Interpretation of Complex Capacitance Using Equivalent Circuit Involving Constant Phase Element

AbstractRelaxor ferroelectrics exhibit both static and dynamic local structural order which controls their frequency-dependent electrical properties. A combination of advanced scattering and microscopy techniques have been used recently to determine the local structure of relaxors. To complement these, here we show an approach to electrical property measurements which identifies local dipoles whose switching is co-operative, temperature-dependent and responsible for the observed dispersion in dielectric properties. Impedance measurements and equivalent circuit analysis of a canonical relaxor, Pb(Mg1/3Nb2/3)O3 single crystal, over the ranges 180–1050 K and 100 Hz–1 MHz, show that incorporation of a single constant phase element into the equivalent circuit used to fit experimental data is able to account fully for the dispersions that characterise the relaxor response, over this frequency range. This allows parametrisation of the relaxor behaviour, gives increased understanding of the relaxation mechanisms responsible and forms the basis for modifying and controlling relaxor characteristics.

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EVALUATING THE PH SENSITIVITY OF CARBON NANOTUBE-POLYANILINE THIN FILMS WITH DIFFERENT DOPANTS

Nano LIFE ◽

10.1142/s1793984412420019 ◽

2012 ◽

Vol 02 (04) ◽

pp. 1242001 ◽

Cited By ~ 4

Author(s):

AILEEN VANDENBERG ◽

KENNETH J. LOH

Keyword(s):

Thin Films ◽

Carbon Nanotube ◽

Frequency Domain ◽

Equivalent Circuit ◽

Time Domain ◽

Constant Phase Element ◽

Ph Sensitivity ◽

Buffer Solutions ◽

Bulk Film ◽

Ph Buffer

The objective of this study is to characterize the pH sensing performance of carbon nanotube-based thin films and compare them to their non-carbon nanotube-based counterparts. A layer-by-layer technique is employed for fabricating the nanocomposites, and pH sensitivity is encoded by incorporating polyaniline (PANI) by itself or with single-walled carbon nanotubes during film fabrication. In particular, polyaniline is doped with different counter ions such as hydrochloric acid (HCl) and methane sulfonic acid (MeSA) for fabricating four different thin film sample sets. The as fabricated films are subjected to various pH buffer solutions ranging from pH 1 to 13 while their electrical properties are simultaneously measured using two different techniques. First, time-domain bulk film resistance measurements have been conducted, and the findings show that all four types of films exhibit pH sensitivity. Their bulk film resistances increase in tandem with increasing pH. Second, frequency-domain electrical impedance spectroscopy (EIS) has also been conducted when the films are exposed to different pH buffers. The recorded EIS spectra have been fit to a proposed equivalent circuit model consisting of resistors, capacitors and a constant-phase element. The results suggest that the MeSA-based films exhibit linear sensitivity, whereas the HCl-based films exhibit a bilinear sensitivity in the time-domain case. Both HCl- and MeSA-based films exhibit a bilinear pH response in the frequency domain. The equivalent circuit has also revealed that the equivalent parallel capacitor and the constant-phase element of the HCl-and MeSA-doped films also exhibit an inverse bilinear sensitivity to pH buffer solutions.

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