Hydrothermal Oxidation−Reduction Methods for the Preparation of Pure and Single Crystalline Alunites: Synthesis and Characterization of a New Series of Vanadium Jarosites

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Abstract
Three new redox-based, hydrothermal, synthetic methods have been developed for the preparation of a new series of jarosites, AV3(OH)6(SO4)2 (A = Na+, K+, Rb+, Tl+, and NH4+), in high purity and in single crystalline form. The V3+ jarosites have been characterized by single-crystal X-ray and elemental analysis, and by infrared and electronic absorption spectroscopy. The synthetic methods employed here represent a new approach for the preparation of the jarosite class of compounds, which for the past several decades, have been notoriously difficult to prepare in pure form. To demonstrate the impact of our new synthetic techniques on the magnetic properties of jarosites, the V3+ jarosites were also prepared according to the nonredox techniques used over the past 30 years. A comparative study of these samples and those prepared by our new synthetic methods reveals widely divergent magnetic properties, thus pointing to the importance of the new redox synthetic methods to future magnetism studies of jarosite compounds.