V. Zima

Thermomechanical and thermoelectrical properties of vanadyl phosphate dihydrate

Thermoelectric power and XRD of layered VOPO[sub 4][center dot]2H[sub 2]O have been studied for dependence on temperature. The results of thermomechanical analysis (i.e. thermal changes of the thickness of the crystal across the layers) correspond to the changes of basal spacing during heating. The values of the dehydration temperatures have been determined. The conductivity caused by positive charge carriers is predominant in vanadyl phosphate hydrates, whereas conductivity in anhydrous VOPO[sub 4] is electronic, as it follows from the thermoelectric power measurements.

Conductivity study on GeS2-Ga2S3-AgI-Ag chalcohalide glasses

A new kind of ion-conducting glasses based on GeS2-Ga2S3-AgI system is prepared. A relatively large amount of silver can be dissolved into this kind of glass system, and the obtained glasses are still transparent in the red part of the visible spectrum. Only a three times increase in the silver concentration can lead to approximately two hundred times increase in the ionic conductivity. The structural contributions to the ionic conductivity of the glasses are discussed. The present glasses show potential to be used as solid state electrolyte.

Quantitative impedance analysis of solid ionic conductors: Effects of electrode polarization

The dependence of impedance spectra on temperature and sample thickness are analyzed for AgAsS2 as a case example. Using the scaling properties of complex conductivity with thickness and temperature, we discuss the bulk and interfacial properties of the materials. Important physical parameters such as the number of mobile ions, diffusion coefficient in the bulk, and interface are deduced. The influence of the thickness of the sample on conductivity behavior is also discussed. A significant electrode polarization effect is observed even for a low number of localized (accumulated) ions (≈2 × 1017 cm−3) near the interface, which is significantly lower than the number of mobile ions (≈8 × 1021 cm−3) in this test material. The presented analytical method can be widely applied to potentially important ionic conducting systems.

Evaluation of impedance spectra of ionic-transport materials by a random-walk approach considering electrode and bulk response

Analysis of impedance spectra by a random-walk approach is proposed for the study of ionic-transport materials with a silver-containing chalcogenide glass as a case example. Through a full analysis of complex impedance spectra including the electrode polarization effect, some important physical parameters, such as the number of mobile ions in bulk and interface regions, the diffusion coefficient, etc., are extracted without using the conventional equivalent electric circuit analysis. A detailed discussion on electrode polarization, which is highly dependent on signal amplitude, is also presented.

Kinetics and reaction products of the photo-induced solid state chemical reaction between silver and amorphous (As0.33S0.67)100−xTex layers

Abstract The kinetics of the photo-induced solid state chemical reaction of silver with a-(As 0.33 S 0.67 ) 100- x Te x (0 ≤ x ≤ 7.6) films in a conventional sandwich structure was measured by monitoring the change in thickness of the undoped chalcogenide using a modified computer-controlled reflection technique. The kinetic data obtained show that there are two stages in the photo-reaction process. The rate coefficients and activation energies for each stage have been measured and a comparison of the composition and structure has been made.

Electrical conductivity of Agx(As40Se60)100−x bulk glasses

Abstract The samples of Ag x (As 40 Se 60 ) 100− x ( x =1–30) bulk glasses were prepared by a standard melt-quenching technique. Thermal and electrical properties were studied on the prepared glasses. Temperature-modulated differential scanning calorimetry was used to measure glass transition, cold crystallization and melting temperatures of the prepared samples. Electrical transport properties were studied by an impedance spectroscopy and dc conductivity measurements. Activation energies of the conductivity were calculated from Arrhenius plots. One-semicircle impedance spectra were found for all the glasses studied except that with 9 at.% of silver. For this sample impedance spectra with two semicircles were obtained. This phenomenon is discussed in the terms of Bauerle’s easy path theory. The compositional dependence of the conductivity showed an increase of the conductivity with increasing silver content.

A Kinetic Study of the Dehydration of VOPO4.2H2O by Thermal Methods

The dehydration of VOPO4.2H2O hasbeen studied by thermogravimetric analysis (TGA),differential thermal analysis (DTA) and differentialscanning calorimetry (DSC). From the shift of the DTA,DTG, and DSC peaks, activation energies of thedehydration processes have been calculated based onKissingers method. The most suitable kinetic modelsfor two-step dehydration have been found.

Ionic conductivity study of LiI-Ga2S3-GeS2 chalcogenide glasses using a random-walk approach

Abstract Electrical properties of a set of lithium-ion conducting sulfide glasses with general formula 20LiI-xGa2S3-(80-x)GeS2 (x = 10, 15 and 20) is studied in the present article. The experimental data obtained using impedance spectroscopy are analyzed by means of a random-walk (RW) model assuming that the conduction takes place by a random motion of Li+ ions. The influences of added gallium on the structural network and on the conductivity of prepared glasses are also analyzed using the RW model. The results are further confirmed by Raman spectral analysis. The results obtained by the random-walk model and by a conventional equivalent electric circuit model are in a good agreement. We observed that the addition of Ga2S3 contributed to phase separation in the prepared glassy system and negatively influenced the conductivity of the studied glasses. Factors contributing to the total conductivity with respect to the amount of both LiI and Ga2S3 are also reported.

Cerium(IV) phenylphosphonates and para-substituted phenylphosphonates: preparation and characterization

Cerium(IV) phenylphosphonates and 4-substituted phenylphosphonates were prepared by reaction of a cerium(IV) salt with corresponding acids (phenylphosphonic, 4-carboxyphenylphosphonic, 4-sulfamoylphenylphosphonic, 1,4-benzenediphosphonic, 1,4-biphenyldiphosphonic and 4-sulfophenylphosphonic acid) and characterized by elemental analysis, energy-dispersive X-ray analysis, TGA, powder X-ray diffraction and infrared spectroscopy. Three different cerium phenylphosphonates can be prepared in dependence on the reaction conditions. On the other hand, only one compound is formed in each 4-substituted phosphonate system regardless the variation of the reaction conditions. All three phenylphosphonates, 4-carboxyphenylphosphonate and 4-sulfamoylphenylphosphonate are layered with the organic parts pointed below and above the plane of the metal phosphonate layers, with the functional groups placed at the end of the organic part. 4-Sulfophenylphosphonate, 1,4-benzenediphosphonate and 4,4′-biphenyldiphosphonate form pillared structures. Cerium 4-carboxyphenylphosphonate is able to intercalate aliphatic amines due to the presence of the free carboxylic groups in its interlayer space.

Multilevel resistive switching in Cu and Ag doped CBRAM device

A new type of memory device, based on Ag and Cu doped Ge2Se3 chalcogenide, was designed and investigated by a new method, referred to as “one pulse SET method”. The device shows multilevel resistance states. A resistance state between ON and OFF states was found with a wide range of bias. The multilevel resistance behavior could be caused by the formation and dissolution of Ag and Cu filaments. The energy-dispersive X-ray spectroscopy mapping and scanning electron microscope results prove the distribution of Cu and Ag elements in the film.