I have observed change in specific capacitance with the shift of peak positions for different metal-oxide polymer composites (for different ratio). Is there any reason behind this?
I think the electrochemical performance is sensitive to FTIR peaks. For instance, we investigated a-Si:H using FTIR, the shift of peak positions represents different microstructures, and therefore often achieve different device qualities.
Capacitance is linearly proportional to dielectric constant of a material. Furthermore, the refractive index is non-linearly proportional to dielectric constant of a material. IR peak position shifts when reflection of the IR radiation occurs, such as in the system of composite material where the filler and matrix have differing refractive indices. Since IR spectrum is both a function of refractive index and absorption, when interfacial reflection occurs, the contribution of refractive index to the frequency becomes strong, thus IR peak position shifts. This effect is minimal when a pure material is observed in transmission where no interfacial reflection exists.
See for example: "Comparison of FT-IR Transmission, Specular Reflectance and Attenuated Total Reflectance Spectra of Polymers," R.T. Graf, J.L. Koenig and H. Ishida in "FT-IR Characterization of Polymers," H. Ishida, Ed., Plenum, New York (1987) p.385.
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