Papers by Keyword: Impedance Spectroscopy

Abstract: We remind the reader to some common features of metallic and oxide glasses. We then introduce the radiotracer method for diffusion studies, which can be applied for both types of glasses. We provide an overview on diffusion in metallic glasses in which we consider both types of metallic glasses – conventional and bulk metallic glasses. In the last part we discuss diffusion and ionic conduction in oxide glasses. For ionic glasses, conductivity measurements are an important complement to tracer diffusion studies. We remind the reader to the method of impedance spectroscopy. We discuss results for soda-lime silicate glasses, single alkali borate glasses and mixed alkali borate glasses and present evidence for collective jump processes in glasses.

Abstract: Bone tissue is a calcium deposit and supporting structure of the human body, it is exposed to several pathologies that modify its mineral content. To determine these changes, different diagnostic procedures are performed with techniques using invasive ionizing radiation, which are limited by the negative effects in the long term on human health. A methodology is explored that could be applicable in the diagnosis of pathologic variations in bone mineral density, using structural monitoring tools. The proposed technique estimates changes in bone conditions by applying impedance spectroscopy with a tooth-borne piezo-device. Bone-tooth samples were prepared to simulate a section of maxillary bone and subsequently treated with chemical agents, simulating pathologic decalcification. The piezo-device is inserted in the slot of an orthodontic bracket, previously bonded to the crown of the tooth, in order to transmit vibration to surrounding bone. The variations in bone micro-architecture were computed by image processing analyzed with samples prepared in transparent resin, allowing the measurement of morphometry before and after the induced changes in mineral content. Using vibrational bone response, impedance measurements allowed to observe the variations in bone mass as the samples were progressively decalcified. In the 5-50kHz spectrum, it was demonstrated the sensitivity of the electro-mechanical impedance during the bone alteration procedure since the electrical resistance signals of the piezo-device consistently changed in the frequency spectrum (5-50kHz). The piezo-device shows to be sensitive to the changes produced by the bone alterations, which were caused by the stiffness variations made in the sample during the decalcifying. These changes were statistically correlated to demonstrate that in a less invasive way, bone alterations could be monitored from the teeth. This result opens the door to search for a new way to diagnose bone density changes in real applications.

Abstract: To date, dye-sensitized solar cells (DSSCs) based on TiO₂ nanoparticles have been widely investigated due to their high conversion efficiency. However, constructing TiO₂ into a structure of nanorods with a high aspect ratio is difficult to be achieved. On the other hand, nanorod/nanowire arrays may provide some advantages, such as an efficient pathway for electron transport and a larger surface area for dye absorption. ZnO is one kind of metal oxides that can be formed into nanorods easily with various methods. Here, we reported our works on the preparation of ZnO nanorods and investigate its DSSC performance. We found that the cell performance was very affected by the diameter of the nanorods, which may then indicate that charge transfer and charge extraction processes are more effective in the cell with a smaller nanorod diameter.

Abstract: Ferroelectric ceramic solid solutions Li_xNa_1-xTa_yNb_1-yO₃ (х = 0.17; у = 0 – 0.5) with the perovskite structure have been obtained by the thermobaric synthesis method. Particularities of their microstructure, elastic properties, electrical conductivity and permittivity have been researched. It has been established that an increase in the thermobaric synthesis temperature leads to a decrease in the Young’s modulus value. Specific static conductivity values have been determined; charge carrier activation enthalpies Н_а have been calculated. The Curie temperature of the samples has been determined to decrease with an increase in tantalum content. A Ferroelectric ceramic solid solution Li_0.17Na_0.83Ta_0.1Nb_0.9O₃ was shown to undergo four structure phase transitions in the temperature range 300-820 К. A Li_0.17Na_0.83Ta_0.1Nb_0.9O₃ has been shown to be a high temperature superionic. Possible mechanisms of the detected phenomena are discussed.

Abstract: Effect of difference silica source, namely commersial silica and silica from rice husk, as Si precursor on the synthesis of lanthanum silicate apatite (LSO) have been investigated. The conductivity of LSO was determined by impedance spectroscopy using LCR meter. The conductivity of LSO based on rice husk extraction (s_700°C = 2.13 ´ 10^-4 S.cm^-1) was ten times lower than that of LSO with commercial silica (s_700°C = 3.11´ 10^-5 S.cm^-1). Carbon content as an impurity on silica from rice husk extraction is suspected to decrease the homogeneity of its morphology so that it has an impact on its conductivity.

Abstract: In this study, influence of nanoparticles size on optical and dielectric properties of TiO₂ nanoparticles is investigated through thermal treatment of hydrous amorphous titania synthesized by chemical precipitation method at temperatures 300 °C and 600 °C. The average sizes of nanoparticles estimated respectively are ~ 8 nm and ~ 22 nm. Although the optical bandgap energy of both samples remains the same the E_g Raman mode observed at 144 cm^-1 for bulk TiO₂ is shifted to 150 cm^-1 only for nanoparticles calcined at 300 °C. The shift is ascribed to the size as well as higher density of surface defects. Moreover, the presence of surface defects like oxygen vacancies which provide effective sites for catalytic reaction are confirmed by EPR and photoluminescence studies. The oxygen vacancies enhances space charge polarization and consequently results in higher dielectric constant. In addition, the peak shift of loss tangent which determines the mobility of charge carriers is found to be size dependent. Hence calcination temperature has significant influence on defect levels which in turn determine the optical and dielectric properties of TiO₂ nanoparticles.

Abstract: The electrochemical properties of the nitrogen-enriched carbons obtained by plant raw treatment as electrode material for supercapacitors were investigated by electrochemical impedance spectroscopy, cycling voltammetry and galvanostatic charge-discharge cycling in KOH aqueous electrolyte. The effect of activation agent (NaOH) concentration and carbonization temperature were analyzed. The separation of double layer and redox capacitance components was done. The dominating role of microporosity for capacitive properties was demonstrated. The capacitance of model capacitors based on carbons obtained at different modes was calculated from both from cycling voltammetry and galvanostatic charge-discharge data. The maximal values of specific capacitance of carbon materials carbonized at 600°C and 900°C are about 100 and 120 F/g, respectively.

Abstract: This paper deals with the study of light conversion efficiency of organic photovoltaic cells with an inkjet-printed graphene oxide layer. The graphene oxide is used in this experiment as a hole-extracting, electron blocking layer in bulk heterojunction organic solar cells based on DPP(TBFu)₂:PC₆₀BM blend. It is also studied the influence of the GO reduction (chemically, by UV radiation and by annealing) on the final efficiency of photovoltaic conversion. Power conversion efficiency and the transport of charge carriers are evaluated by measuring of current-voltage characteristics and mainly by impedance spectroscopy analysis. In this regard, using of graphene oxide and its reduced form showed negative influence on the device performance caused by an inefficient charge carrier collection at the short-circuit condition.

Abstract: Graphene has been employed as electrode materials in various electrochemical biosensors due to its excellent electrical, mechanical, thermal and optical properties. In the present study, Chemical Vapor Deposited (CVD) and epitaxial graphene on SiC were examined as material for electrochemical biosensing application. The surface of both types of graphene were characterized using Raman spectroscopy as well as with Scanning Electron Microscopy (SEM). As the key point for the comparison, the impedance spectroscopy measurements of different graphene films using deionized water and saline 0.9% NaCl solution were performed as well. The method of impedance measurements applied to graphene films expands the range of possibilities for using this material as sensitive biosensors. Based on the comparative tests results, it is possible to draw the first simple conclusions about the advantages of CVD or epitaxial graphene. Based on the results of impedance spectroscopy, it is possible to draw a simple conclusion – single layer graphene has the higher sensitivity.

Abstract: The phase transitions and conductivity of novel compounds (NH₄)₆LiZr_4-nHf_nF₂₃ (n = 1, 3) were studied by DSC and impedance spectroscopy. The structure and the activation energies of the charge transfer in these compounds were estimated. The high ionic conductivity of these fluorocomplexes reaches 10^-2 S/cm at 453 K.