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The ionic dopant additives have different mechanisms of their influence upon MnO2 electrocrystallisation process and depending on dopants added the following polymorphs are stabilised: α-MnO2 (hollandite, I4/m) -- NH4 +; γ-MnO2 (ramsdellite, Pbnm) -- Co2+, Fe2+; layered polymorph δ-MnO2 (birnessite, C2/m) -- Cr3+. The defect states of intergrowth method in ramsdellite matrix and twinning, OH groups studied by X-ray diffraction and the Fourier transform infrared mtehod, respectively, indicate their high content in case of Fe2+ and Co2+- doped manganese dioxide. CVA oxygen reduction reaction peaks were established after experiments in alkaline electrolytes and dioxygen (argon, air) atmosphere. Activity of doped samples studied is comparable with other published data. Both doped with Co2+ and Fe2+ samples display maximal currents and some distinctive features in oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

Manganese dioxide samples were prepared from fluorine containing electrolytes with additives of Co2+ ions. Atomic absorption spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis were the methods of the samples characterisation. Manganese dioxide at the presence of cobalt forms nanosized ramsdellite structure crystallites of mostly needle-like morphology with significant content of hydroxide groups. The main phase state in manganese dioxide samples obtained at the presence of cobalt is γ-MnO2 with ramsdellite structure and low content of intergrowth defects. The sample doped both with lithium and cobalt can be indexed to a hollandite-type structure (tetragonal; space group I4=m) of α-MnO2. [ABSTRACT FROM AUTHOR]

Anorthite and gehlenite crystalline structure and short-range order of anorthite melt have been studied by X-ray diffraction in the temperature range from room temperature up to ~ 1923 K. The corresponding anorthite and gehlenite phases were identified as well as amorphous component for anorthite samples having identical shape to XRD pattern of the anorthite melt. The structure factor and the radial distribution function of atoms of the anorthite melt were calculated from the X-ray high-temperature experimental data. The partial structural parameters of the short-range order of the melt were reconstructed using Reverse Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

A study was made of the electron paramagnetic resonance (EPR), the Mn3+/Mn4+ ratio, the OH− groups contents, the ionic conductivity value and the specific capacity in different electrolytically and chemically prepared manganese dioxides which were intended for use in power sources. Typical EPR signal for the powdered MnO2 samples is wide single line with g=1.94. The replacement of some Mn4+ ions by Mn3+ modified the character of the exchange interaction. A correlation was established between the width of the EPR signal and electrochemical parameters of the samples. It is supposed that the EPR data can be useful for the semi-quantitative expression of chemical and electrochemical activity of different MnO2 samples. [Copyright &y& Elsevier]