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Interface Electrical Phenomena in Ionic Solids
Published in P.J. Gellings, H.J.M. Bouwmeester, Electrochemistry, 2019
Reaction (4.28) results in the formation of doubly ionized oxygen species. These species, which already require stabilization in the crystal field, may be considered as cation vacancies in the outer surface layer. Using the Kröger–Vink notation,31 the formation of metal vacancies in a metal oxide, MO, may be illustrated by the following equilibria: () 1/2O2⇄(VM″)*+2h•+O∘ () (VM″)*+h•⇄(VM′)* () (VM′)*+h•⇄(VM)*
Small polaron hopping-assisted electrical conduction and relaxation in BCT and Mn-doped BCT samples
Published in Journal of Asian Ceramic Societies, 2019
Aanchal Chawla, Anupinder Singh, Mandeep Singh, P.S Malhi
The equilibrium state of the electron concentration (in BCT) is maintained via almost complete delocalization of these electrons by hopping among titanium sites, resulting in poor electric insulation and dielectric behavior. Mn is an acceptor ion which can exist in three valance states, Mn2+, Mn3+ and Mn4+. The doping of Mn (3+ or 4+) at Ti sites leads to electrons trapping, as they are more reducible than Ti4+. Further, the lower concentration of Mn ions restricts the hopping activity of electrons from one Mn/Ti site to another, thereby localizing electrons at these sites [10,42,43]. Also, SEM data have shown that the grain size of BCMT samples is smaller than that of BCT samples. This means that resistive as well as scattering effects of grain boundaries will be more pronounced in BCMT samples. The combination of these two factors leads to a reduction in conductivity (higher activation energy) in Mn-doped BCT ceramics. It has been pointed out in the literature that the activation energy required for singly and doubly ionized oxygen vacancies is in the ranges of 0.3–0.6 eV and 0.7–1.2 eV, respectively [22]. In our samples, the activation energies lie in the latter range, implying the existence of doubly ionized oxygen vacancies in both samples.
Conductivity relaxation and oxygen vacancies-related electron hopping mechanism in Pb1-xLax/2Smx/2Ti1-xFexO3 solid solutions
Published in Journal of Asian Ceramic Societies, 2018
Vandana Sharma, Randeep Kaur, Mandeep Singh, Rachna Selvamani, Surya M. Gupta, Vidya Sagar Tiwari, A. K. Karnal, Anupinder Singh
where τ is relaxation time, R is resistance and C is capacitance, so the respective value of bulk capacitance (Cb) and grain boundary capacitance (Cgb) (given in Table 1) can be calculated using the above relation. It is clear from Table 1 that grain boundaries are more resistive and capacitive than grains in both the sample. The activation energies of grain (bulk) and grain boundary (given in Table 2) for the two compositions are evaluated by plotting ln (Rb) and ln (Rgb) against inverse of absolute temperature (1000/T) as shown in Figure 4(a,b). It has been reported that activation energy of oxygen vacancies lies between 0.3 and 1.0 eV [29]. The values of activation energies for grains (Eg) and grain boundaries (Egb) are 0.70 and 0.43 eV for x = 0.20 and 0.49 and 0.68 eV for x = 0.30, respectively. This means that dielectric relaxations in our case is due to singly and doubly ionized oxygen vacancies (Ea for doubly ionized oxygen vacancies >0.6 eV and for singly ionized oxygen vacancies <0.6 eV). The parameter is calculated after fitting for grain and grain boundary of two compositions as shown in Figure 5(a,b) and it is found that in both the cases confirming non-Debye nature of grain and grain boundary for both compositions.
Reduced graphene oxide foils for ion stripping applications
Published in Radiation Effects and Defects in Solids, 2019
L. Torrisi, L. Silipigni, V. Havranek, M. Cutroneo, A. Torrisi, G. Salvato
Table 2 reports the data relative to the doubly-ionized oxygen ions beam irradiating two rGO stripper foils of 0.5 µm and 5 µm thicknesses using a growing ion energy from 0.25 up to 9 MeV with a current of about 8 nA. Such data are summarized in the plots of Figure 3 indicating that the stripping effect increases linearly with the ion energy above the thresholds of 275 keV and of 7.0 MeV for the thinner and thicker stripper foils respectively. These energy values correspond to those of the oxygen ions having a range of about 0.5 and 5 µm in the rGO foil, assuming a mass density of 1.9 g/cm3, as calculated using the SRIM Code (19). The charge measurements indicate that, for the 5 µm thick rGO stripper foil, at the 7.0 MeV energy, the O2+ ions have a charge transmission factor of 1.15 as reported in Table 2. This means that the effects of ionization and recombination are comparable and the emerging charge is similar to the incoming one. A significant effect of the rGO stripper foil appears at the 9.0 MeV kinetic energy at which the charge transmission factor T assumes the value of 1.95, indicating that practically, in average, each O2+ ion crossing the rGO foil loses other two electrons producing a transmitted double charge. Thus, the stripping efficiency increases significantly when the ion energy is high and corresponds to a range in the crossed material of about 5.7 µm (see Table 2). With regard to the 0.5 µm rGO stripper foil, the O2+ ions with 3 MeV kinetic energy have a charge transmission factor of about 4.2 (see Table 2), evincing that the charge enhancement may reach a value up to O8+ (fully ionized oxygen ions).