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Chemical capacitance proposed for manganite-based ceramics

The measured value of effective electric permittivity \varepsilon_{eff} of several compounds, e.g., (BiNa)(MnNb)O_{3}, (BiPb)(MnNb)O_{3}, and BiMnO_{3} increases from a value \approx 10-100 at the low temperature range (100-300 K) up to the high value reaching the value 10^5 at high temperature range, e.g., 500-800 K. Such features suggest the manifestation of thermally activated space charge carriers, which effect the measured capacitance. The measured high-value effective permittivity of several manganite compounds can be ascribed to the chemical capacitance C_μ=e^2\partial N_{i}/\partial μ_{i} expressed in terms of the chemical potential μ. The chemical capacitance C_μ^{(cb)} = e^2 n_{C}/k_{B}T depends on temperature when the conduction electrons with density n_{C} = N_{C} \exp(μ_{n}- E_{C})/k_{B}T are considered. The experimental results obtained for the manganite compounds, at high temperature range, are discussed in the framework of the chemical capacitance model. However, the measured capacitance dependence on geometrical factors is analysed for BiMnO_{3} indicating that the non-homogeneous electrostatic capacitor model is valid in 300-500 K range.