Electric storage in de-alloyed Si-Al alloy ribbons

The capacitance of de-alloyed Si1−xAlx (x = 0.2, 0.3, and 0.4) alloy ribbons with resistivities of 1-1000 Ωcm was measured as a function of frequency between 1 mHz and 1 MHz from electric charge/discharge pulse curves of 10 V applied at 100 ms-25 ns intervals, respectively, using an exponential transient analysis for electric charging/discharging. The capacitance of the de-alloyed Si-20 at.% Al specimen obtained by prompt charging/discharging decreased logarithmically from 102 μF (0.55 F cm3) to 1.2 pF (53 nF cm3) as frequency increased from 1 mHz to 1 MHz. From the observed electrode distance dependence on capacitance and nonlinear electronic transport behaviour, we deduced that the alloy consisted in a distributed constant equivalent circuit (series with 1.7% parallel), analogous to electric double-layer capacitors.