An investigation of structural, thermal, and electrical conductivity properties for understanding transport mechanisms of CuWO4 and α-CuMoO4 compounds

Recently, inorganic oxide components with high ionic conductivity have been widely explored due to their high stability, safety, and energy density properties. In this context, the present work focuses on the inorganic oxides CuMO4 (M = W, Mo), which have been successfully synthesized using the traditional solid-state method. They were characterized by X-ray powder diffraction, thermal analysis, and complex impedance spectroscopy. X-ray diffraction data refined via the Rietveld method indicated that these compounds are well crystallized in the triclinic system with the P1̄ space group. Besides, the electrical conductivity behavior of these materials was analyzed using the impedance spectroscopy technique in the frequency range of 100 to 106 Hz and in the temperature range of 443 K to 563 K. The absence of a phase transition observed in the calorimetric study was confirmed by the σg and ωh variations as a function of temperature. The AC conductivity was analyzed by Jonscher's power law. The outcomes of the study on charge transportation in CuMO4 (where M = W, Mo) suggest that the overlapping large polaron tunneling (OLPT) mechanism was present in CuMoO4, while the correlated barrier hopping (CBH) and the non-overlapping small polaron tunneling (NSPT) were present in CuWO4. A correlation between the crystal structure and the ionic conductivity was established and discussed. For the two title compounds, modulus analysis revealed that the charge carriers were mobile over short and long distances at low and high frequencies, respectively. The temperature variation of the M'' peak showed a thermally activated relaxation process.

Evaluation of activation parameters of molecular mobility of parylene C using differential scanning calorimetry, dielectric spectroscopy, and thermally stimulated depolarization currents

The molecular kinetics of α-relaxation were studied by dielectric spectroscopy (DS) and thermally stimulated depolarization currents (TSDC) for the thermoplastic semicrystalline parylene C (-H2C-C6H3Cl-CH2-)n thin film. Activation energy of the α-relaxation process brings very close values with both methods (155 ± 2 kJ mol(-1)). Dielectric spectroscopy carried out in a wide temperature range allowed one to determine the α-relaxation time against the temperature and then to estimate the Kauzmann and Angell temperatures for parylene C. From these temperatures and the determination of kinetics and thermodynamics parameters from DSC analysis, it was possible to investigate the cooperative rearranging region (CRR) in parylene C. CRR is quantified in terms of characteristic length (ζCRR), volume (VCRR), number z of rearranging units, and height barrier Δμ of the rearranging unit. Moreover, the fragility index m, calculated from these three methods, is discussed. A value of m = 94 is obtained by DSC confirming a "strong" character of parylene C. A lowest value of 35 ± 4 obtained from electric analyses (DS and TSDC) must be considered with caution because these methods of characterizations bring into play only dipolar relaxations. Last, the kinetic and thermodynamic parameters for parylene C highlighted in this work are positioned in comparison with other organic and inorganic materials.

Experimental investigation of transient pressure waves produced in dielectric liquids

The experimental results reported in this paper mainly concern the two first transient pressure waves emitted after a fast (approximately ns) and localized (approximately micron) injection of electrical energy Wi in insulating liquids. The influence of various parameters (hydrostatic pressure P infinity, injected energy Wi, etc.) on the relative amplitude of these two transient pressure waves are presented and discussed. The analysis shows clearly a difference of behavior, in particular their dependence as a function of hydrostatic pressure, between these two waves. Basically, the physical processes leading to their emission are quite different. The first pressure transient is a consequence of the plasma relaxation, whereas the second one is due to the bubble collapse. According to these results, the chronology of the events is more improved, as well as the theoretical analysis.