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Herein, we review the magnetic, superconducting and structural phase diagrams of the title systems, with an emphasis on our recent results form magnetic and structural neutron diffraction, magnetic susceptibility and system, and indicate the occurrence of frustrated phase separation on a nanoscopic length scale in the La2-xSrxCuO4 system with O < x ≲ 0.05. 139La nuclear quadrupole resonance measurements. The results clarify the miscibility gap in the La2CuO4+δ. © 1994.

Techniques including dielectric relaxation and enthalpy relaxation are used to investigate the molecular relaxation dynamics of glucose and, fructose in their liquids and glassy states. The results indicate that the slower secondary relaxation bears relations to the [alpha]-relaxation, and hence, it is the true Johari-Goldstein secondary relaxation of the monosaccharides.

We have studied mutarotation in anhydrous supercooled L-sorbose by means of dielectric spectroscopy. The phenomenon observed in L-sorbose is much faster than in the structurally similar D-fructose. The kinetics of this process has been determined by applying 1st order kinetics model. Activation energy equal to 68 kJ/mol was obtained from temperature dependence of rate constants. To understand differences in mutarotation rate between D-fructose and L-sorbose, quantum mechanical calculations were performed to study mechanism of this phenomenon. The possible impact of water absorbed from air on the mutarotation in supercooled liquid state has been checked. It turned out that the process is probably intermolecular and the water molecules or other carbohydrate molecules assist in the proton transfer process. Finally we have shown that the rate constant can be alternatively determined from frequency of the maximum of peak, obtained by performing Fourier transform of kinetic curve. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy has been recently used to monitor mutarotation in undercooled D-fructose. This method can be viewed as a universal method to study mutarotation phenomenon in the whole family of monosaccharides. In this paper, we studied kinetics of mutaration of anhydrous D-ribose at ambient pressure as well as pressure effect on the rate constant of this process. Ribose mutarotation behavior is compared to the one obtained for D-fructose. In addition, we attempted to determine the “direction” of mutarotation in undercooled monosaccharides after quenching the melted sample. To this end, analysis of dipole moments of different tautomers of D-fructose and D-ribose have been performed. Conformational analysis of studied carbohydrates was done with use of density functional theory. Geometry optimizations as well as calculations of dipole moments were done on the 6-311++G(d,p)/B3LYP level. Finally, it turned out that data obtained from the mutarotation experiment might be helpful in understanding the origin of γ-process occurring in the whole family of carbohydrates. [ABSTRACT FROM AUTHOR]

Dielectric relaxation measurements on maltose were performed at ambient and increasing pressure. The loss spectra collected below glass transition of this disaccharide revealed presence of two well separated secondary relaxations. Activation energies determined for both modes are Ea=73 kJ/mol and 47 kJ/mol for the slower (β) and faster (γ) relaxation, respectively. From high pressure measurements activation volume ΔV=15.6 ml/mol for the slower secondary relaxation was estimated. Both quantities: activation energy and activation volume for α-process derived from dielectric data, were compared to those obtained from the conformational calculations with use of density functional theory (DFT). We found out satisfactory agreement between both quantities for the molecular motion related to the rotation of the two monosaccharide units around glycosidic linkage in this disaccharide. [ABSTRACT FROM AUTHOR]

Broadband dielectric measurements on leucrose were performed under ambient and high pressure. We showed that in this disaccharide, there are two secondary relaxation modes, a slower one sensitive to pressure and a faster one that is not. This finding clearly indicates that the faster secondary relaxation originates from the intramolecular motion. This conclusion contradicted previous interpretations of this mode observed for trehalose and maltitol, systems very closely related to leucrose. In addition, pressure sensitivity of the slower relaxation confirms our recent interpretation about the character of this process. Furthermore, we discovered that unlike the faster relaxation, the slower secondary relaxation is sensitive to the thermodynamic history of measurements. Finally, monitoring the changes in maximum loss of the slower secondary relaxation measured at the same pressure and temperature conditions for glasses obtained via different thermodynamic routes enabled us to draw a conclusion about the density of the formed glasses. Our observations may be helpful in establishing a new method of suppressing crystallization of amorphous drugs. [ABSTRACT FROM AUTHOR]

Broadband dielectric spectroscopy is employed to investigate the non-Debye relaxation behavior in a dendrimeric alkyd resin. From temperature-dependent measurements at ambient pressure, we found a very broad distribution of relaxation times. This is attributed to the complex geometrical topology of the molecule. However, compression significantly reduces the non-Debye character of the dielectric response; thus, pressure induces dynamic homogeneity in the dendrimeric alkyd resin. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The dielectric spectrum of the organic glass former 1,1'-bis (p-methoxyphenyl) cyclohexane was measured over a range of temperatures and pressures, corresponding to a variation of the structural relaxation time, Τα, by 8 decades. The temperature dependence of Τ[sub α] corresponded to a fragility equal to 72, which is consistent with the correlation of same with the shape (breadth) of the relaxation function. The dependence on pressure of Τ[sub α] could be described as a simple activated process, with a pressure-independent activation volume equal to ∼230 cm³/mol, varying inversely with temperature. The pressure coefficient of the glass temperature, T[sub g], was 240 K/GPa. At frequencies beyond the structural relaxation peak, there is a second, thermally activated process, having an activation energy=74.2 kJ/mol. The relaxation times for this process were invariant to pressure. Extrapolation of these relaxation times (measured below the T[sub g]) intersects the ambient pressure structural relaxation data at a temperature, T[sub β]=268 K. This is about equal to the temperature, T[sub B], at which the structural relaxation times deviated from a single Vogel-FulcherTamman curve. In this respect, the secondary process exhibits the properties of a Johari-Goldstein relaxation. However, since T[sub β] varies with pressure, it remains to be seen whether its equivalence to T[sub B] is maintained at elevated pressure. [ABSTRACT FROM AUTHOR]

Several studies are conducted to explain the different molecular motions that are found to be responsible for the slower secondary ([beta]) relaxation in sucrose. The [beta]-relaxation is shown to lead to the translation motion of the entire molecule of the sugar.

The effect of molecular structure on the dynamical properties of supercooled di-n-butyl phthalate (DBP) and its isomer, diisobutyl phthalate (DiBP) is examined. The results of the dielectric alpha- and beta-relaxations and the ionic conductivity are discussed.

Looks into the effect of pressure on fragility and glass transition temperature in fragile glass-former. Temperature dependences of dielectric relaxation times measured for several different pressures; Findings of the strong fragility analyses carried out for dielectric data; Influence of pressure on glass transition temperature.

Dielectric relaxation measurements are carried out on sorbitol as a function of pressure at various temperatures. The relaxation time for the secondary process is found consistent with the calculation from the coupling model based on identification of the secondary process as the precursor to the highly cooperative structural relaxation.

Provides information on a study which presented copper-nuclear quadrupole resonance frequency and relaxation rates measurements in copper oxide, in the vicinity of the antiferromagnetic ordering temperature T[subN]. Behavior of the relaxation rates; Valence fluctuations in the copper-oxygen bond character.

Focuses on a study which measured the [sup31]phosphorus nuclear magnetic resonance relaxation times in layered antiferromagnets FePSe[sub3] FePS[sub3] and NiPS[sub3] in the presence of different external magnetic fields. Relations of relaxation rates and fluctuations of the hyperfine magnetic fields; Temperature behavior of the relaxation rates.

Investigates the magnetic properties of the layer compounds cesium-vanadium-fluorine and rubidium-vanadium-fluorine. Use of magnetic susceptibility measurements and nuclear magnetic resonance and relaxation measurements; Hyperfine fields generated by the magnetic vanadium ions; Nuclear-spin lattice relaxation rate.