Studied Temperature Range Research Articles

Electrocaloric Effect in (1−x)(0.8Na0.5Bi0.5TiO3-0.2BaTiO3)−xCaTiO3 Solid Solutions at High Electric Fields

Recently, promising results were obtained in studies of the electrocaloric effect in thin films. Therefore, research into this effect at high applied electric field values in bulk ferroelectrics is an important task for those scoping out materials that could be appropriate for cooling devices based on the electrocaloric effect. The present study addresses electrocaloric effect in (1−x)(0.8Na1/2Bi1/2TiO3-0.2BaTiO3)−xCaTiO3 solid solutions by the direct method in electric fields ranging from 0 up to 100 kV/cm and at temperatures of up to 150 °C. The choice of 0.8Na1/2Bi1/2TiO3-0.2BaTiO3 as the starting composition is motivated by high spontaneous polarization within the studied range of electric fields, while CaTiO3 is added to reduce depolarization temperature at, and below, room temperature. In the studied temperature range, the maximal value of electrocaloric effect with temperature change of ΔT = 1.0 °C was found in the composition with x = 0.050 at 100 °C, having significant contribution from the entropy jump at the first-order phase transition induced by an electric field. At increasing CaTiO3 concentration, the attainable ΔT decreases. Measurements of polarization current, which were taken simultaneously with ΔT measurements, allowed us to study differences between ΔT obtained by the direct and the indirect methods.

Modulation in Electric Conduction of PVK and Ferrocene-Doped PVK Thin Films

In this article, the dielectric properties of poly (9-vinylcarbazole) (PVK) and ferrocene-doped PVK thin films are studied. The thin films were grown by the isothermal solution casting technique. Dielectric properties of grown films were studied as function of ferrocene concentration, frequency, and temperature. The relative permittivity (ε′) is increased with increasing ferrocene percentage (~1%) due to the free charge carriers. The relative permittivity decreases for higher ferrocene percentage (~2%). However, the relative permittivity of PVK and ferrocene-doped PVK samples remains almost constant for studied temperature range (313–413 K). The frequency dependence of tan δ for all samples is studied. The frequency dependence of dielectric parameter exhibits frequency dispersion behavior, which suggests all types of polarization present in the lower frequency range. The loss tangent (tanδ) values are larger at higher temperatures in the low frequency region. However, the tan δ values at different temperatures are almost similar in the high frequency region. It is observed that the relative permittivity is maximum, dielectric loss is minimum, and AC conductivity is minimum for 1% ferrocene doped PVK as compared to pure PVK and 2% ferrocene doped PVK samples.

Magnetocaloric effect in amorphous-crystalline microcircuits PrDyFeCoB

In amorphous-crystalline PrDyFeCoB microconductors obtained by ultrafast melt cooling, a negative magnetocaloric effect was detected at 200-250 K (with heat release when the magnetic field is turned on), as well as a positive magnetocaloric effect in the temperature range of 300-340 K (with heat absorption when the magnetic field is turned on). It is established that there are no phase transitions of the first kind in the studied temperature range, which indicates that both of the detected effects are associated with a change in the magnetic part of the entropy. The transition at 200-250 K is due to the presence of metamagnetic states induced by a magnetic field in the spin-glass state of the amorphous part of the PrDyFeCoB alloy, and with their transition to the ferrimagnetic state. The transition at 300-340 K is spin-reorientation, and it occurs in crystalline inclusions identified in the amorphous matrix. Keywords: spin-reorientation transition, spin glass, magnetocaloric effect, entropy. Keywords: spin-reorientation transition, spin glass, magnetocaloric effect, entropy.

Kinetics and thermodynamics of enzymatic decarboxylation of α,β-unsaturated acid: a theoretical study.

Enzymatic decarboxylation of α,β-unsaturated acid through ferulic acid decarboxylase (FDC1) has been of interest because this reaction has been anticipated to be a promising, environmentally friendly industrial process for producing styrene and its derivatives from natural resources. Because the local dielectric constant at the active site is not exactly known, enzymatic decarboxylation to generate β-methylstyrene (β-MeSt) was studied under two extreme conditions (ε = 1 and 78 in the gas phase and aqueous solution, respectively) using the B3LYP/DZP method and transition state theory (TST). The model molecular clusters consisted of an α-methylcinnamate (Cin) substrate, a prenylated flavin mononucleotide (PrFMN) cofactor and all relevant residues of FDC1. Analysis of the equilibrium structures showed that the FDC1 backbone does not play the most important role in the decarboxylation process. The potential energy profiles confirmed that the increase in the polarity of the solvent could lead to significant changes in the energy barriers, especially for the transition states that involve proton transfer. Analysis of the rate constants confirmed the low/no quantum mechanical tunneling effect in the studied temperature range and that inclusion of the fluctuation of the local dielectric environment in the mechanistic model was essential. Because the computed rate constants are not compatible with the time resolution of the stopped-flow spectrophotometric experiment, the direct route for generating β-MeSt after CO2 elimination (acid catalyst (2)) is unlikely to be utilized, thereby confirming that indirect cycloelimination in a low local dielectric environment is the rate determining step. The thermodynamic results showed that the elementary reactions that involve charge (proton) transfer are affected by solvent polarity, thereby leading to the conclusion that overall, the enzymatic decarboxylation of α,β-unsaturated acid is thermodynamically controlled at high ε. The entropy changes due to the generation of molecules in the active site appeared more pronounced than that due to only covalent bond breaking/formation or structural reorientation. This work examined in detail for the first time the scenarios in each elementary reaction and provided insight into the effect of the fluctuations in the local dielectric environment on the enzymatic decarboxylation of α,β-unsaturated acids. These results could be used as guidelines for further theoretical and experimental studies on the same and similar systems.

Effect of Fe substitution on the structural, microstructural and dielectric properties of sodium bismuth titanate

Lead free sodium bismuth titanate (NBT) is widely being studied as an emerging room temperature multiferroic and as a ferroelectric material with potential to replace toxic lead based ceramics. Various elements can be substituted in the A-site or B-site to improve its electrical and magnetic properties. In this work, pure and Fe substituted NBT having the chemical formula Na0.5Bi0.5Ti(1-x)FexO3 (x = 0.00, 0.02) were synthesized using sol gel auto ignition method to study the effect of Fe substitution on the properties of NBT. XRD analysis confirmed the rhombohedral symmetry of the synthesized samples and the crystallite size of the samples were calculated using Scherrer’s formula. The morphological property of the samples was studied from the SEM images. UV–Visible Spectroscopy method was employed to study the optical properties of the samples. The dielectric properties of the samples were measured as a function of frequency in the range 100 Hz to 1 MHz at room temperature and also as a function of temperature in the range of 298 K- 473 K using an Agilent HP4284 LCR meter. Usual dispersive behavior of dielectric constant was observed for both the samples at the studied temperature range. Study of frequency and temperature dependence of the AC conductivity suggested that the conduction process in the materials is thermally activated. Jonchers’ universal power law was used to fit the AC conductivity curves to describe the dynamics of charge carrier with suitable conduction mechanism.

Temperature Dependence of the Rheology of Soft Matter on a MHz-oscillating Solid-liquid Interface.

The temperature dependence of the resonant length, molecular weight, and rheology (shear viscosity and shear modulus) of chemisorbed soft matter on a solid-liquid interface oscillating at a megahertz frequency was studied using a quartz crystal microbalance. As a form of chemisorbed soft matter, self-assembled monolayers (SAMs) formed from six types of mercapto oligo(ethylene oxide) methyl ethers were used. A systematic analysis using the Voigt model showed that the variation in effective hydrated thickness (sensed mass), which is related to the resonant length, was classified into three types based on the molecular weight. As a result, a 2.2-nm change in the resonant length occurred in the studied temperature range from 10 to 35℃. Moreover, the variation in the effective hydrated thickness was dependent on the shear viscosity and shear modulus of the SAMs. A further investigation revealed that the relationships η 1∝M n 0.13 and μ 1∝M n 0.30 could be estimated regardless of the temperature, where η 1 and μ 1 are the shear viscosity and shear modulus of the SAM, and M n is the molecular weight of mercapto oligo(ethylene oxide) methyl ether. As a result, we revealed that the experimental results followed the polymer formula irrespective of temperature.

ВЛИЯНИЕ ХИМИЧЕСКОГО СОСТАВА НА ТВЕРДОРАСТВОРНОЕ И ДЕФОРМАЦИОННОЕ УПРОЧНЕНИЕ МОНОКРИСТАЛЛОВ ГЦК ВЫСОКОЭНТРОПИЙНЫХ СПЛАВОВ

A characteristic feature of high-entropy alloys is high strength at maintaining plasticity, wear and corrosion resistance, and fracture toughness at cryogenic temperatures. Currently, CoCrFeNiMn is the best-investigated high-entropy compound. However, its application is limited in the high-temperature region due to the low values of the deforming stress level at the plasticity breaking point at T>296 K. One of the common ways to improve the material durability is the addition of substitution atoms of larger atomic radius, and Al, Ti, and Mo are some of these atoms. The paper presents the analysis of the mechanical behavior of single crystals of CoCrFeNiMn and CoCrFeNiMо FCC high-entropy alloys (at. %) oriented along the [001] direction: the author studied the temperature dependence of critical shear stresses τcr(T) within the temperature range of T=77–973K, the type of dislocation structure, strain hardening coefficient θII, plasticity and fracture at Т=296 K under tension. The study shows that the alloying with Mo atoms 4 at. % of the CoCrFeNi system (at. %) causes the solid solution hardening, and critical shear stresses τcr increase within the entire studied temperature range. The onset of plastic deformation is associated with slip at all temperature tests. At T=296 K, the author identified a planar dislocation structure with flat dislocation pile-ups and dislocation networks in CoCrFeNiMo while in equiatomic CoCrFeNiMn, at such test temperature, a uniform distribution of dislocations was observed in several systems without flat pile-ups. Work hardening coefficient, plasticity, and the level of stresses before fracture turn out to be similar in [001]-crystals of CoCrFeNiMo and CoCrFeNiMn high-entropy alloys, which are determined by the development of slip deformation simultaneously in several systems. Crystals are destroyed viscously at 296 K at the same level of stress.

Determination of the Drying Kinetics Modeling and Activation Energy of Medium-Grain and Long-Grain Rough Rice under Isothermal Conditions

The available literature revealed a gap in reporting the rough rice drying kinetics parameters under isothermal conditions, particularly for Arkansas medium- and long-grain varieties. Therefore, medium-grain (RO170112 and Titan) and the long-grain (Diamond and Wells) rough rice varieties were dried under isothermal conditions. The drying process occurred under 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, and 100°C in a system emulating the thermogravimetric analyzer. Drying kinetics models were studied for four well-known models: Page, Newton, Logarithmic, and Henderson & Pabis. The drying kinetics constants were determined for the four studied models. The initial moisture content of rough rice was 28.2% db. Profound moisture reduction was observed during the first three hours of drying, followed by less moisture content reduction. The results showed that at the drying temperature of 100°C and after 6 hours of the drying process, the lowest moisture content reached 13.9% (db) for Titan rough rice. The drying rate of rough rice ranged between 7.41 and 2.01%/h during the first hour of drying under the studied temperature range of 40°C to 100°C. The drying rate was higher with the higher temperature levels during the first three hours. Among all the studied models, the Page, Newton, and Logarithmic models best fit 25%, 25%, and 50% of the twenty-eight studied cases. The challenge that arose from these results led to evolving a mathematical solution by joining the three models in one equation. The combined model showed the best fit for all the studied cases, with R2 ranging between 0.9999 and 0.9954 for the medium- and long-grain rice varieties. Increasing the drying temperature increased the effective moisture diffusivity values. The highest effective moisture diffusivity of 18.104 × 10-9 m2/s was obtained at the drying temperature of 100°C for medium-grain rice, Titan. The activation energy values ranged between 17.77 and 24.48 kJ/mol for the four rough rice varieties.

High-Pressure Phase Equilibria Measurements of the Carbon Dioxide + Cycloheptane Binary System

The phase behavior of the carbon dioxide + cycloheptane binary system for which no literature data are available has been examined at temperatures ranging from 292.6 to 372.8 K. Saturation pressures, ranging from 23.9 to 154.8 bar, were acquired by a synthetic and visual method. In concrete terms, an adjustable-volume high-pressure cell was utilized to measure bubble and dew point pressures by visual detection of phase transitions at constant overall composition. A total of 11 different mixtures with mole fractions of carbon dioxide ranging from 0.20 to 0.96 were prepared, and a total of 99 experimental points were reported. The experimental results obtained in this work reveal the absence of liquid–liquid immiscibility in the studied temperature range and make it possible to conclude that the vapor–liquid critical line of the binary system is continuous and uninterrupted between the two pure compounds. Experimental data were correlated with the Peng–Robinson equation of state and classical van der Waals mixing rules with temperature-dependent binary interaction parameters. They were also compared to the PPR78 model, an entirely predictive group contribution method in which the kij depends on temperature.

Investigation of low temperature oxidation behavior of MoNbTaW thin films

MoNbTaW is a promising refractory multi-principal element alloy (RMPEA) that has exhibited good high temperature phase stability in vacuum and exceptional high temperature mechanical properties—even surpassing those seen in Ni superalloys. To date, there have been no detailed studies regarding the environmental resistance of this alloy, which is a primary concern due to the constituent elements being readily oxidizable at elevated temperatures. Therefore, in the current work, in-air anneals of sputtered MoNbTaW films targeting the 200°C–400°C range were conducted to study the low temperature oxidation behavior. An amorphous oxidized layer, which was comprised of three compositionally distinct regions, was observed to form at all in-air annealing temperatures. Furthermore, via nanoindentation, the oxidized layer was determined to be significantly softer and more compliant than the underlying metal. Comparison to pure W samples under the same annealing conditions was also performed. From this, it was determined that MoNbTaW oxidized more quickly and exhibited different oxidation pathways than pure W in the studied temperature range. Through this work, the initial stages of oxidation and their impact on the mechanical properties in this alloy system can begin to be understood.

Electronic, thermoelectric, and optical studies of cubic Hf1-xTixO2: An attempt to enhance the key parameters

In this work, we explore the effect of Ti-doping on the structural, electronic, transport and optical properties of c-HfO2 using first principles calculations for their possible applications in thermoelectric (TE) and optoelectronic devices. Seebeck coefficient of Hf1-xTixO2 shows the p-type behaviour in the entire studied temperature range. It attains a maximum value of 320.311 μVK-1 at 300 ​K for x ​= ​0.03 owing to the new flat band region. Ti doping leads to a significant decrease in electronic thermal conductivity (ke) of c-HfO2, which results in high figure of merit (ZTe) ​∼ ​0.82 ​at 400 ​K for x ​= ​0.03 and at 1200 ​K for x ​= ​0.12, which is the highest value ever reported for c-HfO2. We also calculated various parameters such as dielectric constant and refractive index depicting the effect of Ti doping on optical properties of c-HfO2. The present study predicts the applicability of Hf1-xTixO2 in thermoelectric, optoelectronics.

Radicals and molecular products from the gas-phase pyrolysis of lignin model compounds: Coniferyl alcohol, theory and experiment

Coniferyl alcohol (CFA) is one of lignin’s main building blocks and a relevant model compound. Two aspects of CFA pyrolysis are studied in the current work to gain insight into the molecular mechanism of lignin thermolysis: (i) the nature of intermediate radicals generated from vacuum pyrolysis of CFA, and (ii) the product distribution from pyrolysis of CFA dispersed into the gas phase. Low temperature matrix isolation electron paramagnetic resonance (LTMI-EPR) spectroscopy is employed to investigate the intermediate radicals associated with gas phase low-pressure pyrolysis of CFA. An anisotropic EPR spectrum of radicals trapped at liquid nitrogen temperature was registered throughout the studied temperature range (400–700 °C) characterized by high g-value (≤ 2.0100), and broad EPR line-width (~13.5–13.0 G) prescribed to a mixture of O-centered radicals produced from cleavage of O−CH3 and O−H terminal bonds. Thermal annealing of frozen radicals suggested a major contribution of methylperoxyl (CH3O2) radicals produced by the liberated CH3 and trace amounts of oxygen. The pyrolysis of CFA, for the first time, was conducted in a dispersed, gas-phase conditions to minimize the heterogeneous secondary reactions mediated by particle surfaces typical for condensed-phase pyrolysis in conventional reactors. Several unique products including polyhydroxylated derivatives of mandelic acid and some carboxylic compounds were identified in addition to those normally produced during the conventional pyrolysis - coniferyl aldehyde, vanillin (and its oxidized form homovanilic acid), eugenol and its isomers. A comprehensive analysis of product formation mechanisms, particularly the pathways for generating abundant hydroxylated compounds is performed and the role of trace oxygen is studied at the wB97XD and M06-2X hybrid density functional theory levels.

Influence of Moisture and Temperature on the Thermal Properties of Jack Bean Seeds (Canavalia ensiformis)

The thermal properties (specific heat capacity, thermal conductivity, and thermal diffusivity) of jack bean seed (Canavalia ensiformis) were determined for usage in designing the equipment necessary for thermal processes. These thermal properties were determined at 5, 10, 15, 20, and 25 % moisture contents (wb) and temperatures at 30, 40, and 50oC using the KD2 Pro thermal analyzer. Results showed that the specific heat capacity ranged from 1.55 to 2.47 kJ/kgK, 1.26 to 1.84 kJ/kgK and 1.32 to 1.99 kJ/kgK; thermal conductivity 0.21 to 0.47 W/mK, 0.34 to 0.52 W/mK, and 0.26 to 0.60 W/mK and thermal diffusivity 0.25 to 0.41 x 10-7 m²/s, 0.32 to 0.57 x 10-7 m²/s, and 0.32 to 0.60 x 10-7 m²/s at 30, 40, and 50°C respectively for the moisture ranges studied. The temperature and moisture content effect were not significant (p>0.05) with specific heat and thermal diffusivity but significant (p<0.05) with thermal conductivity in third-order polynomial. A non-linear relationship was established between the three thermal properties and moisture content within the studied temperature range. The resulting regression models for the thermal properties gave a high coefficient of determinations (R2 ≥ 0.7995) which implies that they can be used to describe the relationships between temperature, moisture, and thermal properties of jack bean seeds.

Influence of Cu content on the phase composition and thermoelectric properties of deposited Cu-Se films

In this study, the p-type Cu-Se films with different Cu contents were prepared on SiO2/Si substrates by magnetron sputtering using targets with different atomic ratio ([Cu]/[Se]) of Cu to Se. The relation of Cu content and phase composition in Cu-Se films was systematically studied. The deposited films took place phase transformation from p-CuSe2 to p-CuSe2+γ-CuSe, to γ-CuSe, to γ-CuSe+β-Cu2-xSe, to β-Cu2-xSe, to α-Cu2Se+unknown, to α-Cu2Se+unknown+Cu phase with increasing [Cu]/[Se] in the deposited films from 0.49 to 5.74. At room temperature, the carrier concentration decreases in the order of the CuSe2, CuSe and β-Cu2-xSe phase; but the carrier mobility exhibits an opposite trend. In the studied temperature range, the Seebeck coefficient and the power factor decreases in the order of β-Cu2-xSe, CuSe2 and CuSe phase. The [Cu]/[Se] in deposited films with single β-Cu2-xSe phase exceeds 2.0 of stoichiometric lattice and Cu-rich β-Cu2-xSe phase films forms. The deposited Cu-rich β-Cu2-xSe phase film with [Cu]/[Se]=2.65 has an optimum Seebeck and resistivity value, reaching a high power factor of 2.88 mW·m−1·K−2 at RT and 5.91 mW·m−1·K−2 at 320°C. It is of the guidance meaning for the further study the thermoelectric properties of Cu-Se films in the future.

Solvent‐Dependent Spin‐Crossover Behavior in Semiconducting Co–Crystals of [Fe(1‐bpp)2]2+ Cations and TCNQδ− Anions (0<δ<1)

AbstractCo‐crystallization of the spin‐crossover (SCO) cationic complex, [Fe(1‐bpp)2]2+ (1‐bpp=2,6‐bis(pyrazol‐1‐yl)pyridine) with fractionally charged organic anion TCNQδ− (0<δ<1) afforded hybrid materials [Fe(1‐bpp)2](TCNQ)3.5 ⋅ 3.5MeCN (1) and [Fe(1‐bpp)2](TCNQ)4 ⋅ 4DCE (2), where TCNQ=7,7,8,8‐tetracyanoquinodimethane, MeCN=acetonitrile, and DCE=1,2‐dichloroethane. Both materials exhibit semiconducting behavior, with the room‐temperature conductivity values of 1.1×10−4 S/cm and 1.7×10−3 S/cm, respectively. The magnetic behavior of both complexes exhibits strong dependence on the content of the interstitial solvent. Complex 1 undergoes a gradual temperature‐driven SCO, with the midpoint temperature of T1/2=234 K. The partial solvent loss by 1 leads to the increase in the T1/2 value while complete desolvation renders the material high‐spin (HS) in the entire studied temperature range. In the case of 2, the solvated complex shows a gradual SCO with T1/2=166 K only when covered with a mother liquid, while the facile loss of interstitial solvent, even at room temperature, leads to the HS‐only behavior.

Synthesis, crystal structure, 57Fe Mössbauer spectroscopy and magnetic properties of high-spin iron(III) anionic complexes [Fe(azp)2]- (H2azp = 2,2′- dihydroxyazobenzene) with organic cations

Two new iron(III) complexes, (TrBA)[Fe(azp)2] (1) and (TrPA)[Fe(azp)2] (2) (H2azp = 2,2′- dihydroxyazobenzene, TrBA = tributylammonium and TrPA = tripropylammonium) were prepared by reaction of the azo dye H2azp, tributylamine (or tripropylamine) and FeCl3 in methanolic solution. The crystal structure of 1 was determined by single-crystal X-ray analysis. The asymmetric unit contains one tributylamonnium cation and one [Fe(azp)2]- anion with an octahedrally coordinated Fe(III) ion with an FeN2O4 chromophore – the tridentate ligand azp2- is coordinated by two deprotonated phenolic oxygen atoms and one nitrogen atom from the azo group. The single-crystal X-ray analysis of 1 suggests that an NH⋅⋅⋅O hydrogen bonding interaction between the TrBA cation and the [Fe(azp)2]- anion may induce distortion of the coordination polyhedron resulting in a high-spin complex. Magnetic investigation (DC magnetic data) revealed a high-spin state in the studied temperature range (2–300 K) for both 1 and 2. AC susceptibility measurements for 1 showed a field-induced slow relaxation of magnetization with an atypical temperature dependence of the relaxation time. Moreover, the cryogenic and room temperature 57Fe Mössbauer spectroscopy parameters confirmed the high-spin state of 1. The study was also supported by theoretical calculations at the DFT level of theory.

Probing phase separation in Nd1−xSrxMnO3 (x ≈ 0.4, 0.5) polycrystals through temperature dependent magnetic and Raman spectroscopy studies

The manuscript reports temperature-dependent magnetic transitions correlated to variations in the phonon modes in Nd1−xSrxMnO3. Synthesis of x = 0.4 & 0.5 compounds by the solid-state reaction method was followed by structural/microstructural and electronic characterizations. The crystal structure of both compositions is orthorhombic with Pbnm symmetry, as confirmed by x-ray diffraction. The XPS data confirm the mixed Mn valance with the desired stoichiometry. The phase-separated nature is manifested through the occurrence of various phases, e.g., spin-glass (SG), charge order (CO), ferromagnetic (FM), and paramagnetic (PM), as the temperature is varied from 20 to 300 K. The temperature-dependent Raman measurements reveal that although the material is structurally stable in the studied temperature range of 80–440 K, noticeable discontinuities in the phonon mode shifts were noticed. These phonon mode shifts are found to directly correspond to the magnetic transitions. The change in the frequency of the Raman modes with temperature, which causes the observed shift, could be attributed to various factors such as lattice expansion, anharmonic interactions, spin-phonon coupling, electron-phonon interaction, etc. Here, we have used spin-phonon coupling along with lattice expansion as well as anharmonic interactions to describe the behavior of modes in the FM regime and lattice expansion and anharmonic interaction in the PM phase.

Impact of deep eutectic solvents and their constituents on the aqueous solubility of phloroglucinol dihydrate

Phlorotannins are highly bioactive phenolic compounds mainly found in brown algae. Phloroglucinol is the basic unit from which phlorotannins polymerize. Deep eutectic solvents (DES) are potentially beneficial for increasing phenolics solubility, therefore good solvent candidates for phlorotannins extraction processes. Solubility measurements were performed for phloroglucinol in pure water and aqueous mixtures of DES or their constituents, i.e., different hydrogen bond donors (HBD) and choline chloride (ChCl). The stable crystal form of the phenolic in equilibrium was phloroglucinol dihydrate within the studied temperature range (293.15–313.15 K) and water weight fractions (≥0.25). The water + ChCl + HBD mixtures yielded higher solubility for phloroglucinol dihydrate than the corresponding water + HBD or water + ChCl mixtures. Solubility predicted with PC-SAFT was in quantitative agreement with the experimental data. The solubility behavior of phloroglucinol dihydrate in the different mixtures was related to the hydrogen bonds formed using molecular dynamics and PC-SAFT.

Dynamical properties of lithium borohydride – ammine composite LiBH4·NH3: A nuclear magnetic resonance study

The lithium borohydride – ammine composite LiBH4·NH3 exhibits a high hydrogen density and combines [BH4]− anions and neutral NH3 molecules within the common crystal structure. To study the dynamical properties of this compound, we have measured the 1H, 11B, and 7Li nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates over the temperature range of 18 – 293 K. Our measurements have revealed a coexistence of four types of BH4 reorientational jump processes with different activation energies. One of these processes corresponds to extremely fast BH4 reorientations with the jump rate reaching ~108 s−1 already at 95 K; this fast process is characterized by the activation energy of 78(2) meV. The local coordination of [BH4]− anions in LiBH4·NH3 suggests that the fastest process is represented by rotations around a single 3-fold symmetry axis of the BH4 tetrahedron. The slower processes characterized by the activation energies of 152(5) meV, 216(7) meV, and 297(10) meV may be attributed to reorientations around other symmetry axes of the BH4 tetrahedron. In the studied temperature range up to 293 K, we have not found any signs of diffusive Li+ jumps in LiBH4·NH3 at the frequency scale of ~104 s−1 or higher.

Thermal Expansion and Polymorphism of Slawsonite SrAl2Si2O8

Slawsonite’s (SrAl2Si2O8) structure evolutions depending on temperature (27–1000 °C) have been studied by in situ single-crystal X-ray diffraction. The SrO7 polyhedron expands regularly with the temperature increase. Silicon and aluminum cations are ordered in tetrahedral sites of the studied slawsonite; no significant changes in their distribution as temperature increases were observed. Slawsonite demonstrates a relatively high volume thermal expansion (αV = 23 × 10−6 °C−1) with high anisotropy, typical for framework feldspar-related minerals and synthetic compounds. It was found that, contrary to previously published data, the crystal structure of slawsonite is stable in the studied temperature range and no phase transitions occur up to 1000 °C. The role of Ca and Ba substitution for Sr and Al/Si ordering on polymorphism of natural MAl2Si2O8 (M = Ca, Sr, Ba) is herein discussed.