored in the presence of an external electric field or ions, resulting even in an unexpected inversion of states. Consequently, we confirm the intramolecular character of secondary relaxation in MeBzS 2 and its mechanism related to conformational changes within the heterocyclic ring. The research is based on the combination of broadband dielectric spectroscopy, X-ray diffraction, and quantum density functional theory calculations.

The behavior of hydrogen bonds under extreme pressure is still not well understood. Until now, the shift of the stretching vibration band of the X-H group (X = the donor atom) in infrared spectra has been attributed to the variation in the length of the covalent X-H bond. Herein, we combined infrared spectroscopy and X-ray diffraction experimental studies of two H-bonded liquid hexane derivatives, i.e., 2-ethyl-1-hexanol and 2-ethyl-1-hexylamine, in diamond anvil cells at pressures up to the GPa level, with molecular dynamics simulations covering similar thermodynamic conditions. Our findings revealed that the observed changes in the X-H stretching vibration bands under compression are not primarily due to H-bond shortening resulting from increased density but mainly due to cooperative enhancement of H-bonds caused by intensified molecular clustering. This sheds new light on the nature of H-bond interactions and the structure of liquid molecular systems under compression.

This article presents the synthesis and molecular dynamics investigation of three novel cyclic thioethers: 2,3-(4'-methylbenzo)-1,4,7,10-tetrathiacyclododeca-2-ene (compound 1 ), 2,3,14,15-bis(4',4″(5″)-methylbenzo)-1,4,7,10,13,16,19,22,25-octathiacyclotetracosa-2,14-diene (compound 2 ), and 2,3,8,9-bis(4',4″(5″)-methylbenzo)-1,4,7,10-tetrathiacyclododeca-2,8-diene (compound 3 ). The compounds exhibit relatively high glass transition temperatures ( T g ), which range between 254 and 283 K. This characteristic positions them within the so-far limited category of crown-like glass-formers. We demonstrate that cyclic thioethers may span both the realms of ordinary and sizeable molecular glass-formers, each featuring distinct physical properties. Furthermore, we show that the T g follows a sublinear power law as a function of the molar mass within this class of compounds. We also reveal multiple dielectric relaxation processes of the novel cyclic thioethers. Above the T g , their dielectric loss spectra are dominated by a structural relaxation, which originates from the cooperative reorientation of entire molecules and exhibits an excess wing on its high-frequency slope. This feature has been attributed to the Johari-Goldstein (JG) process. Each investigated compound exhibits also at least one intramolecular secondary non-JG relaxation stemming from conformational changes. Their activation energies range from approximately 19 kJ/mol to roughly 40 kJ/mol. Finally, we analyze the high-pressure molecular dynamics of compound 1 , revealing a pressure-induced increase in its T g with a dT g / dp coefficient equal to 197 ± 8 K/GPa.

A series of four alcohols, n -propanol and its halogen (Cl, Br, and I) derivatives, were selected to study the effects of variation in polarity and halogen-driven interactions on the hydrogen bonding pattern and supramolecular structure by means of experimental and theoretical methods. It was demonstrated on both grounds that the average strength of H-bonds remains the same but dissociation enthalpy, the size of molecular nanoassemblies, as well as long-range correlations between dipoles vary with the molecular weight of halogen atom. Further molecular dynamics simulations indicated that it is connected to the variation in the molecular order introduced by specific halogen-based hydrogen bonds and halogen-halogen interactions. Our results also provided important experimental evidence supporting the assumption of the transient chain model on the molecular origin of the structural process in self-assembling alcohols.

Molecular dynamics simulations supported by x-ray-diffraction experimental data were utilized to demonstrate how replacing the cyclic ring with the phenyl one in molecules of alcohols significantly differentiates their nanostructure by reducing the number of H-bonded clusters. Besides, molecules in the phenyl alcohols associate themselves in clusters via phenyl ring organization which likely is the result of OH⋯π and π⋯π interactions. Thus, at room temperature, the supramolecular structure of phenyl alcohols is more heterogeneous and governed by the formation of various clusters arising due to three types of interactions, while in cyclic alcohols, the H bonding controls the association of molecules. We believe that our methodology could be applied to better understand the fundamental process of association via H bonding and the competitive aggregation caused by phenyl rings.

The nature of H-bonding interactions is still far from being understood despite intense experimental and theoretical studies on this subject carried out by the leading research centers. In this paper, by a combination of unique high-pressure infrared, dielectric and volumetric data, the intramolecular dynamics of hydroxyl moieties (which provides direct information about H-bonds) was studied along various isolines, i.e., isotherms, isobars, isochrones, and isochores, in a simple monohydroxy alcohol (2-ethyl-1-hexanol). This allowed us to discover that the temperature controls the intermolecular hydrogen bonds, which then affect the intramolecular dynamics of OH units. Although the role of density fluctuations gets stronger as temperature rises. We also demonstrated a clear connection between the intra- and intermolecular dynamics of the associating liquid at high pressure. The data reported herein open a new perspective to explore this important aspect of the glass transition phenomenon and understand H-bonding interactions at varying thermodynamic conditions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)

The tendency to crystallize was studied in the selected monohydroxy alcohols: 1-chloro-2-methyl-2-propanol, 1-chloro-2-propanol, 3-chloro-1-propanol, and 8-chloro-1-octanol. Performed calorimetric measurements have proved that the differences in structures of tested alcohols influence the tendency to crystallization. At a sufficiently fast heating rate, no crystallization was observed in the case of 1-chloro-2-propanol and 3-chloro-1-propanol, contrary to other two alcohols. The obtained results suggest that elongation of the alkyl chain or adding a methyl group to the hydrocarbon backbone increases the susceptibility to crystallization., (© 2022. The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.)

Wide-angle X-ray scattering patterns were recorded for a series of aliphatic butanol isomers ( n -, iso -, sec -, tert -butanol) and their phenyl derivatives (4-phenyl-1-butanol, 2-methyl-3-phenyl-1-propanol, 4-phenyl-2-butanol, and 2-methyl-1-phenyl-2-propanol, respectively) to determine their atomic-scale structure with particular emphasis on the formation of supramolecular clusters. In addition, molecular dynamics simulations were carried out and yielded good agreement with experimental data. The combination of experimental and theoretical results allowed clarification of the origin of the pre-peak appearing at low scattering angles for the aliphatic butanols and its absence for their phenyl counterparts. It was demonstrated that the location of the hydroxyl group in the molecule of alkyl butanol, its geometry, and rigidity determine the morphology of the supramolecular clusters, while the addition of the aromatic moiety causes more disordered organization of molecules. The phenyl group significantly decreases the number of hydrogen bonds and size of the supramolecular clusters formed via the O-H···O scheme. The lower association ability of phenyl alcohols via H-bonds is additionally attenuated by the appearance of competing π-π configurations evidenced by the structural models.

Glass-forming ability is one of the most desired properties of organic compounds dedicated to optoelectronic applications. Therefore, finding general structure-property relationships and other rules governing vitrification and related near-glass-transition phenomena is a burning issue for numerous compound families, such as Schiff bases. Hence, we employ differential scanning calorimetry, broadband dielectric spectroscopy, X-ray diffraction and quantum density functional theory calculations to investigate near-glass-transition phenomena, as well as ambient- and high-pressure molecular dynamics for two structurally related Schiff bases belonging to the family of glycine imino esters. Firstly, the surprising great stability of the supercooled liquid phase is shown for these compounds, also under high-pressure conditions. Secondly, atypical self-organization via bifurcated hydrogen bonds into lasting centrosymmetric dimers is proven. Finally, by comparing the obtained results with the previous report, some general rules that govern ambient- and high-pressure molecular dynamics and near-glass transition phenomena are derived for the family of glycine imino esters. Particularly, we derive a mathematical formula to predict and tune their glass transition temperature ( T g ) and its pressure coefficient (d T g /d p ). We also show that, surprisingly, despite the presence of intra- and intermolecular hydrogen bonds, van der Waals and dipole-dipole interactions are the main forces governing molecular dynamics and dielectric properties of glycine imino esters.