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Samples of the system (x = 0, 0.1,..., 0.7) were prepared by the usual ceramic technique. IR absorption spectra were used for analysing the compositions. The AC conductivity and dielectric properties (loss tangent tan , dielectric constant and dielectric loss ) have been measured at various frequencies and temperatures. Three bands were observed in the IR spectra. The band at around and another one at around were assigned to the tetrahedral and octahedral complexes, respectively. A small band at around indicated the octahedral divalent metal-oxygen bond in these complexes. The threshold frequency for the electronic transition seems to increase with increasing content, namely with decreasing concentration. At room temperature (RT), the AC conductivity exhibits dispersion in the frequency range from Hz to Hz. The variation of tan with frequency at RT shows a peak in the range Hz. The electrical conduction mechanism was explained in terms of the electron hopping model. Both effects (temperature and frequency) tend to increase and . The composition dependence of the dielectric properties is divided into two regions. The first one is for x<0.5 (for which long-range order is predominant) and the second one is for (for which short-range order is predominant).

Our NMR experiments confirm the above conclusion. After a sample is quenched the NMR frequencies show time dependencies divided into the same two domains. Moreover, as shown in Fig. 2, we observe strikingly different coexistence curves and critical isochores in our quenched and nonquenched experiments. In the nonquenched experiment long waiting times (over twelve hours) occur before any measurement is made near T^. This insures that the xenon sample has come to equilibrium with the gravitational field. In the quenched experiment all measurements are made after a relatively short time, about 20-30 min following the quench. This time must be long enough to insure equilibrium between the liquid and vapor phases but short enough to insure minimal effects from gravitational gradients. As shown in Fig. 2 the quenching technique eliminates both the excess line broadening and the anomaly of two apparently separate signals (highdensity gas near bottom of sample and low-density vapor near top of sample) which occurs well above T^ in our nonquenched experiments as a result of the warped (sigmoid) gravitational density profile.We wish to acknowledge many helpful discussions with Joseph Sak concerning critical phenomena and with Gary S. Collins concerning computer programs.We present results of light-scattering experiments on thermal acoustic spin waves in EuO. The Brillouin spectra show two peaks which can be shifted by an external magnetic field. One of these is identified as due to a modified bulk spin wave of the material. The other one, by its anomalous behavior on reversal of the magnetic field or change of the scattering geometry, reveals itself as a spin wave propagating along the surface of the crystal.

Different concentrations of metal chlorides/polyvinyl alcohol nanocomposites have been prepared by the typical solvent cast technique. The prepared samples were investigated by different techniques such as X‐ray diffraction, differential scanning calorimetry, and scanning electron microscope. DC and AC conductivities are examined at different temperatures and frequencies. An activation process was found in the DC conductivity versus temperature relation and the activation energy was calculated. The AC conductivity obeyed the ωS power law. The behavior of S with temperature was studied. Various dielectric parameters such as dielectric constant (ε′), dielectric loss (ε″) and loss tangent (tan δ) have been determined in the temperature range 303–443 K at different frequencies. The dielectric parameters were found to decrease with increasing frequency. The study of dielectric relaxation as a function of temperature at constant frequency shows two relaxation mechanisms. The optical band gaps and band tails were estimated from the measured absorption spectra. The applied photon energy found to affect the observed optical band gaps. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013