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The mixed alkali metal effect is a long-standing problem in glasses. Electron paramagnetic resonance (EPR) is used by several researchers to study the mixed alkali metal effect, but a detailed analysis of the nearest neighbor environment of the glass former using spin-Hamiltonian parameters was elusive. In this study we have prepared a series of vanadate glasses having general formula (mol %) 40 V2O5-30BaF2-(30 - x)LiF-xRbF with x = 5, 10, 15, 20, 25, and 30. Spin-Hamiltonian parameters of V(4+) ions were extracted by simulating and fitting to the experimental spectra using EasySpin. From the analysis of these parameters it is observed that the replacement of lithium ions by rubidium ions follows a "preferential substitution model". Using this proposed model, we were able to account for the observed variation in the ratio of the g parameter, which goes through a maximum. This reflects an asymmetric to symmetric changeover of the alkali metal ion environment around the vanadium site. Further, this model also accounts for the variation in oxidation state of vanadium ion, which was confirmed from the variation in signal intensity of EPR spectra.

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This article reports on the impedance spectroscopic study of lithium substituted niobo vanadate glasses and their nickel ferrite doped counterparts using Cole–Cole (Nyquist) plots and electrical conductivity analysis. The glass samples were prepared using the melt quenching technique. Differential scanning calorimetry and x-ray diffractometry were used to determine the thermal properties and the amorphous nature of the glass samples, respectively. Using impedance spectroscopy, the nature and extent of inhomogeneity were investigated and correlated with transport properties in the glasses at different temperature ranges (120–240 °C). Equivalent circuit analysis was adopted to study the glass materials further. The introduction of a constant phase element (Q) in a modified RQ circuit describes the Cole–Cole plot well, which accounts for the frequency dependence of dielectric response. The electrical conductivity analysis is performed using Jonscher’s law and Arrhenius plots. The exponent “n” was found to be a decreasing function of temperature. The DC part of the electrical conductivity is analyzed on the basis of alkali ion distance and alkali-oxygen distance. The activation energy estimated by the Arrhenius equation is found to decrease from 0.54 to 0.39 eV as lithium content increases. The estimated mobility of lithium ions was found to decrease as the lithium content increases in both doped and undoped cases.

We present a corroborative study of the structural characterization of lithium-substituted barium vanadate glasses using Raman and electron paramagnetic resonance (EPR) spectroscopy. Investigation of the thermal and physical properties of these glasses showed a gradual increase in the concentration of nonbridging oxygen. Raman and EPR analysis gave an insight into the changing structure of the glasses. Both the spectroscopic techniques confirmed that vanadium is present in the glasses as distorted VO 6 octahedra. From the analysis of both spectroscopic techniques, it is proposed that the lithium ion prefers to occupy planar positions of the VO 6 octahedra, thus reducing the tetragonal distortion and making the environment around the network-forming unit in the glass matrix more homogeneous as we increase the lithium content. The concentration of V 4+ showed a non-monotonic variation with an increase in Li 2 O as indicated by Raman studies and confirmed by EPR, which indicates a structural change in the distorted VO 6 octahedra.

The Lampert triangle model can be an interesting method for investigating the conduction mechanism in semiconducting polymers. A complete Lampert triangle is observed in PF 6− doped poly (3,4-ethylenedioxythiophene) [PEDOT:PF 6 ] devices, fabricated in a stainless steel/PEDOT/Ag structure and synthesized by electro-polymerization at three different doping levels (high-S1, medium-S2, and low-S3). The temperaturedependent current−voltage characteristics show three distinct regimes limited within a triangular region called the Lampert triangle: Ohmic, trap-limited/filling space charge-limited conduction (TFL-SCLC), and trap-free/trap-filled space chargelimited conduction (TF-SCLC). The vertices of the Lampert triangle represents the transition voltages (V T ) for different conduction mechanisms, and the carrier density (p 0 ), carrier transit time (t t ), and relaxation time (t d ) for different doping levels are estimated through the analysis of the triangle. The mobility of carriers shows significant temperature dependence (Arrhenius type). The Jonscher's double power law fit to AC conductivity data shows that the exponent (in the range 0−1) varies with carrier density and has different trends in bulk and interface. The impedance data and Nyquist plots are analyzed with two parallel RQ circuits (R: resistance; Q: constant phase element) connected in series. The values of onset frequency (ω o ) in the conductivity plot of the different samples (S1, S2, and S3) give insights into their relative disorder. Raman spectroscopy studies have attempted to corroborate the changes in bond deformation with carrier density in correlation with the structure and disorder.