A liquid-electrolyte voltammetric probe of superconducting oxocuprates through the transition temperature T c

Abstract

New free-solute ferrocene/ferricinium electrochemistry, in liquid electrolyte on TI-containing oxocuprate superconducting electrodes studied at several temperatures above and below T, shows no discontinuities or abnormalities at the transition, in contrast with solid-electrolyte behaviour but possibly in accord with theoretical predictions regarding vibronic interactions or reorganisation barriers.

Determination of heterogeneous electron-transfer kinetics of decamethylferrocene at low temperatures (120K<T<200K) by a.c. impedance

“…Following these results, the pre-exponential values (A 0 ) at 298 K, 175 K and 130 K have been calculated by combining the Eqs. (11) and (16) with the assumption that jK p = 60 pm [6,23,42,43]. We observe that the values for A 0 obtained for the THF-based (0.4-10.1 cm s À1 ) and the BuCN-based (0.2-3.5 cm s À1 ) solvents in the 130-175 K temperature range are much lower than our experimental values corrected from solvent dynamics and literature results as shown in Tables 5 and 6.…”

“…Among the many factors (apparatus, analysis) which can induce errors in the low-temperature experimental determination of charge-transfer resistance values, the enormous impedance value and the precipitation in electroactive species at very low temperatures are probably the most likely. A concentration decrease in electroactive species at low temperatures provoked by a precipitation (as already observed by Green et al [11]) would lead to overestimated values of k 0 at the lowest temperatures (from Eq. (8)) and thus lower the activation energy and the preexponential factor.…”

“…The second liquid electrolyte we have used in our experiments is a mixture of chloroethane with tetrahydrofuran and 2-methyl-tetrahydrofuran (16:7:1 in volume ratio), with LiBF 4 as supporting electrolyte. This mixture was developed by Green et al for cyclic voltammetry studies of ferrocene with a platinum macroelectrode at temperatures as low as 99.5 K [11], and for the study of charge transfer at the superconductor/liquid electrolyte interface at temperatures around 115 K by a.c. impedance [12]. The specific cryoequipment and procedure used for our studies with these two mixtures of solvents are detailed in the experimental part.…”

A new probe of superconductivity: quantitative measurements on defined electron transfer with solute at the interface between liquid electrolyte and oxocuprate electrode in the superconducting state

“…A liquid electrolyte (chloroethane with tetrahydrofuran and 2-methyltetrahydrofuran, plus a lithium salt electrolyte) is now available [3][4][5][6] in which the electron-transfer reactions of freely diffusing electroactive species, here ferrocene or decamethylferrocene, at macrosized Pt electrodes could be followed by cyclic voltammetry at temperatures as low as 99.5 K. 5 Next, at specially designed cryorobust HTSC electrodes 6 (including leads for the in situ determination, by a four-point resistivity measurement 6 on the electrode in use, of its superconducting transition temperature), charge transfer between freely diffusing ferrocene and a demonstrably superconducting HTSC microelectrode at 102 K could be clearly detected by cyclic voltammetry. 5 Now we have studied by impedance spectroscopy the temperature dependence of the charge-transfer rate (proportional to the charge-transfer conductance R CT 21 ), and report here our observations on electron transfer between decamethylferrocene and the HTSC Tl 1223 electrode comprising the recently synthesized 7 (Tl 0.5 Pb 0.5 )(Sr 1.6 Ca 0.4 )Ca 2 Cu 3 O 9 . ‡ The equipment has been described in detail.…”

“…Notes and References † E-mail: D.R.Rosseinsky@exeter.ac.uk ‡ The electroactive species was 5 mm decamethylferrocene (DMFc) with 0.2 m LiBF 4 in solvent comprising 16 : 7 : 1 by volume chloroethanetetrahydrofuran-2-methyltetrahydrofuran. The apparatus [3][4][5][6] with the addition of a Solartron 1286 frequency response analyser monitored the electrode response over the frequency range 10-10 5 Hz to a perturbation of ±100 mV superimposed on the HTSC electrode, about the approximate electrode potential for DMFc-DMFc + of 0 V with respect to the commonly used Ag-wire quasi-reference electrode. § Solartron programmes ZPLOT and ZVIEW allow simulation of the observed electrochemical impedance via a model circuit consisting of resistance and capacitance-like (F ≠ 1) circuit elements.…”