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[en] Full text: Nano-dimension topologic-disorder materials constitute an important feature in the development of modern electronics. Among such materials, low-dimensional (1D and 2D) compounds1, like or show amazing properties, for example highly anisotropic super ionic conductivity thanks to hoping-type conductivity in the Tl planes located in between the or nanofiber layers.Here we are interested in the THz spectrum of such materials, which exhibit strong absorption lines that could be attributed to the libration oscillation of the nanofibers.In classical THz time-domain spectroscopy (THz-TDS), one records the temporal waveforms impinging onto and transmitted by the sample.Then a numerical FFT of both signals is performed. The ratio of the transmitted and incident FFT spectra gives the transmission coefficient of the sample. If the origin of time is preserved between the two requested measurements, then the FFT gives both modulus and phase of the transmission coefficient. If the sample is a slab with parallel sides, the index of refraction and the coefficient of absorption could be accurately determined using an inverse electromagnetic method 2. For materials exhibiting high absorption bands, the transmission coefficient is almost zero in modulus, and its phase is unknown. The usual solution to this problem is to perform THz-TDS in reflection. However, the disadvantage of the reflection technique is its weak precision due to the difficulty to get the reference signal with the requested precision. Usually, this reference signal is supplied by a metallic mirror located at the position of the sample, but an even small error in positioning the mirror to lead to huge errors, mostly concerning the refractive index of the sample.Here we propose a combined technique, which takes benefit of both transmission and reflection THz-TDS's. The basic idea is to derive a rough estimation of the refractive index from reflection data, while both refractive index and absorption coefficient are also calculated from transmission data. A Kramers-Kronig calculation allows us to determine the refractive index from the absorption spectrum measured in transmission.In the spectral regions of transparency, both refractive indices determined from reflection and from the Kramers-Kronig calculation should be superimposed. To get this superimposition, we add the necessary 2m phase (minteger) to the phase values just after each high absorption region. The advantage of this method is to benefit from the high precision of the transmission technique, while the missing continuity of the phase in the high absorption regions is obtained by comparison with the reflection technique.Thus we obtain, even in the regions of high absorption, the value of the refractive index with a great precision and a low noise. Moreover, the determination may be improved by fitting the absorption peaks with a Gaussian or a Lorentzian function. We applied our method to determine the index of refraction of low dimensional compounds, like (see figure). Refractive index (full circles) and absorption (dashed line) spectra of the crystal,showing strong absorption bands.
[en] The bond fluctuation model of superionic conductors predicts that the polarizability of solids that exhibit high ionic conduction is large. Based on this background, a study on the nonlinear optical constants in superionic glasses has been started. As a first step, the relationship between the third-order susceptibility χ(3) and the linear susceptibility χ(1) of various kinds of glasses has been studied. It is found that the values of χ(3) of superionic conducting glasses exceed considerably the values predicted by the usual Miller rule. The deviation arises from the increase of the ionic coordinate dependent electronic polarizability, which plays also an important role in the ion transport processes.
[en] Superionic solids and solid electrolytes are a special group of materials showing high ionic conductivity with tremendous technological potential. This book updates the present status of the field. Starting with an overview of recent trends in solid state ionics, the book ends with the assessment of future implications. Different theoretical, experimental (including NMR), and materials aspects have been covered along with applications. Important materials covered include alkali and silver ion conductors, fluorites, Nasicon, heterogeneous solid electrolytes, and glasses. The theoretical topics covered in this volume include phenomenological models, fractal techniques, the pre-exponential problem, and fluctuations
[en] The protonic conductivity (σ) of anhydrous fibrous Ce(IV)(HPO4)2 has been measured in the range 120-350 C. At 180 C σ is 7x10-8 S cm-1 and decreases at higher temperature because of pyrophosphate formation. The hydrated material was investigated as a funciton of temperature from 20 to -60 C and relative humidty (RH) from 90 to 11%. AT 20 C and 90% RH the conductivity ranges from 3x10-5 to 10-4 S cm-1 and goes down to about 5x10-7 S cm-1 at 11% RH. At all relative humidities the Arrhenius plots consist of twolinear regions with different slopes, thus probably indicating the presence of a phase transition occuring at about -20 C in the films of intercalated and/or adsorbed water. 12 refs.; 5 figs.; 2 tabs
[en] The dielectric parameters of the layered structured TlGaSe2 crystals have been studied comparatively before and after gamma radiation (20Mrad). The dielectric parameters - the real and imaginary parts of dielectric permittivity and dielectric loss angle have been studied in the paraelectric phase in the temperature range of 300-500K. The role of free ions in the relaxation process has been determined when it is f <10kHz on the basis of the dielectric parameters in the frequency range of 100-106 Hz. The non-standard mutual dependence of the real and imaginary parts of the dielectric permittivity has been observed
[en] The solid ionic conductor cell Bi2O3Y2O3 was used to study the current-voltage behaviour under different temperatures and voltage scan rate, as is usually done in cyclic voltammetry in three-electrode cells using liquid electrolytes. The result shows that the reactions are different at the electrodes and a hysteresis effect is presented at low temperature and high voltage scanning rates
[en] In this study, an intermediate temperature ionic conductor, Ce0.95Eu0.05P2O7, was prepared by solid state reaction. The variation of conductivities with the pressure pH2O or time were studied. The highest conductivity of Ce0.95Eu0.05P2O7 sample was observed in dry air atmosphere at 300 .deg. C to be 1.1 Χ 10-4 S·cm-1 and in wet air atmosphere (pH2O = 7.4 Χ 103 Pa) at 100 .deg. C to be 1.4 Χ 10-3 S·cm-1, respectively. The log σ ∼ log (pO2) plot result indicated that Ce0.95Eu0.05P2O7 was almost a pure ionic conductor under high oxygen partial pressure and a mixed conductor of ion and electron under low oxygen partial pressure
[en] Topics covered in the conference include: energy storage and other applications; electrode materials and intercalated compounds; diffusion; ionic conductivity techniques; neutron scattering and diffraction techniques; beta aluminas; deuterium and NH4; NASICON and other sodium ion conductors; lithium ion conductors; silver and copper ion conductors; anion conductors; and high conductivity glasses. Thirty-five individual items were prepared separately for the data base