engleski

Fundamental Insights Gained on Polaron Conduction using Impedance Spectroscopy: Case of Iron phosphate Glass-(Ceramics) Containing B2O3 and HfO2

Iron phosphate-based glasses (IPGs) belong to a family of electronically conducting amorphous materials. Due to the presence of transition metal (TM) ions, e.g. iron, in more than one valence state, the conduction mechanism of small polaron hopping (SPH) is present. These materials are of boundless scientific interest due to their potential application as electrode materials for batteries, electronic circuit elements, etc. Here, we report the effect of the addition of modifiers and network formers on the polaronic transport in binary IP glass. The electrical properties of two glass systems HfO2–B2O3–Fe2O3–P2O5 are studied in detail by Solid State Impedance Spectroscopy (SS-IS) over a wide range of frequencies and temperatures, revealing interesting features behind the polaronic transport. The addition of oxides significantly alters the Fe2+/Fetotal ratio, which directly affects the polaron number density and strongly controls the DC conductivity trends for both series. In addition, we found that short-range polaron dynamics are also under the influence of structural changes. Therefore, we studied them in detail using relatively simple but very informative model-free scaling procedures, namely Summerfield and Sidebottom scaling. Both procedures on the conductivity spectra confirmed the validity of the time-temperature superposition (TTS) principle for all glasses. An attempt to construct a super-master curve revealed that hopping lengths of the polarons also change, and Sidebottom scaling results in a super-master curve. In the next step, the spatial extent of the localized motion of the polarons is correlated with the polaron number density and two distinct regions with low and high polaron concentration glasses are confirmed. The transition between these regions is not only related to the polaron number density, but also to the combination of glass compositions and parameters that have an impact on the polaron motions. The relationship between the structural changes and conductivity mechanism is discussed in detail. The obtained results provide new valuable information about the resulting mixed glass network and its effect on the polaron formation and its dynamics.

Iron-phosphate glass ; ceramics ; polaronic transport ; impedance spectroscopy ; model-free scaling

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